heta 96-0198-2651 portsmouth gaseous diffusion plant ... · technician, chemical operator, and...

HETA 96-0198-2651Portsmouth Gaseous Diffusion Plant

Piketon, Ohio

John Cardarelli II, M.S.

This Health Hazard Evaluation (HHE) report and any recommendations made herein are for the specific facility evaluated and may not be universally applicable. Any recommendations made are not to be considered as final statements of NIOSH policy or of any agency or individual involved. Additional HHE reports are available at http://www.cdc.gov/niosh/hhe/reports



This Health Hazard Evaluation (HHE) report and any recommendations made herein are for the specific facility evaluated and may not be universally applicable. Any recommendations made are not to be considered as final statements of NIOSH policy or of any agency or individual involved.


applicable. Any recommendations made are not to be considered as final statements of NIOSH policy or of any agency or individual involved. Additional HHE reports are available at http://www.cdc.gov/niosh/hhe/reports

http://www.cdc.gov/niosh/hhe/reports



ii

PREFACEThe Hazard Evaluations and Technical Assistance Branch of NIOSH conducts field investigations of possiblehealth hazards in the workplace. These investigations are conducted under the authority of Section 20(a)(6)of the Occupational Safety and Health Act of 1970, 29 U.S.C. 669(a)(6) which authorizes the Secretary ofHealth and Human Services, following a written request from any employer or authorized representative ofemployees, to determine whether any substances normally found in the place of employment have potentiallytoxic effects in such concentrations as used or found.

The Hazard Evaluations and Technical Assistance Branch also provides, upon request, technical andconsultative assistance to Federal, State, and local agencies; labor; industry; and other groups or individualsto control occupational health hazards and to prevent related trauma and disease. Mention of company namesor products does not constitute endorsement by the National Institute for Occupational Safety and Health.

ACKNOWLEDGMENTS AND AVAILABILITY OF REPORTThis report was prepared by John Cardarelli II, of the Health-Related Energy Research Branch (HERB),Division of Surveillance, Hazard Evaluations and Field Studies (DSHEFS). Desktop publishing by KathyMitchell.

Copies of this report have been sent to employee and management representatives at the Portsmouth GaseousDiffusion Plant (PORTS) and the OSHA Regional Office. This report is not copyrighted and may be freelyreproduced. Single copies of this report will be available for a period of three years from the date of thisreport. To expedite your request, include a self-addressed mailing label along with your written request to:

NIOSH Publications Office4676 Columbia ParkwayCincinnati, Ohio 45226

800-356-4674

After this time, copies may be purchased from the National Technical Information Service (NTIS) at 5825Port Royal Road, Springfield, Virginia 22161. Information regarding the NTIS stock number may beobtained from the NIOSH Publications Office at the Cincinnati address.

For the purpose of informing affected employees, copies of this report shall beposted by the employer in a prominent place accessible to the employees for aperiod of 30 calendar days.

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Health Hazard Evaluation Report 96-0198-2651Portsmouth Gaseous Diffusion Plant

Piketon, Ohio

John Cardarelli II, MS

SUMMARYOn June 12, 1996, the National Institute for Occupational Safety and Health (NIOSH) received a request fora Health Hazard Evaluation (HHE) to evaluate worker exposures to neutron radiation at the Portsmouthgaseous diffusion plant (PORTS) operated by the Lockheed Martin Utility Services, Inc. (LMUS) in Piketon,Ohio. Another contractor, Lockheed Martin Energy Systems (LMES), operates certain areas at this facilitymaintained by the Department of Energy (DOE). Workers and areas under LMES were also included in thisHHE. The request was submitted by two separate union safety representatives and described the hazard asa chronic exposure to neutron radiation during various production, maintenance and security activities. Italso stated that neutron doses have not been recorded in the workers’ dose histories for the past 40 years.In response to this request, NIOSH conducted two site visits between November 1996 and February 1997to:

1. Determine if potential neutron exposures exist at the site.2. Identify neutron sources.3. Identify work areas or job titles having the greatest potential for neutron exposures.4. Quantify neutron doses by work area or job title.5. Determine past reporting and recording practices regarding neutron doses.6. Assess the feasibility of reconstructing past neutron doses.

The following paragraphs describe, summarize, and discuss the findings, results and conclusions associatedwith each of the listed objectives.

Determine if potential neutron exposures exist at the site: The LMUS PORTS is one of two operatinguranium enrichment production facilities in the United States that use the gaseous diffusion process to enrichuranium. Uranium as found in nature, Unat, is a radioactive element that contains a mixture of three isotopes:238U, 235U, and 234U. The process is designed to enrich the 235U isotope for use in the nation’s commercialand defense nuclear programs. Uranium is primarily responsible for the presence of neutrons at the PORTS.Neutrons are produced mainly from a nuclear reaction when its decay product (an alpha particle) reacts withbonded fluorine atoms. Additionally, neutrons are produced when uranium spontaneously splits into twolighter elements (a spontaneous fission). Since these processes occur naturally, neutron radiation has beenand continues to be present at the site.

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Identify neutron sources: It is clear from the physical nature and characteristics of uranium and itscompounds that appreciable neutron radiation is most likely to be present in areas where uranium is stored(cylinder yards), routinely handled (feed and withdrawal areas) or in areas where uranium forms depositswithin the cascade. The point at which this source becomes a radiological concern depends on severalfactors including neutron production rates, enrichment, neutron moderation factors, geometry, deposit size,detection capabilities, time of exposure, and distance from the source.

Identify work areas or job titles having the greatest potential for neutron exposures: During theNovember 1996 initial survey, locations for area and personnel monitoring were selected by representativesof management and the two unions. Their selections were based primarily on uranium being present in largequantities and job titles having routine tasks in those areas. Area neutron measurements were conducted inthe following locations: process buildings (X-326 and X-330), uranium storage areas (X-745 and X-345),and work areas routinely occupied by workers with selected job titles (Buildings X-705, X-344, and X-343).The job titles selected for monitoring included: Uranium Material Handler, Process Operator, Health PhysicsTechnician, Chemical Operator, and Security Guard.

Quantify neutron doses by work area or job title: In the process buildings (X-326 and X-330), measuredneutron doses ranged from below the limit of detection [0.2 millisieverts (mSv)] to 0.6 mSv. The highestneutron doses (2.1 to 7.1 mSv) were found in the uranium storage area maintained by the DOE (X-745). Inall other locations (X-343, X-345 and X-705), measured neutron doses were at or below the limit ofdetection. None of the personnel monitored during this evaluation received neutron doses above the limitof detection. Although the results of a recent study conducted by the site in 1995 showed that measurableneutron doses were received by workers performing activities similar to those monitored during thisevaluation.

Determine past reporting and recording practices regarding neutron doses: Neutron exposures havealways occurred at the PORTS facility but the occupational doses have been “considered insignificant incomparison with DOE radiation protection standards” to justify routine monitoring. Therefore, personnelneutron dosimetry was not conducted at this or any other gaseous diffusion plant in the past. Recordingdecisions regarding high doses (>2.7 rem) were based on the philosophy that doses of this size were veryunlikely when compared with past doses reported and recorded at the site. Therefore, equipment failure wasoften provided as the reason for the abnormal dose rather than investigating the anomaly.

Assess the feasibility of reconstructing past neutron doses: In early 1981, PORTS introducedthermoluminescent dosimeters (TLDs) to replace film-based dosimeters as a part of the routine radiationmonitoring program. The early film badges (1950s-1980) and the first TLD badges (1981-1990) were notcalibrated for and could not measure neutron exposures. Despite that limitation, an effort to reconstruct pastneutron exposures was attempted by requesting historical computerized data of TLD chip readings from 1981to the present. Data available for this purpose was limited to only the most recent data (1992-1995). Thus,it was not feasible to reconstruct potential neutron before 1992.

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This health hazard evaluation has shown that under certain conditions an acute exposure to neutron radiationcan occur. Therefore, a potential health hazard to neutron radiation exists at this site.

Recommendations include: employ an appropriate phantom material to monitor neutron exposures in the X-345 vault areas properly; inform workers potentially exposed to neutrons about the proper positioning of theTLDs and its angular dependence in detecting incident neutrons; revise minor errors in the neutron dosealgorithm documentation; review and improve linkage issues regarding unaccounted personal doses;reevaluate the use of archive tapes to prevent further loss of historical dosimetry data; continue neutronmonitoring in areas where uranium is routinely stored or handled; reevaluate past maintenance activities andpersonnel involved in physically removing uranium deposits for exposures associated with the slow cookerphenomenon; and report administrative changes or decisions regarding issues in the health physics dosimetryprogram (doses below the limit of detection, abnormal chip ratios, investigative reports, etc.) to the workforceto educate, inform, and solicit questions about how the changes or decisions will affect their dose histories.

Keywords: SIC 2819 (industrial inorganic chemicals, not elsewhere classified), neutrons, TLD,thermoluminescent dosimetry, TED, track-etch dosimetry, neutron dosimetry, radiation exposures, gaseousdiffusion, uranium enrichment, fission, spontaneous fission, slow cookers, criticality.

TABLE OF CONTENTSPreface . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . ii

Acknowledgments and Availability of Report . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . ii

Summary . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . iii

Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2Objectives . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2HHE Authority and Plant Operations . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2Exposure vs. Dose . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2

Background . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3Uranium . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3Gaseous Diffusion Plants . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3Process . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3Major Radiation Sources . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4Minor Radiation Sources . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5Neutrons . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5Uranium Deposits . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6Criticality . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6“Slow Cookers” . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7Historical Neutron Exposures . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8Pacific Northwest Laboratories Neutron Study . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9Epidemiologic Study . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9

Methods . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10Background Material . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10Monitoring Selections and Dosimeters . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10Evaluation of Historical Neutron Doses . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10NVLAP vs. DOELAP . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11

Evaluation Criteria . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 12

Results and Discussions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 12Area and Personal Neutron Measurements . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 12General Limitations . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 13Area Measurement Limitations . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 13Comparing HHE Results to the Regulatory Limit . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 13Historical Health Physics Practices . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 14

Conclusions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 14

Recommendations . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 15

Abbreviations and Terms . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 15

References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 16

Table IUSEC and DOE Portsmouth Facilities Selected for Monitoring . . . . . . . . . . . . . . . . . . . . . . . . 19

Table IIRadiological Units . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 19

Table IIIIsotopes Present in Natural Uranium . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 20

Table IVNeutron Monitoring Selections . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 20

Table VArea Neutron Measurements . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 21

Table VIPersonal Neutron Dosimetry Results . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 23

Appendix AUranium Decay Series, 238U . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 26

Appendix BActinium Decay Series, 235U . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 28

Appendix CRequested Background Documentation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 30

Health Hazard Evaluation Report No. 96-0198-2651

INTRODUCTIONOn June 12, 1996, the National Institute forOccupational Safety and Health (NIOSH) receiveda request for a Health Hazard Evaluation (HHE) toevaluate worker exposures to neutron radiation atthe Portsmouth gaseous diffusion plant (PORTS)operated by the Lockheed Martin Utility Services,Inc. (LMUS) in Piketon, Ohio. Workerrepresentation was provided by the two unions atthe site, Local 3-689 of the Oil, Chemical, andAtomic Workers Union International (OCAW) andLocal 66 of the United Plant Guard Workers ofAmerica (UPGWA). The request described thehazard as a chronic exposure to neutron radiationduring various production, maintenance andsecurity activities. It also stated that past neutrondoses have not been reported in the dose recordsover the past 40 years. Approximately 2,500workers are currently employed at the PORTS andnearly 9,000 workers have been employed at thesite since 1954.

Objectives

During the period between November 1996 andFebruary 1997, area and personal neutron dosemeasurements were co l lec ted us ingthermoluminescent dosimeters and track-etchdosimeters (TLD/TEDs) to address the followingobjectives:

1. Determine if potential neutron exposures existat the site.2. Identify neutron sources.3. Identify work areas or job titles having thegreatest potential for neutron exposures.4. Quantify neutron doses by work area or jobtitle.

In addition, past reporting and recording practicesregarding neutron doses were reviewed todetermine if past doses could be reconstructed.

HHE Authority and Plant Operations

As a result of the Energy Policy Act of 1992,1 theresponsibility for the enforcement of occupationalsafety and health at PORTS was transferred fromthe Department of Energy (DOE) to theDepartment of Labor (DOL) and the NuclearRegulatory Commission (NRC). This act alsomandated that on July 1, 1993, certain buildingsand activities of the DOE-owned gaseousdiffusion plants be transferred to the United StatesEnrichment Corporat ion (USEC), aCongressionally-established, government-ownedcorporation that operates the United States’uranium enrichment facilities. This course ofevents permitted the submission of an HHErequest by the workforce under provisions of theOccupational Safety and Health Act. Althoughseveral buildings remain under DOE control, theywere included in this evaluation. Researchapplicable to an ongoing NIOSH mortality studywas also conducted under a Memorandum ofUnderstanding between DOE and the Departmentof Health and Human Services (DHHS)-NIOSH.2

Although USEC now operates the uraniumenrichment facilities, the DOE maintains andoperates certain buildings and activities at thePORTS. LMUS has been contracted to maintainand operate buildings for USEC regulated by theNRC and OSHA. Lockheed Martin EnergySystems, Inc. (LMES) maintains and operatesbuildings for the DOE under DOE orders. Thebuildings of interest to this HHE and theirresponsible agency are listed in Table I. This isan important distinction between LMUS andLMES because each company has a separateworkforce and employs different dosimetryservices.

Exposure vs. Dose

It is important to note that the terms exposure anddose have specific meanings when usedthroughout this document (see Table II).Exposure is used when referencing the amount ofionizing radiation present at a given point

Health Hazard Evaluation Report No. 96-0198-2651 Page 3

measured in air. Dose refers to the dose equivalentor the amount of ionizing radiation absorbed in thebody adjusted for its relative biologicaleffectiveness. The reporting metric for thisevaluation is in units of dose with a neutronrelative biological effectiveness factor of about 10,so that appropriate comparisons can be made withthe regulatory limits specified in the code offederal regulations.

BACKGROUNDUranium

Uranium as found in nature, Unat, is a radioactiveelement that contains a mixture of three isotopes:238U, 235U, and 234U (Table III). It is used primarilyas fuel for commercial nuclear power plants andnuclear-powered submarines but also in nuclearweapons. In general, the 235U isotope is importantto these industries because it can easily undergofission by capturing a neutron. Fission occurswhen the nucleus splits, forming at least twonuclei, releasing several neutrons and a largeamount of energy. Electricity is produced whenheat generated from this process is transferred to acoolant that is then used to drive turbinegenerators. The 238U isotope is also important toboth industries because it can be transformed into239Pu after capturing a neutron. Plutonium-239 isanother fissile element primarily used in nuclearweapons.

Even without neutron interaction, uranium changesby undergoing natural radioactive decay. Thedecay chains for both uranium isotopes are shownin Appendices A and B (238U - Uranium Seriesincludes 234U, 235U - Actinium Series). In addition,there is also a small probability that uranium willdecay by spontaneous fission; i.e., uranium willfission on its own without assistance from abombarding neutron. For example, the half-life forspontaneous fission in 238U is some 6.5 x 1015

years, as compared with its radiological half-life of4.91 x 109 years. Because this phenomenon is so

rare compared to radioactive decay, it is usuallynot considered a significant radiological concern.However, even this very slow spontaneous fissionrate can be important in the gaseous diffusionprocess since large amounts of uranium arepresent.

Gaseous Diffusion Plants

The LMUS PORTS is one of two operatinguranium enrichment production facilities in theUnited States: PORTS, located in Piketon, Ohio,and the Paducah Gaseous Diffusion Plant (PGDP)located in Paducah, Kentucky. Each plant usesthe gaseous diffusion process to enrich uraniumfrom the natural level of 0.71% 235U to higherconcentrations, which historically have rangedfrom 2% to greater than 97%. The LMUSPORTS has discontinued high assay 235Uproduction and currently produces a product thatis between 2 to 5%, for use in fuel rods incommercial nuclear power plants. The level ofenrichment is determined by physical or chemicalmeasurements of fissionable material (235U)present in the uranium.3

Process

Production of enriched uranium at PORTS beganin late 1954. The two gaseous diffusion plants(PORTS and PGDP) have operated in acomplementary mode. The Paducah facilityperforms the initial enrichment of uranium toabout 1 to 2% 235U. This material serves as afeedstock for PORTS, although the PORTSfacility can also use the same feed materials thatPGDP receives. The uranium is enriched bydiffusing uranium hexafluoride (UF6) through aporous material commonly called the barrier.Lighter molecules (235UF6) travel at a highervelocity than the heavier molecules (238UF6).When the mixture contacts the barrier, the lightermolecules strike the barrier and pass through itmore readily than the heavier molecules. Themaximum separation that can be achieved throughthe barrier is equal to the square root of the ratioof the weights of the gas molecules. Since the


Figure 1: Stage Components

X-745

N

X-333

X-33

0X -

326

X-345

X-344

X-705

0 2000 ftFigure 2: PORTS Facility

square root of that ratio for UF6 molecules is1.0043, many passes through the barrier arerequired to reach the desired enrichment assay of235UF6.4

Each stage in the enrichment process consists of acompressor, converter (contains the barrier), andmotor, (Figure 1). Between eight and 12 stages arelinked together in series to form a cell. Between 10and 20 cells (80 to 240 stages) are assembled toform a functional unit. These units are linkedtogether to form the cascade for uraniumenrichment. The PORTS’ several thousand stagesare housed in three interconnected buildings (X-333, X-330 and X-326) (Figure 2). Each cascadebuilding has two floors, each floor coveringapproximately 1.5 million square feet.5 The overallconfiguration results in a flow of increasinglyenriched 235UF6 toward the top of the process (X-326 building). Depleted 238UF6 flows toward thebottom or "tails" of the process (X-333 building).

Because UF6 is a solid at room temperature, it isdelivered to and shipped from the facility as a solidin various cylinder types and sizes. The cylindersvary between small 5-inch-diameter cylinders to14-ton cylinders to prevent an uncontrolled nuclearchain reaction, also known as a criticality, whichreleases potentially lethal amounts of ionizingradiation (neutrons and high energy photons).

Major Radiation Sources

Major sources of radiation exposures at PORTSare low energy photons from 235U, thorium (231Thand 234Th), beta particles from protactinium(234mPa), and bremsstrahlung radiation producedby the beta particles from uranium daughters andtechnetium (99Tc) (See Appendices A and B).Other potential sources within this category butwith limited exposure potential to the workforceinclude high energy photons from calibrationsources of cesium (137Cs), radium (226Ra), andcobalt (60Co), and machine-generated x-rays attube potentials ranging from 70 to 200 kilovolts(kV).6 Bremsstrahlung refers to the secondaryphoton radiation associated with the decelerationof charge particles (electrons) passing throughmatter.3 Very low levels of gamma andbremsstrahlung radiation (0.2 to 0.1 microsievertsper hour, :Sv/hr) are found throughout theprocess buildings. The highest levels (up to 50:Sv/hr) can be found in UF6 feed cylinderhandling areas.6 Technetium-99 is a beta-emittingfission product introduced into the PORTScascade from reprocessed spent reactor fuel,referred to as recycled uranium (RU). Itconcentrates in the top end of the enrichmentprocess (X-326 building) because it is lighter inrelation to the uranium isotopes.


electron or beta (- charge)mass = 9.109567 x 10-28 grams

proton (+ charge)mass = 1.67261 x 10-24 grams

neutron (no charge)mass = 1.67492 x 10-24 grams

+-

Figure 3: Parts of an Atom

Minor Radiation Sources

The minor sources of radiation exposures atPORTS are from trace amounts of the transuranicelements neptunium (237Np) and plutonium (238Pu,239Pu, 240Pu, 241Pu). These are introduced into theenrichment process through recycled uranium.Additionally, RU contains trace amounts ofuranium isotopes not found in nature, such as 232Uand 236U. The radiological impact of theseimpurities is negligible in many cases. However,chemical processes that concentrate theseradionuclides may require that certain radiologicalcontrols be employed. These exposures maybecome more common as the United Statescontinues to increase the amount of RU processedat these facilities.7

Neutrons

A neutron is an elementary nuclear particle, havingno electrical charge, with a mass approximately thesame as that of a hydrogen atom (one electron andone proton) (Figure 3). Since neutrons carry nocharge, they are not affected by the electric forcessurrounding atoms and interact with the nuclei ofthe target material. As a result, the neutron may beeither totally absorbed (captured) or significantlychanged in its direction or energy.

The principle behind measuring neutron radiationis to use some type of conversion of the incidentneutrons into secondary charged particles that canthen be detected.8 The usefulness of a target

material used in this process is largely dependenton the cross-section (or probability of interaction)of that material relative to the energy of thecolliding neutron. Neutron energies are usuallycategorized into three groups: thermal,intermediate, and fast. Thermal neutron energies(sometimes given as 0.025 electronvolts, eV) aretypically considered to be neutrons with energiesbelow the cadmium cutoff, about 0.5 eV.Cadmium is commonly used as a shield todifferentiate thermal neutrons from higher-energyneutrons. Slow and intermediate neutronstypically range in energy levels between 0.5 eVand 100,000 eV. Fast neutrons have energiesgreater than 100,000 eV.9, 10

The dose (energy deposited per unit mass oftissue) received from neutrons is very difficult tomeasure accurately because of the difficulties indetecting the neutrons and characterizing theirenergies. In addition, neutron dosimetry presentsa difficulty not encountered in electron or photondosimetry. Neutrons produce photons once theyenter the material, creating a problem of mixed-field dosimetry. To assess neutron doses frommixed fields, measurements are made usingseveral thermoluminescent chips with varyingsensitivities to neutrons and photons.11

Neutrons at PORTS are produced from a fissionor spontaneous fission of the uranium isotopes.Neutrons can also be produced by reactionsbetween alpha particles emitted by uraniumisotopes (primarily 234U) with bonded fluorineatoms.6,12 The following nuclear reactionsillustrate how neutrons could be produced at thisfacility:

Spontaneous Fission*

23592

U ÿ 14657

La + 8735

Br + 2 neutrons + energy

Fission*

10n + 235

92U ÿ 147

57La + 87

35Br + 2 neutrons + energy

Interaction*

42" + 19

9F ÿ 22

11Na + neutron + energy

*La = Lanthanum; Br = Bromine; Na = Sodium


It is important to note that the 235U nucleus canfission by some 40 or so methods. Also, 234U isprimarily responsible for neutron production in theinteraction example because it produces alphaparticles (decays by alpha emission) at a rate ofabout 2,900 and 18,000 times faster than 235U and238U, respectively.

It is clear from the physical nature andcharacteristics of uranium and uranium compoundsthat neutron exposures are most likely to occur inareas where uranium is stored (cylinder yards) orroutinely handled (feed and withdrawal areas) andin areas where uranium forms deposits within thecascade. The point at which this exposure becomesa radiological concern depends on several factors,including: neutron production/generation rates,enrichment, neutron moderation factors, geometry,deposit size, detection capabilities, time ofexposure, and distance from a source.

Uranium Deposits

The uranium enrichment process employed atPORTS requires that the uranium compound UF6,be maintained in a gaseous state. However, thereare four basic mechanisms by which uranium in thecascade may solidify and form a deposit: freeze-outs, inleakage, consumption, and adsorption.Freeze-outs are solidification of UF6 due toinappropriate temperature and pressure conditions.Typically these are not a common problem and canbe detected through interpretation of unusualinstrument readings or equipment performanceindicators. Inleakage of atmospheric moisturecauses the formation of uranium oxyfluoride solids(uranyl fluoride or UO2F2) by water vapor reactingwith the UF6. Catastrophic failure of processequipment can cause large amounts of inleakagethat can be readily detected. However, chronicleaks into the system produce deposits that may goundetected for longer periods of time.Consumption is the formation of uranium fluoridesolids by UF6 reduction reactions with cascademetals. Adsorption is the boundary layercondensation of UF6 on internal equipmentsurfaces. Both consumption and adsorption occur

throughout the cascade under normal operatingconditions and routinely remove UF6 from the gasphase. Together, these two mechanisms have beentermed the “retained inventory effect” to account forundetected inventory losses during normal operationconditions.13

Neutron and gamma measurements are used asnondestructive methods to detect and quantify knownuranium deposits within the cascade. Neutronmeasurements serve two purposes. First, theyquantify the amount of material in a piece ofequipment being removed from the cascade.Secondly, they determine the type of special handlingrequired to minimize worker exposures and toprevent a criticality.14 Neutron measurements areprimarily used when the associated gamma emissionsfrom uranium are sufficiently attenuated or shieldedby equipment like compressors and heat exchangers.Gamma-ray measurements are used to supplementneutron data in assessing the size of deposits inconverters and process piping and may also be usedto assess the relative concentrations of 234U, 235U, and238U.12

Material balance techniques have also been employedto determine how much uranium has “fallen out” ofthe gaseous phase within the entire cascade. This“in-process” inventory is determined by computercalculation (using plant gauge data) and comparedwith the physical “book” inventory of inputs vs.outputs to obtain differences in the materialbalance.12 Since neither method accounts forsolidified uranium within the cascade, the differencecould be used as measure of the total amount ofsolidified uranium within the cascade.

Criticality

A criticality occurs when, on the average, a neutronemitted by the methods described earlier causesanother nucleus to fission. When this reactionbecomes self-sustaining so that one fission triggersanother, the phenomenon is termed a critical chain-reaction (Figure 4). A controlled chain-reactionoccurs in nuclear reactors whereby the rate offissioning is maintained after the reactor has reached


Energy

Fission-fragment

Uranium-235

Incidentneutron

Leakage fromsystem

Capture gamma

scattering

Figure 4: Simple schematic of fission chain reaction.

a stage of criticality. A reactor in which the rate offissioning is decreasing is sub-critical, and one inwhich the rate of fissioning is increasing is super-critical. An atomic bomb could be described assuper-super-critical.15

Four main outcomes in this chain reactiondetermine when a criticality has been achieved: (1)a complete loss of neutrons by escape or “leakage”from the system; (2) capture of a neutron by afissile material (235U), resulting in a reaction otherthan fission (such as radiative capture); (3) captureof a neutron by a non-fissile material (impurities);and, (4) capture of a neutron by a fissile materialthat undergoes fission. Physical and chemicalcharacteristics as well as engineering controls mustbe optimized to reduce the loss of neutrons andmaintain a state of criticality. The PORTS facilityhas been designed and operated to minimize thepossibility that these factors reach the levelnecessary to create a critical event. As a result,there have been no critical events in the history ofthe facility.

“Slow Cookers”

Although PORTS has never experienced acriticality, neutrons are produced at the site. Aslow buildup of uranium material within thecascade causes a slight increase in the productionof neutrons. If the buildup continues without

intervention, the “growing” deposit may lead to acritical or super-critical event.16 This phenomenon ofa slow build-up of uranium material that approachescriticality has been termed by the gaseous diffusionindustry as a slow cooker. In essence, a slow cookeris a mass of uranium in which there is amultiplication of neutrons but at a rate below thecritical threshold. Slow cookers are directlyassociated with uranium deposits which haveroutinely occurred at the PORTS since the plant’sinception.17, 18

The danger associated with this phenomenon varieswith the location, size, and type of deposit formedwithin the cascade. In general, the number ofneutrons produced is proportional to the amount ofuranium and the degree of enrichment. For example,an equal number of neutrons can be produced witheither a large amount of low-enriched or depleteduranium (238U) or a small amount of highly enricheduranium (235U). The energy of the produced neutronis proportional to the percent of enrichment. Highlyenriched uranium will result in more energeticneutrons. The potential neutron dose (includingphoton exposures) from of an unknown orunidentified slow cooker depends on the time ofexposure, distance from the source, and the numberand energy of the incident neutrons interacting withthe target material (tissue).

Neutron doses specifically attributable to thisphenomenon could not be addressed in this


evaluation for several reasons. First, slow cookersremain fixed relative to the movements of theworkers within the process buildings, therebymaking it very difficult to link a particular worker’sdose to a specific deposit. Second, the dynamicnature of slow cookers makes them difficult tocharacterize and detect. For example, they canremain stable in size, producing a chronic low-levelradiation field obscured by adjacent radiationfields, and may go undetected for long periods oftime. Or they may continue to build and producean ever increasing radiation field until they areidentified, characterized, and removed from thecascade. This removal action could be completedremotely by chemical treatments or by physicallyremoving the uranium from the cascade.

Historical Neutron Exposures

Neutron exposures have always occurred at thePORTS facility but the occupational doses havebeen “considered insignificant** in comparisonwith DOE radiation protection standards.”7

Therefore, personal neutron dosimetry was notconducted at this or any other gaseous diffusionplant in the past.19 In the mid-1980s, neutronexposures were evaluated using Eberline “rem-balls” in areas where uranium was stored. Theresulting doses were a function of enrichment anddistance from the source. Highly enriched material(5-inch cylinders) produced neutron dose ratesranging from 0.03 mSv/hr (3 mrem/hr) on contactto less than 0.005 mSv/hr (0.5 mrem/hr) at adistance of 1 meter. Lower-enriched material (10-ton cylinders) produced neutron rates around 0.005mSv/hr (0.5 mrem/hr). Based on these results andassuming that three hours was an average exposuretime per work day, an “annual neutron doseequivalent” of 0.75 mSv (75 mrem) wasestimated.20 Since this is 1.5% of the radiationprotection standard, 50 mSv/yr (5000 mrem/yr), thecontractor determined that dosimetry was notrequired.21 It is not clear from the above-

referenced documents if the dose includedcontributions from gamma exposures. If it did not,then the annual estimate would be higher than 0.75mSv but still below the radiation protection standard.The Health Physics Manual of Good Practices forUranium Facilities, released in 1988 stated that “ifpersonnel are required to spend more than a few**

hours per week in close proximity to containers ofuranium fluoride compounds or if their assignmentsrequire them to spend time near storage orprocessing areas for large quantities** of uraniumfluoride compounds, the exposure to neutrons shouldbe evaluated.”7

It wasn’t until 1992 that some workers in theRadiation Calibration Facility and the AppliedNuclear Technology Department at PORTS wereplaced in a routine neutron dosimetry program. InOctober 1994, a new monitoring concept thatmonitored only those workers entering a Controlledor Restricted area was initiated. Simultaneously, anarea monitoring program that measured radiationlevels where unmonitored workers could approachwithout a dosimeter (building exteriors and fencessurrounding posted radiation areas) was initiated.Neutron dose equivalents from the area monitoringprogram were unexpectedly elevated, which led tofurther investigations to explain the anomaly.22

Possible reasons for the elevated results weredescribed as conservative assumptions about theneutron energies used in the dose algorithm and thetype of calibration source used to derive thealgorithm [unmoderated 252Cf (Californium), fastneutrons].

A recent neutron monitoring study conducted by thesite in 1995 showed that neutron doses have beenmeasured for workers performing activities similar tothose involved in this evaluation.23 The studymonitored only Uranium Material Handlersperforming various tasks in eight locationsthroughout the plant. Observed median quarterlyneutron doses were the Feed Plant (0.05 mSv), X-344Autoclave Area (0.07 mSv), Shipping and Receiving(0.07 mSv), Cylinder Lots (0.07 mSv), X-345 (0.03mSv), X-744G (0.02 mSv), X-326 L Cage [belowlimit of detection or (LOD)], and the Burn DrumArea (0.04 mSv). The mean total dose (0.40 mSv) to

** The terms “insignificant”, “few” and “largequantities” were not defined in the referencedreports.7, 19-21


the workers in these areas was due primarily tophoton exposures, while the neutron component(.0.05 mSv) accounted for only about 12.5%. Thisassumes that the dose due to internal exposureswas zero. No conclusions were drawn from thesedata because other neutron characterization effortsthat would provide more accurate informationregarding neutron energies and dosimetryperformance measures were underway.

Pacific Northwest Laboratories NeutronStudy

In September 1995, Pacific Northwest Laboratory(PNL) in Richland, Washington, was contracted tomeasure occupational neutron dose rates and todetermine why PORTS lithium-based dosimetrywas showing higher-than-expected neutronresponses.24 A primary consideration in neutrondosimetry is the range of neutron energies to whichthe workers are exposed. The study conducted byPNL staff used state-of-the-art neutron detectorsand spectrometers. Data were analyzed usingvarious software codes, neutron quality factors, andenergy spectra to obtain neutron dose rates.

Results from this study suggest that the averageneutron energies emitted from depleted and naturaluranium cylinders ranged from 210 to 360 kilo-electronvolts (keV) depending on the type ofmeasuring technology employed (tissue-equivalentproportional counters or lithium iodide detectorswith polyethylene spheres and the highest-sensitivity 3He proportional counters). Slightlyenriched material (2%) emitted energetic neutronsaround 510 keV. Five percent enriched materialemitted more energetic neutrons (770 keV). Themost energetic neutrons (860 keV) were detectednext to the uranium having the highest enrichment(near 97%). The range of neutron energies (210 to860 keV) indicates that thermal neutrons (energiesbelow 0.5 eV) are not a concern at the site.

Measurements of the neutron calibration source252Cf, using both unmoderated and deuterium oxide(D2O)- moderated techniques, denote an averageneutron energy of 1403 keV and 1306 keV,

respectively. Therefore, the neutron radiation fieldssurrounding the PORTS cylinders had much lowerenergy than the fields produced by the calibrationsources.24 This may result in higher dose estimatesunless the energy differential is accounted for in thedose algorithm. The PNL study concluded:

1. Routine occupational exposures to neutrons arewell below the current regulatory limits specified by10 CFR 20.25

2. Dose rates determined by instrumentation can becompared with the response of personal dosimetersexposed to the same neutron fields.3. Neutron energy distributions vary with cylinderstorage configurations, cylinder diameters, anduranium enrichment, which may produce differentresponses in personal dosimeters.4. The typical calibration source, D2O-moderated252Cf, used for neutron dosimetry calibrations, wouldnot lead to accurate estimates of exposures nearuranium cylinders.5. Neutrons emitted by fission vs. (",n) reactionscould not be addressed.6. The proper interpretation of occupationalexposures depends on an accurate understanding ofthe energy distributions of the neutron field exposingthe dosimeters.

Epidemiologic Study

In 1982, NIOSH initiated a retrospective cohort studyto evaluate mortality associated with occupationalchemical and radiological exposures. A report on thestudy findings, issued in January 1987, revealed non-statistically significant elevations in the standardizedmortality ratios (SMRs) for stomach cancer andleukemia.26 This study is currently being updated.

Neutrons were not listed as an exposure of concern atthe beginning of the update study because allreferences to neutron exposures (verbal and written)indicated that they were not materially present at thesite.27 During this HHE, however, NIOSH learnedthat potential neutron exposures have been presentsince 1955. Unfortunately, they are not addressed inthe current NIOSH study because historical neutrondose data do not exist in a format usable for


epidemiologic analysis. Currently, there are noplans to modify the current epidemiologic studyexcept to consider the findings of this HHE wheninterpreting the results of any dose-responseanalyses.

METHODSBackground Material

Upon receipt of the HHE request, backgroundmaterial including historical documents aboutneutron exposures and past practices for neutronmonitoring was requested from the site(Appendix C). Most of these materials describedtechniques used to identify uranium deposits withinthe cascade. A couple of reports providedinformation on neutron energy spectra andidentified locations with the highest potential forneutron exposures.24, 28 These were areas wherelarge amounts of uranium were stored or handled(cylinder inspection, storage, filling, etc.). All ofthe energy spectrum data used in the HHEevaluation were based on the PNL study. NIOSHdid not conduct neutron spectrum measurements;however, neutron monitoring was performed usingthermoluminescent dosimeters combined with tracketched dosimeters (TLD/TEDs) in selected areasand on specified personnel whose job titlessuggested exposure potential.

Monitoring Selections and Dosimeters

During the November 1996 initial survey, locationsfor area and personnel monitoring were selected byrepresentatives of management and the two unions.Workers in the selected job titles were given aTLD/TED badge designed to measure neutrons.The TLD/TEDs were provided by a vendor(Landauer, Inc.) accredited by the NationalVoluntary Laboratory Accreditation Program(NVLAP) and experienced with DOE facilitiesaccredited by the Department of Energy LaboratoryAccreditation Program (DOELAP).29 (See NVLAPvs. DOELAP section below for further

explanation). The Landauer badge, Neutrak ER,combines a TLD albedo dosimeter with an allyldiglycol carbonate-based (CR-39) technology.Neutrons above 30 to 50 keV can be detected byinteractions in the CR-39 either directly or by recoilparticles from the source. Lower-energy neutronsreflected from the body (albedo) are detected by theTLD component.30 By comparing the response ofthese two elements, a qualitative indication ofneutron energies and an estimate of the doseequivalent can be made. Thermal neutrons were notmeasured during this evaluation based on thefindings from the PNL study.24 In addition, neutronsat PORTS are produced at much higher energy levelsthan thermal energy levels.

Job titles selected for monitoring included: UraniumMaterial Handler, Process Operator, Health PhysicsTechnician, Chemical Operator, and Security Guard.Table IV lists number of selected workers in each jobtitle that agreed to participate in the HHE. Areadosimeters were placed on one-gallon polyethylene“cubitainers” filled with either 100% water (indoormeasurements) or a mixture of 50% water and 50%antifreeze (outdoor measurements). The liquid-filled“cubitainers” served as tissue-equivalent phantoms.Antifreeze was deemed necessary by the investigatorto prevent the solution from freezing, which mighthave affected neutron moderation and sensitivity ofthe TLD/TEDs during the winter months (November- February). Three workers agreed to serve as “field”controls and several “NIOSH” controls wereemployed for quality assurance purposes (see TableIV). Each dosimeter stayed in the field forapproximately one calender quarter (November 5 -February 5). Then they were collected and sent tothe vendor for analysis.

Evaluation of Historical Neutron Doses

In addition to performing neutron monitoring oncurrent workers and in selected locations, an attemptwas made to evaluate potential historical doses fromneutron exposures by reviewing TLD chip readingsfrom the past dosimetry programs. In early 1981,PORTS began using TLD technology to replace theirfilm-based dosimeters as a part of their routine


monitoring program. The early film badges(1950s-1980) and the first TLD badges (1981-1990) were neither calibrated for, nor read, neutronexposures.20 The first TLD dosimeters originallyconsisted of four TLD chips. Three were sensitiveto penetrating beta-gamma radiation (Lithium, Li-700) and the fourth (Li-600) was sensitive to bothgamma and neutron radiation. These chips wereshielded by various materials to help determine thetype of dose received by the workers. The ratiobetween the Li-600 and Li-700 chips could be usedas a semi-quantitative indicator of neutronexposure. A chip ratio outside expected rangescould suggest that a chip was damaged or that aneutron exposure had occurred. Unfortunately, thepast health physics practice was to assume thatmost, if not all, abnormal chip ratios were due todamaged chips rather than evaluate them forpotential neutron exposures.

Despite past practices regarding abnormal chipratios, a request was made to obtain historicalcomputerized data containing chip readings from1981 to the present.31 These were to be reviewedto determine if certain worker groups had higherrates of abnormal ratios than other worker groups.This would provide additional information aboutthe existence and relative degree of past neutronexposures to the workforce. However, problemswere encountered in retrieving the data. First, thestorage format and type of dosimetry readingequipment changed through time and would haverequired substantial time and resources to recover.Secondly, the older dosimetry equipment (Harshaw2276) was a direct-reading machine and did notcreate a date field when the results were stored.Finally, many archive tapes had been reused, andmost of the historical data was overwritten withmore recent data.32 Consequently, data availablefor this purpose was limited to only the most recentmeasurements (1992-1995). Thus, it was notfeasible to reconstruct neutron exposures fromprevious TLD chip readings before 1992.

NVLAP vs. DOELAP

The PORTS is maintained and operated by separatecontractors (LMUS and LMES) under differentregulatory agencies (NRC and DOE), as identified inTable I. This introduces a level of complexity inevaluating the neutron exposures at the site sinceeach contractor uses separate dosimetry services.The dosimetry services used by LMUS requireaccreditation through NVLAP. Dosimetry servicesthrough the DOE, used by LMES, requireaccreditation by DOELAP. The special radiologicalenvironments associated with the DOE facilities ledDOE to develop and maintain a separate testingstandard to provide adequate monitoring for theirsites’ unique radiation fields.9, 33 Most facilitiesregulated by the NRC, such as commercial nuclearpower plants, have predictable radiation fields andcan use dosimetry services provided by any vendoraccredited by NVLAP. Accreditation requirementsdiffer between the two agencies. DOELAP onlyaccredits DOE facilities, not commercial vendors,like NVLAP does. The differences between the twoaccreditation programs related primarily tocalibration protocols (type of source, angularresponse, dosimeter location, and backscatter).34

While DOE facilities use commercial vendors, it isthe DOE facility that holds the accreditation, not thevendor. DOE facilities have not sought NVLAPaccreditation since the DOE is more stringent and notsubject to NRC regulation. NVLAP accreditationwould incur additional costs to the sites, and there isno regulatory need unless they are also a NRClicensee, as is the case for PORTS.29

Currently, no resolution has been reached betweenthe NRC and DOE regarding the use of a singledosimetry service for workers exposed to ionizingradiation at PORTS. Therefore, LMUS and LMESworkers are monitored by separate dosimetryprograms, accredited by NVLAP or DOELAP,respectively. This dual monitoring system addsanother level of complexity to the challenge ofassessing neutron exposures at the PORTS.


EVALUATION CRITERIANIOSH field staff employ environmental andoccupational evaluation criteria for the assessmentof most chemical and physical agents as a guide tothe evaluation of the hazards posed by workplaceexposures. These criteria are intended to suggestlevels of exposure to which most workers may beexposed for a working lifetime withoutexperiencing adverse health effects. It is, however,important to note that not all workers will beprotected from adverse health effects even thoughtheir exposures are maintained below these levels.A small percentage may experience adverse healtheffects because of individual susceptibility, apre-existing medical condition, and/or ahypersensitivity (allergy). In addition, somehazardous substances may act in combination withother workplace exposures, the generalenvironment, or with medications or personalhabits of the worker to produce health effects evenif the occupational exposures are controlled at thelevel set by the criterion. These combined effectsare often not considered in the evaluation criteria.Also, some substances are absorbed by directcontact with the skin and mucous membranes, andthus potentially increase the overall exposure.Finally, evaluation criteria may change over theyears as new information on the toxic effects of anagent become available. NIOSH encourages themore protective criterion.

The primary sources of occupational evaluationcriteria applicable to this HHE are: (1) NuclearRegulatory Commission Standards for ProtectionAgainst Radiation, and (2) Department of EnergyOccupational Radiation Protection.25, 35 The doselimit for ionizing radiation requires that dosescombined from internal (alpha) and external (beta,gamma, and neutron) exposures be below50 millisieverts per year (5000 mrem/yr). Thefollowing section addresses the limitationsassociated with comparing the results from thisHHE to the current regulatory limit. Although thegaseous diffusion industry is one of the lowest-exposure industries dealing with radioactivesubstances, historical summary statistics regarding

radiation doses in this industry neither included noraddressed neutron doses.36 Despite this limitation,it will probably remain one of the lowest-exposureindustries among those dealing with radioactivesubstances.

RESULTS ANDDISCUSSIONS

Area and Personal Neutron Measurements

Area and personal neutron doses recorded by theTLD/TEDs placed by NIOSH between November1996 and February 1997 are listed in Tables V andVI. Two areas within Building X-326, ExtendedRange Product Station (ERP) and ProductWithdrawal Area (PW), had measured neutron dosesat or slightly above the detection limit of 0.2 mSv(20 mrem) during the monitoring period. The fourlocations in X-330 included the Tails WithdrawalArea, a location next to a known uranium deposit, arandomly selected location within the building, andthe Low Assay Withdrawal Area (LAW). Neutronswere not detected above the detection limit at theTails Withdrawal Area, the known uranium deposit,or at the randomly selected location. However, theknown uranium deposit was removed at some timeduring the monitoring period, which preventedassessment of potential neutron doses near a knowndeposit. Neutron doses ranging between 0.4 - 0.6mSv (40 - 60 mrem) were measured at the LAWArea. In the X-343 area, where nearly 300 storagecylinders are handled monthly, the neutron resultsranged between non-detectable and 0.2 mSv. Alldoses at the X-345 and X-705 locations were belowthe detection limit. The highest neutron doses werefound within the X-745-c cylinder yard maintainedby the DOE; they ranged between 2.1 and 7.1 mSvin section 44 and 2.1 to 5.1 mSv in section 3.

None of the workers monitored during thisevaluation received neutron doses above theminimum detection limit of 0.2 mSv. However,neutrons were measured in areas commonlyoccupied by workers (LAW Area and cylinderyards).


(1)

General Limitations

The results obtained from this evaluation representonly a brief period of time relative to the plant’sentire history. The results from this evaluationmay not fully represent past or future neutronexposure scenarios. Locations monitored duringthis evaluation will continue to provide a potentialfor future neutron exposures, depending on theamount of uranium stored, solidified, or handled inthe areas. The lack of detectable neutron dosesduring this monitoring period should not begeneralized in a retrospective manner nor appliedto other locations or job titles. Neutron exposurepotential for other areas and workers should beevaluated. Dynamic factors such as unidentifiedslow cookers or emergencies may expose workersto detectable levels of neutrons. It should also benoted that not every exposure scenario wasevaluated during this HHE because severalactivities (removal of known uranium deposits,special decontamination activities, accidents, etc.)either did not occur or were not scheduled prior tothe start of the neutron monitoring.

Area Measurement Limitations

Area neutron measurements obtained in the X-345building (high-assay storage vaults) were limited tothe lobby area within the building. The greatestpotential for neutron exposures exists in the vaultareas within X-345, where the special nuclearmaterial is stored. Neutron monitoring in thevaults was prohibited due to criticality concernsassociated with the use of the NIOSH phantommaterial. Since the lobby area was alreadyequipped with an approved phantom material,neutron measurements were obtained there.

Variability in the area measurements obtained fromthe X-745-c locations suggests that dosimeterorientation to the incident neutron radiation is animportant factor in determining the dose.Detection efficiency could be reduced by nearly afactor of three, depending on the neutron angle ofincidence to the TLD/TEDs.37 This measurementvariability could be a concern if a worker is

performing activities near a suspected neutronsource for an extended period.

Comparing HHE Results to the Regulatory Limit

The results reported in this HHE represent onlydoses from neutron exposures. The regulatory limitis based on a “total” dose concept that alsoincorporates doses from internal (alpha) and otherexternal (beta and gamma) exposures. Comparingthe results of the neutron measurements with theregulatory limit should be done with theunderstanding that only a fraction of the “total” doseis represented in these results. For example, theLAW Area results ranged between 0.4-0.6 mSv (40 -60 mrem) during the quarter. This value wouldrepresent a worker’s neutron dose if he or she spent24 hours per day for 90 days in this work area.Doses from other internal or external exposureswere not obtained; however, applying a conservativeassumption that neutrons account for about 12.5percent of the total dose (assuming zero internaldose), a worker could receive a total radiation dosebetween 3.2 - 4.8 mSv (320 - 480 mrem) during thequarter. This represents the maximum dose aworker could receive in this radiation area,assuming operating conditions remain constant. Amore realistic estimate of a worker’s dose would beto adjust the time spent in the radiation area. Anadjusted result using three hours per work day as anaverage time spent in the radiation area is shown inequation 1.

A neutron dose of 3.6 mrem would imply a totaldose of about 29 mrem (3.6 / 0.125 = 28.8) from allexternal sources if neutrons account for 12.5 percentof the total dose as described earlier. This value ofa total dose could then be directly compared withthe regulatory limit (assuming there is no internaldose component). Continuing with the 12.5 percentassumption, it would take a total external dose ofabout 160 mrem to measure neutrons at theTLD/TED detection limit of 20 mrem (20 / 0.125 =


160). Since most external doses due to gammaexposures are below 160 mrem, it would beunlikely that neutrons could be detected at PORTSand may explain why all the personal TLD/TEDmeasurements were below the limit of detection.

Historical Health Physics Practices

In an effort to reconstruct past neutron exposures,the historical health physics monitoring andreporting practices were reviewed. LMUS andunion personnel indicated that abnormal chip ratiosand high doses (above 2.7 rem) were routinelyassumed to be due to equipment failure (“badbadges”) and little effort was made by the HealthPhysics Department to investigate such doses. The2.7-rem dose supposedly occurred in the early1970s during the removal of a uranium deposit inthe X-326 building (high-assay). However, noreport was found in reviewing the Health PhysicsExposure Investigation Reports regarding thisevent. In addition, no such dose was found inreviewing the computerized Health Physicshistorical data provided by the site to NIOSH insupport of the current epidemiologic study. Pastrecording and reporting activities applied to highdoses were provided as reasons for the lack ofhistorical documents and missing data. Recordingdecisions regarding high doses were based on thephilosophy that doses of this size were veryunlikely when compared with past doses reportedand recorded at the site. Therefore, equipmentfailure was provided as the reason for the abnormaldose, and the recorded dose was entered assomething other than the measured value. Officialdocumentation of this policy for reducing assesseddoses could not be found, however. A measureddose of this size may be possible if the exposureoccurred near a highly enriched uranium deposit.The slow cooker phenomenon could explain dosesin this range.

In addition, this review found that backgroundmeasurements used to correct personal results havechanged throughout time.32 Depending on the typeof dosimetry system used, background was handledin one of three ways: it was calculated using

statistics, manually entered into the dosimetryalgorithm, or determined from badges in or near theworking areas. All these methods have certainlimitations. The latter may not represent truebackground exposures (especially if these locationswere in elevated radiation areas). Another issueregarding reporting and recording practices involvesdoses that could not be linked to individuals. Acomputerized account, setup to store these“unlinkable” doses, is commonly called the bucketdose account.38 A cursory review of this accountindicated that several person-rem could not beassigned to individual workers or visitors. Bothapproaches (background issues and bucket doses)reduce the reportable doses and will eventually leadto an artificially low dose history for the facility.

CONCLUSIONSThis evaluation showed that a potential chronic low-level neutron exposure exists at this site whereuranium is stored, handled, or solidified within thecascade. Areas most likely associated with neutronexposures include the Feed and Withdrawal areas,cylinder storage yards, and places where uraniumdeposits are formed within the cascade. Job titlesmost likely associated with potential neutronexposures would be those involving routine tasks inpotential neutron areas (listed in Table IV). Areaneutron doses ranged from less than the detectionlimit (0.2 mSv) to 7.1 mSv and varied with theamount of uranium present, its enrichment level,geometric configuration, and time spent near thesource. While the area measurements confirmed thepresence of a chronic low-level exposure toneutrons, all personal doses were below the limit ofdetection. Recent neutron monitoring resultsconducted by the site have shown reportable neutrondoses. Historical health physics programs (1954 -1992) neither calibrated nor monitored for neutronexposures. Therefore, potential neutron doses havenot been included in the workers dose histories.Data from this evaluation were based on a smallsample size and may reflect specific production andseasonal conditions during the 3-month period.


The current dosimetry programs at PORTS forLMUS and LMES workers are NVLAP- andDOELAP- accredited, respectively, and nowaccount for potential neutron doses. Eachcontractor uses and calibrates dosimeters that arevirtually identical. Although differences exist inthe specific dose algorithms, it is not a substantialproblem because of the general difficultyassociated with assessing neutron doses.

RECOMMENDATIONSThe following recommendations are based onobservations made during the survey and documentreviews. They are intended to help ensure thesafety and health of the workforce. Theserecommendations stem from the presentunderstanding of the workers’ occupationalexposures and potential health effects associatedwith these exposures.

1. The area TLDs used by LMES (DOEcontractor) should be used with an appropriatephantom material to monitor neutron exposures inthe X-345 vault areas properly.

2. To ensure maximum efficiency in detectingneutrons, workers who are likely to be exposed toneutrons should be informed about the properpositioning of the TLD and its angular dependencein detecting incident neutrons.

3. The document entitled “D2O-ModeratedCalifornium-252 Neutron Calibration Factor (Knd)Determination” dated August 17, 1995, should berevised. A minor error in the calculation should becorrected. The Mean Net Test Responsecalculation used the Mean Gross Test Signalsinstead of the Mean Net Test Signals as referencedin the text.39

4. The linkage issues regarding the “bucket dose”account should be reviewed and corrected toimprove record keeping and reporting activities.Where possible, the “bucket” doses should beassigned to individual workers.

5. Archive tapes should not be recycled to facilitatefuture dose reconstruction efforts for compliance orepidemiologic purposes.

6. Area monitoring should continue to be performedin areas where uranium is routinely stored orhandled to characterize potential neutron exposuresbetter. In addition, efforts should be taken toevaluate potential neutron doses associated withknown uranium deposits within the cascade.

7. Past maintenance activities and personnelinvolved in physically removing uranium depositsshould be evaluated to provide better insight on thedoses attributable to the slow cooker phenomenon.

8. Administrative changes or decisions regardingissues in the health physics dosimetry program(doses below the limit of detection, abnormal chipratios, investigative reports, etc.) should be betterdocumented and routinely reported to the workforceto educate, inform, and solicit questions about howthe changes or decisions will affect their doserecords.

ABBREVIATIONS ANDTERMS

CFR Code of Federal Regulations

DHHS Department of Health and HumanServices

DOE Department of Energy

DOELAP Department of Energy LaboratoryAccreditation Program

DOL Department of Labor

ERP Extended Range Product

HHE Health Hazard Evaluation

LAW Low Assay Withdrawal

LMUS Lockheed Martin Utility Services


1. “Energy Policy Act of 1992,” U.S. Code,Title 42, Pt. 13201 et seq. Oct. 24, 1992.

2. U.S. Department of Energy: Memorandum ofUnderstanding Between Department ofEnergy and Department of Health andHuman Services Washington D.C.,December 19, 1990. [Memo] 14 pgs.

3. Borders, R.J. The Dictionary of HealthPhysics and Nuclear Sciences Terms. Hebron,CT: RSA Publications, 1991, p.25.

4. Martin Marietta Energy Systems, Inc. FinalSafety Analysis Report. Introduction,Summary Safety Analysis, Site, and Facilityand Process Description - Part 1. Portsmouth,OH: Martin Marietta Energy Systems, Inc.GAT/GDP-1073. Volume 1. April 1985.

5. Martin Marietta Energy Systems, Inc.Portsmouth Uranium Enrichment Plant:Technical Site Information. Portsmouth, OH:Martin Marietta Energy Systems, Inc. POEF-2059. June 1992.

6. Goodyear Atomic Corporation:Thermoluminescent Dosimeter Response andCalibration by A.C. Bassett (GAT-S-56).Piketon, OH., 1986.

7. U.S. Department of Energy: Health PhysicsManual of Good Practices for UraniumFacilities. B.L Rich, S.L Hinnefeld, C.R.Lagerquist, W.G. Mansfield, L.H. Munson,E.R. Wagner, E.J. Vallario. (EGG-2530:UC-41) Idaho National Engineering Laboratory:Department of Energy, June 1988.

8. Knoll, G.F.: Radiation Detection andMeasurements. Second Edition. New York:John Wiley & Sons, 1989. pp. 514-554.

9. Higginbotham, J. (ed.): Applications of NewTechnology: External Dosimetry. Madison,WI: Medical Physics Publishing, 1996. pp.175-190, 221-254.

10. Turner, J.E.: Atoms, Radiation, and RadiationProtection. New York: Pergamon Press,1986. pp. 180-187.

11. Greening, J.R.: Fundamentals of RadiationDosimetry. Second Edition. Philadelphia: IOPPublishing Inc. 1985. pp. 104-108.

LOD Limit of Detection

LMES Lockheed Martin Energy Services

NIOSH National Institute for OccupationalSafety and Health

NRC Nuclear Regulatory Commission

NVLAP National Voluntary LaboratoryAccreditation Program

OCAW Oil, Chemical and Atomic WorkersUnion International

PGDP Paducah Gaseous Diffusion Plant

PNL Pacific Northwest Laboratories

PORTS Portsmouth Gaseous DiffusionPlant

PW Product Withdrawal Area

TEPC Tissue Equivalent ProportionalCounter

TLD Thermoluminescent Dosimeter

OSHA Occupational Safety and HealthAct

RU Recycled Uranium

Sv Sievert

UPGWA United Plant Guard Workers ofAmerica

USEC United States Enrichment Corp.

REFERENCES


12. Martin Marietta: Nondestructive AssayMeasurements in Support of HEUSuspension at the Portsmouth GaseousDiffusion Plant by J. Bailey, R.C. Hagenauer, R.L. Mayer II, B.R. McGinnis,R.R. Royce ( POEF-TO-1). Piketon, OH.,Martin Marietta, 1993.

13. Goodyear Atomic Corporation:Characterization of Process Holdup Materialat the Portsmouth Gaseous Diffusion Plantby D.E. Boyd and R.R. Miller (GAT-NM-137). Piketon, OH.: Goodyear AtomicCorporation, 1986.

14. Martin Marietta Energy Systems: PORTSDeposit Detection Program: Chartbook fromTSA Team Revisit by C.J. Van Meter (POEF-T-3498). Piketon, OH., Martin MariettaEnergy Systems, 1988.

15. Foster. A.R., R.L. Wright: Basic NuclearEngineering. Fourth Edition. Boston: Allynand Bacon, Inc. 1983. pp. 4-6.

16. Daderstadt, J.J., L.J. Hamilton: NuclearReactor Analysis. New York: John Wiley &Sons, 1976. pp. 74-86.

17. Health Physics and Applied NuclearTechnologies Personnel: “Uranium Depositsat the PORTS.” November 4-8, 1996.[Private Conversation]. Lockheed Martin,USEC; 3030 U.S. Route 23 South; P.O. Box628; Piketon, OH 45661.

18. Goodyear Atomic Corporation: A Guide toOperations When Checking for UraniumDeposits by J.L. Feuerbacher (GAT-DM-758). Piketon, OH., Goodyear AtomicCorporation. 1959.

19. Goodyear Atomic Corporation: A Guide toOperations When Checking for UraniumDeposits by J.L. Feuerbacher (GAT-DM-758). Piketon, OH., Goodyear AtomicCorporation. 1959.

20. Lockheed Martin: “Neutron Monitoring atPORTS Prior to 1990.” E.R. Wagner.Lockheed Martin, Piketon, OH., January 25,1997. [Memo]

21. Goodyear Atomic Corporation: “Assessmentof Neutron Exposure Potential for UraniumMaterial Handlers; GAT-102-86-112." A.C.Bassett. Goodyear Atomic Corporation,Piketon, OH., February 18, 1986. [Memo]

22. Lockheed Martin: “Neutron Dose Equivalentsand Problem Report PR-PTS-95-0582; POEF-050-95-091.” R. Smith. Lockheed Martin,Piketon, OH., July 14, 1995. [Memo]

23. Lockheed Martin Utility Services, Inc.:Evaluation of Dose Potential for UraniumMaterial Handlers by Safety and HealthDivision, External Dosimetry Program.Piketon, OH., Lockheed Martin UtilityServices, Inc., 1995.

24. Pacific Northwest Laboratory: EnrichedUranium Cylinder Neutron CharacterizationMeasurements at the Portsmouth GaseousDiffusion Plant by R.I. Scherpelz, M.K.Murphy, Richland, WA., Pacific NorthwestLaboratory, 1995.

25. “Standards for Protection Against Radiation,”Code of Federal Regulations Title 10, Part 20.1992.

26. National Institute for Occupational Safety andHealth: Mortality among UraniumEnrichment Workers by D.P. Brown, T.Bloom (NTIS PB 87-188991). Cincinnati,OH., National Institute for OccupationalSafety and Health, 1987.

27. Oak Ridge Associated Universities.“Dosimetry Records and Radiation HazardsQuestionnaire.” September 10, 1982.[Unpublished Information]. Oak RidgeAssociated Universities; P.O. Box 117; OakRidge, TN. 37830.


28. Lockheed Martin Utility Services, Inc.:“PORTS Site Neutron Spectral Information;POEF-050-95-067.” S. Jones. LockheedMartin Utility Services, Inc., Piketon, OH.,May 30, 1995. [Memo]

29. U.S. Department of Energy: “DOELAP /Neutron Calibration.” R. Loesh, U.S.Department of Energy / DOELAPAdministrator, Washington, D.C., January13, 1997. [E-mail]

30. Hadlock, D.E.: US Progress on theDevelopment of Neutron Dosemeters Basedon CR-39. Radiation Protection Dosimetry.Vol. 20 No. 1/2 pp. 117-119 (1987).

31. National Institute for Occupational Safetyand Health: “Follow-up Request forHistorical Computerized Exposure Data.” J.J.Cardarelli II, National Institute forOccupational Safety and Health. Cincinnati,OH., December 2, 1996. [Memo]

32. Bowdle, J., Truitt, M.: “Explanation for Lackof Historical Computerized Data andBackground Radiation Applications.”November 22 and November 26, 1996.[Private Conversation]. Lockheed Martin,USEC; 3030 U.S. Route 23 South; P.O. Box628; Piketon, OH 45661.

33. Federal Register. Vol. 58. No. 238. Tuesday, December 14, 1993. Department ofEnergy. 10 CFR Part 835.

34. NCRP Report 122. Use of Personal Monitorsto Estimate Effective Dose Equivalent andEffective Dose to Workers for ExternalExposure to Low-LET Radiation. NationalCouncil on Radiation Protection andMeasurements. Bethesda, MD. December1995.

35. “Occupational Radiation Protection.” Codeof Federal Regulations Title 10, Part 835. 1997.

36. NCRP Report 101. Exposure of the U.S.Population from Occupational Radiation.National Council on Radiation Protection andMeasurements. Bethesda, MD. June 1989.

37. Decossas, J.L. and Varielle, J.C.: The NeutronEnergy and Angular Response ofConventional Etching Systems Based on CR-39. Radiation Protection Dosimetry. Vol. 20No. 1/2 pp. 42-47 (1987).

38. Dulin, C.: “Explanation of Bucket DoseExposure File.” November 8, 1996. [PrivateConversation]. Lockheed Martin, USEC; 3030U.S. Route 23 South; P.O. Box 628; Piketon,OH 45661.

39. Lockheed Martin Utility Service, Inc.: D2O-Moderated Californium-252 NeutronCalibration Factor (Knd) Determination bySafety and Health Division, ExternalDosimetry Program. Piketon, OH., LockheedMartin Utility Services, Inc., 1995.


Table IUSEC and DOE Portsmouth Facilities Selected for Monitoring

Portsmouth Gaseous Diffusion Plant, Piketon, Ohio (HETA 96-0198-2651)

Facility Description LMUSUSEC (NRC)

LMESDOE

X-326X-330X-333X-344-AX-344-BX-705X-345X-745

Process Building (Highly Enriched U*)Process BuildingProcess Building (Depleted U)UF6* Sampling BuildingMaintenance Storage BuildingDecontamination BuildingSNM* Storage BuildingCylinder Storage Yards

XXXXXX

XX

* SNM = Special Nuclear Material U = Uranium UF6 = Uranium Hexafluoride

Table IIRadiological Units#


Quantity Name Symbol Units

Exposure coulomb per kilogram(roentgen) (R)

C kg-1

(2.58 x 10-4 C kg-1)

Dose Equivalent sievert(rem)

Sv(rem)

J kg-1

(10-2 Sv)# Old units are in brackets.


Table IIIIsotopes Present in Natural Uranium*


Isotope Abundance (%) Half-life (Years)238U235U234U

99.2739 ± 0.00070.7204 ± 0.00070.0057 ± 0.0002

4.46 x 109

7.04 x 108

2.45 x 105

* Source: Shleien, G. The Health Physics and Radiological Health Handbook. Revised Edition, Scinta, Inc.Silver Spring, MD. 1992.

Table IVNeutron Monitoring Selections


Job Titles Number

Chemical operators 11

Health physics technicians 5

Laborers (painters/scrapers) 5

Maintenance 1

Process operators 12

Security guards 5

Uranium material handlers 18

Personal measurements 57

Area measurements 33

Field controls (HP, 2 Union Reps) 3

NIOSH controls 8

Total Measurements 101


Table VArea Neutron Measurements

Portsmouth Gaseous Diffusion Plant, Piketon, Ohio (HETA 96-0198-2651)November 1996 - February 1997

Area orControl

Buildings(Area) Location/Comments TLD/TED

Number†Dose

(mSv)‡

Area X-326

ERP (Dynamics St. #2)ERP (Dynamics St. #2)ERP (Dynamics St. #2)

535455

0.200.200.40

PW (T-57-8-3 Bed #3)PW (T-57-8-3 Bed #3)PW (T-57-8-3 Bed #3)

606166

0.200.200.20

Area X-330

TailsTailsTails

737475

<0.20<0.20<0.20

Deposit; dd-4; 29AB-1Deposit; dd-4; 29AB-1Deposit; dd-4; 29AB-1

576369

<0.20<0.20<0.20

G33; 29-3-7-7 (randomly selected)G33; 29-3-7-7 (randomly selected)G33; 29-3-7-7 (randomly selected)

566268

<0.20<0.20<0.20

LAW (near eye wash)LAW (near eye wash)LAW (near eye wash)

717278

0.600.400.60

Area X-343Typical Movement (300 cylinder/month)Typical Movement (300 cylinder/month)Typical Movement (300 cylinder/month)

596567

<0.20<0.20

0.20

Area X-345Behind Phantom #5 on wallBehind Phantom #5 on wallBehind Phantom #5 on wall

374042

<0.20<0.20<0.20

Area X-705PortalPortalPortal

959698

<0.20<0.20<0.20

Table V (continued)Area Neutron Measurements


Area orControl

Buildings(Area) Location/Comments TLD/TED

Number†Dose

(mSv)‡

Page 22 Health Hazard Evaluation Report No. 96-0198-2651

Area X-745-c

DOE Lot; 11,200; 2-3%; row 22-23 Sec. 44DOE Lot; 11,200; 2-3%; row 22-23 Sec. 44DOE Lot; 11,200; 2-3%; row 22-23 Sec. 44

475276

4.202.107.10

DOE Lot; 11,200; 2-3%; row 20-21 Sec. 3, heelDOE Lot; 11,200; 2-3%; row 20-21 Sec. 3, heelDOE Lot; 11,200; 2-3%; row 20-21 Sec. 3, heel

586470

2.105.103.20

Controls

Stayed at NIOSHStayed at NIOSHStayed at NIOSHStayed at NIOSHStayed at NIOSHStayed at NIOSHStayed at NIOSHStayed at NIOSH

012

92939499

100

<0.20<0.20<0.20<0.20<0.20<0.20<0.20<0.20

† TLD/TED numbers provided only for reference purposes with sample locations.

‡ Deep dose equivalent applies to external whole-body exposures and is the dose equivalent at a tissue depthof 1 cm (1,000 mg/cm2). Dose equivalents for the monitoring period below the limit of detection areindicated by <0.20. All fast and moderate energy neutron dosimeters have a minimum reporting value of0.20 mSv (20 mrem). A neutron quality factor of 10 has been applied to the dose estimate.


Table VIPersonal Neutron Dosimetry Results


Job Title Dept. Buildings (Area) Comments TLD/TEDNumber†

Dose(mSv)‡

Chemical Operators

771791771771771771791771771771721

X-705X-344, X-345, X-744-gX-705X-705X-705X-705X-344, X-345, X-744-gX-705X-705X-705X-326

RecoveryCylinder Lots

RecoverySmall PartsSmall PartsCylinder Lots

TunnelSmall PartsMisc.

35789

101113151745

<0.20<0.20<0.20<0.20<0.20<0.20<0.20<0.20<0.20<0.20<0.20

Heath Physics Techs.

300300300300300

X-344, X-343, X-342X-705X-705X-343X-705

HP coverage in buildingHP coverage in building (shift work)HP coverage in buildingHP coverage in building

2282838586

<0.20<0.20<0.20<0.20<0.20

Laborers

147147147147147

Cylinder YardsCylinder YardsCylinder YardsCylinder YardsCylinder Yards

Paint and Scrap in yards (20 hrs/wk)Paint and Scrap in yards (20 hrs/wk)Paint and Scrap in yards (20 hrs/wk)Paint and Scrap in yards (20 hrs/wk)Paint and Scrap in yards (20 hrs/wk)

7779808184

<0.20<0.20<0.20<0.20<0.20

Table VI (continued)Personal Neutron Dosimetry Results



Dose(mSv)‡


Maintenance 469 X-326 General Activities 39 <0.20

Process Operators

720730730740740720730740720730740740

X-333X-330X-330X-326X-326X-333X-330X-326X-333X-330X-326X-326

Cold RecoveryUnit OperatorTails WithdrawalReliefProduct Withdrawal (PW)ACR Low Assay Withdrawal UtilityTails WithdrawalRoverLow Assay Withdrawal OperatorUnit Operator (tails env.)Extended Range Product StationProduct Withdrawal (PW)

233334384143444648495051

<0.20<0.20<0.20<0.20<0.20<0.20<0.20<0.20<0.20<0.20<0.20<0.20

Security Guards

152151152152152

X-326, X-705, X-345X-326X-326, X-705X-326, X-345X-345, X-705

Product WithdrawalRotation P-12Rotation P-12 - 705Rotation P-12

1436899091

<0.20<0.20<0.20<0.20<0.20

Table VI (continued)Personal Neutron Dosimetry Results



Dose(mSv)‡


Uranium Material Handlers

791791791791791791791791791791791791791791791791791791

X-344, X-745-c, X-745-eX-344X-344X-344, X-745-c, X-745-eX-326X-744-GX-344X-344X-344X-344

X-344, X-744-g X-344X-744-gX-344X-344X-344X-345

Cylinder Lots (movements, inspect, staging)Cylinder Lots

L-CageWarehouse StorageAutoclaveAutoclaveShipping and ReceivingAutoclaveDOE and USEC Lots (mostly UESC)

Shipping and ReceivingPick-up and delivery of cylinders, oxides, etc.AutoclaveAutoclaveCylinder Lot X-745-b, misc.Vault

46

12161819202124252627282930313235

<0.20<0.20<0.20<0.20<0.20<0.20<0.20<0.20<0.20<0.20<0.20<0.20<0.20<0.20<0.20<0.20<0.20<0.20

Controls 300AllAllAll

Safety RepresentativeHealth Physics Tech.Safety Representative

878897

<0.20<0.20<0.20

† TLD/TED numbers provided only for reference purposes with sample locations.‡ Deep dose equivalent applies to external whole-body exposures and is the dose equivalent at a tissue depth of 1 cm (1,000 mg/cm2). Doseequivalents for the monitoring period below the minimum reportable quantity are indicated by <0.20. All fast and moderate energy neutron dosimeters


have a minimum reporting value of 0.20 mSv (20 mrem). A neutron quality factor of 10 has been appliedto the dose estimate.


Appendix AUranium Decay Series, 238U (4n+2)†

Nuclide§ Half-Life

Major Radiation Energies (MeV) and Intensities‡

" $ (

MeV % MeV % MeV %238

92U

9999

4.468 x 109 y 4.154.20

22.976.8

0.0496 0.07

23490

Th9999

24.1 d 0.0760.0950.0960.1886

2.76.2

18.672.5

0.06330.09240.09280.1128

3.82.72.70.24

234m91

Pa9999

1.17 m 2.28 98.6 0.7661.001

0.2070.59

99.87%234

91Pa9999

0.13%234

91Pa IT

9999

6.7 h 22 $sE Avg = 0.224Emax = 1.26

0.1320.5700.8830.9260.946

19.710.711.810.912.0

23492

U9999

244,500 y 4.724.77

27.472.3

0.0530.121

0.120.04

23090

Th9999

7.7 x 104 y 4.6214.688

23.476.2

0.06770.1420.144

0.370.070.045

22688

Ra9999

1600 ± 7 y 4.604.78

5.5594.4

0.186 3.28

22286

Rn9999

3.823 d 5.49 99.9 0.510 0.078

21884

Po9999

3.05 m 6.00 -100 0.33 0.02 0.837 0.0011

99.98%214

82Pb9999

0.02%9999

26.8 m 0.670.731.03

48.042.56.3

0.24190.2950.3520.786

7.519.237.1

1.1

21885

At9999

2 s 6.666.76.757

6.489.93.6

0.053 6.6

21483

Bi9999

19.9 m 5.455.51

0.0120.008

1.421.5051.543.27

8.317.617.917.7

0.6091.121.7652.204

46.115.015.9

5.0

Appendix A (continued)Uranium Decay Series, 238U (4n+2)†

Nuclide§ Half-Life


" $ (

MeV % MeV % MeV %


99.979%

21484

Po9999

9999

9999

0.021%9999

164 µs 7.687 100 0.7997 0.010

21081

Tl9999

9999

9999

9999

9999

1.3 m 1.321.872.34

25.056.019.0

0.29180.79970.8601.1101.211.3101.4102.0102.090

79.199.0

6.96.9

17.021.0

4.96.94.9

21082

Pb9999

22.3 y 3.72 0.000002 0.0160.063

80.020.0

0.465 4.0

21083

Bi9999

5.01 d 4.654.69

0.000070.00005

1.161 -100

-100%210

84Po9999

0.00013%9999

138.378 d 5.305 100 0.802 0.0011

20681

Tl9999

4.20 m 1.571 100 0.803 0.0055

20682

Pb Stable

y = Year " = alpha decayd = Day $ = beta decayh = hour ( = gamma decaym = minute IT = Internal transitions = second MeV = million electron volts:s = microsecond (10-6 s)

† This expression describes the mass number of any member in this series, where n is an integer. Forexample: 206Pb (4n+2)...4(51) + 2 = 206.

‡ Intensities refer to percentage of disintegrations of the nuclide itself, not to original parent of series.Gamma %s in terms of observable emissions, not transitions.§ Shaded areas represent the major sources of radiation exposure at the PORTS along with technetium-99,cesium-137 and machine-generated X-rays.


Appendix BActinium Decay Series, 235U (4n+3)†

Nuclide§ Half-Life


" $ (

MeV % MeV % MeV %235

92U9999

7.038 x 108 y 4.2 - 4.324.3364.3984.5-4.6

10.317.65611.3

0.14380.1630.18570.205

10.54.7

544.7

23190Th9999

25.5 h 0.2050.2870.304

154935

0.02560.0842

14.86.5

23191Pa9999

3.276 x 104 y 4.955.015.0295.058

2325.620.211.1

0.02740.28370.3000.30270.330

9.31.62.34.61.3

22789Ac9999

9999 99999999 99999999 9999

21.77 y 4.944.95

0.530.66

0.0190.0340.044

103554

0.0700.1000.160

0.0170.0320.019

98.62%227

90Th9999

9999

9999

1.38%9999

9999

9999

9999

18.718 d 5.7575.9786.038

20.223.324.4

0.0500.2360.3000.3040.330

8.511.2

2.01.12.7

22387Fr9999

21. 8 m 5.44 -0.006 1.15 -100 0.0500.07980.2349

34.09.23.4

22388Ra9999

11.43 d 5.6075.7165.747

24.152.2

9.45

0.1440.1540.2690.3240.338

3.35.6

13.63.92.8

21986Rn9999

3.96 s 6.4256.556.819

7.412.180.3

0.2710.4018

9.96.6

21584Po9999

1.78 ms 7.386 -100 0.74 -0.00023 0.4388 0.04

Appendix B (continued)Actinium Decay Series, 235U (4n+3)†

Nuclide§ Half-Life


" $ (

MeV % MeV % MeV %


-100%211

82Pb9999

9999

9999

0.00023%

9999

36.1 m 0.260.971.37

4.81.4

92.9

0.4050.4270.832

3.01.382.8

21585At9999

-0.1 ms 8.026 -100 0.404 0.047

21183Bi9999

2.14 m 6.286.62

1684

0.579 0.27 0.351 12.7

0.273%211

84Po9999

9999

9999

99.73%9999

0.516 s 7.42 98.9 0.5700.898

0.540.52

20781Tl9999

4.77 m 1.42 99.8 0.897 0.24

20782Pb stable

y = Year " = alpha decayd = Day $ = beta decayh = hour ( = gamma decaym = minute IT = Internal transitions = second MeV = Million electron Volts:s = microsecond (10-6 s)

† This expression describes the mass number of any member in this series, where n is an integer. Forexample: 207Pb (4n+3)...4(51) + 2 = 207.

‡ Intensities refer to percentage of disintegrations of the nuclide itself, not to original parent of series.Gamma %s in terms of observable emissions, not transitions.

§ Shaded areas represent the major sources of radiation exposure at the PORTS along with technetium-99,cesium-137 and machine-generated X-rays.


Appendix CRequested Background Documentation

Number Date Author TitleGAT-NM-137 06/23/86 Boyd, D.E. Charac. of Process Holdup Material ...

GAT-S-56 04/20/86 Bassett, A.C. Thermoluminescent Dosimetry Response &Calibration

GAT-S-58 01/22/86 Ruggles, D.J. TLD Error Analysis

GAT-S-54 11/20/85 Bassett, A.C. TLD Program Processing Proc’s Harshaw2276 ver BGX1

GAT-S-49 06/28/85 Bassett, A.C. Calibration of TLD Albedo Neutron Dosimeters

GAT-T-866 09/08/61 Baker, D.D. The Use of Radioactivity to Determine theUranium ...

POEF-T-3498 09/14/88 Van Meter, C.J. Ports. Deposit Detection Program:..TSA Team Revision ...

POEF-T-3452 06/11/87 Lewis, D.D. ..Neutron Detectors..Uranium Deposit..InCascade

GAT-DM-1099 07/27/66 Feuerbacher, J.L. Use of a Neutron Probe for AssayMonitoring

GAT-DM-1085 10/20/65 Feuerbacher, J.L. Neutron Probe Monitoring for U-235 Assayof UF6 Be ...

GAT-DM-1017 10/17/62 Feuerbacher, J.L. Neutron Probe Readings for Safe Batches atVarious ...

GAT-DM-833 04/25/60 Feuerbacher, J.L. Nuclear Hazards Consideration for a StorageArea ...

GAT-CM-758 06/01/59 Feuerbacher, J.L. A Guide to Operations when checking forUranium Deposits ...

heta 96-0198-2651 portsmouth gaseous diffusion plant ... · technician, chemical operator, and...

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