Dose consequence of environmental water lld values and implications to derivation of revised values
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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 / 22-24 June 2009. REMP LLDs - General.

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Dose consequence of environmental water lld values and implications to derivation of revised values

Dose Consequence of Environmental Water LLD Values and Implications to Derivation of Revised Values

Ken Sejkora

Entergy Nuclear Northeast – Pilgrim Station

Presented at the 19th Annual RETS-REMP Workshop

South Bend, IN / 22-24 June 2009


Remp llds general

REMP LLDs - General

  • Specified in Table 4.12-1 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  • Values are likely outdated when compared to “modern” standards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

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

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

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

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

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

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

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 1.109 usage values valid or current?

  • Dose coefficients for Adult, Teen, Child, Infant

    • Reg Guide 1.109 (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

Dose Consequence from Current LLD Requirement Concentrations


Derived normalized llds 1 mrem yr dose consequence

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

Derived Water Concentrations for 1 mrem/yr Dose Consequence


Limitations and concerns 1

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

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

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

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

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

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

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 1.109 and LADTAP are likely underestimating total body dose; Reg Guide 1.109 dose coefficients need to be modernized


Ken sejkora entergy nuclear northeast pilgrim station

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