Agenda - 11-17-1998 - 5a - Laserfiche WebLink

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Reactors 39 4.2.E Isolation Condenser System Reliability, 1987 - 1993 AEOD/S96-O1 See Section 3.2.2 of this volume. 4.2.6 Assessment of Spent Fuel Cooling AEOD/596-02 As a result of questions that had been raised about the adequacy of spent fuel pools (SFPs), the Executive Director for Operations requested that AEOD perform an independent study of the likelihood and consequences of an extended loss of SFP cooling. AEOD staff conducted an extensive review of more than 12 years of domestic and foreign operating experience data; visited six nuclear sites (with nine nuclear power plants) and the headquarters of Pennsylvania Power and Light, the operator of the Susquehanna Steam Electric Station (SSES); and met with contract engineers who had submitted a 10 CFR Part 21 report about potential defects and noncompliances at SSES. The staff reviewed previous SFP risk assessments and contracted with the Idaho National Engineering and Environmental Laboratory to perform a limited PRA of the SSES SFP. AEOD also performed independent assessments of the electrical systems, instrumentation, heat loads and radiation levels associated with the SFPs. On the basis of the study findings, the staff concluded that loss of SFP coolant inventory greater than 1 foot has occurred at a rate of about 1 per 100 reactor years, and loss of SFP cooling with a temperature rise greater than 20°F has occurred at a rate of approximately 3 per 1000 reactor years. The consequences of these actual events have not been severe. However, events have occurred that have resulted in the loss of several feet of SFP coolant level and have lasted more than 24 hours. The primary cause of these events has been human error. Both the likelihood and the consequences of loss of SFP cooling events are highly dependent on human performance as well as individual plant design features. From their review of existing SFP risk assessments, the staff found that the relative risk from the loss of spent fuel cooling is low compared to the risk from events involving active fuel in the reactor vessel. As a result of this study, the staff has determined that the typical U.S. plant may need improvements in SFP instrumentation, operator procedures and training, and/or configuration control. The need for specific corrective actions should be evaluated for those plants where failures of reactor cavity or gate seals or ineffective antisiphon devices could potentially cause sufficient loss flf SFP coolant inventory to uncover the fuel or endanger makeup capability. The need for improving configuration controls related to the SFP to prevent and/or mitigate SFP loss of inventory events and loss of cooling events should be evaluated on aplant-specific basis. The need for plant modifications at some multi-unit sites to account for the potential effects of SFP boiling conditions on safe shutdown equipment for the operating unit, particularly during full core off-loads, should be evaluated on aplant-specific basis. The need for improved procedures and training for control room operators to respond to SFP loss of cooling events consistent with the time frames over which events can proceed, recognizing the heat load and the possibility of loss of inventory, should be evaluated on a plant- specific basis. The need for improvements to instrumentation and power supplies to the SFP equipment to aid operator response to SFP events should be evaluated on aplant-specific basis. 4.2.7 Emergency Diesel Generator Power System Reliabiiity,1987 - 1993 AEOD/S96-03 See Section 3.2.1 of this volume. 4.3 Engineering Evaluations 4.3.1 Motor-Operated Valve Key Failures 33 Reports