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NUREG 0933
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DESCRIPTION This item was originally identified in NUREG-0371 [1] and was later declared a USI in NUREG-0510. [2] (See Item A-3 for further details.) CONCLUSION This item was RESOLVED and requirements were established. (See Item A-3 for further details.) …
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DESCRIPTION During the conduct of a large scale testing program for an advanced design BWR pressure suppression containment system (MARK III), new suppression pool hydrodynamic loads associated with a postulated LOCA were identified which had not been …
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DESCRIPTION During testing for an advanced BWR containment system design (MARK III), suppression pool hydrodynamic loads were identified which had not been considered in the original design of the MARK I containment system. To address this issue, a MARK I …
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DESCRIPTION Operation of BWR primary system pressure relief valves can result in hydrodynamic loads on the suppression pool retaining structures or those structures located within the pool. These loads result from initial vent clearing of relief valve …
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DESCRIPTION Pipe cracking has occurred in the heat-affected zones of welds in primary system piping in BWRs since mid-1960. These cracks have occurred mainly in Type 304 stainless steel which is the type used in most operating BWRs. The major problem is …
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DESCRIPTION The rationale for normal and postaccident containment cooling will be reviewed to determine the adequacy of the design requirements imposed on the containment ventilation systems. By reviewing typical designs, the staff will develop a basic …
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DESCRIPTION Historical Background The possibility of thermal-hydraulic instability in a BWR had been investigated by GE since the start-up of early BWRs. Analytical methods and codes were formulated on the basis of these early investigations to predict …
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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 Surface cracks have been discovered in control rod drive internal parts at some operating BWR plants. Although only observed to be localized in nature, this cracking, if propagated, could potentially affect the capability of the control rod …
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DESCRIPTION The BWR pressure relief system is designed to prevent overpressurization of the reactor coolant pressure boundary (RCPB) under the most severe abnormal operational transient: closure of the main steam line isolation valves (MSIVs) with failure …
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DESCRIPTION Historical Background Dose calculations by AAB/NRR in 1975 indicated that operation of the main steam isolation valve leakage control system (MSIVLCS) required for some BWRs could result in higher offsite accident doses than if the system were …
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DESCRIPTION Historical Background A BWR RHR system is designed for: (1) containment spray/suppression pool cooling, (2) fuel pool cooling augmentation, (3) low pressure coolant injection, and (4) bringing the reactor down to a cold shutdown condition. …
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DESCRIPTION BWRs are operated in such a manner as to attempt to produce an axial power distribution with as little peaking as possible. When the reactor moderator is not boiling (e.g., during startup and heatup), the axial flux distribution is much more …
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DESCRIPTION Historical Background This issue apparently originated as a DOR proposal and was discussed in SECY-80-325. [1] The issue as previously evaluated [2] is whether periodic replacement of the squib charges and circuit checks of the traveling …
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DESCRIPTION Historical Background A memorandum [1] from AEOD to NRR dated May 23, 1980 drew attention to the generic issue of BWR jet pump integrity. The concern that motivated the AEOD memo was a February 1980 jet pump failure at Dresden Unit 3, together …
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DESCRIPTION This issue involves a potential deficiency in the ability to control leakage past the main steam isolation valves (MSIV) in BWR plants. Requirements for MSIV leakage control systems outlined in Regulatory Guide 1.96 [1] were developed as a …
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DESCRIPTION This issue concerns the slow loss of control air pressure in the scram system of BWRs. [1] Air pressure dropping at a certain rate will first allow some of the CRD scram outlet valves to open slightly, thus filling the scram discharge volume …
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DESCRIPTION This issue was identified in a 1980 AEOD memorandum [1] and concerned the slow loss of control air pressure in the pneumatic control system of BWR scram systems. Air pressure loss at certain low rates can allow a sufficient discharge of water …
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DESCRIPTION Historical Background On April 3, 1981, AEOD published draft NUREG-0785, "Safety Concerns Associated with Pipe Breaks in the BWR Scram System." [1] As a result of the development of these safety concerns and the findings presented in the …
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DESCRIPTION Historical Background On June 28, 1980, during a routine shutdown of the Browns Ferry Unit 3 reactor, a manual scram from approximately 36% power failed to insert about 40% of the control rods. Two additional manual scrams followed by an …
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DESCRIPTION Historical Background In January 1982, AEOD published a report (AEOD/C201 [1] ) on safety concerns associated with reactor vessel level instrumentation in BWRs. The report was forwared to NRR for further action. Safety Significance BWRs use …
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DESCRIPTION Historical Background In response to a 1967 ACRS concern relative to the potential of melting and subsequent disintegration of a portion of a fuel assembly due to inlet orifice flow blockage, GE submitted NEDO-10174 [1] in May 1970. As a …
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DESCRIPTION Historical Background The SRVs of a BWR plant provide protection against overpressurization of the reactor primary system. During normal operation, the SRVs which are mounted in the main steam lines open on high pressure permitting steam to …
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DESCRIPTION Historical Background BWRs are required to be operated within set thermal limits to maintain the integrity of the fuel cladding during postulated events. One of the established thermal limits is the minimum critical power ratio (MCPR). The …
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DESCRIPTION Historical Background This issue was identified by the ACRS in 1978 during the operating license reviews of some BWRs. The ACRS posed questions concerning the likelihood and effects of a LOCA which could cause interactions with the CRD …
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Page Last Reviewed/Updated 3/1/2026
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