Gamma-ray spectrometry measurements of the radioactive waste packages in compliance with storage,

transport, disposal requirements and proof of compliance

Workshop on the Implementation of Decommissioning Schemes under the Research reactor Decommissioning Demonstration Project (R2D2P): Dismantling of the Higher Active Parts

22-26 June, Magurele-Bucharest, Romania

Daniela Gurau, PhD daniela.gurau@nipne.ro

Radiological Characterization Laboratory/ Reactor Decommissioning Department/

Center of Decommissioning and Radioactive Waste Management/ Horia Hulubei National Institute for Physics and Nuclear Engineering

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Th

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• core component in decommissioning

• large amount of radioactive materials

Effective management involves:

• segregation,

• characterization,

• handling,

• treatment,

• conditioning

• and monitoring prior to final disposal.

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Different types of radiation require different forms of protection:

• Alpha radiation cannot penetrate the skin and can be blocked out by a sheet of paper, but is

dangerous in the lung.

• Beta radiation can penetrate into the body surface but can be blocked out by a sheet of

aluminum foil.

• Gamma radiation can go deeply into the body and requires several centimeters of lead or

concrete, or a meter or so of water, to block it.

All of these kinds of radiation are, at low levels, naturally part of our environment, where we are all

naturally exposed to them at low levels.

Any or all of them may be present in any classification of radioactive waste.

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Types of radioactive waste (radwaste)

Low-level Waste

• It comprises paper, rags, tools, clothing, filters etc. which contain small amounts of mostly short-lived radioactivity.

• It is not dangerous to handle, but must be disposed of more carefully than normal garbage.

• Usually it is buried in shallow landfill sites.

• To reduce its volume, it is often compacted or incinerated (in a closed container) before disposal.

• Worldwide it comprises 90% of the volume but only 1% of the radioactivity of all radwaste.

Intermediate-level Waste

• Contains higher amounts of radioactivity and may require special shielding.

• It typically comprises resins, chemical sludge's and reactor components, as well as contaminated materials from reactor decommissioning.

• Worldwide it makes up 7% of the volume and has 4% of the radioactivity of all radwaste.

• It may be solidified in concrete or bitumen for disposal.

High-level Waste

• May be the used fuel itself, or the principal waste separated from reprocessing this.

• While only 3% of the volume of all radwaste, it holds 95% of the radioactivity.

• It contains the highly-radioactive fission products and some heavy elements with long-lived radioactivity.

• It generates a considerable amount of heat and requires cooling, as well as special shielding during handling and transport.

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Wastes from decommissioning nuclear plants

• In the case of nuclear reactors, about 99% of the radioactivity is associated with the fuel.

• Apart from any surface contamination of plant, the remaining radioactivity comes from “activation products” such as steel components which have long been exposed to neutron irradiation.

• Their atoms are changed into different isotopes such as 55Fe, 60Co, 63Ni and 14C.

• The first two are highly radioactive, emitting gamma rays, but with correspondingly short half-lives so that after 50 years from final shutdown their hazard is much diminished.

• Some 137Cs may also be in decommissioning wastes.

• Some scrap material from decommissioning may be recycled, but for uses outside the industry very low clearance levels are applied, so most is buried.

Generally, short-lived intermediate-level wastes (mainly from decommissioning reactors) are buried, while long-lived intermediate-level wastes (from fuel reprocessing)

will be disposed of deep underground.

• Low-level wastes are disposed of in shallow burial sites.

The contamination of the VVR-S reactor is due to:

• reactor operation

• radioisotope production in hot cells

• depleted uranium processing

• research activities

The radionuclides from VVR-S nuclear research reactor with a significant contribution to the radionuclide inventory can be classified into the following classes:

• beta-gamma emitters;

• alpha emitters;

• hard-to-detect radionuclides.

Activity of hard-to-detect radionuclides is difficult to be measured but it can be correlated with the activity of radionuclides that emit strong gamma rays (for example 60Co).

Radioactive contaminants generated by the radioisotope production in hot cells

• Radioisotope production generated a significant contamination in the reactor main building, ventilation system and radioactive leakage drainage, overflow and collecting system.

• Major radioactive contaminants generated by this activity (with the half life higher than one year) are: 60Co, 134Cs, 137Cs and 241Am.

Radioactive contaminants generated by depleted uranium processing and research activities

• Radioactive contaminants generated by these activities are: 238U and 241Am.

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Th

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logi

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• impose

• advanced measurement methods and technologies

• objective

• the radioactive materials are handled or disposed of in a safe and economical manner

Ad

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• to avoid the economical/ social/ environmental negative consequences

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The Radiological Characterization Laboratory (LCR)

- from the Reactor Decommissioning Department (DDR)

- is part from the Decommissioning and Radiological Waste Management Center (CMDDR).

LCR has the notification (accreditation) from the National Commission for Nuclear Activities Control (CNCAN).

The quality management system applied by LCR is integrated in the DDR management system.

The activity of the LCR runs in conformity with the system procedures and work instructions contained in the Integrated Management Manual for the VVR-S Nuclear Reactor decommissioning.

The LCR activities:

1. Radiological characterization of the nuclear installation and workspaces from VVR-S RN, in accordance with characterization plans previously developed.

2. The free release under the authorization of materials and equipment’s from VVR-S RN.

3. Evacuation of the waste from the surveillance zone of the VVR-S RN.

4. Radiological characterization of the radioactive waste drums resulted from the decommissioning of the VVR-S RN.

Romanian Regulatory Framework

Regulatory body

National Commission for Nuclear Activities Control (CNCAN)

NSR-01

Order no. 14/2000 of CNCAN on the approval of Radiological Safety Fundamental Regulations (based on the Council Directive 96/29/EURATOM laying down basic safety standards for the protection of the health of workers and the general public against the dangers arising from ionizing radiation)

all practices need to be authorized;

dose limits;

concepts on justification and optimization of practices and limitation of doses;

exemption, exclusion requirements, levels;

discharge, radioactive waste requirements;

environment monitoring, emergency.

Dose optimization

The applicant or the authorization owner

is obligate to demonstrate that all actions are undertaken to optimize radiation protection, in the sense of ensuring that all exposures, including potential, of the practice developed to be kept to the lowest level reasonably practicable, taking into account economic and social factors - the ALARA principle.

Specific requirements for dose limitation

Effective dose limit for occupationally exposed workers is 20 mSv per year.

Equivalent dose limits:

150 mSv for the lens;

500 mSv for the skin;

500 mSv for the extremities of the hands and feet.

Effective dose limit for population is 1 mSv per year.

Equivalent dose limits:

15 mSv for the lens;

50 mSv for the skin.

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The free release of specific materials from decommissioning

has been accepted at European level a few years ago.

Complex process

requires measurement methods adapted to very low level of radioactivity for the measured materials.

The nuclear facilities decommissioning involves the characterization of large amounts of material.

The release of materials from the regulatory control

unconditional

the materials can be subsequently used without any restriction;

the material must meet the exclusion requirements of the NSR-01 for a single radionuclide;

for a mixture of radionuclides, the release criterion is:

Λ𝑖

𝑅𝐿𝑖

𝑛𝑖=1 < 1

were 𝑛 is the number of radionuclides in the material,

Λ𝑖 is the activity and

𝑅𝐿𝑖 is the release level corresponding to the ith nuclide.

conditional

the materials can be recycled/reused only according to the release conditions.

Free release

Activation Products

Exclusion levels

No. Radionuclide Emitted radiations Half life (Years) Surface activity (Bq/cm2) Specific activity (Bq/g) Remarks

Activation products

1 3H Beta (100%) 12.3 1000 200 Hard-to-detect

2 14C Beta (100%) 5730 30 20 -

3 22Na Beta+, EC, gamma 2.6 3 3 Not important for VVR-S.

4 36Cl Beta, EC 3.105 3 10 -

5 39Ar Beta (100%) 269 - - Not important for VVR-S.

6 41Ca EC 1.03.105 - - Hard-to-detect

7 55Fe EC, X 2.7 300 30 Hard-to-detect

8 63Ni beta 100 1000 70 Hard-to-detect

9 60Co Beta, gamma 5.3 3 1 Key radionuclide for activation products

10 93Zr Beta, gamma 15.105 100 40 Hard-to-detect

11 93Mo EC, X 3500 300 40 Hard-to-detect

12 94Nb Beta, gamma 2.104 3 6 Not important for VVR-S.

13 125Sb Beta, gamma 2.76 10 9 Not important for VVR-S.

14 133Ba EC, X, gamma 10.5 - - -

15 134Cs Beta, gamma 2 3 0.5 -

16 152Eu EC, X, beta, gamma 13.5 10 7 -

17 154Eu Beta, gamma, X 8.6 3 5 -

18 155Eu Beta, gamma, X 4.76 30 30 -

19 166mHo Beta, gamma, X 1200 3 7 -

Fission products

1 90Sr+90Y Beta 28.7 3 0.4 -

2 99Tc Beta 2.13.105 3 10 -

3 106Ru Beta, gamma 1 3 1 -

4 129I Beta, X 1.6.107 1 0.09 Correlated with Cs-137. Not important for VVR-S.

5 137Cs Beta, gamma 30 3 0.8 Key radionuclide for fission products

Actinides

1 238Pu Alpha 87.7 0.3 0.04 -

2 239Pu Alpha 2.41.104 0.3 0.04 -

3 241Pu Beta 14.3 10 2 -

4 241Am Alpha, gamma 432 0.3 0.05 Key radionuclide for actinides

5 244Cm Alpha 18.1 0.3 0.08 -

6 232U Alpha 69 0.3 0.03 -

7 233U Alpha 1.6.105 1 0.02 -

8 234U Alpha 2.5.105 1 0.02 -

9 235U Alpha 7.108 1 0.02 -

10 236U Alpha 2.3.107 1 0.02 -

11 238U Alpha 4.5.109 1 0.02 -

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1. Direct measurement of surface contamination

2. Indirect measurement of surface contamination (wipe testing)

3. Measurement of the activity using gamma spectrometry systems

4. Measurement of the activity using the box monitor with plastic scintillators (Cobalt coincidence method)

5. Measurement of radioactive waste drums using ISOCART systems

Methods of measurement performed Radiological Characterization Laboratory

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Portable radiation monitors used for dose rate and contamination measurements

Survey Instruments

Detector probes Specifications

PORTABLE RADIATION MONITOR

E-600

SHP-380 AB - Application: alpha/beta surveys - Detector type: alpha: ZnS(Ag); beta: NE102 plastic scintillator - Window Area: 100 cm2

- Background: 5 cps - Efficiency (4): 22% 90Sr+90Y; 9% 99Tc; 18% 239Pu. - AMD: 0.5 Bq/cm2 (measuring time=20 s; efficiency=5%)

SHP-360 - Application: alpha/beta/gamma surveys - Detector type: pancake G-M detector with mica window - Window Area: 15 cm2 - Background: 0.65 cps - Efficiency (4): 16% 60Co; 22% 137Cs; 6% 14C; 32% 90Sr+90Y; 15% 99Tc; 25% 241Am. - AMD: 1.3 Bq/cm2 (measuring time=20 s; efficiency=5%)

SSPA-3 - Application: high sensitivity gamma measurements - Detector type: NaI(Tl) 5.1x5.1 cm2 - Energy range: 60 keV – 2 MeV - Background sensitivity: 2.104 cps/mR/h (137Cs)

SHP-210 T - Application: alpha/beta/gamma surveys - Detector type: pancake G-M detector with mica window - Window Area: 15 cm2 - Background: 0.45 cps - Efficiency (4): 16% 60Co; 22% 137Cs; 6% 14C; 32% 90Sr+90Y; 15% 99Tc; 25% 241Am. - AMD: 1.1 Bq/cm2 (measuring time = 20 s; efficiency = 5 %)

SMART DETECTOR EXTENDER

POLE

- Application: dose rate measurements - Detector type: two halogen , energy compensated G-M tubes - Background: 0.1 Sv/h - Energy dependence: 20% from 70 keV to 1.3 MeV - Measurement range: 1 Sv/h …10 Sv/h - Accuracy: 20%

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Portable radiation monitors used for dose rate and contamination measurements

Survey Instruments

Detector probes

Specifications

PORTABLE RADIATION MONITOR

UMo LB 123

LB-1231 - Application: beta-gamma surveys - Detector type: Xenon proportional detector with titanium window - Window Area: 200 cm2 - Background: 16 cps - Efficiency (4): 7% 60Co; 9% 137Cs; 4% 14C; 18% 90Sr+90Y. - AMD: 0.43 Bq/cm2 (measuring time=20 s; efficiency=5%)

LB-1238 - Application: beta-gamma surveys - Detector type: proportional detector with mica window - Window Area: 6.6 cm2 - Background: 0.3 cps - Efficiency (4): 10% 60Co; 12% 137Cs; 20% 90Sr+90Y; - AMD: 2.1 Bq/cm2 (measuring time = 20 s; efficiency=5%)

LB-1236 - Application: dose rate measurements - Detector type: energy compensated proportional counter tube - Energy dependence: 30% from 30 keV to 2 MeV - Background: 0.1 Sv/h - Measurement range: 10-2 Sv/h …104 Sv/h - Accuracy: 20%

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Examples of the types of materials that have been released

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Gamma-ray spectrometry

The most detailed analysis of the gamma emitting radionuclides

can be obtained using gamma-ray spectrometry.

In assaying wastes using gamma spectra

it is neither necessary nor desirable to measure all the gamma-emitting radionuclides and selection criteria must be established.

In general, isotopes with half-lives of less than a year

can be disregarded since they have little bearing on the potential detriment to man during most decommissioning operations and in waste disposal.

The selection of the remaining radionuclides to be measured depends on the waste stream.

Accurate characterization requires that a small representative sample taken from the material stream or package be characterized.

The spectrum of gamma radiation from the sample is measured and from it the constituents and their activities are deduced.

Assuming that the sample is representative of the stream, the total activity per unit weight of stream can be calculated.

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• experimental methods

• theoretical

• simulation (Monte Carlo)

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NaI(Tl) detector

ScintiPack Photomultiplier Base type 296

DigiDART Digital Portable Multichannel Analyzer

In-situ measurements Qualitative measurements - Radionuclide identification Quantitative measurements - Point source - Surface contamination - Volume source

Low resolution gamma spectrometry

Point sources

Peak efficiency for disk sources

using reference point source geometry located at 10 cm distance from the front of the detector

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Primary circuit pipe - internal contamination

Floor from reactor basement - Surface contamination

Ventilation system - internal contamination

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Decommissioning complex

a pioneering activity in Romania

Several techniques based on gamma-ray measurements:

ISOCART, QED, IQ3, SGS, TGS, etc., are commonly available

of great utility in this area;

they specifically provide simple and cost effective solutions to these gamma-ray measurement problems.

In particular, the ISOCART method for waste assay is the most versatile

ability to measure a wide range of waste containers including large containers and objects that can only be measured in situ.

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Radioactive waste measurements

integral view of the sample one spectrum

detector is collimated or not collimated sees the entire sample

partial view of the sample one spectrum per segment

detector is collimated sees only the measured

segment

Measuring the gamma and X-ray intensity external to the package

is the easiest and least expensive means of characterizing radioactive waste;

requires that the waste arising from facilities has fixed ratios of alpha and beta to gamma activity that can be predetermined by laboratory measurements;

in many cases these ratios are not constant and other methods will be required.

Measurements of total radiation fields due to gamma and X-radiation from waste containers can provide an acceptable estimate of the activity if the relationship between activity content and radiation field has been well established.

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Gamma spectrometry technologies

The measurement geometry with integral view of the sample

Integral gamma scanning (IGS)

Simplicity

Good efficiency

Promptitude advantage of measurement

Sensitive to the activity and density distribution

The measurement geometry with partial view of the sample

Segmented gamma scanning (SGS)

Complex

Mechanical system

Computed tomography (CT)

Advanced

Expensive

Restricted application

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Vertical scanning

Segmented gamma scanning (SGS)

Horizontal scanning Angular scanning

The basic machine part of the scanner consists of:

• Detection module of vertical elevation (DM).

• Rotational module with a weighing mechanism (RM).

• Linear slide rail (RAILS).

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ISOCART

Typical geometries include: − Cylinders (lined and solid): used for drums, pipes, and bottles

− Boxes: used for large rectangular shaped containers such as B-25

boxes and crate

− Discs: used for localized contaminated areas on floors and walls or down looking on cylinders

− Point Sources: used for radioactive "hot spots" anywhere

− Infinite Plane: used for fall-out measurements

Integral gamma scanning (IGS)

An optimized transport system for in-situ waste measurements.

Ideal solutions for a wide variety of in-situ gamma-ray measurement requirements.

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Drums without protection (low activity)

Drums with concrete protection

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Radiological properties for radioactive waste storage

Radionuclide content and activity for the package

Maximum admissible activity/package is according to the licensee for Radioactive Waste Management Department – Baita-Bihor no. DMDR11/2009

Radionuclide Max. act. per 1m3 Max. act. per drum

14C 10 GBq (*) 2.2 GBq

59Ni 20 GBq 4.4 GBq

94Nb 0.2 GBq 44 MBq

99Tc 1.5 GBq 0.33 GBq

129I 3 MBq 0.66 MBq

36Cl 0.15 GBq 33 MBq

α emitters with T1/2>5 years 0.1 GBq (**) 0.022 GBq

Β-γ emitters with T1/2>5 years 5 GBq (**) 1.1 GBq

(*) Total activity for 14C allowed to be disposed at DNDR Baita Bihor is 5x1011 Bq

(**) Exceeding of the above limits can be in exceptionally cases approved by CNCAN on the case by case evaluation basis

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Radionuclide Max. act. per 1m3 Max. act. per drum

3H 150 GBq 33 GBq

60Co 2 TBq 436.6 GBq

63Ni 1 TBq 218.3 GBq

90Sr 50 GBq 10.73 GBq

137Cs 50 GBq 10.73 GBq

Emitters with T1/2<5 years 3 TBq (**) 0.66 TBq

Radiological properties for radioactive waste storage

Radionuclide content and activity for the package

Maximum admissible activity/package is according to the licensee for Radioactive Waste Management Department – Baita-Bihor no. DMDR11/2009

(**) Exceeding of the above limits can be in exceptionally cases approved by CNCAN on the case by case evaluation basis

In the case of a radionuclide mixture, is necessary that the sum of the reports between each radionuclide activity and the maximum admissible activity for the specific radionuclide to be less than 1.

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General requirements for disposal

1. Geometry and dimensions:

Drum 220L Diameter -max. 64.5 cm

h -max. 93.0 cm

Drum 420L Diameter -max. 82.0 cm

h -max. 115.0 cm

2. Weight:

Type A package for radioactive waste transport 220L CDR-A-X

max. weight 700kg

Type A package for radioactive waste transport 420L CA-420-X

max. weight 1200kg

Thank you for your attention! Daniela Gurau, PhD

daniela.gurau@nipne.ro Radiological Characterization Laboratory/

Reactor Decommissioning Department/ Center of Decommissioning and Radioactive Waste Management/

Horia Hulubei National Institute for Physics and Nuclear Engineering