ML20211Q475
| ML20211Q475 | |
| Person / Time | |
|---|---|
| Issue date: | 04/19/1999 |
| From: | Harris T NRC OFFICE OF NUCLEAR MATERIAL SAFETY & SAFEGUARDS (NMSS) |
| To: | Murphy A NRC OFFICE OF NUCLEAR REGULATORY RESEARCH (RES) |
| Shared Package | |
| ML20211Q152 | List: |
| References | |
| FOIA-99-281 NUDOCS 9909150076 | |
| Download: ML20211Q475 (2) | |
Text
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b Note to:
Andy Murphy, RES g
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From:
Tim Harris, NMSS Date:
April 19,1999
Subject:
Chemetron Stability Analysis On April 16,1999, I met with a DPO panel regarding the Chemetron site. During this meeting, I was asked to provide a summary of my analysis of the slope stability.
During the submission of the Decommissioning Plan (DP), I raised questions relative to the siope stability, in particular, a layer of alluvium was present at the bottom of the ravine (where the proposed disposal cell would be located). I was concerned that this material would make the slope unstable, and the DP was revised to indicate that this material would be removed.
Other assumptions made by the licensee, regarding the slope stability analyses, were deemed acceptable.
Prior to construction of the disposal cell, the licensee indicated that the waste material contained a large percentage of " oversized" non-soil material (e.g., brick, concrete, metal) and that the standard means of determining the percent compaction where not appropriate. Based on preliminary testing, the waste was also " wet" of optimum moisture. The licensee proposed using admixtures to " dry" the waste and eliminating the compaction requirement. Based ca these conditions, staff deemed that the current conditions were not compatible with the assumptions made during the previous slope stability analysis. That is that assumed shea r strength parameters for the waste in this previous analysis were no longer appropriate.
The licensee addressed this concern by conducting additional laboratory testing ( including shear strength testing of the amended and unamended waste, and geocomposite testing to determine the interface angles) and performing additional slope stability analysis. The testing program was discussed extensively with the licensee, its consultant, Ohio EPA, and NRC staff.
The licensee used conservative assumptions in evaluating the laboratory test results and used these values as input to its slope stability calculations.
d The licensee performed both Watic and pseudo-static analysis. The licensee's static analysis indicated acceptable factors of safety. For the pseudo-static analyr.is, the licensee used the ground acceleration value recommended by Ohio EPA. Staff four.d this value to be acceptable.
The minimum factors of safety for the project were based on Ohio EPA guidance on landfills.
NRC guidelines provided in Regulatory Guide 3.11 were slightly lower for the pseudo-static case. To obtain factors of safety above the minimum value, the licensee added 275 psf cohesion to the shear strength of the waste. I reviewed this approach and found it to be inappropriate. I also ciscussed my finding with Doug Evans (Ohio EPA) who concurred.
To resolve this issue, I reviewed the laboratory test data and concluded that other shear strength values, while still conservative, could be interpreted from the data. The licensee had in the general casa used values from the higher stress ranges, where the friction angle was the smallest and not included the cohesion value (which in most cases was very large). The slope stability analyses indicated the critical fail' ire surface. I interpreted the laboratory data using the stress range along the critical failure surface. The friction angle for the waste was larger than that used by the licensee. Using this value, I performed independent analysis using the STABL v
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computer code and obtained acceptable factors of safety, I discussed my results with Doug Evans who had performed a similar independent analysis and obtained similar results. In
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addition to selecting shear values in the appropriate stress range, other considerations in deeming that higher shear strength values for the waste was reasonable included (1) values were based on the fine fraction of the waste, (2) the test were performed on samples which had higher moisture contents than would be allowed by the revised specifications, (3) the brick, concrete, metal materials in the waste would increase the shear strength, and (4) some of the waste would be c. mended with kiln dust which would increase the shear strength.
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