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The Accident Sequence Precursor (ASP) Program of United States Nuclear Regulatory Commission (U.S.NRC) identifies and categorizes operational events at nuclear power plants in terms of the potential for core damage. The ASP analys...
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The Accident Sequence Precursor (ASP) Program of United States Nuclear Regulatory Commission (U.S.NRC) identifies and categorizes operational events at nuclear power plants in terms of the potential for core damage. The ASP analysis has been performed on yearly basis and the results have been published in the annual reports. This paper describes the trends in initiating events and dominant sequences for 459 precursors identified in the ASP Program during the 1969-94 period and also discusses a comparison with dominant sequences predicted in the past Probabilistic Risk Assessment (PRA) studies. These trends were examined for three time periods, 1969-81, 1984-87 and 1988-94. Although the different models had been used in the ASP analyses for these three periods, the distribution of precursors by dominant sequences show similar trends to each other. For example, the sequences involving loss of both main and auxiliary feedwater were identified in many PWR events and those involving loss of both high and low coolant injection were found in many BWR events. Also, it was found that these dominant sequences were comparable to those determined to be dominant in the predictions by the past PRAs. As well, a list of the 459 precursors identified are provided in Appendix, indicating initiating event types, unavailable systems, dominant sequences, conditional core damage probabilities, and so on. (author)
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We report the calculated results of neutronic performance of cold moderators in a reference target-moderator-reflector system at the projected 5 MW pulsed spallation neutron source in Japan Atomic Energy Research Institute (JAERI)...
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We report the calculated results of neutronic performance of cold moderators in a reference target-moderator-reflector system at the projected 5 MW pulsed spallation neutron source in Japan Atomic Energy Research Institute (JAERI). The cold neutron intensities in present reference model are about 2.3-2.5 times higher than that from the decoupled solid methane (S-CH4) and close to the values obtained at other facilities (LANSCE Upgrade, NSNS, etc.). The H2O premoderator (PM) reduces the energy deposition in a liquid-hydrogen (L-H2) moderator by about a factor of 2 compared with that in a decoupled L-H2 moderator. The dependence of reflector on the neutron intensity and the energy deposition in the cryogenic moderators is also discussed. Although the pulse shapes were not obtained because of time consuming Monte Carlo calculations, we will discuss the pulse shapes based on experiments. (auth)
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The working group meeting was chaired by Watanabe. This working group was convened to set up an effort to characterize moderators at existing sources. The desired outcome was a formulation of the criteria, timing, and plans for th...
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The working group meeting was chaired by Watanabe. This working group was convened to set up an effort to characterize moderators at existing sources. The desired outcome was a formulation of the criteria, timing, and plans for the necessary
experiments. The results of the deliberations of this working group are summarized here. (auth)
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The CUT-TD code has been developed to find minimal cut sets for a given fault tree and to calculate the occurrence probability of its top event. This code uses an improved top-down algorithm which can enhance the efficiency in der...
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The CUT-TD code has been developed to find minimal cut sets for a given fault tree and to calculate the occurrence probability of its top event. This code uses an improved top-down algorithm which can enhance the efficiency in deriving minimal cut sets. The features in processing techniques incorporated into CUT-TD are as follows: (1) Consecutive OR gates or consecutive AND gates can be coalesced into a single gate. As a result, this processing directly produces cut sets for the redefined single gate with each gate not being developed. (2) The independent subtrees are automatically identified and their respective cut sets are separately found to enhance the efficiency in processing. (3) The minimal cut sets can be obtained for the top event of a fault tree by combining their respective minimal cut sets for several gates of the fault tree. (4) The user can reduce the computing time for finding minimal cut sets and control the size and significance of cut sets by inputting a minimum probability cut off and/or a maximum order cut off. (5) The user can select events that need not to be further developed in the process of obtaining minimal cut sets. This option can reduce the number of minimal cut sets, save the computing time and assists the user in reviewing the result. (6) Computing time is monitored by the CUT-TD code so that it can prevent the running job from abnormally ending due to excessive CPU time and produce an intermediate result. The CUT-TD code has the ability to restart the calculation with use of the intermediate result. This report provides a users' manual for the CUT-TD code. (author). (ERA citation 18:007481)
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This document consists of two parts and an Appendix. Part I provides a summary of worldwide experiences and subsequent recommendations regarding the implementation of the Three Mile Island-Unit 2 incident lessons learned. Part II ...
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This document consists of two parts and an Appendix. Part I provides a summary of worldwide experiences and subsequent recommendations regarding the implementation of the Three Mile Island-Unit 2 incident lessons learned. Part II gives in a summary fashion, specific responses and actions of the mentioned countries and international organizations as categorized into ten (10) subject areas. The Appendix, on the other hand, contains examples of the experiences of Brazil, Germany (F.R.), Hungary, and the Philippines, on the implementation of TMI lessons learned. This document should be useful to countries with nuclear power development programmes in that it provides a means for comparison of their actions with others. For countries which are embarking on their first nuclear power project, the document should provide a useful reference for specific TMI-related issues that need to be considered in their nuclear programmes. (Atomindex citation 14:806222)
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We have tested a resonance detector spectrometer at the KENS neutron source, using exp 181 Ta, exp 121 Sb and exp 149 Sm absorbers and bismuth germanate (BGO), NaI and plastic scintillators. In the process we uncovered and solved ...
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We have tested a resonance detector spectrometer at the KENS neutron source, using exp 181 Ta, exp 121 Sb and exp 149 Sm absorbers and bismuth germanate (BGO), NaI and plastic scintillators. In the process we uncovered and solved numerous background problems, and discovered a time-focussing principle. We measured the scattering from a number of materials and so far have analyzed and present results for bismuth and graphite. Tests of cooled absorbers have indicated that resolution of 70 MeV is possible with exp 181 Ta. (ERA citation 08:021571)
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