ML20195E195
| ML20195E195 | |
| Person / Time | |
|---|---|
| Issue date: | 04/20/1999 |
| From: | Mcgaffigan E NRC COMMISSION (OCM) |
| To: | Vietticook A NRC OFFICE OF THE SECRETARY (SECY) |
| Shared Package | |
| ML20195E165 | List: |
| References | |
| SECY-99-074-C, SECY-99-74-C, NUDOCS 9906100219 | |
| Download: ML20195E195 (4) | |
Text
.
NOTATION VOTE l
RESPONSE SHEET j
TO:
Annette Vietti-Cook, Secretary FROM:
COMMISSIONER MCGAFFIGAN
SUBJECT:
SECY-99-074 - STAFF REVIEW OF U.S. DEPARTMENT OF i
ENERGY-VIABILITY ASSESSMENT FOR A HIGH-LEVEL
. RADIOACTIVE WASTE REPOSITORY AT YUCCA MOUNTAIN, NEVADA i
Approved I Disapproved Abstain Not Participating COMMENTS-i
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See attached comments and edits.
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SIGNSTURE
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Commissioner McGaffiaan's Comments on SECY-99-074 l approve sending the proposed letter to the Department of Energy (DOE) to transmit staff comments on the Viability Assessment (VA).. The ongoing cooperative effort between NRC and DOE staff is evidenced by the staff's ability to review and provide valuable comments on a,
voluminous document in a relatively short period of time. I join my fellow Commissioners in commending the staff for their effort and I encourage continued close coordination with DOE on these important matters. I offer the following comments for the staff's consideration.
In approving the transmittal of the staff comments, I am not independently judging their validity, but I consider the staff comments essential for fostering continued deliberations on certain key technical issues. For this reason, I do not offer specific edits to the staff comments, with one exception. I suggest that the discussion on " repository design" be edited as indicated on the attached to recognize that flexibility in design improvements during the pre-closure period is, as the Advisory Committee on Nuclear Waste (ACNW) points out in its April 8,1999 letter to Chairman Jackson, " essential to achieve the best results." However, at the same time, the License Application and supporting information on the License Application design must be well developed to allow NRC to make a finding of reasonable assurance of safety, I should note that I am intrigued by both ACNW and the Nuclear Waste Technical Review Board (NWTRB) suggestions that a " low temperature" repository design may improve reposibry performance, reduce several uncertainties about repository performance, such as thermal effects, and simplify licensing.
Regarding staff comments on the " Volcanic Disruption of the Waste Package" section, I am concerned about the continued lack of consensus between the NRC staff and every other technical opinion expressed to.date on whether the risk from volcanism during the time of compl;ance has been adequately addressed in the VA. In the April letter, the ACNW disagrees with the staff's concern about the need for more work on igneous activity and requests to review the staff's detailed justification for its position. In view of the ACNW comments, those of the l
Total System Performance Assessment Peer Review Panelin its February 1999 report on the VA and the 1997 letter report from the NWTRB stating that the issue of volcanism can be considered resolved for most purposes, I suggest that the staff critically evaluate its current position. The purpose of such a review would be to ensure that the NRC staff is not taking an overly conservative approach on this issue and thus inadvertently negatively impacting the process by diverting scarce DOE and NRC resources from more safety significant issues. The staff should also ensure that its position is transparent and well documented. I encourage the staff to work closely with DOE to resolve ~ the issue of volcanism in a timely manner.
Also, I agree with Commissioner Dieus' suggested additional text on page 2 regarding defense-in-depth.
.The ACNW is generally supportive of the staff's work to date and the staff's comments to DOE
'on the VA, and DOE may benefit from considering ACNWs comments. Therefore, I suggest that the recent ACNW letter be provided as an enclosure to the DOE letter.
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Repository Design ad well dQJ Ag1 v
skd The reference repository gn presented in VA keeps open numerous options such that the overall concept remainsjuid. Significant changes in the repository design may affect the timely availability of dataYto be used for repository PA that is necessary for developing a K
complete and defensible LA. Although appreciating the importance and need for flexibility in design, the lack of a more focused design may not permit DOE sufficient time to address all pertinent issues and prepare a complete LA within its current schedule.
Importance:
Many aspects related to the repository design, especially the thermal load and temperature attematives; option for backfilling the emplacement drifts and its timing; ground support options
- and maintenance of underground facility; selection of emplacement stratum; and ventilation
- attematives may be important to understanding repository performance. Design altematives being considered by DOE could result in substantially different approaches than the current
' reference design.- Design options being considered (U.S. Department of Energy,1998) include different thermal loads, backfilling of the emplacement drifts, continuous pre-closure ventilation, timing of repository closure, type of ground support systems, near-field rock l
treatment, and repository horizon elevation. Additional enhancement features such as drip shields and Richard's barrier are'also being studied. Adequate documentation of design development and traceability of design changes are very important to the completeness and defensibility of the DOE LA. It is important to establish that the data being gathered and the suite of. analyses being performed are sufficient to cover all the design altamatives under
. consideration. it is equally important to develop analytical tools that can make quantitative comparisons of alternatives so that the preference of one over the rest could be established on a rationalbasishf Nd e e thyw J <Avat
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8tatus of Resolution:
The NRC staff has to date concentrated on the design control process being employed by the DOE to document designs and design changes. However, the staff has yet to review the DOE process for the design of the repository. The staff has been observing many DOE meetings and workshops where design attematives are being discussed and compared based mostly on engineering judg$ ment or qualitative criteria. DOE plans to complete the selection
. of the LA design in May 1999 and the final design in N vember 2000 (US Department of Energy,1998).
Additlanal
Background:
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Saturated Zone Flow and Transport Comment:
In NRC sensitivity studies, flow in the saturated zone has been shown to be an important component of the natural barrier. At this time, the saturated zone (SZ) has not been sufficiently characterized from the repository out to the proposed 20-km receptor location to adequately assess its contribution to performance. This is an issue because it creates uncertainty about the SZ flow and transport models and the SZ representation in the TSPA.
Furthermore, it may render the LA incomplete because the SZ remains an integral part of the DOE repository safety strategy.
Importance:
The SZ is the primary pathway for radionuclide transport from the repository to the receptor location, and is an integral part of the DOE repository safety strategy. The SZ has been identified in the TSPA-VA as one of 19 " principal factors" affecting postclosure perfo mance.
In its 19 8 report to Congress, the Nuclear Waste Technical Review Board (NWTRB) stated that it believes that the SZ "is an essential natural component of a defense-in-depth repository design for Yucca Mountain" (NWTRB,1998, PP 45).
DOE indicates that radionuclide travel time in the SZ constitutes a significant fraction of the 10,000 year compliance period (DOE,1998a: Vol 3, pp 6-16). In addition, sensitivity analyses performed by DOE (DOE,1998a: Vol 3, pp 4-71-80; 5-40-43) indicate that all three SZ attributes examined in the analyses (SZ dilution, method of combining flow in the SZ flowtube model, and the alluvium traction in the SZ flow path) have some measure of importance to repository performance, and that SZ dilution is an important parameter affecting the calculated dose for the 10,000-year simulation. Sensitivity analyses by NRC and Center for Nuclear Waste Regulatory Analyses (CNWRA) staff suggest that the SZ is a relatively important subsystem for overall repository performance (Jarzemba et al.,1998).
Status of Resolution:
DOE has low " current confidence" and a low " confidence goal" in the SZ flow and transport representation in the TSPA (DOE,1998a: Volume 4, pp 2-20,2-38). DOE plans to conduct additional SZ work activities to improve confidence in the SZ representation in the TSPA for the LA (DOE,1998a: Vol 4, pp 2-47; pp 3-15,3-16). In cooperation with DOE, Nye County will implement an "Early Warning Drilling Program," involving installation and testing of shallow and deep wells downgradient of the repository. These wells are expected to provide data about the hydraulic and transport properties of the aquifers along the flow path downgradient from the repository. The scope of the drilling program is limited, however, and may not adequately characterize the SZ, especially the alluvial aquifer. According to DOE (DOE, 1998a: Volume 4, pp 2-39,313), the scope of the planned SZ work was constrained by the available time before the site recommendation (SR) decision and the LA submittal.
Furthermore, DOE has assigned a relatively low priority to the planned SZ work (DOE,1998a:
Volume 4, pp 2-20,2-39).
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