ML20195E655

Trip Rept of 880502 Visit W/R Schultz to Review Progress & Direction of FIN B-8958 & Provide Regulatory Insight & Ideas on How Goals Can Best Be Achieved

ML20195E655
Person / Time
Issue date:	05/18/1988
From:	Matt Young NRC OFFICE OF NUCLEAR MATERIAL SAFETY & SAFEGUARDS (NMSS)
To:	Starmer R NRC OFFICE OF NUCLEAR MATERIAL SAFETY & SAFEGUARDS (NMSS)
References
CON-FIN-B-8958, REF-WM-3 NUDOCS 8806240102
Download: ML20195E655 (4)

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$ %dK& 1 REPORT FROM BERKELEY TRIP

.1 1 MAY 18 '1988 MEMORANDUM FOR: R. John-Starmer, Section Leader

. Technical Branch Division of Low-Level Waste Management and Decomissioning, NMSS FROM: Michael Young, Hydrogeologist Technical Branch Division of Low-Level Waste Management and Decommissioning, HMSS

SUBJECT:

REPORT ON CONTRACT MEETING WITH DR. ROBERT SCHULTZ, UNIVERSITY OF CALIFORNIA, BERKELEY, MAY 2, 1988 On May 2, 1988, I visited Dr. Robert K. Schultz, principal investigator for NRC contract FIN B-8958 entitled "Contrci of Water Infiltration Into Hear Surface LLW Disposal Units." Dr. Ed O'Donnell (NRC/RES) is the Project Manager for the contract. The purpose of the contract is to test the conductive layer barrier concept for limiting infiltration. Two large-scale lysimeters, located in Beltsville, Maryland, will be devoted to testing this concept.

The purpose of my visit was to review the progress and direction of the project, provide regulatory insights on specific NMSS needs with respect to results, and provide some ideas on how our goals can best be achieved.

Although Derek Widi.ayer (LLTB) is the-NMSS cognizant individual for this project, I am the LLWM contact point for issues relating to infiltration through cover systems for both LLW and uranium mill tailings disposal sites.

The contract review was restricted to Monday mcrning because of. the need to travel to Richland, Washington that afternoon. The meeting was divided into a discussion on the theory of the conductive layer barrier approach for limiting-infiltration into the waste material, followed by a tour of two laboratories-where we viewed testing equipment and small analog models of thc proposed test covers. In this trip re) ort, I will discuss our meeting and the conductive layer barrier concept, tie tour of the laboratories and some recomendations.

Briefly, suc ess of the conductive layer barrier concept relies on the requirement that water infiltrating through the clay restrictive layer-is removed from the vicinity of the waste via matric suction at a rate exceeding the infiltration rate. Enclosed is a figure that will further explain this concept. So long as the rate of removal (or wicking) exceeds the rate of infiltration, water will not come in contact with the waste, and leachate production will be reduced to a minimum. If for any reason water is allowed to ,

enter the conductive layer faster than the matric potential can remove it, water will easily flow through the underlying cobble and contact the waste.

Some possible conditions leading to failure include, but are not limited to, (1) poor material choice for the conductive layer barrier such that the matric potential is low for a given moisture content leading to a decreased wicking '

rate, (2) the field hydraulic contiuctivity of the clay layer is higher than the design specification, thup allowing too much infiltration through the cover, or g 62 g 880518

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1 REPORT FROM BERKELEY TRIP (3) a significant amount of material migration occurs decreasing the parameter contrast between either overlying or underlying materials. Therefore, a goal of the operator is to locate a material that can retain a high suction at relatively high moisture contents. If the contractor or site operator has sufficient controls on the materials used in construction, then the concept should work.

During a tour of the laboratories, Dr. Schultz presented three small-scale models and one large-scale model which demonstrates the conductive layer barrier concept for a variety of materials. Dr. Schultz termed these analog models "soil beams." Using these soil beams, Dr. Schultz intends to measure the matric suction, and the rate at which the material can "wick away" percolating water. He mentioned that these analog models could then be useful for determining an acceptable material for the cover. The results of these experiments will be written up and transmitted to NRC. Dr. Schultz also will set-up a soil beam at the Beltsville site for demonstrating the conductive layer barrier concept and for testing material before placement.

General Observations Following a review of the current direction of the contract, and the goals that Dr. Schultz envisions for the project, I have a few observations and recomendations.

1. Project Goals - Dr. Schultz's goal for the project appears to be designing a cover that does not leak water. Thus, a cover that leaks water would lead to a failed experiment. This goal seems to be overly specific. A broader goal which could yield more applicable information for HMSS would be to understand the processes of the conductive layer barrier concept by measuring the flow of water '.nrough the cover system. With this broader goal, failure to measure flow of water reduces the understanding of how the barrier concept works, which reduces the utility of the project results.

2. Material Measurements - Dr. Schultz intends to measure the properties of the clay and conductive layer barrier material after this year's construction season, or over the 1988-89 winter. He explained that material analyses could not be performed until personnel are free from construction. This delay in mai.erial testing increases the possibility that the in-place material properties will differ from the design values.

This may cause significant problems if the cover needs to be modified or replaced. I recommended that, if possible, the material be tested prior to placement.

3. Material Control - Past experiments testing the conductive layer barrier concept, that did not proceed as designed, indicate that material choice and control are extremely important. To provide a large margin of safety in the experiment, Dr. Schultz is utilizing a diatomaceous material from Nevada which he termed "unique." However, rperators of actual LLW

t REPORT FROM BERKELEY TRIP MAY 1819"8 disposal facilities will not have access to "unique" material, which could.

lead to a poor cover system. I discussed this concern with Dr. Schultz.

4. Cover Amendment - To eliminate the need for a unique material that can wick away water quickly, I suggested that Dr. Schultz amend the clay cover with sodium bentonite to reduce the hydraulic conductivity and infiltration rate. Though "a-was hesitant to commit to the task of amending the cover, Dr. Schult. mentioned that he would consider the suggestion.

Bottom Line The theory behind the conductive layer barrier has been tested in the laboratory over many years, which shows that if properly constructed, the cover system should remove water continuously via moisture suction.

However, poor control on the cover material or construction could lead to a failure of the system and enhanced infiltration into the waste zone. With proper control during the study, I believe the experiment will yield useful results.

If you have any questions regarding my visit or this trip report, please contact me at any time.

Michael Young, Hydrogeologist Technical Branch Division of Low. Level Waste Management and Decommissioning, HMSS Enclosure As stated DISTRIBUTION: j Central File' LLWM/SF NMSS r/f LLTB r/f '

RBangart, LLWM JGreeves, LLWM JJSurmeier, LLTB MTokar, LLTB MYoung, LLTB 0'Donnell, RES BJagannath, LLTB JKane, LLTB DWidnayer, LLTB MWeber LDeering 0FC :LLTB  :  :  :  :  :  : ,

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DATE :05/l'?/88  :  :  :  :  :  :

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