Dose Consequence of Environmental Water LLD Values and Implications to Derivation of Revised Values Ken Sejkora Entergy Nuclear Northeast – Pilgrim Station Presented at the 19 th Annual RETS-REMP Workshop South Bend, IN / June 2009

REMP LLDs - General Specified in Table of NUREG-1302/1302 Derived in late 1960s to early 1970s… limited documentation of pedigree, “gray-hair” phenomenon Loosely based on dose consequence and assumption of “reasonable survey” Nuclide list based on major nuclides anticipated to be seen in radwaste source term Values are likely outdated when compared to “modern” standards

REMP LLDs - Dose Original dose factors based on ICRP-2, circa 1950s Dose coefficients have undergone several revisions… ICRP-26/30, ICRP-68/72, newer. Newer factors used throughout international community, limited endorsement by EPA in Federal Guidance Report series. Concept of ‘risk’ based dose consequence based on effective dose equivalent… basis of effluent control limits in 10CFR20 Appendix B, Table 2

REMP LLDs – Reasonable Survey Based on “state-of-the-art” in 1960s What is a “reasonable survey”? Length of counting time – 1hr? Over-night? Analyze as-is, or process? Separation required? Underlying assumptions not documented Function of sample volume, sample geometry, detector efficiency, interfering nuclides (including natural activity) Significant improvements in detector efficiencies and nuclide identification algorithms since 1960s Caveat – just because we can “see” tritium down to 150 pCi/L doesn’t mean we have to set the LLD at 150 pCi/L!

REMP LLDs – Critical Nuclides Origin of current list unknown… GALE source term? How does list compare to what has been seen in 30+ years of power reactor operation? Assuming 100 reactors operating for an average of 20 years, over 2000 “reactor-years” of REMP and effluent data are available for analysis; these are REMP LLDs – emphasis should be on historical REMP sample results Is current list based on activity levels anticipated, or dose impact anticipated? Should some nuclides be removed, and others added? Largely gamma emitters… what about hard-to-detects?

Reason For Concern - 1 Current list of nuclides and LLD values is nearly 40 years old, poorly documented Current list may not reflect modern standards or past operating experience Current list was proposed for inclusion in DG- 4013, the new revision to Regulatory Guide 4.1 Do we want to incorporate LLD values from 40 years ago, with undocumented pedigree, into new standards?

Reason For Concern - 2 What rationale is to be used to derive required LLDs for nuclides and/or exposure pathways not in current list? Need to have consistent approach for all licensees to apply if posed with deriving their own LLDs for a specific nuclide or pathway LLDs chosen should result in a similar dose/risk consequence -- Dose-based LLDs!

Method of Approach Evaluate dose impact of current LLD requirements Age-specific dose coefficients; ICRP-2 and ICRP-72 Age-specific media usage factors Derive revised LLD values based on a normalized dose impact of 1 mrem/yr I am NOT suggesting or endorsing 1 mrem/yr as the limiting dose for establishing LLDs! “Normalized” factor allows easy scaling to any dose target deemed “acceptable”

Dose Impact – Current Water LLDs Illustrate technique. Need to repeat for other exposure pathways and nuclides Dose = Concentration * Usage * Dose Factor mrem/yr pCi/L L/yr mrem/pCi Usage factors for Adult, Teen, Child, Infant Are Regulatory Guide usage values valid or current? Dose coefficients for Adult, Teen, Child, Infant Reg Guide (LADTAP) values – Outdated, but provide insight to what may have been used in derivation of original values Avoid ICRP-30 factors… single age group (Adult), occupational ICRP-72 factors… used 4 of 6 available age classes

Dose Consequence from Current LLD Requirement Concentrations Nuclide Required Water LLD pCi/L Resulting Maximum Dose Consequence: mrem/yr ICRP-2 Maximum Organ ICRP-2 Total Body ICRP-72 EDE H Infant 0.18 Infant Mn Adult0.02 Infant0.10 Infant Fe Adult0.21 Infant1.44 Infant Co Adult0.04 Infant0.13 Infant Co Adult0.13 Infant0.99 Infant Zn Infant0.35 Child1.33 Infant Zr Adult3.5E-4 Child0.31 Infant Nb Adult5.0E-5 Infant0.08 Infant I Infant0.01 Infant0.22 Infant Cs Infant1.32 Adult0.78 Adult Cs Infant0.94 Adult0.66 Adult Ba Infant0.17 Infant2.33 Infant La Adult1.1E-5 Infant0.36 Infant

Derived Normalized LLDs – 1 mrem/yr Dose Consequence Existing LLD concentration will yield corresponding dose consequence Only accounts for drinking water ingestion. Other exposure pathways not included If existing dose consequence is less than 1 mrem/yr, increase LLD proportionally If existing dose consequence is greater than 1 mrem/yr, decrease LLD proportionally How? -- Multiply arithmetic inverse of dose consequence by existing LLD concentration value

Derived Water Concentrations for 1 mrem/yr Dose Consequence Nuclide Drinking Water Concentration to yield 1 mrem/yr ICRP-2 Maximum Organ ICRP-2 Total Body ICRP-72 EDE H-317,000 11,000 Mn Fe Co Co Zn Zr ,00096 Nb , I Cs Cs Ba La ,400,00042

Limitations and Concerns -1 Only addresses drinking water pathway Data from 2007 RETS-REMP Presentation indicate including other pathways may increase dose by 2x to 600x over drinking water alone… nuclide dependent However, the above effect is offset if analysis of other pathways (fish, shellfish, crops) shows buildup is not occurring and contributing to increasing total dose from all pathways Approach assumes water concentration is at or above LLD 100% of the time In reality, concentration is likely much less than LLD, and dose consequence is much less than 1 mrem/yr

Limitations and Concerns -2 Calculated EDE dose from ICRP-72 dose factors is often much higher than “Total Body” dose calculated from ICRP-2 factors Potential to grossly underestimate true “total body” dose used to demonstrate compliance with dose limits… NON-CONSERVATIVE ICRP-72 factors are more modern and widely accepted and used by the international community

Where to from here… - 1 Encourage NRC to derive new dose-based LLD targets for inclusion in revision to Regulatory Guide 4.1 Based on use of ICRP-72 or newer dose coefficients Provide guidance and methodology for deriving LLDs for nuclides of interest not addressed in table Endorse application of stochastic, EDE-based dose/risk assumptions… eliminate need for non-stochastic, organ-specific dose calculations

Where to from here… - 2 Encourage revision of list of critical nuclides included in LLD table Primary emphasis should be on those nuclides yielding majority of dose; secondary consideration to activity Consider data gleaned from review of historical REMP and effluent data from over 2000 reactor-years of operation to determine most-important nuclides; 1˚ emphasis on REMP sample data, 2˚ consideration on effluent data… EPRI? Industry working group? Graduate student research project?

Where to from here… - 3 Encourage establishment of dose/risk based LLDs with risk commensurate with other regulatory programs The same dose/risk value used to derive MARSSIM DCGLs should be considered for establishing dose- based LLDs; already accepted and endorsed by NRC, EPA, and DOE agreement MARSSIM DCGL values may prove to be a viable alternative to dose-based LLDs

Summary - 1 Current REMP LLD values are likely outdated, poorly documented, and may be non- conservative in some cases The current list of critical nuclides may not be representative of those observed through 30+ years of commercial power reactor operations Existing/current REMP LLD values are not “robust” enough for inclusion in new revisions to NRC guidance documents

Summary - 2 Establishment of EDE-based LLDs would provide a consistent, uniform approach and risk-basis across various nuclides and pathways Current ICRP-2 dose coefficients from Regulatory Guide and LADTAP are likely underestimating total body dose; Reg Guide dose coefficients need to be modernized

Questions?