soluble uranium definition for regulatory compliance. · 100 % class y 100 % class w 100 % class d...

SOLUBLE URANIUM DEFINITION FOR REGULATORY COMPLIANCE

2014 Health Physics Society’s Radiation Safety Conference (July 13–17, 2014)

Roland Benke, Ph.D., CHP (Center for Nuclear Waste Regulatory Analyses)Tanya Oxenberg, Ph.D. (U.S. Nuclear Regulatory Commission)

James Webb (U.S. Nuclear Regulatory Commission)

Background

2

Uranium extraction practices have evolved over decades Existing regulatory guidance is being expanded to address

in-situ recovery processes and operations CNWRA and U.S. Nuclear Regulatory Commission (USNRC) are

updating Regulatory Guide 8.30, Health Physics Surveys in Uranium Recovery Facilities

Regulatory Limits

3

Radiological and chemical toxicity considerations apply to occupational uranium intakes

o Annual radiation dose limits in 10 CFR 20.1201o Weekly intake limit of 10 mg of soluble uranium per 10 CFR 20.1201(e)

Occupational limits for soluble uranium exist to prevent chemical toxicity effects on kidney function due to uranium accumulation in the kidney and its persistence with time

Regulatory Definition Gap

4

In operational settings at uranium recovery facilities, uranium tends to be a mixture of chemical compounds and multiple inhalation classes.

Uranium ore is an exception; singular inhalation class W applies

No soluble uranium definition in 10 CFR Part 20

Guidance needed on which inhalation classes relate to soluble uranium so that weekly occupational intakes can be compared to the 10-mg limit specified in 10 CFR 20.1201(e)

Recommended Definition

5

Recommended definition for soluble uranium

Technical basis addressed by remainder of presentation

INHALATION CLASS BLOOD UPTAKE FRACTION, f1 REGULATORY POSITION

D 0.05 Soluble

W 0.05 Soluble

Y 0.002 Insoluble

Biokinetic Modeling

6

Biokinetic models represent the human body by a group of interconnected compartments.

o Regions of the human respiratory system o Organs (e.g., kidney)

Transfer rates specified between compartments

Compute transfer to, accumulation in, and removal or excretion from compartments

Uranium Concentration in the Kidney

7

Biokinetic modeling for uranium has been described.o NUREG–0874, Internal Dosimetry Model for Applications to Bioassay

at Uranium Mills, U.S. Nuclear Regulatory Commission, Washington, DC, July 1986.

Calculated kidney concentrationso Various uranium compound mixtureso Inhalation and ingestion o Single and continuous intakes

Internal Dosimetry Calculation

8

Influenced by aerosol particle size and chemical form

Aerosol deposition fractions influenced by particle size

Transfer rates among compartments influenced by chemical form (Inhalation classes)


9

o NP,Bo TB,Bo P,B

Calculated time dependent solution for each pathway

TB,B P,BNP,B

3 pathways via lung compartments through blood

Many distinct pathways to kidney


10

o NP,GIo TB,GI o P,GI(fast)o P,GI(slow)


TB,GI P,GINP,GI

3 pathways via lung compartments through gastrointestinal tract

(4 solutions)


o NP,Bo TB,Bo P,B


11

o P,L,B


P,L,B

1 pathway via pulmonary lung through lymph node and blood


o NP,Bo TB,Bo P,Bo NP,GIo TB,GI o P,GI(fast)o P,GI(slow)


12

o NP,B,So TB,B,So P,B,S


3 additional systemic pathways via blood and other organs

TB,B,S P,B,SNP,B,S


o NP,Bo TB,Bo P,Bo NP,GIo TB,GI o P,GI(fast)o P,GI(slow)o P,L,B


13

o NP,GI,So TB,GI,So P,GI(fast),So P,GI(slow),S


NP,GI,S TB,GI,S P,GI,S

3 additional systemic pathways via gastrointestinal

tract and other organs(4 solutions)





14

o P,L,B,S


1 additional systemic pathway via lymph node, blood, and other organs

o NP,GI,So TB,GI,So P,GI(fast),So P,GI(slow),S




P,L,B,S

Continuous Inhalation: 2-Compartment Solution

15

Presenting examples for continuous inhalation intake In-vivo pathways dictate number of compartments and solutions Fractional transfer through blood and gastrointestinal tract (GI)

does not require separate compartment modeling

Lung compartment

Kidney

C1 × Intake rate

C2 × λ1

λ2

via blood

via GI and blood

or

KidneyIntake rate 1 1

16


via blood

via blood

via GI and blood

or

Lung compartment

Kidney

C1 × Intake rate

C2 × λ1

λ3

Lymph node

C3 × λ2

Kidney Intake rate1

Lung compartment

Kidney

C1 × Intake rate

C2 × λ1

λ3

Systemic, organs other than kidney

C3 × λ2

17


Intakerate 1

via blood

via blood

via GI and blood

or

Lung compartment

Kidney

C1 × Intake rate

C2 × λ1

λ4

Lymph node

C3 × λ2

Systemic, organs other than kidney

C4 × λ3 via blood

Kidney

Continuous inhalation intake Applied 2-, 3-, and 4-

compartment solutions for fractional contributions of each inhalation class in the uranium mixture

o Class D (no pathway contributions from pulmonary lung to gastrointestinal tract)

o Class Wo Class Y

Selected Results for Inhalation Intakes

18

Class D — Readily transferred to kidney

Class W — Lesser effectiveness for elevating uranium concentrations in the kidney

Class Y — Least effectivenesso Lower by more than an order of

magnitude at shorter timeso Increased contribution at longer

timeso For single intake, long-term kidney

burden is significantly lower than short-term values

o For continuous intake, long-term burden is significantly lower compared to burden from more soluble compounds

0.000001

0.00001

0.0001

0.001

0.01

0.1

1

1 10 100 1,000Kid

ney

Bur

den

(Ura

nium

Mas

s in

Kid

ney

per U

nit

Inta

ke M

ass)

Time (days)

100 % Class Y

100 % Class W

100 % Class D

0.000001

0.00001

0.0001

0.001

0.01

0.1

1

10

1 10 100 1,000 10,000Kid

ney

Bur

den

(Ura

nium

Mas

s in

Kid

ney

per U

nit

Dai

ly In

take

Mas

s)

Time (days)

100 % Class Y

100 % Class W

100 % Class D

Single Inhalation Intake

Continuous Inhalation Intake

1E-06

1E-05

0.0001

0.001

0.01

0.1

1

1 10 100 1,000Kid

ney

Bur

den

(Ura

nium

Mas

s in

Kid

ney

per U

nit

Dai

ly In

take

Mas

s)

Time (days)

100 % Class Y

100 % Class W100 % Class D

0.000001

0.00001

0.0001

0.001

0.01

0.1

1

1 10 100 1,000Kid

ney

Bur

den

(Ura

nium

Mas

s in

Kid

ney

per U

nit

Inta

ke M

ass)

Time (days)

100 % Class Y

100 % Class W

100 % Class D

Selected Results for Ingestion Intakes

19

Ingestion less effective compared to inhalation

Classes D and W more readily transferred to kidney

Same behavior for Classes D and W following ingestion

Substantially smaller contributions from Class Y

Single Ingestion Intake

Continuous Ingestion Intake

0.0001

0.001

0.01

0.1

1

1 10 100 1,000 10,000

Kid

ney

Bur

den

(Ura

nium

Mas

s in

Kid

ney

per

Dai

ly M

ass

Inta

ke)

Time (days)

Total (All Classes)

Class Y Contribution

Class W Contribution

0.000001

0.00001

0.0001

0.001

0.01

0.1

1 10 100 1,000Kid

ney

Bur

den

(Ura

nium

Mas

s in

Kid

ney

per U

nit

Inta

ke M

ass)

Time (days)

Total (All Classes)



Selected Inhalation Results for Uranium Mixture

20

Uranium compound mixtureo Class D

o Class W

o Class Y

Class D—Dominant contribution to maximum kidney burden

Class W—Small contribution

Class Y—Negligible contribution

Single Inhalation Intake

Continuous Inhalation Intake

0.000001

0.00001

0.0001

0.001

0.01

0.1

1

1 10 100 1,000 10,000

Kid

ney

Bur

den

(Ura

nium

Mas

s in

Kid

ney

per

Dai

ly M

ass

Inta

ke)

Time (days)

Total (All Classes)



0.000001

0.00001

0.0001

0.001

0.01

0.1

1 10 100 1,000Kid

ney

Bur

den

(Ura

nium

Mas

s in

Kid

ney

per U

nit

Inta

ke M

ass)

Time (days)

Total (All Classes)



Selected Ingestion Results for Uranium Mixture

21

Uranium compound mixtureo Class D

o Class W

o Class Y

Classes D & W — Significant (equal) contributions to maximum kidney burden

Class Y — Negligible contribution

Single Ingestion Intake

Continuous Ingestion Intake

Radiotoxicity vs. Chemotoxicity

22

Biokinetic modeling of maximum kidney burden provides technical basis from chemotoxic perspective

Radiological limits also apply to uranium intakes

Most restrictive limit (radiological or chemical) depends on relative abundances of the different uranium compounds

Applying the recommended soluble uranium definition for the inhalation of soluble and insoluble mixtures

o Radiotoxicity is limiting when Class Y abundance > ~9 percento Chemotoxicity is limiting when Class Y abundance < ~9 percent

Conclusions

23

Calculation results support defining soluble uranium as those chemical compounds associated with Inhalation Classes D and W and blood uptake fractions of 0.05.

Class Y compounds with a blood uptake fraction of 0.002 are insoluble and provide small contributions to the maximum uranium concentration in the kidney.

Neglecting the insoluble contribution to the uranium concentration in the kidney is acceptable because radiotoxicity is more limiting than chemical toxicity for inhaled mixtures of soluble and insoluble uranium with significant Class Y contributions.

Acknowledgement

24

This presentation is an independent product of the Center for Nuclear Waste Regulatory Analyses and does not necessarily reflect the view or regulatory position of USNRC. The USNRC staff views expressed herein are preliminary and do not constitute a final judgment or determination of the matters addressed or of the acceptability of any licensing action that may be under consideration at USNRC.

soluble uranium definition for regulatory compliance. · 100 % class y 100 % class w 100 % class d...

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