Implications of Tritium Dose Conversion Factors in Deriving by 1ANH47O1

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									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
     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
        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
        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.
        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
        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
        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
     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
     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
     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
     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.
    Beware…


   Organically-bound tritium

   Strontium-90
        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
        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
        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
        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
        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
Conclusion



    This IS a dose issue

								
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