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Ken Sejkora Entergy Nuclear Northeast – Pilgrim Station

Implications of Tritium Dose Conversion Factors in Deriving Regulatory Limits for Drinking Water and Effluent Compliance. Ken Sejkora Entergy Nuclear Northeast – Pilgrim Station Presented at the 16 th Annual RETS-REMP Workshop Mashantucket, CT / 26-28 June 2006. Reason for Concern.

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Ken Sejkora Entergy Nuclear Northeast – Pilgrim Station

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  1. Implications of Tritium Dose Conversion Factors in Deriving Regulatory Limits for Drinking Water and Effluent Compliance Ken Sejkora Entergy Nuclear Northeast – Pilgrim Station Presented at the 16th Annual RETS-REMP Workshop Mashantucket, CT / 26-28 June 2006

  2. Reason for Concern • Issue of tritium in groundwater has crossed jurisdictional boundaries… NRC, EPA, state radiation control programs are involved • Various limits exist governing effluent compliance, safe drinking water standards, and dose/risk assessment • Recognize the different limits, reasons for differences, and implications/applicability

  3. EPA Drinking Water Standard …from the beginning • Specified in 40 CFR 141.25 • Refer to: www.epa.gov/safewater/rads/radfr.pdf • 20,000 pCi/Liter, assumed to yield committed dose of 4 mrem/yr • Based on drinking water consumption of 2 liters/day = 730 liters/yr • 20,000 pCi/L * 730 L/yr = 1.46E+7 pCi/yr • 4 mrem / 1.46E+7 pCi = 2.74E-7 mrem/pCi

  4. EPA Drinking Water Standard …why it’s important • Standard limit adopted by state regulatory agencies… often takes precedence over ODCM limits if groundwater is involved • Used as basis for tables in standard ODCM guidance – NUREG-1301/1302 • Table 3.12-2, “Reporting Levels”… 20,000 pCi/L for drinking water; 30,000 pCi/L for non-DW • Table 4.12-1, “Lower Limit of Detection”… set at 1/10 of Reporting Level = 2,000 pCi/L for DW; 3,000 pCi/L for non-DW.

  5. EPA Drinking Water Standard … where did it come from? • Roots in ICRP-2, circa late 1950s • “Second generation derivative” of NRC maximum permissible concentration (MPC) value • 1 MPC = 500 mrem/yr total body • Early MPC for tritium: 3E-3 uCi/mL • (4 mrem / 500 mrem) * 3E-3 uCi/mL = 2.4E-5 uCi/mL = 24,000 pCi/L • Rounded to 20,000 pCi/L… one significant figure • “Gray-hair” phenomenon… derivation not documented, exists only in recollection of experts involved

  6. Other ICRP-2 based Factors • Direct activity-to-dose factors… • not “back-calculated” from concentration limit • Age-specific dose factors • Regulatory Guide 1.109, Ingestion dose factors, Tables E-11 through E-14 • Adult: 1.05E-7 mrem/pCi Child: 2.03E-7 mrem/pCi • Teen: 1.06E-7 mrem/pCi Infant: 3.08E-7 mrem/pCi

  7. Other ICRP-2 based Factors …continued • LADTAP Factors… refinement of RG-1.109 factors • Adult: 5.99E-8 mrem/pCi Child: 1.16E-7 mrem/pCi • Teen: 6.04E-8 mrem/pCi Infant: 1.76E-7 mrem/pCi • RG-1.109 and LADTAP dose conversion factors are the de facto values used in most plants’ ODCMs, effluent control programs, and effluent dose calculation software

  8. ICRP-30 based Factors • Based on ICRP-26 “standard man” approach, occupational exposure… circa early 1970s • Single age class = adult male • Basis for current values in 10CFR20 Appendix B, and EPA Federal Guidance Report 11 • Ingestion DCF = 6.40E-8 mrem/pCi • Table 2, Column 2 Concentration Limit - Public = 1E-3 uCi/mL, or 1,000,000 pCi/L assumed to yield committed dose of 50 mrem/yr

  9. ICRP-60/72 Factors • Based on ICRP-60 metabolic models… most modern, circa late 1990s • Non-occupational exposure, latest risk quality factors, multiple age classes, • Adult: 7.09E-8 mrem/pCi 5-yr: 1.25E-7 mrem/pCi • 15-yr: 7.07E-8 mrem/pCi 1-yr: 2.04E-7 mrem/pCi • 10-yr: 9.06E-8 mrem/pCi Infant:  2.79E-7 mrem/pCi • Standard among international community, but not widely adopted in USA, nor endorsed by NRC; however, adopted in EPA FGR-13

  10. Side-by-side Comparison • EPA DW Standard: 2.74E-7 mrem/pCi • Reg Guide 1.109 • Adult: 1.05E-7 mrem/pCi Child: 2.03E-7 mrem/pCi • Teen: 1.06E-7 mrem/pCi Infant: 3.08E-7 mrem/pCi • LADTAP • Adult: 5.99E-8 mrem/pCi Child: 1.16E-7 mrem/pCi • Teen: 6.04E-8 mrem/pCi Infant: 1.76E-7 mrem/pCi • ICRP-30: 6.40E-8 mrem/pCi • ICRP-72 • Adult: 7.09E-8 mrem/pCi 5-yr: 1.25E-7 mrem/pCi • 15-yr: 7.07E-8 mrem/pCi 1-yr: 2.04E-7 mrem/pCi • 10-yr: 9.06E-8 mrem/pCi Infant: 2.79E-7 mrem/pCi

  11. Which Limit to Use? • RG-1.109/LADTAP for ODCM effluent release compliance, possible extension to REMP samples • EPA Safe Drinking Water Standard adopted by most state programs… comes into play if offsite groundwater is involved • ICRP-72 is not used (except for EPA FGR-13), despite being most modern and based on best available technology • When dealing with the recent groundwater issue, one could argue we should use the most up-to-date methodology and science available.

  12. Beware… • Organically-bound tritium • Strontium-90

  13. Organically-bound tritium • Existing limits (EPA, NRC) are based on tritium in the form of tritiated water • High metabolism, rapid turnover/clearance from body • Relatively low dose impact • Organically-bound tritium, once incorporated into tissue, has much longer residence time in body • More time = Higher dose impact • Could result in lower limits than those based on conventional tritiated water metabolism • Organically bound tritium is not of concern in drinking water, but could result in modifying concentration limits to account for higher dose/risk once in the body

  14. Strontium-90 • Exists at low levels in environment from weapons testing in 1950s through 1970s; often seen in REMP samples • Has been detected at low levels in groundwater by some licensees • There is a separate EPA drinking water standard for Sr-90 listed in 40CFR141 • According to Federal Register, based on assumption that 8 pCi/L Sr-90 will yield 4 mrem/yr to bone marrow. • Similar rationale to that used for H-3 at 20,000 pCi/L

  15. Strontium-90 -- …error in drinking water standard? • 1 MPC = 1500 mrem/yr critical organ (bone) • MPC for Sr-90: 3E-7 uCi/mL • (4 mrem / 1500 mrem) * 3E-7 uCi/mL = 8E-10 uCi/mL = 0.8 pCi/L, NOT 8 pCi/L • 8 pCi/L * 730 L/yr = 5840 pCi/yr intake • 5840 pCi/yr * 7.58E-3 mrem/pCi = 44 mrem/yr, NOT 4 mrem/yr • EPA standard for Sr-90 appears to be 10X too high! • Compliance with the EPA standard of 8 pCi/L would exceed the 10CFR50 Appendix I organ dose limit of 15 mrem/yr by about 3X

  16. Summary • Several limits exist for tritium in water • EPA drinking water limit = 20,000 pCi/L • NRC effluent limit = 1,000,000 pCi/L (1E-3 uCi/mL) • Fractional limits imposed by states? • Various limits are based on different assumptions, different bases • EPA: 20,000 pCi/L = 4 mrem/yr, based on ICRP-2 • NRC: 1,000,000 pCi/L = 50 mrem/yr, based on ICRP-30

  17. Summary (continued) • Other nuclides, forms may come into play • Organically-bound tritium, Sr-90 • Concern about non-conservative Sr-90 drinking water standard • If one has to deal with multiple nuclides, it makes sense to use a single standard, and presumably the most modern one… ICRP-72

  18. Conclusion This IS a dose issue

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