ML20246E699
| ML20246E699 | |
| Person / Time | |
|---|---|
| Issue date: | 06/30/1989 |
| From: | Surmeier J NRC OFFICE OF NUCLEAR MATERIAL SAFETY & SAFEGUARDS (NMSS) |
| To: | Silberberg M NRC OFFICE OF NUCLEAR REGULATORY RESEARCH (RES) |
| References | |
| CON-FIN-B-2934, REF-WM-3 NUDOCS 8907120355 | |
| Download: ML20246E699 (4) | |
Text
i o
427.5.2/MFW/89/05/25/B2934 MEMORANDUM FOR:
Melvin Silberberg, Chief Waste Management Branch Division of Engineering, RES ggs 3 0 BB9 FROM:
John J. Surmeier, Chief Technical Branch Division of Low-Level Waste Management and Decommissioning, NMSS
SUBJECT:
REVIEW 0F PNL'S LETTER REPORT NO. 2 -- HYDROLOGIC PARAMETERS AFFECTING INFILTRATION INTO LOW-LEVEL WASTE SITES Thank you for transmitting PNL's Letter Report No. 2 on " Hydrologic Parameters Affecting Infiltration into Low-Level Waste Sites," which was prepared under FIN 82934. This report is significantly better than Letter Report No. I because it provides the types of information that NMSS staff needs to perform regulatory reviews of uranium tailings and low-level waste disposal. The report is particularly relevant to our current review; of cover designs for uranium mill tailings.
This report is the type of product that the NRC can use as the basis for developing timely and effective regulatory guidance such as Standard Review Plans and technical positions.
We appreciate RES's and PNL's responsiveness to our needs and intend to continue to work together as a team to ensure that products under FIN B2934 are integrated into NRC's Performance Assessment Methodology for Low-Level Waste.
Based on our review of the report, we have several comments and suggestions that could improve our application of the report. These comments are provided in the enclosure to this memorandum.
Please contact Michael Weber at telephone extension 20565 if you have any questions or comments about our review.
ISWW MN J. Sup3gElER John J. Surmeier, Chief Technical Branch Division of Low-Level Waste Management and Decommissioning, NMSS
Enclosure:
Comments
, DISTRIBUTION:
CENIRAL FILE:'PDR'SUBJ'427.5.2, FINB2934 RBangart JGreeves PLohaus MBell JSurmeier MFit%el RJStarmer LDeering MWeber EHawkins, URF0 LLOB rf NMSS rf l
1 PDR YES /T7 l
ACNW YES /T7 NO / /
SUBJECT ABSTR\\CT:
COMMENTS ON PNL LETTER REPORT N0. 2 (FIN B2934) 1sC W OFC :LLOB W :LLO/' (:LLTB
- LLTB
- LLTB NAME:MWeber
- MF11egel :L ring :R l
r JSur fer 89/ h 8 /
89/05 e9o7a2oass evo6ao Ap.Q DA 9 06
.8 /0 0
.L 1
LLWM COMMENTS ON PNL'S LETTER REPORT NO. 2:
HYDROLOGIC PARAMETERS AFFECTING INFILTRATION INTO LOW-LEVEL WASTE SITES MAY 1989 General Letter Report No. 2 is very good.
LLWM staff intends to use the report in performing ongoing reviews of designs for uranium tailings and low-level waste disposal. The report provides an effective summary of existing literature related to infiltration in arid environments, useful guidance on estimation of soil characteristic and relative conductivity curves, insights into the limitations of various approaches used to estimate infiltration, and recommendations on approaches for estimating uncertainties associated with infiltration estimates.
In its present form, the report provides a preliminary basis for developing regulatory guidance on infiltration for uranium recovery and low-level waste disposal.
Responses to the comments listed below will help LLWM staff apply the conclusions, observations, and recommendations provided in Letter Report No. 2.
Specific 1.
Page 1, Purpose and Approach From LLWM's perspective, the purpose and approach of the project as stated in this section are right on target.
2.
Page 7, Climatic Variations The text states that site-specific meteorologic data may be required if accurate records of precipitation are needed. However, the text does not describe when such records would be necessary to estimate infiltration rather than data from a regional meteorological monitoring station. Letter Report No. 2 could be improved by providing guidance to determine when accurate records of precipitation are necessary to estimate infiltration.
3.
Page 7 Climatic Variatior.s The text states that it is possible to extend climate predictions for a site over several hundred years if climatic records are available.
The letter report could be improved by describing the types and amounts of climatic records necessary to extrapolate climate over several hundred years and by assessing the reliability of such predictions in terms of predicting long-term infiltration.
4.
Page 9, Soil Variability The text states that a future report will describe factors that control the surface boundary condition for estimating infiltration. LLWM staff looks I
l L
L 1
2 forward to receipt and review of this future report because of the controversial nature of estimating the surface boundary. condition for infiltration modeling.
- 5..Page 13, Selection of Assessment Methods for Soil Properties The text cites the 1987 edition of the staff's Standard Review Plan. PNL should use the updated version of the Standard Review Plan, which was issued in1988(CopyAttached).
6.
Page 21, Model Selection Text appears to be missing from the middle of the first full paragraph on this page in the. sentence beginning "Therefore the only possible justification..."
7.
Page 23, Processes Influencing Water Flow in Covers The concluding statement of-this. section states that "the physics of water flow at these interfaces must be better understood if one is to accurately
. pose and simulate water flow within cover systems." The intent of this statement in the text is unclear.
If PNL considers that the physics of interface flow is insufficiently understood to simulate cover performance, then'PNL should identify specific research efforts required to improve the understanding of the processes.
In contrast, if such understanding is not necessary to estimate long-term infiltration at disposal sites for uranium tailings and low-level waste, then the text should explain why greater theoretical understanding of the processes is not necessary.
8.
Page 24, Detailed Analyses of Water Flow Similar to comment number 7, this section concludes with a discussion of spatial and-local variability in field samples, but without a clear recommendation about how the variability should be treated in infiltration analyses for real sites. The Letter Report could be improved by providing specific recommendations about how variability should be treated or by identifying research needs and explaining their significance in terms of estimating long-term infiltration.
- 9.. Page 25, Basis for and Applicability of Unit Hydraulic Gradient Theory The last sentence in this section warns that the unit gradient approach cannot be used to predict flow through covers. This statement is ambiguous and could easily be:taken out of the context of the section for multi-layered covers, such as those being used for uranium mill tailings.
In the context of the section, the statement would appear to apply only to the uppermost layers of multi-1gyered covers that are affected by transient climatic and vegetation processes. Lower layers of such covers may be insulated from temporal variations and, therefore, could be represented by a unit gradient for estimating long-term infiltration.
The Letter Report could be improved by
4 o
3 l
clarifying the concluding statement of this section in terms of the applicability of the unit gradient approach for estimating inffitration in multi-layered covers.
- 10. Page 27, The Need for Uncertainty Analysis The text states that uncertainty in numerical code limitations can be assessed by verification and validation procedures. This statement is only partially correct.
Verification of numerical codes assesses part of the uncertainty associated with the results of numerical models by ensuring that the code properly represents the mathematical model.
It is unlikely that numerical models of infiltration can be validated at the temporal and spatial scales (e.g.,100s of years and 10s of meters) of real covers. Thus, validation will probably not fully assess the uncertainties associated with numerical models because the models will only be partially validated using relatively brief, small-scale laboratory and field experiments.
In addition, verification and validation do not fully assess other sources of uncertainty associated with numerical models, including uncertainties with the conceptual model of the physical system and the theoretical description of governing processes. The Letter Report could be improved by expanding the description of uncertainties associated with numerical models and describing limitations of current approaches in quantifying the magnitude of the uncertainties.
11.
Page 31, Recommendation of an Uncertainty Methodology The text provides useful insights into the strengths and weaknesses of alternative approaches for uncertainty analysis of infiltration.
LLWM staff endorses PNL's recommendation to pursue application of Monte Carlo techniques for infiltration uncertainty analyses. However, staff cautions that PNL's efforts under FIN B2934 should not be overly distracted by development and refinement of Monte Carlo applications for infiltration analyses.
The thrust i
of the project should be on the development of the infiltration evaluation methodology with the Monte Carlo methods as a subset for uncertainty analysis.
____ ___