Information Notice No. 87-59: Potential RHR Pump Loss
IN 87-59 UNITED STATES NUCLEAR REGULATORY COMMISSION OFFICE OF NUCLEAR REACTOR REGULATION WASHINGTON, D.C. 20555 November 17, 1987 Information Notice No. 87-59: POTENTIAL RHR PUMP LOSS Addressees: All holders of operating licenses or construction permits for nuclear power reactors. Purpose: This information notice is provided to alert addressees to potential problems with safety injection pumps having common recirculation lines. It is expected that recipients will review the information for applicability to their facili- ties and consider actions, as appropriate, to avoid similar problems. However, suggestions contained in this information notice do not constitute NRC requirements; therefore, no specific action or written response is required. Description of Circumstances: Westinghouse Electric Corporation has notified all utilities with Westinghouse-designed nuclear steam supply systems of two concerns they have identified regarding the design of the minimum flow (miniflow) recirculation line configuration for the residual heat removal (RHR) pumps which also function as low pressure safety injection (LPSI) pumps. The first concern involves the potential for dead heading one of two RHR pumps in systems that have a common miniflow recirculation line serving both pumps. The second concern involves the adequacy of the miniflow recirculation line capacity even for single pump operation. In addition, Westinghouse has stated that these concerns might also be applicable to high pressure safety injection pumps. Discussion: A small-break loss-of-coolant accident causes a safety injection signal to be generated, which starts both RHR pumps and for some plants, circulates coolant through a common miniflow recirculation line until the reactor coolant system (RCS) is depressurized to below the pump shutoff head; the point at which the RHR pumps can deliver coolant to the RCS. The flow resistance of the miniflow line is great enough that during recirculation the RHR pumps are operating close to their shutoff head. Thus, even modest degradation of one pump can result in it being dead headed by the other pump. Westinghouse has stated that an RHR pump supplied by one vendor can, under certain conditions, operate dead headed for a maximum of only 10.4 minutes without resulting in pump damage. For this reason, generic emergency operating procedures for Westinghouse reactors require that a dead headed pump be stopped. To avoid loss of safety margin, it is important that this action be taken before pump damage is sustained. 8711120027 . IN 87-59 November 17, 1987 Page 2 of 2 Westinghouse indicates that, traditionally, the design criteria for miniflow lines have been based on the need to limit the temperature rise in the pumped liquid and pump casing. However, that design criteria should include consideration of the potential for pump operation at conditions close to the pump shutoff head. The NRC staff believes that this issue may be relevant to all water-cooled reactor designs, regardless of the pump application or the NSSS manufacturer. This is based on the belief that miniflow lines have traditionally been de- signed for only 5% to 15% of pump design flow, while some pump manufacturers are advising that their pumps should have minimum flow capacities of 25% to over 50% of best efficiency flow for extended operation. The information herein is being provided as an early notification of a poten- tially significant matter that is still under consideration by the NRC staff. If NRC evaluation so indicates, specific licensee actions may be requested. No specific action or written response is required by this information notice. If you have any questions about this matter, please contact the technical contact listed below or the Regional Administrator of the appropriate regional office. Charles E. Rossi, Director Division of Operational Events Assessment Office of Nuclear Reactor Regulation Technical Contact: Roger W. Woodruff, NRR (301) 492-7096 Attachment: List of Recently Issued NRC Information Notices
Page Last Reviewed/Updated Tuesday, March 09, 2021
Page Last Reviewed/Updated Tuesday, March 09, 2021