ML20212J984
| ML20212J984 | |
| Person / Time | |
|---|---|
| Issue date: | 01/09/1995 |
| From: | Bell M NRC OFFICE OF NUCLEAR MATERIAL SAFETY & SAFEGUARDS (NMSS) |
| To: | Joseph Holonich NRC OFFICE OF NUCLEAR MATERIAL SAFETY & SAFEGUARDS (NMSS) |
| Shared Package | |
| ML20212J942 | List: |
| References | |
| FOIA-99-311, REF-WM-63, REF-WM-70 NUDOCS 9910060067 | |
| Download: ML20212J984 (6) | |
Text
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,. 6 January 9,1995
.y MEMORANDUM TO: Joseph J.1Holonich, Chief
{i HLUR/DWM/NMSS t-g FROM:
MichaelJl. Bell, Chief e
ENGB/DWM/NMSS
SUBJECT:
. EVALUATION OF PAGE CHANGES TO THE HAT / MON REMEDIAL ACTION PLAN IN RESPONSE TO RADIO. LOGICAL ISSUES The attached evaluation is submitted to document'the status of radiological issues related to the Uranium Mill Tallings Remedial Action Project Remedial Action Plan for the codisposal and stabilization.of the Monument Valley and Mexican Hat uranium mil 11tallings at Mexican Hat, Utah. A telephone conference was held with' DOE staff on September 9, 1994, to resolve the remaining issues.
It is' our understanding that ' additional information and page changes will be provided by DOE.
The page changes evaluated were submitted by letter dated July 20, 1994, and were in response to NRC staff comments and discussions of May 13, April I4, September 20, and Novembei-29, 1993. DOE also provided supplemental radiological data as part'of the response to 1: sue 32. One issue remains open (requires additional page changes), and two others require information that could appear in the Completion Report.
If you have any questions on the evaluation, please call Elaine Brummett at 415-6606.
j A'tachment: As stated N
CISTRIBUTION:
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'. STAFF TECHNICAL REVIEV '0F THE REMEDIAL ACTION PLAN PAGE CHANGES FOR MONUMENT VALLEY AND MEXICAN HAT, UTAH INIRESPONSE TO RADIOLOGICAL ISSUES p
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By letter dated July 20,? 994, the Department of Energy (DOE) provided page 1
changes for the Remediali Action Plan (RAP) for the codisposal and stabilization of the Moriument Valley and Mexican Hat uranium mill tailings at Mexican Hat, Utah. DOE also provided supplemental radiological data as part of the response to issue 32. A brief summary of the radiological and geotechnical issues and,r,esponses, and the eval,uation of responses follow.
I' QPEN ISSUE 29 Discuss site cleanup standards and verification procedures, including Th-230.
Pages C-3, C-6, and C-7 of Appendix C sho: tid be revised:
r Page C-3 should have's suanary of the radiological characterization data, a.
and a discussion of how the data supports t'he conclusion of Section 3.2.
b.
Page C-6 should be revised to reflect DOE's'new generic thorium policy.
DOE provided revised page C-3 that states that characterization indicated elevated levels of thorium in some areas at the, Mexican Hat site, and that some samples would be analyzed for Th-232. Page C-6 was apparently not changed, but revised page C-7 contains the excavation and verification proto. col for Th-230 that reflects the generic policy.
NRC staff determined:
The main cleanup and verification items have been incorporated into the revised pages and this issue is closed.
OPEN ISSUE 30 DOE is inconsistent on the volume of contaninated naterial to be pluced in the~
cell. The Executivs Sunnary of the Text, Text pages 16 and 17, and page 5 of the Information for Reviewers should agree on the estinated volune.
DOE provided a revised volume in the new Executive Summary, but a revised page 5 for the Information for Reviewers was not provided. Also, DOE had stated in a response to issues dated July 1993, that the cell capacity is 4.3 million cubic yards which leaves a reserve capacity of about 0.5 million cubic yards. Thus, minor variations in the estimated volume of material to be placed will not affect the cell design.
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NRC staff determined:
This is no longer an issue.because the differences.in volume estimates will l
not impact the design. lo/ provide consistency in the RAP, DOE should provide a revised page 5 of the Info'rmation for Reviewers with the appropriate volume estimate, or explain why the page change was not provided.
OPEN ISSUE 31 i;
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Provide a suneary of parameter data and use conservative values for estinated parameters in a revised RAECOM analysis, as follows:
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For each parameter based on test results, the suanary should indicate:
a.
(1) sample number and locations; (2) sample ch'sracteristics; (3) test conditions; and (4) range, average, and standard deviation or standard error of the mean (SEM). For estinated parameters, include the i
i justification for assumptfons made.
b.
Revise the sensitivity analysis using the appropriate SEM values, if there is a significant difference between the SEM used and the recalculated value.
1 Provide additional diffusion coefficient data for the Monument Valley c.
(MON) naterials (only one sample each for the heap leach and new pfle), or use suitably conservative values in the RAECOM anslysis.
d.
The RAEC0:4 analysis should reflect t e current model for contaminated materials placement, and conservative thicknesses.
The RAECOM analysis should nodel, or DOE otherwise address, the effects of e.
frost (freeze-thaw) damage to the radon barrier layer on the side slopes.
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The sensitivity analysis indicates that the side slopes require 25.3 inches of amended radon barrier. NRC staff does not agree with the DOE procedure that allows this result to be ignored because it is within 40 The basis percent of the result from the nodel using all average values.
for this procedure should be provided.
Correct the discrepancy in the Mexican Hat (HAT) background radon
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concentration input (0.3 versus 0.6 pCl/1), even though it is not a signifIcant paraneter.
DOE provided a sumary of RAECOM parameters, RAECOM analyses, and discussion of the above subissues in the July 1993 response to issues. RAP page changes l
related to this issue were not provided, apparently because most of the information will be presented in the Completion Report.
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-a
.NRC staff determined:
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Dataorjustificatiofforsomeparameterswerenotprovidedinthe a.
sumary. This is acceptable at this point because conservative or as-f built values were used for important RAECOM model parameters.
b.
DOE stated (July 1993) that NRC had agreed tb the SEM methodology described in DOE's Technical Approach Document (TAD). NRC staff did not concur in the TAD, btit the SEM issue is mindi and does not warrant further discussion..
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.g DOE did not provide additional MON diffusion' coefficient data. The c.
justification is that the side slope is conservatively medeled with only HAT material (slightly higher Ra-226 concentration), and the side slope model is critical to' the radon barrier thickness design, not the top DOE did use i conservative value for the MON diffusion coefficient slope.
in the sensitivity analysis, and the resulting flux required less barrier thickness than is to be placed. This part o,f the issue is clo:ed.
d.
DOE indicated that th'e model used in the ort'ginal RAECOM code for the top slope is still validt'for contaminated materials placement. The top slope will have at least 20' feet of less-contamintted MON materials next to the radon barrier (see issue 32). This part of:the issue is closed, and the final model and analysis will be provided ih the Completion Report.
DOE modeled maximum freeze-thaw damage, assuming 14 percent increase in e.
porosity and diffusion coefficient, for the top 5 inchas (maximum frost penetration) of the radon barrier. The required barrier thickness to meet the radon flux for this model is 22 inches, which is less than the 24 inches of barrier material in the design. NRC staff analyzed a different model (coriservative emanation fraction for the HAT material with 11 percent increase in barrier porosity with code-calculated density and hat some areas of the side slopes diffusion coefficient) and concludes }/s after freeze-thaw damage.
could exceed a radon flux of 20 pCi/m However, the average cell cover radon flux will not exceed the limit, so this part of the issue is closed.
f.
NRC staff cannot substantiate DOE's statement (July 1993) that HRC has agreed to the protocol for radon barrier design described in the TAD.
Staff does agree with the statement in the TAD that "... the average radioactivity and other parameters for the slyed material may be used; however, sufficient characterization is necessary to ensure that the average values are adequately known."
DOE and NRC staff apparently differ on interpretation of " adequately known" for the average values of the RAECOM analysis. This part of the issue is considered closed, since the end resuit, the required radon barrier thickness, is acceptable (provides reasonable assurance of meeting the radon flux standard) to both agencies.
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- s. ' DOE said (July 1993) that the 0.6 pCi/1 background Rn-222 concentration would be used in the final RAP. DOE apparently meant to indicate the value would be used in'the final RAECOM analysis in the Completion Report.
If so, this part of the, issue is closed.
NRC staff will discuss aspects of Issue 31 in more detail in the Technical that some parameters of th'e DOE radon attenuation';NRC staff has Evaluation Report for the final RAP.
In summary, model are conservative or representative of the longhterm condition of the niaterial/ layer modeled, but some estimated values used'by DOE are not conserv' tive. However, considering a
as-built conditions, thereiis reasonable assurance that the design radon barrier thickness will limit the long-tern radon fiux to meet the standard.
Therefore, this issue is closed.
OPEN ISSUE 32 s
DOE should demonstrate that' there will be a sinin'un of 10 feet of lower-level Ra-226 naterial on all sides and on the top of the disposal cell. DOE should explain or correct the material thickness discrepancies indicated below:
Sheet 6 of calculation '9-421-03-00 versus sheets 5 and 6 of calculation a.
9-239-05-03 (HAT off-pile material);
t b.
Sheet 11 of calculation 9-421-03-00 versus calculation 9-420-01-00 (MON naterial on top);
h Sheet 6 of calculatfon 9-239-0S-03 says that 0 to 25 feet of relocated c.
contaminated materials 'will be placed on the ' side slopes. DOE should demonstrate that the Tower-level contaminated naterial will be greater that 10-feet-thick on'the side sinpes without clean fill dike material, as well as on the top; and d.
Construction drawing 05-10-021S should indicate that at least 10 feet pf low-level contaminated naterial will be on the side slopes between the radon barrier and the HAT lower plie tailings. In addition, this drawing should reflect the current design for relocated contaminated saterial thickness.
DOE did not provide RAP page changes for this issue but did submit revised cross-section sketches of the disposal cell that indicate the approximate layer thickness and general type of material. DOE's response to subissues (c) and (d) was partially provided in the sunplemental radiological data (July 20, 1994) indicating that conservative Ra-226 values'for the side slopes were used in the model. DOE used a value of 58.7 pC1/g while 14 measurements at 5 locations on the west side slope (to depths of' 6 feet) averaged 30.5 pCi/g.
DOE also provided radon flux measurements on the west side slope to demonstrate that the area meets the flux limit without barrier material.
For ons on the contaminated material, the highest value was four locatj/s. For five locgttons on the 2-foot-thick radon barrier, the 13.7 pC1/m highest value was 0.23 pC1/m /s.
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tjRC'staffdetermined:f Subissues a, b, and c !are clarified by the ceil cross-section sketches, but the RAP does not contii~n a clear, complete di'scussion of the placement and f
layer thickness of thf various relocated mate' rials. Since some statements in the various RAP calculations related to the radon attenuation design are confusing or contradic' tory, and there is no discussion of the radon barrier in the RAP Text, DOE should add an appendix to the Text volume of the RAP to incorporate details of the radon attenuation design and a comprehensive sumary of the radon model parameters.
s Related to subissue d,0 DOE modeled all HAT ma'terial on the side slopes,
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indicating that the model was more conservati've than one incorporating MON j
material. NRC staff determined that modeling' HON material on the side slopes f
is more conservative. 'Also, Ra-226 values were provided for the west side slope but only had two, measurements at the 6-foot level and none deeper. The limited data provide an indication of the radium content of the upper contaminated material.S The radon flux measurements are also limited but provide some additional basis for determining that the west slope will not f
adversely impact the average cell long-term radon flux.
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All the subissues will be resolved by the as-built drawings in the Completion Report, but DOE should consider providing sketches of disposal cell cross-sections in the RAP toiclarify the radon attenuation design.
This issue is closed with the condition that DOE consider the high-lighted suggestions above.
OPEN ISSUE 33 4
y The Text Executive Summary and page 9 indicate that all the nill buildings have been demolished,rbut pages 13, 17, and C-3, and the site drawinc indicate two buildings remain. ' DOE should be consistent in describing the sisJClures remaining on the HAT site.
DOE provided a revised Text Executive Summary, but it did not indicate (as proposed July 1993) that the sheet metal shop and a mill building used as a health clinic were still on the site. Pages 9 and 13 were also to be revised with a similar statement to be consistent with information on page 17 of the Text.
Revised page 9 no longer mentions the buildings, and revised page 13 indicates all buildings were demolished. Revised page 17 indicates that the health clinic building is on a vicinity property, and that the building was not contaminated and was excluded from the program. Page 17 still indicates that the sheet metal shop will be decontaminated and left intact, which reflects the statement on page C-3 (Appendix C).
NRC staff detennined:
THIS IS STILL AN OPEN ISSUE. DOE should provide RAP pages changes so that the Text Executive Sumary, pages 9,13,17, and C-3 are consistent in describing the mill buildings that will remain and those that,will be decontaminated and verified under the RAP.
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