DRC-2025-001670

299 South Main Street, Suite 1700 Salt Lake City, Utah 84111
[phone] Fax: [phone] www.energysolutions.com
May 19, 2025 CD-2025-107
Mr. Doug Hansen, Director
Division of Waste Management and Radiation Control
195 North 1950 West
Salt Lake City, UT 84114-4880
Subject: Federal Cell Facility Application: Responses to Round 2 Request for Information (per DRC-
2025-001480)
Dear Mr. Hansen:
EnergySolutions hereby responds to the Utah Division of Waste Management and Radiation Control’s May, 8
2025 (DRC-2025-001480) Requests for Information (RFI) on our Federal Cell Facility Application. A
response is provided for each request using the Director’s assigned reference number.
Each RFI letter is addressed individually, with the text of the RFI quoted in bold italics followed by its
response. Multiple follow-up RFI letters are addressed in this response, with each letter preceded by a solid
line.
The following attachments are also electronically provided to this response submission.
1. FOLDER: Reference to AB-7b-1 Response
2. FOLDER: RESRAD Input and Output
Appendix AB: Operational Period Modeling
AB-7,b-1: (from DRC-2025-001480): The review of revision 3 of Appendix AB and NAC-0023_R7
confirmed that the RESRAD-OFFSITE inventory has been updated. Revision 3 of Appendix AB states,
“Because DU PA v4.0 includes distributions for uranium isotopes from both SRS and GDP populations,
the higher concentrations from GDP waste were used for U-234, U-235, U-236, and U-238. The GDP
waste does not report U-233 concentrations, so SRS waste is used here.” After comparing the reported U-
234, U-235, U-236, and U-238 concentrations of SRS waste and GDP waste in NAC-0023_R7, it was
confirmed that the GDP waste concentrations are higher for U-234, U-235, and U-238, but SRS waste
has a higher U-236 concentration than GDP waste (GDP = 2.17E+2 pCi/g; SRS = 4.91E+3 pCi/g).
In review of the spreadsheet “DU waste concs and RESRAD results-Feb 2025.xlsx,” it was found that in
the calculations for the RESRAD-OFFSITE radionuclide inventory, the lower U-236 concentration for
GDP waste was used with the SRS mass. For U-234, U-235, and U-238, the higher GDP concentrations
were used with the GDP mass. Please rerun the model with the updated inventory to use the higher SRS
U-236 concentration in these calculations.
A screening calculation of potential radionuclide concentrations in the groundwater, surface
water, biota, and air pathways is conducted for the Federal Cell Facility using the waste
inventory and other applicable parameters from the Depleted Uranium (DU) PA v4.0. The
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modeling is performed using RESRAD-OFFSITE version 4.0. Parameter values are tabulated
below. An operational period of 20 years is assumed1.
The operational period model assumes that a groundwater well is located 90 ft from the edge
of the contaminated zone, and applies DU PA model Kd values for silty sand (contaminated
zone and vadose zone; Unit 3), silty clay (liner material and pond sediment; Unit 4), and clay
(saturated zone; Unit 2) as well as DU model physical characteristics for the waste disposal
layer and the vadose and saturated zones.
The RESRAD-OFFSITE model requires that the volume of the contaminated zone be
constant. The operational period analysis incorporates the simplifying assumption that the
time-averaged concentrations of disposed radionuclides in the contaminated zone during the
emplacement period are one-half of the waste concentrations. Practically, this has the effect
of protectively overestimating potential releases in the first half of the operating period.
The release of radionuclides from the disposed waste over time is protectively modeled as
occurring immediately upon placement, such that functionally no “credit” is taken for the
integrity of waste containers. In summary, the following protective assumptions are invoked:
1. the time-averaged disposed waste inventory for the Federal Cell is assumed to exist
beginning at model year 0 (the beginning of disposal operations); and,
2. radionuclides are assumed to be freely available for environmental transport based on
instantaneous equilibrium desorption from soil-like material, as defined by Kd values;
Because there are no natural surface water bodies in the vicinity of the site, EnergySolutions’
permitted artificial evaporation pond constructed to store runoff water during active disposal
operations is evaluated. A surface water evaporation pond with an area of 88,200 ft
2
(EnergySolutions 2000) and an average volume of 2.2 million gallons (EnergySolutions 2020
annual groundwater report values for the permitted 2000 Evaporation Pond (EnergySolutions
2021a)) is assumed to be the receiving medium for radionuclides transported with runoff
from the Federal Cell during the operational period. Retained evaporation pond sediments
will be disposed at the time of site closure. As noted above, all radionuclides are assumed to
exist within a soil-like material and the surface erosion rate from the Federal Cell footprint to
the evaporation pond is assumed to be 0.001 cm/yr, based on combined gully and sheet
erosion modeling performed for the PA.
Radionuclide concentrations in the open disposal cell were derived from the DU PA v4.02
GoldSim model. The initial inventory of each radionuclide in the disposal cell at the time of
closure was assigned to the volume of the closed disposal cell (338,500 m
3) and was
expressed as activity per unit mass using the dry bulk density of silty sand (Unit 3) and DU
1 RESRAD-Offsite was run for 50 years so results are available for longer operational periods, if desired. In this report,
results are displayed to 25 years to facilitate evaluating trends, if any, beyond the assumed 20-year operational period.
2 Because DU PA v4.0 includes distributions for uranium isotopes from both SRS and GDP populations, the higher
concentrations from GDP waste were used for U-234, U-235, and U-238. The GDP waste does not report U-233
concentrations, so SRS waste is used here. See tab “Inventory Conv.” in the Excel file “DU waste concs and RESERAD
results-May2025.xlsx.”
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waste applied in the GoldSim model (1.609 g/cm
3). As described above, one-half of the as-
disposed radionuclide concentrations were used in the RESRAD-OFFSITE modeling to
represent average concentrations across the virtual 2.4-m thick zone of primary
contamination. The derivation of the time-averaged radionuclide concentrations used in the
RESRAD-OFFSITE modeling is shown in Table 1 below.
Table 1 - Time-Averaged Radionuclide Concentrations
Used in the RESRAD-OFFSITE Modeling
Species Initial
Inventory
(Bq)
Initial
Concentration
(Bq/g)
Initial
Concentration
(pCi/g)
Time-Averaged
Concentration
(pCi/g)
Sr-90 3.77E+10 6.93E-02 1.87E+00 0.94
Tc-99 3.22E+13 5.91E+01 1.60E+03 799
I-129 1.49E+10 2.74E-02 7.41E-01 0.37
Cs-137 9.71E+09 1.78E-02 4.82E-01 0.24
Ra-226 6.09E+08 1.12E-03 3.02E-02 0.015
U-233 4.25E+12 7.80E+00 2.11E+02 105
U-234 9.98E+14 1.83E+03 4.95E+04 24772
U-235 9.06E+13 1.66E+02 4.50E+03 2249
U-236 3.94E+12 7.24E+00 1.96E+02 98
U-238 5.81E+15 1.07E+04 2.88E+05 144076
Np-237 4.56E+09 8.37E-03 2.26E-01 0.11
Pu-238 1.69E+08 3.10E-04 8.37E-03 0.0042
Pu-239 1.03E+09 1.89E-03 5.10E-02 0.025
Pu-240 2.73E+08 5.01E-04 1.35E-02 0.0068
Pu-241 3.24E+09 5.95E-03 1.61E-01 0.08
Am-241 1.14E+10 2.09E-02 5.66E-01 0.28
Modeling of transport to groundwater and a surface water retention pond was conducted for
several open disposal cell geometries. The dimensions evaluated include:
a) a 100 × 100 ft area (30.48 m × 30.48 m [929 m
2]);
b) one-quarter of the disposal cell (133.5 m × 239.5 m [3.2E+04 m
2]);
c) one-half of the disposal cell (267 m × 239.5 m [6.4E+04 m
2]); and
d) the entire footprint of the DU waste disposal cell (267 m × 479 m [1.3E+05 m
2]).
Model results were output at the following model years: 1, 5, 10, 15, 20, and 25 years. The
assumed operational period is 20 years. Results are shown to 25 years to facilitate evaluating
trends, if any, beyond year 20. Among the isotopes of uranium, results are shown for
uranium-238. Because physical transport characteristics are identical for all the long-lived
uranium isotopes, the other uranium isotopes would show identical characteristics with their
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modeled concentrations in various media proportional to their initial inventory. Based on
initial inventory and transport characteristics, results are also shown for radium-226 (the
parent of radon-222) and the highly soluble radionuclide technetium-99.
1. Well Water Radionuclide Concentrations. No breakthrough of any radionuclides at the
well located 90 ft from the edge of the contaminated zone occurs within 25 years for any
of the four open operational area cases evaluated. Even assuming no cover is placed on
the disposed DU waste, and taking no credit for containerization, breakthrough of Tc-99
at the well does not occur until model year 200 in the RESRAD-OFFSITE evaluation.
Other radionuclides do not see breakthrough within 500 years. Longer-term modeling of
releases to groundwater from the closed disposal cell is the subject of the DU PA.
Figure 1. No Breakthrough at 90-ft Well from Edge of Contaminated Zone.
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2. Radon Flux above Open DU Waste. Radon-222 flux above the open area of the disposal
cell, based on decay of the Ra-226 parent, is independent of the assumed dimensions of
the open portion of the disposal cell during operations. Modeled radon flux is based on
the assumption that containers do not restrict release of radon gas, and the radium-226
source concentration in the DU waste is represented as a time-averaged concentration in a
homogenous soil source of 2.4-m thickness. The initial ground surface flux of
approximately 0.01216 pCi/m2-s decreases very slightly to about 0.01203 pCi/m2-s at
model year 25. The rate at which radon-222 flux decreases is roughly proportional to the
1,600-year half-life of radium-226.
Figure 2. Radon-222 Flux Above the Open Area of the Disposal Cell,
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3. Concentrations of Particulate-Phase Radionuclides in Air above Open DU Waste.
Concentrations of radionuclides above the assumed soil source term of the open disposal
cell are modeled using default RESRAD-OFFSITE particulate resuspension and
atmospheric mixing assumptions. Air concentrations are directly proportional to the
virtual soil concentrations of these radionuclides, and these concentrations are essentially
static across the modeling period. Although not evident on the scale of the plots, the
radium-226 air particulates concentration decreases slightly over time in the same manner
as radon-222 flux.
Figure 3. Particulate Air Concentrations above a 929 m2 (100 ft x 100 ft) Open Disposal Area
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Figure 4. Particulate Air Concentrations above a 3.2E+04 m2 (Quarter Cell) Open Disposal
Area
Figure 5. Particulate Air Concentrations above a 6.4E+04 m2 (Half Cell) Open Disposal Area
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Figure 6. Particulate Air Concentrations above a 1.3E+05 m2 (Full Cell) Open Disposal Area
4. Concentrations of Radionuclides in Retention Pond Water. Radionuclide transport to the
retention pond through erosion of the open disposal area by runoff and atmospheric
deposition is tracked through modeled water concentrations, which are in equilibrium
with pond sediments having an assumed active partitioning layer of 10-cm thickness.
Pond water concentrations of radionuclides increase quickly and then begin to level off
over time as incoming sediments eventually comprise all of the 10-cm mixing layer on
the pond bottom. Technetium-99 reaches 90% of its pond water value at model year 25
by approximately year 12, and radium-226 pond concentrations reach 90% of their model
year 25 value by model year 17. For uranium isotopes, 90% of peak pond water
concentrations occur at approximately model year 14. Concentrations of radionuclides in
pond water are directly proportional to the assumed size of the open operational area.
Figure 7. Radionuclide Concentrations in Retention Pond Water for a 929 m2 (100 ft x 100 ft)
Open Disposal Area
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Figure 8. Radionuclide Concentrations in Retention Pond Water for a 3.2E+04 m2 (Quarter
Cell) Open Disposal Area
Figure 9. Radionuclide Concentrations in Retention Pond Water for a 6.4E+04 m2 (Half Cell)
Open Disposal Area
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Figure 10. Radionuclide Concentrations in Retention Pond Water for a 1.3E+05 m2 (Full Cell)
Open Disposal Area
5. 5. Concentrations of Radionuclides in Retention Pond Crustacea. RESRAD-OFFSITE
includes modeling of radionuclide uptake into fish and crustacea inhabiting a surface
water body. The stormwater retention body is assumed to host small invertebrates, which
are represented by crustacea in the RESRAD-OFFSITE model. Crustacea tissue
concentrations are modeled in RESRAD based on element-specific partitioning among
three media: pond water, pond sediment, and crustacean tissue. Over the 25-year
modeling period, modeled concentrations in pond crustacea (assuming any exist) follow a
similar pattern to pond water. As with pond water, concentrations of radionuclides in the
tissues of crustacea are directly proportional to the assumed size of the open operational
area.
Figure 11. Radionuclide Concentrations in Retention Pond Crustacea for a 929 m2 (100 ft x
100 ft) Open Disposal Area
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Figure 12. Radionuclide Concentrations in Retention Pond Crustacea for a 3.2E+04 m2
(Quarter Cell) Open Disposal Area
Figure 13. Radionuclide Concentrations in Retention Pond Crustacea for a 6.4E+04 m2 (Half
Cell) Open Disposal Area
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Figure 14. Radionuclide Concentrations in Retention Pond Crustacea for a 1.3E+05 m2 (Full
Cell) Open Disposal Area
If you have further questions regarding these responses to the director’s request of DRC-2025-
001480, please contact me at [phone].
Sincerely,
Vern C. Rogers
Director, Regulatory Affairs
Electronic enclosures
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