Impact of License Extension on Radionuclide Buildup Assumptions Ken Sejkora Entergy Nuclear...
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Transcript of Impact of License Extension on Radionuclide Buildup Assumptions Ken Sejkora Entergy Nuclear...
Impact of License Extension on Radionuclide
Buildup Assumptions
Ken SejkoraEntergy Nuclear Northeast – Pilgrim Station
Presented at the 18th Annual RETS-REMP WorkshopCharlotte, NC / 23-25 June 2008
Reason for Concern Regulatory Guide 1.109 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 1.109 assumes buildup period (tb) 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-1.109 equations 3, 4, A-4, A-6,
A-7, A-8, A-13, C-1, and C-5 General form of equation:
i
bi t
)exp(1
Where: λi = nuclide decay constant, yr -1
tb = buildup period, yr
Buildup Factor by Nuclide
NuclideHalf-life
years Lambda
Buildup Factor by Buildup Period
15-yr 40-yr 60-yr
Mn-54 0.856 8.10E-01 1.24E+00 1.24E+00 1.24E+00
Fe-59 0.122 5.67E+00 1.76E-01 1.76E-01 1.76E-01
Co-60 5.271 1.32E-01 6.55E+00 7.56E+00 7.60E+00
Zn-65 0.669 1.04E+00 9.65E-01 9.65E-01 9.65E-01
Sr-90 28.600 2.42E-02 1.26E+01 2.56E+01 3.16E+01
I-131 0.022 3.15E+01 3.18E-02 3.18E-02 3.18E-02
Cs-134 2.062 3.36E-01 2.96E+00 2.97E+00 2.97E+00
Cs-137 30.170 2.30E-02 1.27E+01 2.62E+01 3.26E+01
Buildup Factor Ratio by Nuclide
Nuclide
Ratio to 15-yr Buildup Factor
15-yr 40-yr 60-yr
Mn-54 1.00 1.00 1.00
Fe-59 1.00 1.00 1.00
Co-60 1.00 1.16 1.16
Zn-65 1.00 1.00 1.00
Sr-90 1.00 2.04 2.51
I-131 1.00 1.00 1.00
Cs-134 1.00 1.01 1.01
Cs-137 1.00 2.06 2.57
Clarification of Buildup Equation for Vegetation Pathways
i
bivI
Eiv
Ei
P
tBf
Y
tr ie
)]exp(1[)]exp(1[
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
Eiv
Ei
Y
tr e
)]exp(1[
Where:
r = fraction of deposited activity retained on leaf/plant surface
λEi = weathering removal rate constant, 14-day half-life & nuclide half-life
te = exposure time to deposition fallout; forage = 30d, crops = 60d
Yv = vegetation yield; forage =0.7 kg/m2, crops = 2 kg/m2
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
i
bivI
P
tBf i
)]exp(1[
Where:
fI = fraction of year forage/crops are growing or irrigated (“exposed”)
Biv = soil-to-plant uptake factor for nuclide i
P = effective “surface” soil density, 240 kg/m2
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
NuclideDeposition
Term
Uptake Term
15-yr 40-yr 60-yr
Mn-54 1.04E+02 1.31E+00 1.31E+00 1.31E+00
Fe-59 9.04E+01 4.25E-03 4.25E-03 4.25E-03
Co-60 1.07E+02 2.25E+00 2.60E+00 2.61E+00
Zn-65 1.04E+02 1.41E+01 1.41E+01 1.41E+01
Sr-90 1.07E+02 7.80E+00 1.59E+01 1.96E+01
I-131 2.48E+02 2.32E-02 2.32E-02 2.32E-02
Cs-134 1.06E+02 1.08E+00 1.09E+00 1.09E+00
Cs-137 1.07E+02 4.63E+00 9.55E+00 1.19E+01
Forage ConcentrationBuildup Factor Ratio by Nuclide
Nuclide
Ratio to 15-yr Buildup Factor
15-yr 40-yr 60-yr
Mn-54 1.00 1.00 1.00
Fe-59 1.00 1.00 1.00
Co-60 1.00 1.00 1.00
Zn-65 1.00 1.00 1.00
Sr-90 1.00 1.07 1.10
I-131 1.00 1.00 1.00
Cs-134 1.00 1.00 1.00
Cs-137 1.00 1.04 1.06
Crop Concentration Terms
NuclideDeposition
Term
Uptake Term
15-yr 40-yr 60-yr
Mn-54 4.43E+01 1.31E+00 1.31E+00 1.31E+00
Fe-59 3.61E+01 4.25E-03 4.25E-03 4.25E-03
Co-60 4.57E+01 2.25E+00 2.60E+00 2.61E+00
Zn-65 4.39E+01 1.41E+01 1.41E+01 1.41E+01
Sr-90 4.59E+01 7.80E+00 1.59E+01 1.96E+01
I-131 8.84E+01 2.32E-02 2.32E-02 2.32E-02
Cs-134 4.53E+01 1.08E+00 1.09E+00 1.09E+00
Cs-137 4.59E+01 4.63E+00 9.55E+00 1.19E+01
Crop ConcentrationBuildup Factor Ratio by Nuclide
Nuclide
Ratio to 15-yr Buildup Factor
15-yr 40-yr 60-yr
Mn-54 1.00 1.00 1.00
Fe-59 1.00 1.00 1.00
Co-60 1.00 1.01 1.01
Zn-65 1.00 1.00 1.00
Sr-90 1.00 1.15 1.22
I-131 1.00 1.00 1.00
Cs-134 1.00 1.00 1.00
Cs-137 1.00 1.10 1.14
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-1.109 equations or buildup assumptions to account for additional buildup from additional years of operation.