Publications

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This paper describes the MELCOR Accident Consequence Code System, Version 2(MACCS2), parameters and probabilistic results of offsite consequences for the uncertainty analysis of the State-of-the-Art Reactor Consequence Analyses unmitigated long-term station blackout accident scenario at the Peach Bottom Atomic Power Station. Consequence results are presented as conditional risk (i.e., assuming the accident occurs) to individuals of the public as a result of the accident - latent-cancer-fatality (LCF) risk per event or prompt-fatality risk per event. For the mean, individual, LCF risk, all regression methods at each of the circular areas around the plant that are analyzed (10-mile to 50-mile radii are considered) consistently rank the MACCS2 dry deposition velocity, the MELCOR safety relief valve (SRV) stochastic failure probability, and the MACCS2 residual cancer risk factor, respectively, as the most important input parameters. For the mean, individual, prompt-fatality risk (which is zero in over 85% of the Monte Carlo realizations) within circular areas with less than a 2-mile radius, the non-rank regression methods consistently rank the MACCS2 wet deposition parameter, the MELCOR SRV stochastic failure probability, the MELCOR SRV open area fraction, the MACCS2 early health effects threshold for red bone marrow, and the MACCS2 crosswind dispersion coefficient, respectively, as the most important input parameters. For the mean, individual prompt-fatality risk within the circular areas with radii between 2.5-miles and 3.5-miles, the regression methods consistently rank the MACCS2 crosswind dispersion coefficient, the MACCS2 early health effects threshold for red bone marrow, the MELCOR SRV stochastic failure probability, and the MELCOR SRV open area fraction, respectively, as the most important input parameters.

This paper describes the MELCOR Accident Consequence Code System, Version 2 (MACCS2) dose-truncation sensitivity of offsite consequences for the uncertainty analysis of the State-of-the-Art Reactor Consequence Analyses unmitigated long-term station blackout severe accident scenario at the Peach Bottom Atomic Power Station. Latent-cancer-fatality (LCF) risk results for this sensitivity study are presented for three dose-response models. LCF risks are reported for circular areas ranging from a 10-to a 50-mile radius centered on the plant. For the linear, no-threshold, sensitivity analysis, all regression methods consistently rank the MACCS2 dry deposition velocity and the MELCOR safety relief valve (SRV) stochastic failure probability, respectively, as the most important input parameters. For the alternative dose-truncation models (i.e., USBGR (0.62 rem/yr) and HPS (5 rem/yr with a lifetime limit of 10 rem)) sensitivity analyses, the regression methods consistently rank the MACCS2 inhalation protection factor for normal activity, the MACCS2 lung lifetime risk factor for cancer death, and the MELCOR SRV stochastic failure probability as the most important input variables. The important MELCOR input parameters are relatively independent of the dose-response model used in MACCS2. However, the MACCS2 input variables depend strongly on the dose-response model. The use of either the USBGR or the HPS dose-response model emphasizes MACCS2 input variables associated with doses received in the first year and deemphasizes MACCS2 input parameters associated with long-term phase doses beyond the first year.

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Extensive work has been carried out by the U.S. Department of Energy (DOE) in the development of a proposed geologic repository at Yucca Mountain (YM), Nevada, for the disposal of high-level radioactive waste. As part of this development, a detailed performance assessment (PA) for the YM repository was completed in 2008 and supported a license application by the DOE to the U.S. Nuclear Regulatory Commission (NRC) for the construction of the YM repository. The following aspects of the 2008 YM PA are described in this presentation: (i) conceptual structure and computational organization, (ii) uncertainty and sensitivity analysis techniques in use, (iii) uncertainty and sensitivity analysis for physical processes, and (iv) uncertainty and sensitivity analysis for expected dose to the reasonably maximally exposed individual (RMEI) specified the NRC's regulations for the YM repository. © 2011 Elsevier Ltd.

Weak link (WL)/strong link (SL) systems are important parts of the overall operational design of high-consequence systems. In such designs, the SL system is very robust and is intended to permit operation of the entire system under, and only under, intended conditions. In contrast, the WL system is intended to fail in a predictable and irreversible manner under accident conditions and render the entire system inoperable before an accidental operation of the SL system. The likelihood that the WL system will fail to deactivate the entire system before the SL system fails (i.e., degrades into a configuration that could allow an accidental operation of the entire system) is referred to as probability of loss of assured safety (PLOAS). This report describes the Fortran 90 program CPLOAS_2 that implements the following representations for PLOAS for situations in which both link physical properties and link failure properties are time-dependent: (i) failure of all SLs before failure of any WL, (ii) failure of any SL before failure of any WL, (iii) failure of all SLs before failure of all WLs, and (iv) failure of any SL before failure of all WLs. The effects of aleatory uncertainty and epistemic uncertainty in the definition and numerical evaluation of PLOAS can be included in the calculations performed by CPLOAS_2.

Weak link (WL)/strong link (SL) systems are important parts of the overall operational design of high-consequence systems. In such designs, the SL system is very robust and is intended to permit operation of the entire system under, and only under, intended conditions. In contrast, the WL system is intended to fail in a predictable and irreversible manner under accident conditions and render the entire system inoperable before an accidental operation of the SL system. The likelihood that the WL system will fail to deactivate the entire system before the SL system fails (i.e., degrades into a configuration that could allow an accidental operation of the entire system) is referred to as probability of loss of assured safety (PLOAS). Representations for PLOAS for situations in which both link physical properties and link failure properties are time-dependent are derived and numerically evaluated for a variety of WL/SL configurations, including PLOAS defined by (i) failure of all SLs before failure of any WL, (ii) failure of any SL before failure of any WL, (iii) failure of all SLs before failure of all WLs, and (iv) failure of any SL before failure of all WLs. The effects of aleatory uncertainty and epistemic uncertainty in the definition and numerical evaluation of PLOAS are considered.

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