ML20234E414
| ML20234E414 | |
| Person / Time | |
|---|---|
| Issue date: | 11/20/1987 |
| From: | Lohaus P NRC OFFICE OF NUCLEAR MATERIAL SAFETY & SAFEGUARDS (NMSS) |
| To: | Arthur J ENERGY, DEPT. OF |
| References | |
| REF-WM-43 NUDOCS 8801080061 | |
| Download: ML20234E414 (5) | |
Text
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" 4.h N John Arthur, Acting Project Manager Uranium Mill Tailings Project Office
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U.S. Department of Energy Albuquerque Operations Office NOV 20 m P.O. Box 5400 Albuquerque, NM 87115
Dear Mr. Arthur:
The Nuclear Regulatory Commission staff has completed its review of the preliminary final CADSAR for the Lcwman, Idaho site. Our review consisted of a bread overview looking for fatal flaws and potential issue areas. The CADSAR is a preliminary document, which does not identify detailed environmental data and is produced before detailed engineering data is available. With this in mind, we did not see any fatal flaws at this time which would preclude use of the stabilization-on-site alternative.
The enclosed comments identify potential issue areas and omissions that should be addressed in either the final CADSAR or draft RAP as appropriate.
If you have any questions regarding these comments, please contact Maxine Dunkelman at FTS 427-4316.
Sincerely, Paul H. Lohaus, Chief Operations Branch Division of Low-Level Waste Management and Decommissioning Office of Nuclear Material Safety and Safeguards
Enclosure:
As stated DISTRIBUTION:
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OFFICIAL RECORD COPY e801000061 871120 PDR WASTE PDR WM-43
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_1-Lowman, Idaho NRC Staff Geology - Seismology Final Cadsar 1 Page: 22 Section 5.1 (Seismicity) refers to Section 3.2 regarding bedrock accelerations of 0.45g to 0.50g.
Nothing is contained in Section 3.2 about these accelerations or about earthquake magnitudes that could cause the accelerations.
The comment responses document (comment 2, page 9) states that a Richter magnitude of 7.3 is to be used as the design event. However, no mention is made of the 7.3 event in the text of the final CADSAR. Consideration should be given to having Section 3.2 of the final CADSAR contain comprehensive information about earthquake accelerations and the Richter magnitudes.
.- Site:
Lowman Date:
10/29/87 Commentor:
NRC Groundwater Comment:
CADSAR GW 1 Page:
21 DOE states in the preliminary final CADSAR (page 21) that the below grade design will be at a maximum depth of 35 feet below the existing ground surf ace, and that the bottom of the excavation will be maintained a minimum of five feet above the high seasonal groundwater levels. DOE has not yet characterized the seasonal variation in groundwater levels under the proposed stabilized pile or the site as a whole, hence it is premature to assign a fixed maximum depth of 35 feet for the excavation at this time considering that groundwater levels could seasonally rise above this depth.
In addition, maintaining for only a five foot interval between the tailings and the water table is a highly nonconservative design, as maximum water level fluctuations may be difficult to adequately characterize within a one year sampling period. Placing the tailings within the zone of water table fluctuation could result in lateral leachate migration through the shallow, unconfined aquifer system toward Clear Creek, and subsequently, failure to comply with EPA standards.
DOE should revise the final CADSAR to indicate that the feasibility of the proposed below grade design is dependent upon the results of at least a full year of water level measurements to adequately characterize seasonal fluctuations, and that the details of the proposed design (i.e., maximum depth of excavation) will be determined based on these sampling results.
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_3-Site:
Lowman Date:
10/29/87 Commentor:
NRC Groundwater Comment:
CADSAR GW 2 Page:
22 00E has omitted groundwater as a significant issue in the preliminary final CADSAR (page 22). Based on NRC staff review of groundwater infonnation provided in this document (e.g., water level measurements, flow direction, groundwater discharge, and groundwater use), there appears to be no technical basis for deleting groundwater as significant. DOE should revise the final CADSAR to reinstate groundwater as a significant issue, or provide justification as to why groundwater is no longer considered a significant issue.
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Lowman Date:
11/16/87
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Commentor: NRC Engineering Comment:
CADSAR GT 1
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Page:
12
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Comment GT/1: Slope Stability Analysis - Static Conditions In the draft Comparative Analysis of the Disposal Site Alternatives Report (CADSAR) for the UMTRA Project Lowman Site, it is stated that the major geotechnical consideration at the site is foundation stability..It is explained that steep slopes and the presence of potentially weak residual soils will require careful consideration during the the design of the stabilized pile.
The preliminary final CADSAR states that the major geotechnical consideration at the site is foundation stability of the steeper slopes under earthquake loading. It is explained that liquefaction does not appear to present a problem as the soils become dense to very dense near the groundwater table.
The discussiom in the preliminary final CADSAR represents an important change in the characterization of the proposed disposal site at Lownan.
While the importance of the stability of the steeper slopes under earthquake loading has increased due to an increase in the magnitude of the design bases earthquake, the st'bility of the foundation soils under static loading conditions a
should still receive careful consideration. The first seil layer is described in Section 3.2 of the preliminary final'CADSAR as a " loose to medium-dense silty.
and clayey sand," and the area labeled as a recharge zcne in Figure 3.6 may be susceptible to saturation under certain conditions. Therefore, the potential for liquefaction still exists for the reasons stated in the draft CADSAR. The ground and surface water flow systems and the soils require full characterization in the steeper areas of the disposal site so that the slope stability analysis will fully consider the static loading conditions.
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