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Information Notice No.80-23 – Loss of Suction to Emergency Feedwater Pumps
SSINS No.: 6835 Accession No.: 8005050061 UNITED STATES NUCLEAR REGULATORY COMMISSION OFFICE OF INSPECTION AND ENFORCEMENT WASHINGTON, D. C. 20555 May 29, 1980 Information Notice No. 80-23 LOSS OF SUCTION TO EMERGENCY FEEDWATER PUMPS Description of Circumstances: On April 7, 1980, Arkansas Nuclear One, Unit 2, suffered a loss of offsite power due to tornado damage to 500 kv transmission towers. The unit tripped from 98% power; the diesel generators started and supplied vital loads; natural circulation in the reactor coolant system was established; and the emergency feedwater (EFW) pumps supplied feedwater to the steam generators. The suction of the EFW pumps was aligned to the Condensate Storage Tanks (CST) and to the Startup and Blowdown Demineralizer effluent in parallel. Approximately 15 minutes after the unit tripped, both EFW pumps lost suction. Prompt operator action was taken to isolate the EFW pump suction from the Startup and Blowdown Demineralizer and to vent the EFW pumps. EFW flow was re-established within one minute. Investigation revealed that the EFW pump suction loss was caused by flashing in the main feedwater train forcing hot water through the Startup and Blowdown Demineralizers to the EFW pump suction where it flashed to steam. The steam caused cavitation of the EFW pumps, and the pressure in the EFW suction header prevented flow from the CST. The licensee has submitted Licensee Event Report No. 50-368/80-18/03L-0, dated May 5, 1980, describing this event. Action to prevent recurrence included revising the EFW system operating procedure and the Plant Startup Procedure to require shutting the EFW suction valve from the Startup and Blowdown Demineralizers during plant startup at about 5% full power after the steam generator feedwater source has been shifted to a main feedwater pump. In addition, the EFW suction valve from the Startup and Blowdown Demineralizers will be verified closed once per shift during Mode 1 operation. This Information Notice No. is provided as an early notification of a possibly significant matter that is still under review by the NRC staff. It is expected that recipients will review the information for possible applicability to their facilities. No specific action or response is requested at this time. If NRC evaluations so indicate, further licensee actions may be requested or required. No written response to this Information Notice No. is required. If you have any questions regarding this matter, please contact the Director of the appropriate NRC Regional Office.
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