Preliminary Performance-Baes Analysis Relevant to Dose-Based Performance Measures for a Proposed Geologic Repository at Yucca Mountain PDF Download
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Author: U.s. Nuclear Regulatory Comion Publisher: Createspace Independent Publishing Platform ISBN: 9781494939502 Category : Nature Languages : en Pages : 262
Book Description
The National Academy of Sciences' Committee on Technical Bases for Yucca Mountain Standards recommended that standards for the disposal of high-level radioactive waste at Yucca Mountain should 1. set a limit on the risk of individuals, 2. use the critical group approach, as defined by the international Commission on Radiological Protection; 3. define the critical group using present knowledge and cautious, reasonable assumptions; 4. use a time period for conducting compliance assessment that includes the period of greatest risk; and 5. use a stylized calculation to assess whether the repository's performance would be substantially degraded as a consequence of a postulated intrusion.
Author: U.s. Nuclear Regulatory Comion Publisher: Createspace Independent Publishing Platform ISBN: 9781494939502 Category : Nature Languages : en Pages : 262
Book Description
The National Academy of Sciences' Committee on Technical Bases for Yucca Mountain Standards recommended that standards for the disposal of high-level radioactive waste at Yucca Mountain should 1. set a limit on the risk of individuals, 2. use the critical group approach, as defined by the international Commission on Radiological Protection; 3. define the critical group using present knowledge and cautious, reasonable assumptions; 4. use a time period for conducting compliance assessment that includes the period of greatest risk; and 5. use a stylized calculation to assess whether the repository's performance would be substantially degraded as a consequence of a postulated intrusion.
Author: Publisher: ISBN: Category : Languages : en Pages : 1
Book Description
Regulatory requirements being addressed in the US geological repository program for spent nuclear fuel and high-level waste disposal specify probabilistically defined mean-value dose limits. These dose limits reflect acceptable levels of risk. The probabilistic approach mandated by regulation calculates a ''risk of a dose, '' a risk of a potential given dose value at a specific time in the future to a hypothetical person. The mean value of the time-dependent performance measure needs to remain below an acceptable level defined by regulation. Because there are uncertain parameters that are important to system performance, the regulation mandates an analysis focused on the mean value of the performance measure, but that also explores the ''full range of defensible and reasonable parameter distributions'' ... System performance evaluations should not be unduly influenced by ... ''extreme physical situations and parameter values''. Challenges in this approach lie in defending the scientific basis for the models selected, and the data and distributions sampled. A significant challenge lies in showing that uncertainties are properly identified and evaluated. A single-value parameter has no uncertainty, and where used such values need to be supported by scientific information showing the selected value is appropriate. Uncertainties are inherent in data, but are also introduced by creating parameter distributions from data sets, selecting models from among alternative models, abstracting models for use in probabilistic analysis, and in selecting the range of initiating event probabilities for unlikely events. The goal of the assessment currently in progress is to evaluate the level of risk inherent in moving ahead to the next phase of repository development: construction. During the construction phase, more will be learned to inform a new long-term risk evaluation to support moving to the next phase: accepting waste. Therefore, though there was sufficient confidence of safety at the end of the site-characterization phase to warrant moving ahead to construction, the expectation is that still more confidence may be had in the next evaluation of risk for a repository at Yucca Mountain. More confidence does not always mean lower risk, just as less uncertainty does not necessarily mean lower risk. What needs to be shown is that there is a basis for confidence in the outcome of such evaluations, meaning that the potential repository promises to provide acceptable public safety, as defined by the regulation, at every phase in its long life.
Author: Publisher: ISBN: Category : Languages : en Pages : 7
Book Description
The U.S. Environmental Protection Agency is currently revising the regulatory guidance for high-level nuclear waste disposal. In its draft form, the guidelines contain dose limits. Since this is likely to be the case in the final regulations, it is essential that the US Department of Energy be prepared to calculate site-specific doses for any potential repository location. This year, Pacific Northwest Laboratory (PNL) has made a first attempt to estimate doses for the potential geologic repository at Yucca Mountain, Nevada as part of a preliminary total-systems performance assessment. A set of transport scenarios was defined to assess the cumulative release of radionuclides over 10,000 years under undisturbed and disturbed conditions at Yucca Mountain. Dose estimates were provided for several of the transport scenarios modeled. The exposure scenarios used to estimate dose in this total-systems exercise should not, however, be considered a definitive set of scenarios for determining the risk of the potential repository. Exposure scenarios were defined for waterborne and surface contamination that result from both undisturbed and disturbed performance of the potential repository. The exposure scenarios used for this analysis were designed for the Hanford Site in Washington. The undisturbed performance scenarios for which exposures were modeled are gas-phase release of 14C to the surface and natural breakdown of the waste containers with waterborne release. The disturbed performance scenario for which doses were estimated is exploratory drilling. Both surface and waterborne contamination were considered for the drilling intrusion scenario.
Author: Publisher: ISBN: Category : Languages : en Pages : 16
Book Description
The U.S. Department of Energy (DOE) is considering the possible recommendation of a site at Yucca Mountain, Nevada, for the potential development of a geologic repository for the disposal of high-level radioactive waste and spent nuclear fuel. To facilitate public review and comment, in May 2001 the DOE released the Yucca Mountain Science and Engineering Report (S & ER) (1), which presents technical information supporting the consideration of the possible site recommendation. The report summarizes the results of more than 20 years of scientific and engineering studies. Based on internal reviews of the S & ER and its key supporting references, the Total System Performance Assessment for the Site Recommendation (TSPA-SR) (2) and the Analysis Model Reports and Process Model Reports cited therein, the DOE has recently identified and performed several types of analyses to supplement the treatment of uncertainty in support of the consideration of a possible site recommendation. The results of these new analyses are summarized in the two-volume report entitled FY01 Supplemental Science and Performance Analysis (SSPA) (3,4). The information in this report is intended to supplement, not supplant, the information contained in the S & ER. The DOE recognizes that important uncertainties will always remain in any assessment of the performance of a potential repository over thousands of years (1). One part of the DOE approach to recognizing and managing these uncertainties is a commitment to continued testing and analysis and to the continued evaluation of the technical basis supporting the possible recommendation of the site, such as the analysis contained in the SSPA. The goals of the work described here are to provide insights into the implications of newly quantified uncertainties, updated science, and evaluations of lower operating temperatures on the performance of a potential Yucca Mountain repository and to increase confidence in the results of the TSPA described in the S & ER (1). The primary tool used to evaluate the implications of the three types of supplemental information described in the SSPA (3,4) is the Yucca Mountain integrated TSPA model.
Author: Publisher: ISBN: Category : Languages : en Pages : 5
Book Description
The DOE identified a variety of uncertainties, arising from different sources, during its assessment of the performance of a potential geologic repository at the Yucca Mountain site. In general, the number and detail of process models developed for the Yucca Mountain site, and the complex coupling among those models, make the direct incorporation of all uncertainties difficult. The DOE has addressed these issues in a number of ways using an approach to uncertainties that is focused on producing a defensible evaluation of the performance of a potential repository. The treatment of uncertainties oriented toward defensible assessments has led to analyses and models with so-called ''conservative'' assumptions and parameter bounds, where conservative implies lower performance than might be demonstrated with a more realistic representation. The varying maturity of the analyses and models, and uneven level of data availability, result in total system level analyses with a mix of realistic and conservative estimates (for both probabilistic representations and single values). That is, some inputs have realistically represented uncertainties, and others are conservatively estimated or bounded. However, this approach is consistent with the ''reasonable assurance'' approach to compliance demonstration, which was called for in the U.S. Nuclear Regulatory Commission's (NRC) proposed 10 CFR Part 63 regulation (64 FR 8640 [DIRS 101680]). A risk analysis that includes conservatism in the inputs will result in conservative risk estimates. Therefore, the approach taken for the Total System Performance Assessment for the Site Recommendation (TSPA-SR) provides a reasonable representation of processes and conservatism for purposes of site recommendation. However, mixing unknown degrees of conservatism in models and parameter representations reduces the transparency of the analysis and makes the development of coherent and consistent probability statements about projected repository performance difficult. Likewise, a demonstration of the magnitude of conservatisms in the dose estimates that result from conservative inputs is difficult to determine. To respond to these issues, the DOE explored the significance of uncertainties and the magnitude of conservatisms in the SSPA Volumes 1 and 2 (BSC 2001 [DIRS 155950]; BSC 2001 [DIRS 154659]). The three main goals of this report are: (1) To briefly summarize and consolidate the discussion of much of the work that has been done over the past few years to evaluate, clarify, and improve the representation of uncertainties in the TSPA and performance projections for a potential repository. This report does not contain any new analyses of those uncertainties, but it summarizes in one place the main findings of that work. (2) To develop a strategy for how uncertainties may be handled in the TSPA and supporting analyses and models to support a License Application, should the site be recommended. It should be noted that the strategy outlined in this report is based on current information available to DOE. The strategy may be modified pending receipt of additional pertinent information, such as the Yucca Mountain Review Plan. (3) To discuss issues related to communication about uncertainties, and propose some approaches the DOE may use in the future to improve how it communicates uncertainty in its models and performance assessments to decision-makers and to technical audiences.
Author: Publisher: ISBN: Category : Languages : en Pages :
Book Description
A performance assessment is required to demonstrate compliance with the post-closure performance objectives for the Yucca Mountain Project (YMP), as stated in 10 CFR Part 63.1 13 (66 FR 55732, p. 55807). A performance assessment is defined in 10 CFR 63.2 (66 FR 55732, p. 55794) as an analysis that: (1) identifies the features, events, and processes (FEPs) that might affect the potential geologic repository; (2) examines the effects of those FEPs upon the performance of the potential geologic repository; and (3) estimates the expected dose incurred by a specified reasonably maximally exposed individual as a result of releases caused by significant FEPs. The performance assessment must also provide the technical basis for inclusion or exclusion of specific FEPs in the performance assessment as stated in 10 CFR 63.114 (66 FR 55732, p. 55807). An initial approach for FEP development, in support of the Total System Performance Assessment for the Site Recommendation (TSPA-SR) (CRWMS M & O 2000e), was documented in Freeze et al. (2001). The development of a comprehensive list of FEPs potentially relevant to the post-closure performance of the potential Yucca Mountain repository is an ongoing, iterative process based on site-specific information, design, and regulations. Although comprehensiveness of the FEPs list cannot be proven with absolute certainty, confidence can be gained through a combination of formal and systematic reviews (both top-down and bottom-up), audits, and comparisons with other FEP lists and through the application of more than one classification scheme. To support TSPA-SR, DOE used a multi-step approach for demonstrating comprehensiveness of the initial list of FEPs. Input was obtained from other international radioactive waste disposal programs as compiled by the Nuclear Energy Agency (NEA) of the Organization for Economic Co-operation and Development (OECD) to establish a general list of FEPs. The list was subsequently refined to include YMP-specific FEPs that account for the uniqueness of the design and setting (unsaturated fractured tuff). FEPs were then categorized to assess potential interactions and to establish the framework for scenario development and assessment. The level of detail of each individual FEP was determined to be the lowest level that would support model development activities. Although the level of detail between FEPs varies, the level of detail is considered appropriate to demonstrate the safety case.
Author: Publisher: ISBN: Category : Languages : en Pages : 8
Book Description
The U.S. Department of Energy (DOE) is considering the possible recommendation of a site at Yucca Mountain, Nevada, for the potential development of a geologic repository for the disposal of high-level radioactive waste and spent nuclear fuel. Consequences of hypothetical disruption of the Yucca Mountain site by igneous activity or human intrusion have been evaluated in the Yucca Mountain Science and Engineering Report (S & ER) (1), which presents technical information supporting the consideration of the possible site recommendation. Since completion of the S & ER, supplemental analyses have examined possible impacts of new information and alternative assumptions on the estimates of the consequences of these events. Specifically, analyses of the consequences of igneous disruption address uncertainty regarding: (1) the impacts of changes in the repository footprint and waste package spacing on the probability of disruption; (2) impacts of alternative assumptions about the appropriat e distribution of future wind speeds to use in the analysis; (3) effects of alternative assumptions about waste particle sizes; and (4) alternative assumptions about the number of waste packages damaged by igneous intrusion; and (5) alternative assumptions about the exposure pathways and the biosphere dose conversion factors used in the analysis. Additional supplemental analyses, supporting the Final Environmental Impact Statement (FEIS), have examined the results for both igneous disruption and human intrusion, recalculated for a receptor group located 18 kilometers (km) from the repository (the location specified in 40 CFR 197), rather than at the 20 km distance used in the S & ER analyses.
Author: Publisher: ISBN: Category : Languages : en Pages : 5
Book Description
This Letter Report presents the results of calculations to assess long-term performance of commercial spent nuclear fuel (CSNF), U.S. Department of Energy (DOE) spent nuclear fuel (DSNF), high-level radioactive waste (HLW), and Greater Than Class C (GTCC) radioactive waste and DOE Special Performance Assessment Required (SPAR) radioactive waste at the potential Yucca Mountain repository in Nye County Nevada with respect to the 10,000-year performance period specified in 40 CFR Part 197.30 (66 FR 32074 [DIRS 155216], p. 32134) with regard to radiation-protection standards. The EPA Final Rule 40 CFR Part 197 has three separate standards, individual-protection, human-intrusion, and groundwater-protection standards, all with a compliance timeframe of 10,000 years. These calculations evaluate the dose to receptors for each of these standards. Further, this Letter Report includes the results of simulations to the 1,000,000-year performance period described in 40 CFR Part 197.35 (66 FR 32074 [DIRS 155216], p. 32135) which calls for the calculation of the peak dose to the Reasonably Maximally Exposed Individual (RMEI) that would occur after 10,000 years and within the period of geological stability. In accordance with TSPA-SR the ''period of geologic stability'' is from zero to 1,000,000 years after repository closure. The calculations also present the 5th and 95th percentiles, and the mean and median of the set of probabilistic simulations used to evaluate various disposal scenarios.
Author: U.s. Nuclear Regulatory Comion
Author: U.s. Nuclear Regulatory Comion
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