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NUREG 0933
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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 …
1
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 …
1
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 …
1
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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DESCRIPTION Historical Background This issue was initiated in response to an immediate action memorandum [1] issued by AEOD in September 1981 regarding desiccant contamination of instrument air lines. NRR responded to the AEOD memorandum by establishing a …
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DESCRIPTION Historical Background In December 1981, AEOD completed a survey of valve operator-related events that occurred during 1978, 1979, and 1980 and submitted a draft report [1] to NRR for comment. In this study, AEOD established that motor- …
1
DESCRIPTION Historical Background This issue was identified at an NRC Operating Reactor Events meeting on January 7, 1982, [1] and addressed fire protection system (FPS) actuations that resulted in adverse interactions with safety-related equipment at …
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DESCRIPTION Historical Background Increasing attention has recently been focused on the integrity of RCP seals due to loss of cooling to the seals both in connection with PRA studies which are currently under review and from operating experience. [1] , …
1
DESCRIPTION Historical Background PORVs and block valves were originally designed as non-safety components in the reactor pressure control system for use only when plants are in operation. The block valves were installed because of expected leakage from …
1
DESCRIPTION Historical Background The HPCI steam supply line has two containment isolation valves in series: one inside and one outside of the containment. Both are normally open in most plants; however, two plants were found to operate with the HPCI …
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DESCRIPTION Historical Background This issue was recommended [1] for prioritization by DSI after a review of the AEOD engineering evaluation report (AEOD/E325) [2] on vapor binding of the AFW pumps at H.B.Robinson Unit 2. Further AEOD study of the event …
1
DESCRIPTION Historical Background This issue was identified during the staff review of the Indian Point 2 and Zion PRAs [1] ; in both of these studies, the dominant interfacing systems LOCA events were estimated to be through the RHR suction valves. The …
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DESCRIPTION Historical Background During the review of LaSalle, ASB identified a potential problem which could be generic to all BWRs. [1] [2] The problem relates to ability of the CRD accumulators to retain pressure for a sufficient period of time after …
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DESCRIPTION Historical Background On April 17, 1984, a DSI memorandum [1] on the subject of RHR interlocks for W plants described staff concerns that the design basis for RHR interlocks had been misunderstood and that these concerns had not been …
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DESCRIPTION Historical Background Issue B-63, which was resolved and implemented as MPA B-45, required leak-testing of the check valves that isolate those low pressure systems that are connected to the RCS outside the containment. However, except for …
1
DESCRIPTION Historical Background This issue was identified in a DST/NRR memorandum [1] which addressed a condition in which some protective devices intended to trip active engineered safety features (ESF) components, under indication of equipment …
1
DESCRIPTION The loss of all feedwater event at Davis-Besse on June 9, 1985, resulted in the formation of an NRC project team to investigate the event. The team's findings were published in NUREG-1154 [1] and were subsequently reviewed by DL/NRR. As a …
1
DESCRIPTION In 1985, operating experience as well as staff and industry studies indicated that AFW systems continued to fail at a high rate. These studies also indicated that plants with similar AFW system reliabilities (as calculated in accordance with …
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DESCRIPTION Background The reliability of PWR main steam safety valves (MSSVs) was identified as a generic issue in a DSRO memorandum on March 1986 [1] in which it was noted that individual PWR plant FSARs assume credit for MSSV functional capability to …
1
DESCRIPTION Historical Background This issue was identified in a May 1986 DSI memorandum [1] in which 21 instances of BWR vessel draining through various paths in the RHR system piping were described. Later, in August 1986, AEOD/E609 [2] was issued …
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DESCRIPTION Historical Background This issue was identified as an alternative approach to the Finding 15 recommendation [1] discussed in Issue 125.I.5, "Safety Systems Tested in All Conditions Required by DBA," which states that "[t]horough integrated …
1
DESCRIPTION Historical Background This issue was identified [1] by DSIR/RES following ACRS concerns raised during the review of the resolution of Issue 87, "Failure of HPCI Steam Line Without Isolation," which addressed the design bases for those MOVs …
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DESCRIPTION Historical Background The reliability of essential service water (ESW) systems and related problems have been an ongoing staff concern which has been documented in NUREG/CR-2797, [1] IE Bulletins 80-24 [2] and 81-03, [3] Generic Letter No. …
1
DESCRIPTION Historical Background This issue was identified [1] by NRR after reactor operating experience and research results on MOVs, SOVs, AOVs, and HOVs indicated that testing under static conditions did not always reveal how these valves would …
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DESCRIPTION Historical Background This issue was identified [1] by NRR and addressed concerns involving centrifugal pumps operating at some point below the best efficiency point (BEP) on their characteristic curves that could cause hydraulic instability …
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Page Last Reviewed/Updated 3/1/2026
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