HomeMy WebLinkAboutDRC-2021-005542 - 0901a06880e6d462Radioactive Material License Application / Federal Cell Facility
Page N-1 Appendix N April 9, 2021
Revision 0
APPENDIX N
NEPTUNE EROSION ANALYSIS
(NEPTUNE, 2021)
NAC-0166_R0
Clive DU PA Model—Response
to DWMRC 1-28-2021
Comments
5 April 2021
Prepared by
NEPTUNE AND COMPANY, INC.
1435 Garrison St, Suite 201, Lakewood, CO 80215
Clive DU PA Model—Response to DWMRC 1-28-2021 Comments
5 April 2021 ii
1. Title: Clive DU PA Model—Response to DWMRC 1-28-2021 Comments
2. Filename: Clive DU PA Model - Response to DWMRC 1-28-2021 Comments.docx
3. Description: Responses to UDEQ Letter “Technical Report,” dated January 28, 2021.
Name Date
4. Originator Kelly Crowell, Paul Duffy, and Lauren Foster 5 April 2021
5. Reviewer Paul Black and Sean McCandless 5 April 2021
6. Remarks
Clive DU PA Model—Response to DWMRC 1-28-2021 Comments
5 April 2021 iii
CONTENTS
CONTENTS ................................................................................................................................... iii
FIGURES ....................................................................................................................................... iv
ACRONYMS AND ABBREVIATIONS ........................................................................................ v
Executive Summary ......................................................................................................................... 1
1.0 Introduction ............................................................................................................................ 5
2.0 Revised Federal Cell Design .................................................................................................. 6
2.1 Embankment Footprint ..................................................................................................... 6
2.2 Top Slope Surface Layer Thickness ................................................................................. 8
2.3 Transition Zone and Side Slope Frost Protection Layer ................................................... 9
3.0 Results from the DU PA v1.4 Model ................................................................................... 10
4.0 UDEQ Comments and Responses ........................................................................................ 12
4.1 UDEQ Comment 1.1: Erosion Protection Using NUREG-1623 & NUREG/CR-
4620—Design of Erosion Protection for Long-term Stabilization ................................. 13
4.1.1 Comment 1.1 Response ............................................................................................. 13
4.1.1.1 Permissible Velocity Calculation ........................................................................ 13
4.1.1.2 SIBERIA Model of Revised Federal Cell Design ............................................... 16
4.2 UDEQ Comment 1.2: Use of SIBERIA and USLE to Model Federal Cell Erosion ...... 16
4.2.1 Comment 1.2 Response ............................................................................................. 17
4.3 UDEQ Comment 1.3: Hybrid Cover .............................................................................. 17
4.3.1 Comment 1.3 Response ............................................................................................. 17
4.4 UDEQ Comment 3: Resulting Infiltration ...................................................................... 18
4.4.1 Comment 3 Response ................................................................................................ 18
4.4.1.1 Cover Erosion ...................................................................................................... 18
4.4.1.2 Cover Naturalization ........................................................................................... 19
4.4.1.3 Erosion Implementation in DU PA v1.4 ............................................................. 19
4.4.1.4 Cover Naturalization Implementation in DU PA v1.4 ........................................ 21
5.0 Conclusion ............................................................................................................................ 22
6.0 Attachments .......................................................................................................................... 22
7.0 References ............................................................................................................................ 22
Clive DU PA Model—Response to DWMRC 1-28-2021 Comments
5 April 2021 iv
FIGURES
Figure ES-1. DU PA v1.4 dose results, R313-25-20 dose limit, and typical background dose. ..... 3
Figure 1. Revised (2021) Federal Cell footprint (from drawing 14004-C01, rev 2). ...................... 7
Figure 2. Former (2020) Federal Cell footprint (from drawing 14004-C-01, rev. 0). ..................... 8
Figure 3. Top Slope Detail (from drawing 14004-C05, rev. 1). ...................................................... 9
Figure 4. Transition Zone (2021) Detail (from drawing 14004-C05, rev. 1). ................................. 9
Figure 5. Former Transition Zone (2020) Detail (from drawing 14004-C05, rev. 0). .................. 10
Figure 6. DU PA v1.4 dose results, R313-25-20 dose limit, and typical background dose. ......... 12
Clive DU PA Model—Response to DWMRC 1-28-2021 Comments
5 April 2021 v
ACRONYMS AND ABBREVIATIONS
CSM conceptual site model
DEQ (Utah) Department of Environmental Quality
DU depleted uranium
DWMRC Division of Waste Management and Radiation Control
ET evapotranspiration
GWPL groundwater protection limits
LLRW low-level radioactive waste
MOP member of the public
NRC (United States) Nuclear Regulatory Commission
PA performance assessment
SCS Soil Conservation Service
SER Safety Evaluation Report
TEDE total effective dose equivalent
UDEQ Utah Department of Environmental Quality
Clive DU PA Model—Response to DWMRC 1-28-2021 Comments
5 April 2021 1
Executive Summary
The Clive depleted uranium (DU) performance assessment (PA) evaluates the range of likely
impacts of disposal of DU in a new Federal Cell to be located in the southwest corner of the
licensed area. The DU PA is created as a systems-level model using the GoldSim probabilistic
modeling platform and is currently at version 1.4. The DU PA v1.4 model and supporting
documentation have been evaluated by the Utah Department of Environmental Quality (UDEQ)
and their contractor, SC&A Inc., for a number of years since its initial publication in 2015
(Neptune 2015b).
The current round of questions (Utah DEQ 2021) ask that the “hybrid” cover design introduced
in the 2020 response to interrogatories (Neptune 2020b) be subject to additional verification. The
hybrid cover features an evapotranspiration (ET) cover system of native soils and vegetation on
the large top slope area; and rip rap armoring of the steeper side slope area. The ET cover has
been selected for its superior performance in minimizing infiltration of atmospheric precipitation
into the waste; while the rock armor cover has been selected for its improved assurance in
minimizing the potential for erosion of the steeper side slopes.
The concerns expressed in Utah DEQ (2021) could be distilled to a simple question: If one
engineers a pile of rocks and soil in Utah’s west desert, will that structure remain in place for
10,000 years or more? Natural forces such as erosion might be expected to have some effect on
the embankment. This response quantifies the likely behavior of these forces; and discusses how
that behavior has been accounted for within the DU PA v1.4 model.
To address these comments, additional erosion modeling of the full hybrid cover system has
been performed using the SIBERIA landscape evolution model, which provides three-
dimensional projections of the effects of sheet and gully erosion. As detailed below, this
modeling projects that the hybrid cover design will provide excellent resistance to erosion. The
DU PA v1.4 actually models greater levels of sheet and gully erosion than projected in the
current work. Accordingly, the disposal system remains within the bounds of previous analyses
that demonstrate acceptable embankment performance.
The Final Report for the Clive DU PA Model, Clive DU PA Model v1.4 (Neptune 2015b)
provides the following summary of DU PA v1.4 results for the quantitative compliance period of
10,000 years. Additional work preparing interrogatory and comment responses after creation of
version 1.4 has not changed the principal analysis and reported conclusions.
Compliance with the performance objectives for the inadvertent intruder dose of 500 mrem
in a year and for the MOP of 25 mrem in a year is clearly established for all three types of
potential future receptors. This indicates that for the disposal configuration where DU wastes
are placed below grade, doses are expected to remain well below applicable dose
thresholds…
Results are also available for the offsite (MOP) receptors. None of the 95th percentile dose
estimates for these receptors exceeds 1 mrem in a year, and all of the peak mean dose
estimates are at or below 0.1 mrem in a year.
Clive DU PA Model—Response to DWMRC 1-28-2021 Comments
5 April 2021 2
Table ES-1. Peak TEDE: statistical summary
peak TEDE (mrem in a yr) within 10,000 yr
receptor mean median
(50th %ile) 95th %ile
ranch worker 6.2E-2 5.1E-2 1.5E-1
hunter 4.5E-3 3.8E-3 9.9E-3
OHV enthusiast 8.4E-3 7.5E-3 1.8E-2
Results are based on 10,000 realizations of the Model.
TEDE: Total effective dose equivalent
For those radionuclides for which GWPLs exist, as specified in the facility’s permit (UWQB
2009), results are shown in Table ES-2. For all such radionuclides compliance with the
GWPLs is clearly demonstrated.
Table ES-2. Peak groundwater activity concentrations within 500 yr, compared to
GWPLs
peak activity concentration within 500 yr (pCi/L)
radionuclide GWPL1
(pCi/L) mean median
(50th %ile) 95th %ile
90Sr 42 0 0 0
99Tc 3790 26 4.3E-2 150
129I 21 1.7E-2 4.3E-11 1.1E-1
230Th 83 2.2E-28 0 0
232Th 92 1.4E-34 0 0
237Np 7 1.5E-19 0 3.7E-27
233U 26 5.6E-24 0 3.9E-28
234U 26 2.1E-23 0 2.2E-28
235U 27 1.6E-24 0 2.0E-29
236U 27 2.7E-24 0 3.3E-29
238U 26 1.5E-22 0 1.8E-27
1GWPLs are from UWQB (2009) Table 1A.
Results are based on 10,000 realizations of the Model.
Figure ES-1 displays Table ES-1 dose results graphically in context with the dose limit of 25
mrem/year for members of the public under R313-25-20. Typical background radiation dose is
also provided on this figure as a point of reference. DU PA v1.4 results are 2 to 3 orders of
magnitude below the dose limit.
Clive DU PA Model—Response to DWMRC 1-28-2021 Comments
5 April 2021 3
Figure ES-1. DU PA v1.4 dose results, R313-25-20 dose limit, and typical background dose.
As detailed in Section 4.4.1.3 below, DU PA v1.4 overestimates the volume, depth, and impact
of gully erosion. Based on SIBERIA modeling of the clay borrow pit at Clive, DU PA v1.4
calculates how deep the gullies excavate and a volume of gully material is eroded from the
“waste” layers1 when the full cover thickness is penetrated. For the deterministic run, the deepest
gullies reach the top 3 out of 27 waste layers (as a fraction of the overall surface area); and the
averaged activity concentration from the waste layers in gullies is used in the dose calculations.
Results of the deterministic model with gullies turned on/off show no difference in the doses to
onsite receptors, but they do show small differences in uranium hazard. The uranium hazard
quotients are very small (~1e-15); compared with a target threshold of 1.
In comparison, SIBERIA modeling of the hybrid cover design (Neptune 2021a) projects that the
deepest gullies do not penetrate the full cover profile into the waste layers. Accordingly, DU PA
v1.4 overstates likely impacts of erosion on embankment performance.
1 It is acknowledged that the embankment layers between DU and the cover will not be permitted to contain Class A
LLRW until a specific performance assessment authorizing such is approved. Modeled as clean soil fill initially in
DU PA v1.4, this material is discussed in supporting documentation as “waste” since it is expected to accumulate
some activity from the DU waste placed at the cell floor via radon emanation/decay and diffusion.
1.E-03
1.E-02
1.E-01
1.E+00
1.E+01
1.E+02
1.E+03
Mean Median 95th %ile
Do
s
e
(
m
r
e
m
/
y
e
a
r
)
Ranch worker (DU PA v1.4)
Hunter (DU PA v1.4)
OHV enthusiast (DU PA v1.4)
Dose limit
Typical radiation dose in U.S.
Clive DU PA Model—Response to DWMRC 1-28-2021 Comments
5 April 2021 4
DU PA v1.4 demonstrates compliance with the dose and groundwater protection requirements of
Utah regulations relating to DU disposal. The interrogatory and response process has added to
the record supporting these conclusions but has not caused the quantitative model itself to require
revision. Accordingly, DU PA v1.4 remains the basis for demonstrating compliance of the
disposal facility.
Compliance with UAC R313-25-9(5)(a) is affirmed by DU PA v1.4, together with the supporting
documentation as supplemented by the interrogatory/response cycle.
Clive DU PA Model—Response to DWMRC 1-28-2021 Comments
5 April 2021 5
1.0 Introduction
Beginning in 2009, EnergySolutions contracted Neptune to create a probabilistic performance
assessment (PA) for the disposal of large quantities of depleted uranium (DU) at their Clive,
Utah low-level radioactive waste (LLRW) disposal facility.
The initial model was submitted as version 1.0 on June 1, 2011 (Neptune 2011) and was revised
to version 1.2 on June 5, 2014 (Neptune 2014). A Safety Evaluation Report (SER) based on
review of version 1.2 was issued by UDEQ in April 2015 (SC&A 2015).
On November 25, 2015, EnergySolutions submitted Radioactive Material License UT2300249:
Safety Evaluation Report for Condition 35.B Performance Assessment; Response to Issues
Raised in the April 2015 Draft Safety Evaluation Report (EnergySolutions 2015). This document
included version 1.4 of the DU PA (Neptune 2015b), prepared in response to open primary and
new interrogatories raised after development and Division of Waste Management and Radiation
Control (DWMRC) review of version 1.0; included in Appendix C and Appendix B,
respectively, of the SER.
On May 11, 2017, UDEQ provided Amended and New Interrogatories Related to Clive DU PA
Modeling Report Version 1.4 Dated November 2015 (Utah DEQ 2017). This document contains
clarifications to the original interrogatories from DU PA version 1.0 that remained open,
clarifications to the interrogatories newly raised with version 1.2 and new interrogatories
introduced with version 1.4 of the DU PA.
On April 2, 2018, EnergySolutions submitted Radioactive Material License UT2300249:
Responses to Amended and New Interrogatories Related to Clive DU PA Modeling Report
Version 1.4 Dated November 2015 (EnergySolutions 2018). As suggested by UDEQ, this
document included seven topical reports organized consistently with the themes expressed in the
interrogatory package (Utah DEQ 2017).
On July 25, 2019, UDEQ provided Depleted Uranium Performance Assessment (DU PA); Clive
Facility; Model Version 1.4 Amended Interrogatories; Radioactive Materials License #2300249
(Utah DEQ 2019). This document contains amended interrogatories of open issues regarding
version 1.4 of the DU PA model, closes several interrogatories, and introduces two more new
interrogatories. Neptune responded to these interrogatories on April 24, 2020 (Neptune 2020b).
In the 2020 response to interrogatories, a new “hybrid” cover design was introduced. This cover
design incorporates an evapotranspiration cover on the top slope; and a rock armor cover on the
side slope.
On December 3, 2020, UDEQ provided “Comments on EnergySolutions Cover Design System
Described in the DU PA, Draft Federal Cell License Application” (Utah DEQ 2020). This letter
poses 12 technical questions relating to the hybrid cover design. Neptune is preparing a response
to those issues as a separate report (Neptune 2021c).
Clive DU PA Model—Response to DWMRC 1-28-2021 Comments
5 April 2021 6
Additional UDEQ comments were provided under separate cover “RE: Technical Report” dated
January 28, 2021 (Utah DEQ 2021). This second comment document includes concerns relating
to erosion and embankment stability, and is the subject of this response document.
Full text of each comment is quoted using blue text in Arial font, size 10.5 pt, and is indented to
visually distinguish the comment from the response. An example is shown below:
Sample format for quoting comment text.
Utah DEQ (2021) includes comments under three general headings: (1) surface drainage and
erosion protection; (2) geotechnical stability; and (3) infiltration. This response will address
items 1.1, 1.2, and 1.3; and Section 3. Item 1.4 indicated “No applicant response is expected
from this list at this time” and is assumed to be addressed by EnergySolutions under separate
cover.
Comments under Section 2 will be addressed by EnergySolutions under separate cover. Based on
prior assessments of stability for other, larger embankments at the Clive site (Neptune 2015e),
this report assumes that geotechnical stability of the Federal Cell will be affirmed by that work.
2.0 Revised Federal Cell Design
In the 2020 response to interrogatories, the Federal Cell cover design was revised to adopt a rock
armor cover for the side slopes (Neptune 2020b). The ET cover previously analyzed for the top
slopes is retained. The ET cover has been selected for its superior performance in minimizing
infiltration of atmospheric precipitation into the waste; while the rock armor cover has been
selected for its improved assurance in minimizing the potential for erosion of the steeper side
slopes.
The 2020 design has been further revised as discussed below. These revisions have been carried
through new and updated modeling as applicable. Updated drawings 14004-C01 through 14004-
C05 are included as Attachment 1.
2.1 Embankment Footprint
EnergySolutions has revised the embankment footprint in order to provide greater separation
between the Federal Cell and the 11e.(2) Cell to the east. The revised footprint is slightly
narrower east to west and slightly longer north to south than it was in prior drawings. The grade
of the top and side slope areas is unchanged; and the thickness of the cover layers are unchanged
from the drawings submitted previously.
The revised embankment footprint has slightly shorter top slope lengths; and a longer
embankment crest. Figure 1 shows the revised embankment footprint; Figure 2 shows the version
Clive DU PA Model—Response to DWMRC 1-28-2021 Comments
5 April 2021 7
previously analyzed. Side slope lengths are unchanged. These changes result in a peak
embankment elevation at the crest that is one foot lower than that of the previous footprint2.
The current embankment footprint has been considered in SIBERIA-2D modeling performed to
address UDEQ comments.
The current embankment footprint has also been incorporated in HYDRUS-2D modeling of
erosion, with results presented under separate cover (Neptune 2021c).
Figure 1. Revised (2021) Federal Cell footprint (from drawing 14004-C01, rev 2).
2 Embankment thickness is considered in DU PA v1.4 in the context of radon emanation. This is modeled as an
average thickness of material between the DU waste and the surface, calculated to be 39.7 feet. The revised
embankment footprint changes this dimension to be 39.6 feet.
Clive DU PA Model—Response to DWMRC 1-28-2021 Comments
5 April 2021 8
Figure 2. Former (2020) Federal Cell footprint (from drawing 14004-C-01, rev. 0).
2.2 Top Slope Surface Layer Thickness
In the 2020 design change to utilize rip rap armoring on the side slopes, the top slope surface
layer thickness was increased from 6 inches to 12 inches. This change slightly increases the
storage capacity of the ET cover design. SIBERIA-2D evaluation of the full hybrid cover
includes this revision. Figure 3 provides the top slope layering.
Clive DU PA Model—Response to DWMRC 1-28-2021 Comments
5 April 2021 9
Figure 3. Top Slope Detail (from drawing 14004-C05, rev. 1).
2.3 Transition Zone and Side Slope Frost Protection Layer
The transition zone revision from the ET cover top slope to the rip rap cover side slope has been
revised from that presented in the 2020 design. The revision moves the transition zone to the
shoulder of the embankment and reduces its width. These changes were made to reduce the
impact of increased infiltration through the rip rap portion of the cover. Figure 4 provides the
transition zone detail as currently modeled; Figure 5 displays the prior design.
Figure 4. Transition Zone (2021) Detail (from drawing 14004-C05, rev. 1).
Clive DU PA Model—Response to DWMRC 1-28-2021 Comments
5 April 2021 10
Figure 5. Former Transition Zone (2020) Detail (from drawing 14004-C05, rev. 0).
Concurrent with this change, the material used as the frost protection layer for the side slope has
been changed. The current design specifies this material to be the same bank run as used for the
frost protection layer on the top slope, where the 2020 design used native clay soils for the side
slope. This material was changed in order to ensure consistent drainage properties from the top
slope onto the side slope at this layer in the cover system. The change also improves
constructability of the transition zone.
SIBERIA-2D evaluation of the full hybrid cover includes these revisions.
3.0 Results from the DU PA v1.4 Model
Since initial submittal of DU PA v1.4 (Neptune 2015b), many technical issues have been
resolved relating to the probabilistic performance assessment (PA) model, through the
interrogatory/response process summarized in Section 1.0. Based on prior evaluations of the
potential for erosion, the DU PA v1.4 model assumes ongoing embankment stability throughout
the 10,000-year compliance period (Neptune 2015e). In this report, Neptune presents analyses of
the hybrid cover design performance in relation to this assumption. If the hybrid cover is
demonstrated to retain stability for the 10,000-year period of performance, then the results of DU
PA v1.4 can be considered to hold as well.
The Final Report for the Clive DU PA Model, Clive DU PA Model v1.4 (Neptune 2015b)
provides the following summary of DU PA v1.4 results for the quantitative compliance period of
10,000 years. Additional work preparing interrogatory and comment responses after creation of
version 1.4 (Neptune 2015b) has not changed the principal analysis and reported conclusions.
Compliance with the performance objectives for the inadvertent intruder dose of 500 mrem
in a year and for the MOP of 25 mrem in a year is clearly established for all three types of
potential future receptors. This indicates that for the disposal configuration where DU wastes
are placed below grade, doses are expected to remain well below applicable dose
thresholds…
Clive DU PA Model—Response to DWMRC 1-28-2021 Comments
5 April 2021 11
Results are also available for the offsite (MOP) receptors. None of the 95th percentile dose
estimates for these receptors exceeds 1 mrem in a year, and all of the peak mean dose
estimates are at or below 0.1 mrem in a year.
Table ES-1. Peak TEDE: statistical summary
peak TEDE (mrem in a yr) within 10,000 yr
receptor mean median
(50th %ile) 95th %ile
ranch worker 6.2E-2 5.1E-2 1.5E-1
hunter 4.5E-3 3.8E-3 9.9E-3
OHV enthusiast 8.4E-3 7.5E-3 1.8E-2
Results are based on 10,000 realizations of the Model.
TEDE: Total effective dose equivalent
For those radionuclides for which GWPLs exist, as specified in the facility’s permit (UWQB
2009), results are shown in Table ES-2. For all such radionuclides compliance with the
GWPLs is clearly demonstrated.
Table ES-2. Peak groundwater activity concentrations within 500 yr, compared to
GWPLs
peak activity concentration within 500 yr (pCi/L)
radionuclide GWPL1
(pCi/L) mean median
(50th %ile) 95th %ile
90Sr 42 0 0 0
99Tc 3790 26 4.3E-2 150
129I 21 1.7E-2 4.3E-11 1.1E-1
230Th 83 2.2E-28 0 0
232Th 92 1.4E-34 0 0
237Np 7 1.5E-19 0 3.7E-27
233U 26 5.6E-24 0 3.9E-28
234U 26 2.1E-23 0 2.2E-28
235U 27 1.6E-24 0 2.0E-29
236U 27 2.7E-24 0 3.3E-29
238U 26 1.5E-22 0 1.8E-27
1GWPLs are from UWQB (2009) Table 1A.
Results are based on 10,000 realizations of the Model.
Figure 6 displays Table ES-1 dose results graphically in context with the dose limit of
25 mrem/year for members of the public under R313-25-20. Typical background radiation dose
is also provided on this figure as a point of reference. DU PA v1.4 results are 2 to 3 orders of
magnitude below the dose limit.
Clive DU PA Model—Response to DWMRC 1-28-2021 Comments
5 April 2021 12
Figure 6. DU PA v1.4 dose results, R313-25-20 dose limit, and typical background dose.
DU PA v1.4 demonstrates compliance with the dose and groundwater protection requirements of
Utah regulations relating to DU disposal. The interrogatory and response process has added to
the record supporting these conclusions but has not caused the quantitative model to require
revision. Accordingly, DU PA v1.4 remains the basis for demonstrating compliance of the
disposal facility.
Compliance with UAC R313-25-9(5)(a) is affirmed by DU PA v1.4, together with the supporting
documentation as supplemented by the interrogatory/response cycle.
Ultimately, the DU PA v1.4 evaluates an above-grade embankment located in a terminal desert
basin. Annual potential evapotranspiration in Utah’s west desert far exceeds precipitation, which
is quite low at an average of roughly 8 inches per year. There are five comparable embankments
for radioactive waste disposal in the immediate vicinity of the proposed Federal Cell, with
comparable dimensions and similar cover designs. Projections of ongoing stability for an
embankment in this context are not only reasonable, they are to be expected.
4.0 UDEQ Comments and Responses
Each comment is quoted in full followed by Neptune’s response.
1.E-03
1.E-02
1.E-01
1.E+00
1.E+01
1.E+02
1.E+03
Mean Median 95th %ile
Do
s
e
(
m
r
e
m
/
y
e
a
r
)
Ranch worker (DU PA v1.4)
Hunter (DU PA v1.4)
OHV enthusiast (DU PA v1.4)
Dose limit
Typical radiation dose in U.S.
Clive DU PA Model—Response to DWMRC 1-28-2021 Comments
5 April 2021 13
4.1 UDEQ Comment 1.1: Erosion Protection Using NUREG-1623 &
NUREG/CR-4620—Design of Erosion Protection for Long-term
Stabilization
Questions on the potential for erosion were raised in Section 4.4.2 of the April 2015 DU PA SET
(SC&A 2015). The Division expressed concern that gullies will form and enhance radon diffusion,
deep infiltration, and contaminant transport. For this subject matter, interrogatories INT CR
R313-25-8(4)(a)-71/1; INT CR R313-25-25(4)-201/1 and INT CR R313-25-25(4)-205/1 have
been identified to track inquiries and responses regarding various aspects of erosion analysis. In
the latest status of interrogatory 71 (SC&A 2019), SC&A concluded “With the maximum
permissible velocities recommended by NRC and SCS, and the NAC-0108_R0 calculated flow
velocities, gullies can be expected to form. Because the permissible velocity assumptions are
less conservative than NRC recommendations, this interrogatory remains open.”
Within DU PA Final Report (NAC-0147_R), pg 23, 4/24/20) Neptune responded to interrogatory
201 that the erosion analysis using NUREG-1623 had been revised but Neptune appears to
continue to contend that the higher maximum permissible velocity should be satisfactory. This
may not be an appropriate response, particularly for the side slopes, for which an ET cover
system design has been replaced by a rock-armor cover system design. In an unpublished
document SC&A confirmed, “EnergySolutions agreed that the rainfall intensity had been
calculated incorrectly and provided revised calculations [in App. F]. The revised flow velocities for
the top and side slopes were 2.37 and 2.07 feet per second (ft/sec), respectively. Based on a
maximum permissible velocity of 2.5 ft/sec, EnergySolutions concluded that gullies would not
form in an ET cover. Since the ET cover design has been replaced, it appears to the Division that
parameters for the new hybrid cover design have not been accounted for and analyzed properly.”
SC&A has indicated to the Division that no similar calculations were provided for a riprap cover
or the new hybrid cover. In addition, SC&A points out that, work by other investigators (i.e., Smith
and Benson, 2016) has shown that deep gullies can form in riprap covers.
EnergySolutions/Neptune need to provide a quantitative as well as a mechanistic explanation for
the conflicting results and justify, in similar manner, why the hybrid cover design would be
effective for all or part of the compliance period.
The Division needs to restate that the DU PA modeling should rely on engineered barriers during
the initial 500 years or out to the specified service life as determined by barrier design with
adequate technical justification. As explained earlier, it is the Division’s understanding that the
DU PA needs to account for degradation resulting from erosion and discontinued functioning of
the engineered barriers after they have been in service for 500 years or more.
4.1.1 Comment 1.1 Response
This comment is addressed in two parts: (1) permissible velocity calculation for the side slopes;
and (2) SIBERIA modeling of the revised Federal Cell design.
4.1.1.1 Permissible Velocity Calculation
A permissible velocity calculation for the revised embankment geometry and hybrid cover
design is provided below. NUREG-1623 (NRC 2002) describes the permissible velocity method
of evaluating erosion potential of covers.
Note that the comment incorrectly assigns revised flow velocities for the Federal Cell in Neptune
(2018). The cited values of 2.37 and 2.07 ft/sec are associated in that document with the Class A
Clive DU PA Model—Response to DWMRC 1-28-2021 Comments
5 April 2021 14
West Cell. Calculated flow velocities for the Federal Cell, with shorter top and side slope
dimensions, were 1.60 ft/sec for the top slope and 2.03 ft/sec for the side slope. Regardless, the
calculation is repeated for the current embankment geometry (Figure 1). Because the slopes
remain the same and the dimensions are only slightly different, the results are very similar to
those in Neptune (2018).
Slope Description
The Federal Cell is designed as a covered embankment with relatively steeper sloping sides
nearer the edges. The upper part of the embankment referred to as the top slope has a slope of 2.4
percent, while the side slope is steeper with a slope of 20 percent. The length of the side slope is
175 ft. Top slopes of the embankment have different lengths. The longest top slope length is
477.2 ft.
Flow Concentration
The peak flow unit discharge, Q (cubic feet per second per foot [cfs/ft]), is calculated using the
Rational Formula (NRC 2002):
𝑄=𝐹× 𝑐× 𝑖× 𝐴
where
F is flow concentration factor,
c is dimensionless runoff coefficient,
i is rainfall intensity (inches/hour [in/hr]), and
A is catchment area (acres).
A default value of 3 is recommended in NRC (2002) for the flow concentration factor, F.
A value for the runoff coefficient of 0.5 is recommended for a graveled surface in Table 4.6 of
NUREG 4620 (NRC 1986). NUREG 4620 does not include a runoff coefficient for riprap;
EnergySolutions (2012) rock cover calculations use a runoff coefficient of 0.8 based on an
example calculation in Appendix D of NUREG-1623 (NRC 2002). Accordingly, the value of 0.5
is used for the gravel-amended ET cover top slope and 0.8 is used for the riprap side slope.
The rainfall intensity used for the projection is 18.3 inches for the top slope and 19.8 inches for
the side slope of the Federal Cell. See the response to UDEQ Interrogatory 201 (Neptune 2018)
for a description of the method used to calculate these values.
The catchment area is the area of a 1-ft wide strip along the length of the slope. Using these
values, the peak flow unit discharge, Q, for the top slope and side slope are found to be 0.301
and 0.191 cfs/ft respectively.
Clive DU PA Model—Response to DWMRC 1-28-2021 Comments
5 April 2021 15
Flow Depth
The flow depth, y, is then calculated using the Manning equation for normal depth on a one-foot-
wide strip of the slope. This equation is given by NRC (2002) as
𝑦!"#=𝑄𝑛
*1.486 𝑆$%#23
where
y is flow depth (ft),
n is Manning n, and
S is slope (ft/ft).
A value of 0.05 is used for the Manning’s n based on the calculation method of Bray for natural
channels described in Coon (1998).
Using the previously calculated values for Q and the Manning’s n, flow depths are calculated to
be 0.195 ft for the top slope and 0.078 ft for the side slope.
Maximum Permissible Velocity
A value of 5.0 ft/s is chosen as the maximum permissible velocity (MPV) based on the
characteristics of the channel. This is the value listed for gravel in Table CH13-T103 of Colorado
Water Conservation Board (CWCB 2006) and in Table 4.7 of Nelson et al. (1986). Additional
justification for this value is provided in Neptune (2020b).
The NRC (2002) method requires that the MPV be adjusted to account for the flow depth.
Correction factors developed by Chow are provided in Appendix A of NRC (2002). The
correction factor for flows less than 0.25 ft in depth is 0.5. The adjusted MPV values for both the
top slope and the side slope are adjusted to 2.5 ft/s.
Actual Flow Velocity
The actual flow velocity is determined by dividing the discharge by the flow depth:
𝑉&=𝑄𝑦5
Using this equation, the top slope and side slope velocities are 1.54 ft/s and 2.45 ft/s.
These velocities for the top slope and side slope do not exceed the adjusted MPV, so the design
is acceptable. These empirical calculations are confirmed by RHEM and SIBERIA modeling of
the hybrid cover design, as discussed in Section 4.1.1.2 and 4.1.1.3, respectively.
Clive DU PA Model—Response to DWMRC 1-28-2021 Comments
5 April 2021 16
4.1.1.2 SIBERIA Model of Revised Federal Cell Design
Neptune (2021b) summarizes a SIBERIA model of the full hybrid cover system, prepared to
evaluate landform evolution of the Federal Cell for 10,000 years. This modeling projects that the
hybrid cover design will provide excellent resistance to erosion. The DU PA v1.4 actually
models greater levels of sheet and gully erosion than projected in the current work, as discussed
in more detail in Section 4.4.1.
4.2 UDEQ Comment 1.2: Use of SIBERIA and USLE to Model Federal
Cell Erosion
Questions on the application of SIBERIA and USLE as intended for modeling erosion of the
embankment cover have been outstanding for some time. For this subject matter the following
seven interrogatories: INT CR R313-25-7(2)-191/1; INT CR R313-25-25(4)-197/1; INT CR R313-
25-25(4)-198/1; INT CR R313-25-25(4)-199/1; INT CR R313-25-25(4)-200/1; INT CR R313-25-
25(4)-202/1; and INT CR R313-25-25(4)-205/1 have been identified to track inquiries and
responses regarding various aspects of applying and utilizing SIBERIA and USLE to model land
form evolution.
In the latest status of interrogatories (SC&A 2019), among many issues, SC&A pointed out that
use of USLE to model cover erosion does not consider effects of gully erosion and may be
inadequate to analyze a dual-slope erosion line. Regarding SIBERIA, SC&A comments that the
“Use of the borrow pit at Clive to model land form evolution with SIBERIA is flawed because no
attempt is made to rationalize the borrow pit parameters with those of the Federal Cell.
Additionally, the description of the borrow pit modeling in Appendix 10 to DU PA v1.4 is
confusing and lacking in detail.” Within the discussion for interrogatory 199 it was surmised that
the SIBERIA modeling may add “little to the ability to characterize the erosion behavior of the
Federal Cell. Six of the seven interrogatories remained opened as of July 2019 (SC&A 2019).
The SIBERIA model used to model erosion in the DU PA not only fails to account for any rock
armor on the side slopes but it is calibrated to the results of an older version of another model,
RHEM, applied to a soil cover. RHEM is described in Nearing et al. (2011) and Al-Hamdan et al.
(2015) as not having been intended for modeling erosion of disturbed soil when that erosion
occurs due to flow concentration. Based on experience at the Facility, the Division believes that
erosion of disturbed soil due to flow concentration is likely to be the case at the proposed Federal
Cell and to continue to be that way for extremely long periods of time. Erosion of the
embankment could be great in magnitude, and it could be an essentially perpetual problem. This
concern needs to be resolved and justification provided for ensuring the Federal Cell is stable
over long periods of time.
As explained within several interrogatories of the DU PA Final Report (NAC-0147_R, 4/24/20)
Neptune’s analysis of erosion and landform evolution appears to have been discontinued. Many
of Neptune’s responses to these interrogatories indicate that “EnergySolutions has chosen to
apply rock armor to the embankment side slopes; therefore, the discussion of SIBERIA and its
applicability no longer applies.”
SC&A has indicated to the Division that in their response, EnergySolutions/Neptune note that rip-
rap is now proposed for the side slopes of the Federal Cell. EnergySolutions has provided no
design basis or information on the expected performance of the rip-rapped side slopes. Modeling
studies by Smith and Benson (2016) using SIBERIA show that, at 1,000 years, the maximum
erosion in a semi-arid climate was about 7 m (23 ft) for a riprap embankment side slope of 41 m
(134 ft) (Smith & Benson 2016, Figure D.1). At 1,000 years (the simulation end date), the rate of
Clive DU PA Model—Response to DWMRC 1-28-2021 Comments
5 April 2021 17
erosion was increasing at a rate of about 1.8 meters per year (6 ft/yr). This study emphasizes the
need for detailed cover modeling to demonstrate the feasibility that rip-rap side slopes will
perform adequately for an assumed 10,000 year compliance period. EnergySolutions/Neptune
need to provide quantitative analysis of the cover’s long-term response to erosional forces and
explain the analysis mechanistically.
Contrary to what is implied or said in the draft license application [on p. 6-4], it does not appear
that the modeling done to date for erosion at the proposed Federal Cell in the DU PA is
appropriate or adequate. The borrow pit modeled by EnergySolutions/Neptune and proposed as
an analog for the Federal Cell does not seem to offer a suitable match useful for modeling the
erosion potential of the proposed Federal Cell. The materials, dimensions and slopes involved
seem dramatically different. The borrow pit model was for a cover of fine-grained soil. The
borrow pit model is not applicable to the top slope because of substantial differences in
dimensions and slope gradient. The addition of only 15% gravel to the top slope of the proposed
Federal Cell may also not effectively limit erosion to the extent needed. There seems to be no
validated modeling evidence presented to date to indicate that erosion would be prevented or
minimized by that relatively low percentage of gravel. The fractional coverage assumed and
described for plants growing on the cover system, which may affect the modeled rate of erosion,
also seems unlikely.
4.2.1 Comment 1.2 Response
Neptune (2021b) summarizes a SIBERIA model of the full hybrid cover system, prepared to
evaluate landform evolution of the Federal Cell for 10,000 years. This modeling projects that the
hybrid cover design will provide excellent resistance to erosion. The DU PA v1.4 actually
models greater levels of sheet and gully erosion than projected in the current work, as discussed
in more detail in Section 4.4.1.
Appendix B of Neptune (2021b) briefly assesses differences between the SIBERIA
implementations in the current work and Smith and Benson (2016).
4.3 UDEQ Comment 1.3: Hybrid Cover
EnergySolutions has not presented site-specific models of erosion of the proposed hybrid cover
system of the Federal Cell, with an evapotranspirative (ET) cover on the top slope, rock-armor
cover on the side slope, and transitional material on the shoulders. Contrary to what is implied or
said in the draft License Application [on p. 10-21], there is no modeling done to date, which the
Division is aware, that indicates that velocities of flow down the rock-armored side slopes of the
proposed Federal Cell would be less than the threshold velocity initiating erosion. Erosion
modeling for the new hybrid cover must be performed. Consequently, there currently appears to
be no peer review and interrogatory history on the hybrid-cover design.
4.3.1 Comment 1.3 Response
Neptune (2021b) summarizes a SIBERIA model of the full hybrid cover system, prepared to
evaluate landform evolution of the Federal Cell for 10,000 years.
Section 4.1.1 addresses the question of threshold velocity calculations for the riprap side slopes.
Clive DU PA Model—Response to DWMRC 1-28-2021 Comments
5 April 2021 18
4.4 UDEQ Comment 3: Resulting Infiltration
The Introduction and Sections 1 and 2 of this report have highlighted the Division’s concerns
regarding the potential for enhanced infiltration following the expected service life of engineered
features of the disposal site. As previously highlighted NUREG-1573 states “Because site
conditions and the physical properties of engineered barriers will not remain the same throughout
the period covered by the performance assessment analysis, infiltration into the disposal unit
may increase over time. For example, infiltration may be enhanced if the site experiences a
change or loss in vegetation (Gee et al., 1992; and Smyth et al., 1990) and cover performance
may be reduced by plant and animal intrusion, settling and slumping, or erosion.”
It is the Division’s impression that the DU PA modeling treated the end of service life and
subsequent degradation of the proposed engineered cover as a non-contributing factor for
infiltration. Subsequently, the possibility for enhanced infiltration after the initial service life has
apparently not been integrated into the infiltration modeling. However, as NUREG-1573
recommended, the infiltration modeling might approach the progressive stages of cover
performance with the use of temporal variations of the input parameters. “A key feature of the
approach is how progressive stages of cover performance degradation over time are captured in
the infiltration analysis by using ranges of percolation rates and hydraulic parameters for
engineered materials. At each stage of cover degradation, hydraulic parameter values for
engineered materials are developed to represent the state of cover degradation for the stage.”
EnergySolutions/Neptune need to explain quantitatively and mechanistically how the DU PA has
accounted for the potential for enhanced infiltration due to the potential erosion of the cover.
4.4.1 Comment 3 Response
The DU PA, v1.4 accounts for the potential for enhanced infiltration due to long-term
naturalization of the embankment cover by evaluating the potential for damaging erosion; and by
assuming that cover materials themselves naturalize and do not retain as-built hydraulic material
properties.
Evidence at the site and in the local area, as demonstrated in the conceptual site model (CSM)
(Neptune 2015e) and in SIBERIA landscape evolution modeling discussed in Neptune (2021b),
shows that erosion of the cover will not likely occur to a large extent on the embankment. As
discussed in Section 5.6.1.3 of Neptune (2021c), the proposed ET cover is not expected to
degrade to a point where the hydrology of the cover changes significantly, if at all, from erosion
over the 10,000-year period modeled.
4.4.1.1 Cover Erosion
Net sheet erosion of the cover is projected to be negligible. There are several lines of evidence
that point to this conclusion, as described in Neptune (2015d), Neptune (2015e), and Neptune
(2021b). Recent work to evaluate the hybrid cover design has not changed this fundamental
conclusion.
Erosion potential for the hybrid cover design is assessed using the SIBERIA landscape evolution
model, which provides three-dimensional projections of the effects of sheet and gully erosion.
While gullies do develop over time, the depth of the 95th percentile of erosion in these gullies is
only 5 cm after 500 years, and only 34 cm after 10,000 years. The mean values are much lower,
1 cm and 11 cm respectively. Additionally, these results do not include aeolian depositional
Clive DU PA Model—Response to DWMRC 1-28-2021 Comments
5 April 2021 19
processes, which were estimated to be around 55 cm after 10,000 years or about five times the
rate of erosion over the same time period (Neptune 2020a). Without considering aeolian
deposition the cover remains stable over the next 10,000 years; if deposition is considered, then
it is likely to dominate erosional processes over this same time period.
4.4.1.2 Cover Naturalization
As discussed in Neptune (2015e), Section 8.3, engineered covers can be subject to degradation
processes such as biointrusion, freeze-thaw, and erosion. For the embankment at the Clive Site,
however, these processes will be very slow to develop. The structure of the cover is designed
with an Evaporative Zone and Frost Protection Layer which inhibit biotic intrusion, freeze-thaw
processes and infiltration.
As discussed in Section 5.6.1.3 of Neptune (2021c), a capillary-barrier style ET cover inhibits
downward flow of water through the cover system by creating a capillary break between layers
of different pore size. This type of cover facilitates evapotranspiration via water storage in upper-
layer fine-grained soil and limits downward water movement into lower layers. Radon barrier
layers deeper in the cover limit upward radon movement by retaining water, which limits the
airspace available for gaseous transport. Partially saturated clays maintain low pressure heads
due to the fine pore structure, which inhibits liquid flow upward.
Evidence of slow progress of pedogenesis at the site and surrounding environment is found in the
stratigraphic studies at the Clive site (Neptune (2015e), Section 3.3.3). Recent field studies
(Neptune 2015f) show weak development of soil profiles in the natural setting, with preserved
layers of eolian silt deposits at and beneath the current soil surface. One of the conclusions of
this work is that there is not significant enough soil structural development to influence soil
hydraulic properties at depth (Neptune (2015e), Section 3.3.3). Surficial soils are expected to
have higher hydraulic conductivity (compared to, for example, laboratory testing) due to surface
process like plant and animal activity. However, the coarse nature of the frost protection layer is
designed to isolate these processes to the top of the cover system.
In addition, the Cover Test Cell deconstruction project (EnergySolutions 2020) showed very
little change from the as-built specifications for the upper and lower radon barrier layers after 17
years. No degradation was evident. Absent any plausible mechanistic explanation for soil texture
evolution, and given the observed stability of both natural and constructed soil layers, it is very
difficult to imagine how hydraulic properties of the radon barrier would change appreciably in
this environment. Nevertheless, the consequences of hypothetical degradation of the radon
barrier are incorporated into the DU PA Model v1.4 via the Ksat distribution used in the v1.4
HYDRUS simulations and the GoldSim model; this is discussed further in Section 4.4.1.4.
4.4.1.3 Erosion Implementation in DU PA v1.4
Gully erosion is evaluated in DU PA v1.4 as discussed below. Neptune (2021b) develops a
SIBERIA model for the hybrid cover design over the Federal Cell. Results of this updated
analysis show that DU PA v1.4 overestimates the volume, depth, and impact of gully erosion.
Erosion is considered in DU PA v1.4 as follows (Neptune 2015b):
Clive DU PA Model—Response to DWMRC 1-28-2021 Comments
5 April 2021 20
The impact of sheet and gully erosion in the Model is evaluated by the application of results
of landscape evolution models of hillslope erosion loss and channel development conducted
for a borrow pit at the site…
A subset of the borrow pit model domain was selected to represent the cover. Gully depths
estimated by the erosion model were extrapolated to 10,000 years and a statistical model was
developed that generated values of the percentage of the cover where gullies ended within a
given depth interval. This model provided an estimate of the volume of embankment cover
material removed by gullies. The depositional area of the gully fan is assumed to be the same
as the area of waste exposed in the gullies, using projections onto the horizontal plane. If
these embankment materials include DU waste components, then this leads to some
contribution to doses and uranium hazards. No associated effects, such as biotic processes,
effects on radon dispersion, or local changes in infiltration are considered within the gullies.
Accordingly, there are gully erosion calculations in the DU PA v1.4, based on SIBERIA
modeling of the borrow pit. That modeling derived a maximum gully depth of less than 3.5
meters and areal coverage for all gullies of less than 1 percent of the cover area at 10,000 years.
In a deterministic run, DU PA v1.4 calculates the total volume of gullies to be 1,127 m3 at
10,000 years; with a total surface area of 1,508 m2 at that time.
Implementation of the gully erosion calculations in DU PA v1.4 was the subject of Interrogatory
CR R313-25-25(4)-205/1; which questioned the relative depth of gullies in probabilistic model
runs. In responding to this comment, Neptune (2018) concludes:
The April 2015 SER (SC&A 2015) also notes that the embankment’s performance with
respect to radon flux would be adequate even with complete removal of the cover system, as
predicted doses are several orders of magnitude below regulatory limits. Thus, the
comparison of the Clive DU PA Model v1.4 with other radon flux predictions, which show
only modest differences at relevant depths, does not detract from the conclusion that radon
fluxes are adequately attenuated by the embankment due to the depth of burial of radon-
generating wastes and the prevailing site conditions.
Based on prior SIBERIA modeling of the borrow pit, DU PA v1.4 calculates how deep the
gullies excavate and a volume of gully material is eroded from the “waste” layers3 when the full
cover thickness is penetrated. For the deterministic run, gullies reach the top 3 out of 27 waste
layers (as a fraction of the overall surface area). Out of 10,000 realizations of DU PA v1.4 (seed
2), 69% of the realizations have gullies that reach the top three or four waste layers, while 8% of
realizations do not get as deep as waste layer 1, and no realizations reach waste layer 5.
Based on the gully volume excavated in each waste layer, weighted average activity
concentrations from the waste layers in gullies are used in the dose calculations to first calculate
plant concentrations in the gullies and then used as part of the concentration of contaminants in
3 It is acknowledged that the embankment layers between DU and the cover will not be permitted to contain Class A
LLRW until a specific performance assessment authorizing such is approved. Modeled as clean soil fill initially in
DU PA v1.4, this material is discussed in supporting documentation as “waste” since it is expected to accumulate
some activity from the DU waste placed at the cell floor via radon emanation/decay and diffusion.
Clive DU PA Model—Response to DWMRC 1-28-2021 Comments
5 April 2021 21
beef and game meat. Those concentrations are incorporated into the dose calculations for the
Rancher and Hunter; and into the uranium hazard calculations for rancher and hunter.
Results of the deterministic model with gullies turned on/off show no difference in the doses to
onsite receptors (rancher, hunter), but they do show small differences in uranium hazard
quotients. The uranium hazard quotients are very small (~1e-15); compared with a target
threshold of 1.
These results reflect that the gullies are shallow enough that the concentrations of contaminants
in the gullies do not contribute to doses for the deterministic run, although they do contribute to
the uranium hazard quotients. If long-lived radionuclides were disposed closer to the cover, these
results would be expected to increase though they could remain within applicable dose criteria.
Local changes to infiltration associated with gully development are not considered in DU PA
v1.4. In development of DU PA v1.4, the small area and volume of gullies modeled to be present
at 10,000 years was considered reasonable assurance that gully erosion would have a negligible
impact on infiltration at model year 500, the point of compliance for GWPLs. After this time, the
non-potable groundwater is not considered a dose pathway for the exposure scenarios affecting
onsite and offsite receptors.
SIBERIA modeling of the hybrid cover explicitly evaluates erosion impacts at model year 500 in
order to better quantify the approach taken in DU PA v1.4. The mean erosion observed in this
time period is 1 cm, with the 95th percentile of erosion at 5 cm, indicating that no local changes
to infiltration are expected on the cover during this 500-year period. Additional results are
discussed in Neptune (2021b).
4.4.1.4 Cover Naturalization Implementation in DU PA v1.4
The potential for increased infiltration associated with cover naturalization is addressed by the
incorporation of increased radon barrier Ksat distributions used in the v1.4 HYDRUS simulations
that inform infiltration in the DU PA v1.4 model; and by having the radon barrier clay saturated
hydraulic conductivity (Ksat) values change from the as-built conditions to naturalized conditions
for both the lower and upper radon barriers within the DU PA v1.4 model. As-built Ksat values
are 4e-3 cm/day and 8.6e-2 cm/day for the upper and lower radon barriers, respectively (Neptune
2015c). Average Cover Test Cell deconstruction project found that these values were 5e-3 and
1e-2 cm/day, respectively (EnergySolutions 2020); indicating essentially no change from the as-
built condition over 18 years.
Nonetheless, in DU PA v1.4, Ksat values for both radon barriers are modeled to reflect
naturalized values chosen from the log-normal distribution: LN(3.37, 3.23), with a right shift of
0.00432, in cm/day units. These values are two to three orders of magnitude higher than as-built
conditions. The naturalized Ksat values are the same for the upper and lower radon barriers.
These changes are implemented at time zero for the model so that naturalization occurs at the
beginning of the model run. This timing is much earlier than what would be expected to occur at
the site, per Section 4.4.1.2 and validated by the Cover Test Cell deconstruction.
Clive DU PA Model—Response to DWMRC 1-28-2021 Comments
5 April 2021 22
As described in Neptune (2015a), average annual infiltration was incorporated into the GoldSim
DU PA model with a regression equation developed from HYDRUS-1D simulation results.
Average percolation through the cover was not found to be sensitive to saturated conductivity
(Ksat) of the radon barrier, as percolation is determined by the performance of the capillary
barrier in the overlying cover layers. Average water contents in the radon barrier layers,
however, were found to be sensitive to Ksat; higher Ksat was associated with lower average water
content. Section 5.4.1 of Neptune (2021c) discusses this issue in more detail.
As such, increasing the Ksat of the radon barrier at the outset of a model realization to account for
a hypothetical naturalized condition results in lower moisture content in the radon barrier. A
lower moisture content in the radon barriers means that the radon barriers are not functioning as
effectively at keeping radon from migrating to the surface, resulting in higher radon flux.
A test case of DU PA v1.4 was run with naturalization occurring at 500 years to evaluate this
effect. Radon flux results and related dose results decrease about 1–3% under this scenario,
compared with the assumption of immediate naturalization that is embedded in DU PA v1.4.
5.0 Conclusion
DU PA v1.4 demonstrates compliance with the dose and groundwater protection requirements of
Utah regulations relating to DU disposal. The interrogatory and response process has added to
the record supporting these conclusions; but has not caused the quantitative model to require
revision. Accordingly, DU PA v1.4 remains the basis for demonstrating compliance of the
disposal facility.
Compliance with UAC R313-25-9(5)(a) is affirmed by DU PA v1.4 and Deep Time model v1.5,
together with their supporting documentation as supplemented by the interrogatory/response
cycle.
6.0 Attachments
1. Federal Cell engineering drawings, series 14004
7.0 References
Coon, W.F., 1998. Estimation of Roughness Coefficients for Natural Stream Channels with
Vegetated Banks, U.S. Geological Survey Water-Supply Paper 2441, prepared in
cooperation with the New York State Department of Transportation, U.S. Geological
Survey, U.S. Department of the Interior, Denver CO, 1998
CWCB, 2006. Chapter 13, Hydraulic Analysis and Design, Section 1 Open Channels. In
Colorado Floodplain and Stormwater Criteria Manual, pp. CH13-100–CH13-F124,
Colorado Water Conservation Board, Denver CO
Clive DU PA Model—Response to DWMRC 1-28-2021 Comments
5 April 2021 23
EnergySolutions, 2012. Clive Facility, Class A West (CAW) Rock Cover Design Calculations,
prepared for Utah Division of Radiation Control, EnergySolutions LLC, Salt Lake City
UT, February 2012
EnergySolutions, 2015. Radioactive Material License UT2300249: Safety Evaluation Report for
Condition 35.B Performance Assessment; Response to Issues Raised in the April 2015
Draft Safety Evaluation Report, EnergySolutions LLC, Salt Lake City UT, November
2015
EnergySolutions, 2018. Radioactive Material License UT2300249: Responses to the Amended
and New Interrogatories Related to Clive DU PA Modeling Report Version 1.4 Dated
November 2015, EnergySolutions LLC, Salt Lake City UT, April 2018
EnergySolutions, 2020. Radioactive Material Licenses UT 2300249 Cover Test Cell
Deconstruction Study Final Report, CD20-0123, EnergySolutions LLC, Salt Lake City
UT, August 2020
Nelson, J.D., et al., 1986. Methodologies for Evaluating Long-Term Stabilization Designs of
Uranium Mill Tailings Impoundments, NUREG/CR-4620, ORNL/TM-10067, United
States Nuclear Regulatory Commission (NRC), Washington DC, June 1986
Neptune, 2011. Final Report for the Clive DU PA Model version 1.0, Neptune and Company
Inc., Los Alamos NM, June 2011
Neptune, 2014. Final Report for the Clive DU PA Model, Clive DU PA Model v1.2, NAC-
0024_R2, Neptune and Company, Inc., Los Alamos NM, August 2014
Neptune, 2015a. Unsaturated Zone Modeling for the Clive PA, Clive DU PA Model v1.4, NAC-
0015_R4, prepared for EnergySolutions, Neptune and Company Inc., Los Alamos NM,
October 2015
Neptune, 2015b. Final Report for the Clive DU PA Model, Clive DU PA Model v1.4, NAC-
0024_R4, Neptune and Company Inc., Los Alamos NM, November 2015
Neptune, 2015c. Model Parameters for the Clive DU PA Model, Clive DU PA Model v1.4, NAC-
0026_R4, Neptune and Company Inc., Los Alamos NM, November 2015
Neptune, 2015d. Erosion Modeling for the Clive DU PA, Clive DU PA Model v1.4, NAC-
0017_R4, Neptune and Company Inc., Los Alamos NM, October 2015
Neptune, 2015e. Conceptual Site Model for Disposal of Depleted Uranium at the Clive Facility,
Clive DU PA Model v1.4, NAC-0018_R4, Neptune and Company Inc., Los Alamos NM,
November 2015
Clive DU PA Model—Response to DWMRC 1-28-2021 Comments
5 April 2021 24
Neptune, 2015f. Neptune Field Studies, December, 2014, Eolian Depositional History Clive
Disposal Site, NAC-0044_R0, Neptune and Company Inc., Los Alamos NM, March 2015
Neptune, 2018. Erosion Responses for the Clive DU PA Model, NAC-0108_R0, Neptune and
Company Inc., Lakewood CO, February 2018
Neptune, 2020a. Deep Time Assessment for the Clive DU PA, Deep Time Assessment for the
Clive DU PA Model v1.5, NAC-0032_R5, Neptune and Company Inc., Los Alamos NM,
March 2020
Neptune, 2020b. Clive DU PA Model—Response to Model Version 1.4 Amended Interrogatories,
NAC-0147_R0, Neptune and Company Inc., Lakewood CO, April 2020
Neptune, 2021a. Clive DU PA Model—Response to DWMRC 1-28-2021 Comments, NAC-
0166_R0, Neptune and Company Inc., Lakewood CO, March 2021
Neptune, 2021b. Surface Erosion Modeling at the EnergySolutions Clive, Utah Facility, NAC-
0167_R0, Neptune and Company Inc., Lakewood CO, 2021
Neptune, 2021c. Clive DU PA Model—Response to DWMRC 12-3-2020 Comments, NAC-
0165_R0, Neptune and Company Inc., Lakewood CO, March 2021
NRC, 1986. Update of Part 61 Impacts Analysis Methodology, Methodology Report, Volume 1,
NUREG/CR-4370, United States Nuclear Regulatory Commission, Washington DC
NRC, 2002. Design of Erosion Protection for Long-Term Stabilization, NUREG-1623, United
States Nuclear Regulatory Commission, Washington DC, 2002
SC&A, 2015. Utah Division of Radiation Control, EnergySolutions Clive LLRW Disposal
Facility, License No: UT2300249; RML #UT 2300249, Condition 35 Compliance Report;
Appendix A: Final Report for the Clive DU PA Model, Safety Evaluation Report, Volume
1, prepared for Utah Department of Environmental Quality, SC&A Inc., Vienna VA,
April 2015
Smith, C.L., and C.H. Benson, 2016. Influence of Coupling Erosion and Hydrology on the Long-
Term Performance of Engineered Surface Barriers, NUREG/CR-7200, United States
Nuclear Regulatory Commission (NRC), Washington DC, May 2016
Utah DEQ, 2017. Division of Waste Management and Radiation Control, EnergySolutions Clive
LLRW Disposal Facility License No: UT2300249; RML #UT 2300249, Amended and
New Interrogatories Related to Clive DU PA Modeling Report Version 1.4 Dated
November 2015, Utah Department of Environmental Quality (DEQ), Salt Lake City UT,
May 2017
Clive DU PA Model—Response to DWMRC 1-28-2021 Comments
5 April 2021 25
Utah DEQ, 2019. Depleted Uranium Performance Assessment (DU PA); Clive Facility; Model
Version 1.4 Amended Interrogatories; Radioactive Materials License #2300249, Utah
Department of Environmental Quality, Salt Lake City UT, July 2019
Utah DEQ, 2020. Comments on EnergySolutions Cover System Described in the DU PA, Draft
Federal Cell License Application, DRC-2020-DRC-019244, Utah Department of
Environmental Quality, Salt Lake City UT, December 2020
Utah DEQ, 2021. Technical Report, Performance Objective R313-25-23, Stability of the
Disposal Site after Closure, DRC-2021-001162, Utah Department of Environmental
Quality, Salt Lake City UT, January 2021
Clive DU PA Model—Response to DWMRC 1-28-2021 Comments
5 April 2021 1
Attachment 1:
Federal Cell Drawings 14004-C01 through 14004-C05