ML20245C298
| ML20245C298 | |
| Person / Time | |
|---|---|
| Issue date: | 04/18/1989 |
| From: | Fliegel M NRC OFFICE OF NUCLEAR MATERIAL SAFETY & SAFEGUARDS (NMSS) |
| To: | Tokar M NRC OFFICE OF NUCLEAR MATERIAL SAFETY & SAFEGUARDS (NMSS) |
| References | |
| REF-WM-68 NUDOCS 8904270099 | |
| Download: ML20245C298 (2) | |
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t 'APR 1 s tagri MEMORANDUM FOR: Michael. Tokar, Section Leader Technical Branch Division of Low Level Waste Managment and Decommissioning, NMSS FROM: Myron Fliegel, Section Leader Operations Branch Division of Low Level Waste Management and Decommissioning, NMSS
SUBJECT:
FINAL TER FOR GREEN RIVER UMTRA PROJECT In your memorandum of March 25, 1989, you indicated four unresolved
. design issues that resulted in your not being able to concur with the actions proposed by DOE in the Final Remedial Action Plan (RAP). As a result of the agreements reached in the April 5, 1989 meeting between NRC and DOE-three of these issues have been adequately resolved. As you discussed in your memorandum and the attached TER, the fourth issue concerned the potential for the migration of fines into the voids of the riprap layer, resulting in decreased erosional stability and in the need for maintenance.
At the same time the memo indicated that geotechnically the migration of fines would not effect the stability of the design. The purpose of this memorandum is to address this specific concern related to the acceptability of the design of the riprap layer from an erosion protection standpoint.
In our erosion protection and surface water hydrology reviews, we routinely consider the effects of potential erosion in the areas of riprap toes and other energy dissipation areas. These reviews are conducted to assure that headward advancement of gullies or the occurrence of erosion downstream of riprap toes will have no effect on the stability of the remediated pile for a
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1000-year period. In this specific case, we conducted a review of the adequacy of the rock toe design and concluded that the design was adequate (See Section 4.6 of our TER, dated April 20,1989). While we did not address the specific problems related to the movement of fines in our TER, we did consider this poLential phenomenon.
Whether or not the movement of fines occurs, we have concluded that it will.not affect the stability of the pile. This conclusion is based on the following factors:
(1) It is expected that some fines will be transported into the larger voids of the riprap. The eventual filling-up of the voids will have no effect on the stability of the rock layer, as it relates to erosion. In a recent
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report entitled " Development of Riprap Design Criteria by Riprap Testing in Flumes: Phase I", NUREG/CR 4651 (1987), it was determined that riprap with voids filled with soil will be at least as stable as riprap with no soil in the voids, and in some cases may actually be more stable. '
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APR 181999 (2) It is expected that some subsidence will occur in the vicinity of the rock toe due to movement of fines into the rock layer. We also expect that preferred flow paths and areas of flow concentration will occur in this area.
It must be emphasized that the riprap in this area is designed for the occurrence of much more severe phenomena. The rock is designed for the cccurrence of a very large headward-advancing gully, which is transporting the runoff from an occurrence of a PMP/PMF event. The small amount of flow concentration resulting from some erosion and/or' subsidence will have no effect on the stability of the tailings, even if additional erosion occurs following the subsidence. Therefore, it can be seen that no maintenance will be needed to protect the pile from erosion, since no credit has been give for maintenance in the design of the toe, even if cumulative gull) erosion occurs over the long term.
In summary, we conclude that no additional actions are required by DOE.
We conclude that the design is adequate to meet the requirements of 40 CFR 192, with regard to the ability of the erosion protection design to be effective for up to 1000 years without tne need for routine maintenance. Therefore, since the disposal cell design is adequate to meet the EPA standard with regard to both sta)ility and erosion protection, we consider this issue to be resolved.
This review was performed by Ted Johnson. If you have any questions, he may be reached at x2-3440.
ORIGil'lAL SIGiED BY Myron Fliegel, Section Leader Operations Branch Division of Low Level Waste Management and Decommissioning, NMSS Distribution:
'CantralFFile # WM 68 9 RBangart, R IV JGreeves, LLWM Glear, LLWM JSurmeier, LLTB PLohaus, LLOB MFliegel, LLOB SWastler, LLOB TJohnson,LLOB RHall, URF0 JJones, LLOB rf NMSS rf PDR YES /X /
PDR NO / / Category: Proprietary / / or CF Only / /
ACNW YES /X / NO / /
SUBJECT AB3 TRACT:
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