ML20059L970
| ML20059L970 | |
| Person / Time | |
|---|---|
| Issue date: | 11/04/1993 |
| From: | Bell M NRC OFFICE OF NUCLEAR MATERIAL SAFETY & SAFEGUARDS (NMSS) |
| To: | Birk S EG&G IDAHO, INC. |
| References | |
| REF-WM-3 NUDOCS 9311180043 | |
| Download: ML20059L970 (19) | |
Text
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November 4,1993 Sandra Birk EG&G Idaho, Inc.
765 Lindsay boulevard Idaho Falls, ID 83415-2420
Dear Ms. Birk:
Enclosed please find both a hard copy and a disk copy of the paper titled: " Low-Level Waste Performance Assessment: Development of NRC's Branch Technical Position."
We are submitting the paper to be published in the conference proceedings and presented in the afternoon "PA Perspectives" session, on December 1,1993, at the 15th Annual Department of Energy Low-Level Radioactive Waste Management Conference.
If you have any questions concerning the paper, please comact Andrew C. Campbell of my staff at (301) 504-2500.
Sincerely, (OrWrd Si;r 3j
_)
Michael J. Bell, Chief Low-Level Waste Management Branch Division of Low-Level Waste Management and Decommissioning Office of Nuclear Material Safety and Safeguards
Enclosures:
As stated Distribution: (
) Central File LLWBr/f NMSS r/f NMSS:
JGreeves Plohaus MBell JThoma ACampbell FRoss IE S:
MSilberberg EO'Donnell TNicholson PDR YES XX PDR NO _
Category:
Proprietary _ or CF Only _ _
ACNW YES _
NO_X _
SUBJECT ABSTRACT: Paper for 15th Annual DOE /LLW Management Conf.
OFC LLWB gjgg LLWB LLWB,
NAME ACampbell JTho D MBeilb DATE
& /4/93 H /P/93 il /Y/93 P: Concur-5.LLW OFFITIAL RECORD COPY 9311180043 931104
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15TH DOE LOW-LEVEL RADI0 ACTIVE WASTE MANAGEMENT CONFERENCE Letter of Release I
Title of Paper / Abstract:
LOW-LEVEL WASTE PERFORMANCE ASSESSMENT:
DEVELOPMENT OF NRC's BRANCH TECHNICAL POSITION Title of Ccnference:
15TH DOE LOW-LEVEL RADI0 ACTIVE WASTE MANAGEMENT CONFERENCE Date of Conference:
December 1-3, 1993 Location of Conference: Phoenix, Arizona SoonsorshiJ Department of Energy l
The undersigned organization or individual has no objections to, and agrees to publication of, the above-mentioned paper / abstract in the proceedings of the conference cited above.
The paper contains no restricted data or other classified matter and hae no patent-sensitive information.
Submitted by:
[Name(s) and Position (s)]
i l
Andrew C. Campbell Geochemist Frederick W. Ross Hydrogeologist Thomas J. Nicholson Hydrologist i
Oroanization:
Low-Level Waste Management Branch l
Divisbn of Low-Level Waste Management and Decommissioning Office of Nuclear Material Safety and Safeguards U.S. Nuclear Regulatory Commission Washington, DC 20555 Sianature:
Date:
November 4,1993 Sandra Birk EG&G Idaho, Inc.
765 Lindsay boulevard Idaho Falls, ID 83415-2420
Dear Ms. Birk:
Enclosed please find both a hard copy and a disk copy of the paper titled: " Low-Level Waste Performance Assessment: Development of NRC's Branch Technical Position."
We are submitting the paper to be published in the conference proceedings and presented in the afternoon "PA Perspectives" session, on December 1,1993, at the 15th Annual Department of Energy Low-Level Radioactive Waste Management Conference.
If you have any questions concerning the paper, please contact Andrew C. Campbell of my staff at (301) 504-2500.
Sincerely, Michael J. Bell, Chief Low-Level Waste Management Branch Division of Low-Level Waste Management and Decommissioning Office of Nuclear Material Safety and Safeguards
Enclosures:
As stated Distribution: (
) Central File LLWBr/f NMSS r/f NMSS:
JGreeves PLohaus MBell JThoma ACampbell FRoss RES:
MSilberberg EO'Donnell TNicholson PDR YES XX_
PDR NO _
Category:
Proprietary _ or CF Only _ _
j ACNW YES _
NO E _
SUBJECT ABSTRACT: Paper for 15th Annual DOE /LLW Management Conf.
OFC LLWB gjgt LLWB LL_WB,
NAME ACampbell JThmTff Mdefk DATE
& /4/93 88 /P/93 il /Y/93 P: Concur-5.LLW OFFICIAL RECORD COPY
t LOW-LEVEL WASTE PERFORMANCE ASSESSMENT:
DEVELOPMENT of NRC's BRANCH TECHNICAL POSITION Andrew C. Campbell, Frederick W. Ross, Thomas J. Nicholson U.S. Nuclear Regulatory Commission Washington, D.C. 20555 ABSTRACT The U.S. Nuclear Regulatory Commission is developing a Draft Branch Technical Position on Performance Assessment of low-Level Radioactive Waste Disposal Facilities. The draft technical position will address important issues in performance assessment modeling and provide a framework and technical basis for conducting and evaluating performance assessments in a disposal facility license application. The technical position is being develooed to address specific guidance needs identified through State and NRC experience and will augment existing NRC guidance pertaining to LLW performance assessment.
INTRODUCTION The NRC is developing a Draft Branch Technical Position (BTP) on Performance Assessment of Low-Level Radioactive Waste (LLW) Disposal Facilities.
The 4
principal guidance objective of the BTP is to provide the applicant with an acceptable methodology for performing technical analyses required in 10 CFR 61.13 to demonstrate compliance with the 10 CFR 61.41 performance objectives.
This includes giving: (1) general guidance on an acceptable performance assessment process that integrates site characterization and performance assessment modeling; and (2) specific guidance on implementing the NRC's performance assessment methodology (PAM). The PAM was developed by NRC as one approach that l
may be followed in conducting a performance assessment for a LLW disposal 4
facility (Kozak' and others,1990).
The objectives of each of the main sections of the BTP are as follows: (1) to define low-level waste performance assessment in the context of the 10 CFR Part 61 regulatory requirements for LLW facility performance; (2) to describe an over all process for conducting performance assessment modeling activities; (3) to address important technical policy issues concerning interpretation and l
l
implementation of 10 CFR Part 61 technical requirements; and (4) to provide guidance on acceptable modeling approaches for addressing technical issues about processes controlling LLW facility performance.
This paper will address the first two areas above in some detail and provide an overview of the last two areas.
The BTP is being developed as part of NRC's LLW Performance Assessment Program.
One of the main goals of the program is to enhance staff capabilities to review and evaluate a license applicant's performance assessment.
Another important goal of the program is to develop an in-house LLW performance assessment j
capability to serve as the basis for developing improved regulatory guidance and j
for providing technical assistance to States.
This work will identify and resolve technical issues in performance assessment and develop acceptable approaches for performance assessment modeling.
l The LLW performance assessment program is being implemented in two phases. Phase I (FY92-94) is focussing on developing the BTP and gaining experience with integrated performance assessment modeling.
Part of this work includes
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evaluating codes suitable for LLW performance assessment and identifying areas requiring further work.
Phase II (FY 94 and beyond) will focus on developing NUREG documentation of NRC test case modeling, carrying out more detailed and extensive analyses of problem areas, and factoring new developments into the performance assessment methodology.
BACKGROUND AND GUIDANCE NEEDS l
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A range of land disposal technologies can be applied in the disposal of LLW including shallow-land burial, earth mounded concrete bunkers, below ground I
vaults, above ground vaults with no earthen covers, mined cavities, and augured holes. Previously, all commercially generated LLW has been disposed near-surface by shallow land burial.
These disposal systems generally rely on relatively simple designs to isolate wastes from infiltrating water and on natural site characteristics to attenuate any potential releases that might occur. Many of the designs being considered by applicants for future LLW facilities focus on engineering enhancements, such as concrete vaults and multi-layered covers, to help isolate waste from the accessible environment.
Therefore, guidance is needed, not only on how to model and analyze natural systems, but also on
engineered barriers and how much reliance can be placed upon engineering enhancements in demonstrating that performance objectives will be met.
The guidance presented in the BTP is intended to be generally applicable to any method of land disposal, however, only technical issues that specifically concern the performance of near surface disposnl technologies are addressed. Performance issues related to land disposal above ground (above ground vaults) or deeper than 30 meters (mined cavities and augured holes) will need to be evaluated and addressed separately.
l Several specific areas requiring further guidance for performance assessment have l
been identified through State and NRC experience, and documented in the National Low-Level Waste Management Program's assessment of the status of each of-the host l
States.
These guidance needs include: (1) an overall understanding of the performance assessment process; (2) the relationship between site characterization and performance assessment data collection; (3) modeling of infiltration rates, source term releases and concrete degradation; (4) transport of radionuclides in the environment; (5) verification and validation of computer models; (6) the use of generic data in performance assessment; and (7) uncertainty and sensitivity analyses.
NRC documents that currently provide some general guidance about LLW performance assessment related issues include: the Standard Format and Content Guide, NUREG-2 3
1199 (U.S. NRC,1991); the Standard Review Plan, NUREG-1200 (U.S. NRC,1991).
NUREG-1200 provides guidance applicable to evaluating a performance assessment and presents the process that would be used by NRC staff in reviewing a license application.
NUREG-1199 details the necessary components of a license application for a LLW disposal facility required under 10 CFR Part 61. One of the goals of the BTP is to provide more specific guidance on LLW performance assessment to supplement these NUREG's.
DEFINITION OF PERFORMANCE ASSESSMENT Performance assessment is concerned with analyses of the long-term performance i
of a LLW facility and is not intended to address all of the issues that may arise in developing a complete safety analysis report required for a LLW disposal facility license application (as set forth in NUREG-1199).
Performance assessment, therefore, is not intended to address radiation safety issues related
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to demonstrating compliance with 10 CFR Part 61 performance objectives governing j
protection of individuals from inadvertent intrusion (f 61.42), protection of individuals during operations (s 61.43), and stability of the disposal site after closure (f 61.44).
For example, operational performance objectives and technical analyses required to meet them are not dealt with in performance assessment, unless particular aspects of the facility operations will have an impact on tne long-term perfor.cance of the facility. Similarly, issues relating to site characterization, and the design and construction of a faci-lity are not discussed except insofar as they relate to assessing the post closure performance of the site and facility.
ITERATIVE PERFORMANCE ASSESSMENT PROCESS The NRC formulated a performance assessment strategy in 1987, that promotes a modular approach to LLW facility systems modeling (Starmer and others,1988).
The goal is to quantify the potential release and transport of radionuclides through significant environmental pathways. A Performance Assessment Methodology (PAM) was subsequently developed around this strategy (see Kozak' and others, 1990, and reference therein). The PAM embodies a generalized conceptual model of a LLW disposal facility and environs for doing performance assessment analyses and is sketched conceptually in Figure 1.
The PAM is broken into individual sub-modeling components including: (1) infiltration; (2) source term; (3) engineered 1
barriers; (4) transport via (a) ground water, (b) surface water, and (c) air; and (5) dose. The modular approach allows a mix of both complex and simple models to be used in the overall performance assessment.
The appropriate degree of modeling complexity within a module is determined by the availability of suitable data and its associated uncertainty.
Attributes and Goals In developing an acceptable performance assessment process a number of desirable attributes and goals have been considered. The process incorporates an iterative approach that starts with relatively simple conservative models using both generic and site information and becomes more facility and site specific as l
required to demonstrate compliance with E 61.41 or to rule out a site.
The j
performance assessment process is intended to be integrated with site characterization and design activities, so that information necessary for l
l
demonstrating compliance with the ! 61.41 performance objectives are developed in the initial stages of the process and are intrinsic to it.
The strategy provides a process for making a regulatory decision (i.e., there is a clear endpoint to the process and there are criteria for determining when that endpoint has been reached).
The strategy should incorporate a formal treatment of uncertainty as an intrinsic part of the performance assessment decision making process and also to build confidence that there is reasonable assurance that the facility will meet the performance objectives. A final consideration related to the defensibility of the analyses is that independent quality assurance auditors should be able to trace all modeling results, thus demonstrating that they can be reproduced. In addition the entire performance assessment process, including the iterations should be documented.
Updating data parameterization and conceptual models must be based on valid information, reasoning, and professional judgement, not simply that the analyst didn't like the result, or believed they were overly conservative.
Proposed Acoroach An overview of the proposed approach is presented in Figure 2 and each step is discussed below.
L Performance assessment begins with an evaluation of available site data, preliminary facility design, and inventory information to develop an initial knowledge base about the site and facility.
Use of generic as well as site specific and regional information is appropriate. Preliminary assessments done with this basic data may be used in site characterization and facility design activities for the express purpose of evaluating the adequacy of existing information and directing further data collection efforts towards specific information necessary to demonstrate compliance.
L The initially available information should next be used to develop assumptions about the behavior of the disposal site (i.e., engineered and natural features) and to develop site-specific conceptual models.
The applicant would also focus on developing data and parameter distributions (including correlations) for each conceptual model.
It may be appropriate to make subjective judgements about the behavior of the site based on the availability of " soft" data about the site, past experience with similar sites, precedent, and
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professional judgement. However, assumptions and conceptual models should be as broad as possible within the constraints of the available information to reflect the level of uncertainty in the behavior of the system.
This means that when l
only sparse or generic data are available, conceptual models should include more I
conservative conditions than would be the case when more_ site-specific information is available.
L The next step is to devise mathematical representations of the conceptual models and assumptions. Within this strategy, the choice of models should drive the selection of computer codes that adequately represent and implement the model, not visa-versa.
The goal of having multiple conceptual models is to represent the uncertainty structure of the overall disposal system.
l L The goal of consequence analysis is to propagate parameter uncertainty and (if defensible) to propagate correlations through the mathematical models to produce a distribution of doses for each conceptual model. A number of different approaches can be used for conducting such an analysis, (e.g., Monte Carlo 5
analysis) (see Zimmerman and others, 1990).
t L
Sensitivity analysis is performed to evaluate which models and i
combinations of parameters were most significant in producing the resulting l
doses. It is especially important when the initial consequence modeling yields potential doses approaching or exceeding the performance objective. The goal is j
to focus additional site characterization work on the most important areas, thus optimizing efforts.
It also is important, from a regulatory standpoint, to recognize which parameters are not significant in making a decision.
This analysis is accomplished using correlation techniques on the consequence analysis results.
52 This step involves the evaluation of results and determination of their adequacy. In principle this could be a simple comparison between the consequence analyses and the performance objectives.
If the comparison shows that the performance objective has been met, the analysis is done assuming that the analyst is satisfied that the assessment is defensible.
This would include evaluating the relative conservatism among models and parameter sets and the degree of confidence that the results truly bound uncertainties about the
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performance of the system. If the system does not meet the performance objective or if there is too large an uncutainty, the analyst must determine if more data will reduce the uncertainty or if decreasing the conservatism of the model(s) is
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warranted.
L This phase of the analysis has two functions in the performance f
assessment process. Both functions are performed by the applicant, as this area 1
is primarily concerned with the allocation of resources to develop further information necessary to demonstrate compliance.
The first function is to identify which information and assumptions have the greatest impact on demonstrating compliance with 5 61.41.
Entering into this evaluation would be the sensitivities of the result to different parameters and assumptions, the relative uncertainties of the data, the degree of conservatism, and the cost of producing more or better data.
The second function is equally important, but again is the concern of the applicant.
If the data needed to eliminate a conceptual model or parameter range from consideration are very extensive, owing to site complexity or other factors, it may_ be more cost effective to reject the
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site and proceed with another site.
L Once sensitivity analysis has identified the critical information needed to reduce regulatory uncertainty, that information must be gathered.
Information developed can be one of four types: new site characterization data, changes to facility design, adjunct modeling studies, or new dosign basis information. New disposal site data may be generated by, for instance, drilling j
a new well. Changes to facility design might influence, for example, how barrier i
l degradation is modeled.
A new facility design might also permit adjunct geochemical modeling to be used to allow credit for solubility limitations. New design basis information might consist of specifying inventory limitations to reduce calculated off site doses in the subsequent iteration. Any of these l
sources of new information may significantly affect the subsequent consequence
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analysis iteration. The applicant must provide adequate supporting information that justifies revising the assumptions in the new antlysis.
L The principles of this step are the same as the initial assumption step.
In this case, however, assumptions are modified based on a larger knowledge base.
Subsequent model formulation may involve elimination of a conceptual model, modification of a conceptual model, or introduction of new l
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models as suggested by additional information.
It should be noted that if the i
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initial step included a broad range of conceptual models, the updated models will
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always trend toward less conservatism, however, models should always be
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conservative relative to the information available when they are formulated.
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Role of the Regulator l
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The burden of proof for demonstrating regulatory compliance resides with the license applicant.
Once the applicant believes tt.at an adequate performance l
assessment has been developed, it is submitted as part of the overall license l
d application. It is the job of the regulator to provide an independent evaluation 1
of the applicant's performance assessment to determine whether it provides reasonable assurance of regulatory compliance. This is indicated in Figure 2 by j
the activities below the dotted line. The regulator (s) evaluate the performance 4
i assessment and develop questions about various aspects of it. The feedback loop to the applicant is through a reevaluation of data and assumptions by the a
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applicant.
It is intended that the further iterations in the process would be j
followed by license applicants who would then submit their answers to the questions.
As noted above, it is important to the regulatory staff that a comprehensive documentation of the process be provided in the application.
l I
Review of the application by the regulatory agency would not necessarily involve-I i
t conducting an indeper. dent performance assessment or an independent repetition of 4
I every part of the overall process, however, the regulatory agency should follow the process as a guide to their review and to help support their regulatory findings.
The regulatory staff may, in some cases, conduct independent performance assessment modeling in selected subsystem areas to corroborate i dependently the applicant's results. The amount of independent modeling would be based on technical judgement, the level of confidence the staff has in the i
data, assumptions, models, and codes used by the applicant, and the relative
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significance of subsystem modeling results to the overall compliance demonstration provided by the applicant. As with the applicant, regulatory staff modeling should be compatible with the quality and amount of data available to support the performance assessments. At a minimum, the regulatory staff should critically evaluate the span of models and parameters used in each iteration to i
ensure completeness and conservatism, and to evaluate the justification for 1
modifying assumptions at each step of the process.
That is, the license
applicant should be prepared to identify which adverse conditions were considered, and how those conditions were addressed as part of the process. The regulatory review should emphasize (1) selection of assumptions and conceptual models, (2) basis for model input data selection, (3) appropriateness of computer model application, (4) integration of subsystem models, and (5) analysis of uncertainties.
1 TECHNICAL POLICY ISSUES Technical policy issues are fundamental questions pertaining to interpreting and implementing 10 CFR Part 61 performance objectives and technical requirements.
Staff positions on five key technical policy issues that affect how performance assessments are conducted and evaluated are being considered.
The level of guidance provided is general since individual factors for any particular disposal l
site must be addressed on a disposal site specific basis. The technical policy issues include: (1) the role of the site and consideration of sit; conditions, processes, and events; (2) the role of engineered barriers; (3) the time frame for performance assessment analyses; (4) approaches to uncertainty and sensitivity analyses; rd (5) the role of performance assessment during l
operational and closure periods.
Specific means of resolving these issues are l
currently being considered by NRC staff.
TECHNICAL ISSUES IN PERFORMANCE ASSESSMENT In modeling LLW disposal systems there are key technical concerns that are the cause of much of the data and model uncertainty in performance assessment. These concerns must either be modeled directly, or in some way accounted for in assessing disposal site performance.
Infiltration The purpose of modeling infiltration is to calculate the flux of water into the disposal units. Several important technical areas need to be considered in such an analysis including: (1) transient surficial processes (e.g., precipitation);
(2) changes in site conditions through time (e.g., climatic variability); (3) changes in the performance of the engineered system over time (e.g., degradation of the cover); and (4) how to handle uncertainty in the analysis.
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Engineered Barriers Current knowledge about the long-term durability cf materials limits the ability to assess and predict how engineered barriers will perform over long periods of time. Thus, the degree of credit that can be assumed for them in a performance assessment is also limited.
The primary concern related to the long-term degradation of engineered barriers is the effect such degradation will have on the flux of water through the engineered system over time. The main issues that will need to be addressed in this area include: (1) the role of engineering judgement and degree of conservatism in performance assessment; (2) predicting long-term performance of materials and engineered elements; (3) consideration of variations in weather patterns in performance assessment; and (4) field verification of (a) engineered material design properties and (b) impact of material heterogeneity on performance of engineered elements.
Source Term The performance of waste forms and containers are evaluated as part of the source term.
The main focus of the source term modeling area is to calculate the possible flux of radionuclides from the waste forms and containers in the disposal units to the surrounding environment.
Source Term issues that will need to be addressed include: (1) development of a general approach and screening methods; (2) development of an inventory by waste class (A, B, & C), waste streams and waste form; (3) credit for container lifetimes (especially for high integrity containers (HIC's) for B/C waste); and (4) chemical considerations that can be included in the source term modeling (e.g., solubility limits).
l Transport Identification of the most important environmental transport media and exposure pathways is a fundamental issue in performance assessment modeling that must be done for each individual disposal site.
Principal transport media that are 1
likely to be significant at a LLW disposal site include groundwater, surface i
water, air, and biota.
Ground Water
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Technical issues that need to be addressed for ground water include: (1) evaluation of site data and analysis from site characterization and identification of ground-water transport pathways; (2) selection of ground-water flow and transport modeling approach; (3) estimation of model input parameters and identification of initial and boundary conditions; (4) calculation of transport to the accessible environment; (5) determination of radionuclide concentrations at receptor locations (e.g., wells, springs, and surface-water bodies); and (6) assessment of uncertainties due to input parameter estimation and ground-water modeling assumptions.
Surface Water Similarly for the surface-water system, the major technical issues that need to be addressed include: (1) evaluation of watershed data and site conditions for identifying surfa e water transport pathways including: (a) the groundwater-surface water linkage, and/or (b) direct surface discharge from the facility; (2) selection of surface water modeling approach (e.g., a stream reach or a watershed model, and assumptions regarding dilution, dispersion, and sediment uptake); (3) determination of channel hydraulic parameters for transport analysis (e.g.,
velocity field and flow geometries);
(4) calculation of radionuclide j
concentrations at receptor locations; (5) assessment of uncertainties due to 1
input parameter estimation and modeling assumptions.
Air i
Technical issues for the air pathway analyses include: (1) identification of gaseous release scenarios (e.g.,
steady-state vs. transient releases and distributed vs. point releases) and associated exposure pathways; (2) selection of air transport modeling approach; (3) estimation of model input parameters and l
identification of initial and boundary conditions (e.g.,
wind direction, topography, and stability class); (4) calculation of transport to the accessible environment; (5) determination of radionuclide concentrations at receptor locations; (6) assessment of uncertainties due to input parameter estimation and l
modeling assumptions.
l Biota l
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The biosphere includes natural plants and animals, cultivated crops, and livestock. It is important for two reasons: (1) it provides an exposure path to humans through the consumption of contaminated foodstuffs; and (2) succession of vegetation at the site may have an impact on the design life of the engineered features, such as the cover. Calculation of possible exposure of humans should
.I be dealt with by considering the maximally exposed individual, who is assumed to reside at the disposal site boundary and whose activities include living in a j
household, drinking water from a well, and consuming foodstuffs from gardening and animal husbandry at the homestead. Other scenarios involving consumption of l
foodstuffs and drinking surface water pathway must also be considered if this.
j could be a significant pathway (i.e., five percent or more of total dose exposure l
as stated in NUREG-1200 page 6.1.3-2).
1
SUMMARY
AND CONCLUSIONS In summary the NRC is developing a BTP for LLW performance assessment that will 1
address a number of important issues is performance assessment modeling and provide guidance for resolving those issues.
The BTP defines low-level waste performance assessment in the context of the 10 CFR Part 61 regulatory requirements for facility performance in the post closure time frame. The BTP describes an over all process for performance assessment modeling that integrates I
site characterization and design activities with performance assessment modeling.
l The goal of the process is to help support determination of reasonable assurance i
l that a proposed LLW disposal facility will meet the 10 CFR Part 61 performance objectives.
The BTP will also provide specific guidance on certain technical policy issues. And, finally, the BTP provides specific guidance on implementing the NRC's performance assessment methodology.
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REFERENrES 1.
M.W.
- Kozak, M.S.Y.
Chu, and P. A.
Mattingly, "A Performance Assessment Methodology for Low-Level Waste Facilities," NUREG/CR-5532, U.S.
Nuclear l
Regulatory Commission, Washington, D.C, 1990.
2.
U. S. Nuclear Regulatory Commission, " Standard Format and Content of a License Application for a low-Level Radioactive Waste Disposal Facility," NUREG-l 1199 Rev. 2, January 1991.
l 3.
U. S. Nuclear Regulatory Commission, " Standard Review Plan for the Review of a License Application for a low-level Radioactive Waste Disposal. Facility,"
NUREG-1200 Rev. 2, January 1991.
4.
R.J. Starmer, L.G. Deering, and M.F. Weber, " Performance Assessment Strategy for Low-Level Waste Disposal Sites," Proc. of the Tenth Annual DOE LLW Management Conference, CONF-880839-Ses.11., 1988.
i 5.
D. A. Zimmerman, K.K. Wahl, A.L. Gutjahr, and P. A. Davis, "A Review of Techniques for Propagating Data and Parameter Uncertainties in High-Level l
Radioactive Waste Repository Performance Assessment Models, "NUREG/CR-5393 i
(SAND 89-1432) U.S. Nuclear Regulatory Commission, Washington, D.C.,
February i
1990.
l l
l l
+
t Infiltration i
Vadose-Zone Flow iv Engineered Barrier Performance i
i Container Breach g
Wasteform, Leach Source Term i
=
g rg e
==
," Near-Field Transport T
if Vadose-Zone Transport il l
l fl Saturated-Zone Saturated-Zone Flow Transport
'~ ~
11 t
i fl Surface-Water Transport 11 Air Transport i
11 Id Food Chain and Dosimetry
= =
Figure 1.
Modular Conceptual Model of Processes in Low-Level Waste Performance Assessment (modified from Kozak and others, 1990) i
4 Start i
e 1
- 1. Initial Data Evaluation i
e i
- 2. Initial Conceptual Models
& Parameter Distributions i
e 1
- 3. Formulate Mathematical Models
- 9. Update Conceptual Models and
& Parameter Distributions Select Code (s) i
- 8. Develop New Information
- 4. Consequence Modeling i
^
i Yes v
1
- 5. Sensitivity Analyses No Continue?
End v
No
- 6. Adequate ?
- 7. Reevaluate Data
& Assumptions I
Yes Submit I
v i
No Adequate ?
Questions Yes v
Compliance Figure 2.
Flowchart of Overall Performance Assessment Process