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Information Notice No. 87-01: RHR Valve Misalignment Causes Degradation of ECCS in PWRS
SSINS No.: 6835 IN 87-01 UNITED STATES NUCLEAR REGULATORY COMMISSION OFFICE OF INSPECTION AND ENFORCEMENT WASHINGTON, D.C. 20555 January 6, 1987 Information Notice No. 87-01: RHR VALVE MISALIGNMENT CAUSES DEGRADATION OF ECCS IN PWRS Addressees: All pressurized-water reactor facilities holding an operating license or a construction permit. Purpose: This information notice is provided as notification of a potentially significant problem pertaining to residual heat removal (RHR) valve alignment in the low-pressure emergency core cooling system (ECCS). It is expected that recipients will review the information for applicability to their facilities and consider actions, if appropriate, to preclude a similar problem from occurring at their facilities. However, suggestions contained in this information notice do not constitute NRC requirements; therefore, no specific action or written response is required. Description of Circumstances: In late May 1985, plant operators at Callaway isolated the RHR crossover line (by closing the normally open valves X1 or X2 in Figure 1 on the next page) to perform an operability test of train A of the low-pressure ECCS. This action would allow the B train to feed only two reactor coolant system (RCS) loops. When an NRC inspector questioned the advisability of this configuration, the licensee requested technical assistance from Westinghouse. Westinghouse indicated that the licensing bases for the ECCS analysis assume that all four RCS cold legs are being supplied water from at least one RHR pump. Isolation of the crossover line to place the A train in the test condition violated this analysis assumption. At this facility, however, the degraded configuration was never in existence for longer than 1 hour. Subsequently, Byron Unit 1 identified numerous occasions in 1985 when the RHR system would have been capable of injection to only two RCS loops. 8612300151 . IN 87-01 January 6, 1987 Page 2 of 3 On March 31, 1986, Trojan issued licensee event report (LER) 50/344-86/03 informing the NRC that their technical specification (TS) requirements for injection by RHR to all four RCS cold legs was violated when the A pump discharge valve was closed for maintenance while the plant was at 100% power. Closing of the A pump discharge valve (A2) prevented flow to two RCS cold legs. Escalated enforcement action was taken against the licensee for this violation. Discussion: The ECCS analyses for the plants mentioned assumes RHR injection into all four RCS cold legs. The isolation of RHR flow to any of the RCS cold legs including surveillance while the reactor is in modes 1, 2, or 3 will place these facilities outside their design bases. In some instances, confusion has existed with regard to the appropriate lineup to test a "train" of RHR. The diagram below (Figure 1) depicts a typical RHR schematic. Neither the A pump nor the B pump delivers flow to all four RCS loops, so that no independent set of pumps, pipes, and valves that would constitute a "train" exists. In this design configuration, the crossover valves (X1 and X2) must be open when one pump is inoperable. Further, to account for a potential failure of one of the RHR pumps during a loss-of-coolant accident, these valves may be required to be open at all times. The decision to isolate components of this system therefore, has to consider the operability requirements and design basis analysis for ECCS. Figure 1 is a simplified diagram of RHR flow. Valves A1 and B1 can isolate a pump with valves A2, B2, X1, and X2 open and provide flow to all four RCS loops, but the closure of A2 or B2 or the closure of X1 or X2 with one pump inoperable would render the system capable of providing flow to only two RCS loops. Trojan opened their crossover valves and revised their procedures to ensure that they were operating within licensing bases during surveillance. Callaway also revised their procedures. Byron not only revised procedures but also submitted a revised ECCS analysis based on the one-pump-to-two-cold-legs configuration and requested a TS change to allow one-pump-to-two-cold-legs operation for a short time in mode 3 to allow for maintenance. . IN 87-01 January 6, 1987 Page 3 of 3 No specific action or written response is required by this information notice. If you have any questions about this matter, please contact the Regional Administrator of the appropriate regional office or this office. Edward L. Jordan Director Division of Emergency Preparedness and Engineering Response Office of Inspection and Enforcement Technical Contact: Mary S. Wegner, IE (301) 492-4511 Attachment: List of Recently Issued IE Information Notices .
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