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NUREG 0933
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The objectives of this task were to: (1) decrease reliance on the emergency core cooling system (ECCS) for events other than LOCAs; (2) ensure that the ECCS design basis reliability and performance were consistent with operational experience; (3) reach a …
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The objectives of this task were to perform systems reliability analyses and to effect changes in emergency operating procedures and operator training to improve the capability of plants to mitigate the consequences of the small-break LOCAs and …
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DESCRIPTION The issue was raised after the occurrence of various incidents of water hammer that involved steam generator feedrings and piping, emergency core cooling systems, RHR systems, containment spray, service water, feedwater, and steam lines. The …
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DESCRIPTION Historical Background Prior to May 1978, tests conducted by GE showed that the presence of steam and/or increased pressure in and above the upper core region of BWRs could adversely affect the distribution of flow from certain types of core …
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DESCRIPTION Historical Background This NUREG-0371 [1] item involves the development of consistent and formalized acceptance criteria regarding the conversion to higher density storage racks (increased storage capacity) in existing spent fuel storage …
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DESCRIPTION At all nuclear plants, overhead cranes are used to lift heavy objects in the vicinity of spent fuel. If a heavy object such as a spent fuel shipping cask or shielding block were to fall onto spent fuel in the storage pool or reactor core …
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DESCRIPTION Numerical reliability goals and methods of analysis have not been established by the NRC. The current basis for plant licensing continues to be NRC regulations which require, among other things, that the consequences of a LOCA be suitably …
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DESCRIPTION Historical Background This NUREG-0471 [1] item concerned staff positions [2] BTP EISCB 18 and BTP RSB 6-11 which required physical locking out of electrical sources to specific MOVs in the ECCS. The existing staff positions established the …
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DESCRIPTION A number of applicants for operating licenses have been performing sump tests to demonstrate ECCS operability during the recirculation phase following a postulated loss-of-coolant accident. These tests have shown that vortex formation is not …
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DESCRIPTION Most vendors, in the conduct of internal audits of emergency core cooling performance computer codes, discovered errors in coding and/or logic which had significant effects on the prediction results of approved models. This NUREG-0471 [1] task …
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DESCRIPTION Historical Background This issue was identified in NUREG-0471 [1] and addressed the establishment of surveillance test intervals and allowable equipment outage periods, using analytically-based TS criteria and methods. At the time the issue …
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DESCRIPTION Following a plant transient or accident, provisions are required for long-term decay heat removal. Redundancy of components is required as necessary to assure that a failure in the RHR system will not impair the ability to maintain the plant …
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DESCRIPTION Historical Background As identified in NUREG-0471, [1] Appendix K of 10 CFR 50 specifies the requirements for LWR ECCS analysis. These requirements call for specific conservatisms to be applied to certain models and correlations used in the …
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DESCRIPTION This issue was documented in NUREG-0471 [1] and stemmed from an ACRS recommendation that the staff explore diverse means of obtaining ECCS capability for future plants. The ACRS also recommended the staff explore the issue in the context of …
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DESCRIPTION Historical Background This issue is identified in Appendix D of NUREG-0572 [1] and is one of the key observations made after the ACRS requested its members and consultants to make comprehensive reviews of all Licensee Event Reports (LERs) …
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DESCRIPTION Background This issue was identified [1] after a review of LERs involving the failure or degraded performance of essential equipment that resulted from the failure of protective devices such as fuses and circuit breakers. The affected systems …
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DESCRIPTION Background Flow-induced vibrations caused by vortex shedding resulting from rapid area change, buffeting due to random flow turbulence, fluid structures interaction instability, leakage excitation, steady operation of positive displacement …
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DESCRIPTION Historical Background This concern was identified by the ACRS as a result of their review [1] of LERs covering a period from 1976 through 1978 and, subsequently, a comprehensive review of the problem was completed which covered the LERs and …
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DESCRIPTION Under the scope of the TMI Action Plan Item II.K.3 in NUREG-0660, [1] the NRC Bulletin and Orders Task Force conducted generic reviews of the loss-of-feedwater and small-break loss-of-coolant events on all operating reactors. These reviews …
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DESCRIPTION Historical Background In the event of a LOCA in which offsite power remains available, the reactor operator may choose to shut down the emergency diesel generators shortly after the LOCA. If, after the diesels are shut down, offsite power is …
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DESCRIPTION Historical Background This issue effects all PWR-type reactors (Westinghouse, CE, B&W). The issue as described, [1] , [2] , [3] concerns postulated accidents resulting from a steam line break which consequentially results in a steam generator …
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DESCRIPTION Background This issue addressed the high rate of reactor coolant pump (RCP) seal failures that challenge the makeup capacity of the ECCS in PWRs. At the time this issue was identified [1] in 1980, RCP seal failures in BWRs occurred at a …
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DESCRIPTION Historical Background This issue was raised by the staff following a review [1] , [2] of operating events that indicated a significant number of ECCS spurious actuations, particularly, the four events that occurred at Davis-Besse during 1980. …
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DESCRIPTION In a San Onofre Unit 1 Preliminary Notification issued in September 1980, it was reported that, during testing, the licensee had identified a problem with the design of the diesel generator sequencing circuitry. This problem occurred when a …
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DESCRIPTION Historical Background This issue was identified [1] when AEOD expressed concerns about the use inside containment of a particular polymer coating that could flake off and fail when subjected to DBA conditions. In addition to the concern for …
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Page Last Reviewed/Updated 3/1/2026
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