Impact of License Extension on Radionuclide Buildup Assumptions Ken Sejkora Entergy Nuclear Northeast – Pilgrim Station Presented at the 18 th Annual RETS-REMP Workshop Charlotte, NC / June 2008

Reason for Concern Regulatory Guide accounts for buildup of radioactivity for the following exposure pathways: Waterborne Nuclides in Shoreline Deposits Waterborne Nuclides in Irrigated Foods Deposition of Airborne Nuclides on Ground Plane Deposition of Airborne Nuclides on Soil and Crops… forage, produce, vegetables, milk, meat

Reason for Concern (continued) Regulatory Guide assumes buildup period (t b ) of 15 years “…approximate midpoint of facility operating life…” per Equations A-4 and C-1 Many facilities have operated for well beyond 15 years, and many are pursuing license extension for an additional 20 years of operation… total span of up to 60 years

Reason for Concern (continued) What is the impact on dose calculations of assuming buildup during entire duration of 40-year license? What is the impact on dose calculations of assuming 20 years of additional operation?

Buildup Equation Used in RG equations 3, 4, A-4, A-6, A-7, A-8, A-13, C-1, and C-5 General form of equation: Where: λ i = nuclide decay constant, yr -1 t b = buildup period, yr

Buildup Factor by Nuclide Nuclide Half-life yearsLambda Buildup Factor by Buildup Period 15-yr40-yr60-yr Mn E E+00 Fe E E-01 Co E E E E+00 Zn E E-01 Sr E E E E+01 I E E-02 Cs E E E+00 Cs E E E E+01

Buildup Factor Ratio by Nuclide Nuclide Ratio to 15-yr Buildup Factor 15-yr40-yr60-yr Mn Fe Co Zn Sr I Cs Cs

Clarification of Buildup Equation for Vegetation Pathways Equation for Buildup in Vegetation: External Surface Contamination Term… Short-term weathering Internal Plant-Soil Uptake Term… Long-term metabolism Affects equations for irrigated crops, produce, vegetables, and forage (which in turn affects milk and meat)

Vegetation: External Contamination Term Where: r = fraction of deposited activity retained on leaf/plant surface λ Ei = weathering removal rate constant, 14-day half-life & nuclide half-life t e = exposure time to deposition fallout; forage = 30d, crops = 60d Y v = vegetation yield; forage =0.7 kg/m 2, crops = 2 kg/m 2 The external contamination term from deposition fallout typically accounts for 75 to 100% of the total radionuclide activity in and on vegetation. Not dependent on duration of buildup period.

Vegetation: Internal Plant-Soil Uptake Term Where: f I = fraction of year forage/crops are growing or irrigated (“exposed”) B iv = soil-to-plant uptake factor for nuclide i P = effective “surface” soil density, 240 kg/m 2 The metabolic uptake term from soil typically accounts for less than 10% of the total radionuclide activity in and on forage (cow-milk pathway), and less than 20% in the crop pathway.

Forage Concentration Terms Nuclide Deposition Term Uptake Term 15-yr40-yr60-yr Mn E E+00 Fe E E-03 Co E E E E+00 Zn E E+01 Sr E E E E+01 I E E-02 Cs E E E+00 Cs E E E E+01

Forage Concentration Buildup Factor Ratio by Nuclide Nuclide Ratio to 15-yr Buildup Factor 15-yr40-yr60-yr Mn Fe Co Zn Sr I Cs Cs

Crop Concentration Terms Nuclide Deposition Term Uptake Term 15-yr40-yr60-yr Mn E E+00 Fe E E-03 Co E E E E+00 Zn E E+01 Sr E E E E+01 I E E-02 Cs E E E+00 Cs E E E E+01

Crop Concentration Buildup Factor Ratio by Nuclide Nuclide Ratio to 15-yr Buildup Factor 15-yr40-yr60-yr Mn Fe Co Zn Sr I Cs Cs

Summary Extended buildup period has negligible impact on ingestion pathway concentrations and doses from irrigated crops, produce, vegetables, milk, and meat… less than 25% increase for worst-case nuclide (Sr-90) for 60-year buildup period; most nuclides exhibit <1% increase

Summary (continued) Ground plane or sediment exposure can be affected up to 2-times the 15-year assumption, but these exposure pathways typically contribute less than 0.05% of the total dose Buildup equations assume uniform release rates (Ci/yr) over duration of buildup period. Current and future release rates are likely much lower than those when plants began operation

Conclusion Increased buildup time posed by license extension carries negligible impact for affecting effluent dose calculations. There is no need to modify RG equations or buildup assumptions to account for additional buildup from additional years of operation.