Ken Sejkora

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• Ken Sejkora
• Entergy Nuclear Northeast Pilgrim Station
• Presented at the 19th Annual RETS-REMP Workshop
• South Bend, IN / 22-24 June 2009

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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• Values are likely outdated when compared to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

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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

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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 doesnt mean we have to set the LLD
  at 150 pCi/L!

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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?

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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?

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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!

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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

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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

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Dose Consequence from Current LLD Requirement
Concentrations
Nuclide Required Water LLD pCi/L Resulting Maximum Dose Consequence mrem/yr Resulting Maximum Dose Consequence mrem/yr Resulting Maximum Dose Consequence mrem/yr
Nuclide Required Water LLD pCi/L ICRP-2 Maximum Organ ICRP-2 Total Body ICRP-72 EDE
H-3 2000 0.12 Infant 0.12 Infant 0.18 Infant
Mn-54 15 0.15 Adult 0.02 Infant 0.10 Infant
Fe-59 30 0.74 Adult 0.21 Infant 1.44 Infant
Co-58 15 0.17 Adult 0.04 Infant 0.13 Infant
Co-60 15 0.44 Adult 0.13 Infant 0.99 Infant
Zn-65 30 0.62 Infant 0.35 Child 1.33 Infant
Zr-95 30 0.68 Adult 3.5E-4 Child 0.31 Infant
Nb-95 15 0.23 Adult 5.0E-5 Infant 0.08 Infant
I-131 1 4.59 Infant 0.01 Infant 0.22 Infant
Cs-134 15 3.48 Infant 1.32 Adult 0.78 Adult
Cs-137 18 3.63 Infant 0.94 Adult 0.66 Adult
Ba-140 60 3.39 Infant 0.17 Infant 2.33 Infant
La-140 15 1.01 Adult 1.1E-5 Infant 0.36 Infant
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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

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Derived Water Concentrations for 1 mrem/yr Dose
Consequence
Nuclide Drinking Water Concentration to yield 1 mrem/yr Drinking Water Concentration to yield 1 mrem/yr Drinking Water Concentration to yield 1 mrem/yr
Nuclide ICRP-2 Maximum Organ ICRP-2 Total Body ICRP-72 EDE
H-3 17,000 17,000 11,000
Mn-54 98 670 150
Fe-59 40 140 21
Co-58 91 340 110
Co-60 34 120 15
Zn-65 48 86 23
Zr-95 44 85,000 96
Nb-95 65 300,000 180
I-131 0.22 160 4.4
Cs-134 4.3 11 19
Cs-137 5.0 19 27
Ba-140 18 340 26
La-140 15 1,400,000 42
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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

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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

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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

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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?

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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

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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

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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

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• Questions?