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IN79029 November 16, 1979 MEMORANDUM FOR: B. H. Grier, Director, Region I J. P. O'Reilly, Director, Region II J. G. Keppler, Director, Region III K. V. Seyfrit, Director, Region IV R. H. Engelken, Director, Region V FROM: Norman C. Moseley, Director, Division of Reactor Operations Inspection, IE SUBJECT: Information Notice No. 79-29, LOSS OF NONSAFETY-RELATED REACTOR COOLANT SYSTEM INSTRUMENTATION DURING OPERATION The subject document is transmitted for issuance on November 16, 1979. The Information Notice should be issued to all power reactor facilities holding operating licenses and construction permits. Also enclosed is a draft copy of the transmittal letter. Norman C. Moseley, Director Division of Reactor Operations Inspection Office of Inspection and Enforcement Enclosure: 1. Draft Transmittal Letter 2. Information Notice No. No. 79-29 CONTACT: H. W. Woods, IE 49-28180 . (Transmittal letter for Information Notice No. 79-29 to each holder of an NRC Operating License and Construction Permit.) Information Notice No. 79-29 Addressee: This Information Notice is provided as an early notification of a possibly significant matter. It is expected that recipients will distribute this Notice to their operating personnel and will review the information for possible applicability to their facilities. No specific action or response is requested at this time. However, we anticipate that further NRC evaluations will result in issuance of an IE Circular, Bulletin, or NRR Generic Letter in the near future which will recommend or request specific applicant or licensee actions. If you have questions regarding the matter, please contact the Director of the appropriate NRC Regional Office. Sincerely, Signature (Regional Director) Enclosures: 1. Information Notice No. No. 79-29 2. List of IE Information Notices Recently Issued . SSINS No.: 6300 Accession No.: 7910250490 UNITED STATES NUCLEAR REGULATORY COMMISSION OFFICE OF INSPECTION AND ENFORCEMENT WASHINGTON, D.C. 20555 November 16, 1979 Information Notice No. 79-29 LOSS OF NONSAFETY-RELATED REACTOR COOLANT SYSTEM INSTRUMENTATION DURING OPERATION This notice contains information regarding a loss of reactor coolant system instrumentation as a consequence of a failure of a static transfer switch to transfer to an alternate supply. At 3:15 p.m. on November 10 with Unit 3 of the Oconee Station at 100 percent power, the main condensate pumps tripped, apparently as a result of a technician performing maintenance on the hotwell level control system. This led to reduced feedwater flow to the steam generators, which resulted in a high reactor coolant system (RCS) pressure reactor trip and simultaneous turbine trip at 3:16:57 p.m. At 3:17:15 p.m., the inverter power supply, nonsafety-related, feeding all power to the integrated control system (ICS) tripped and failed to automatically transfer its loads from the DC power source to the regulated AC power source. The inverter had tripped due to blown fuses, resulting in loss of RCS indicators and recorders in the control room, except one wide range RCS pressure recorder. This condition existed for approximately three minutes, until an operator could reach the equipment room and switch the inverter manually to the regulated AC source. As a result of the power failure to the ICS, all valves controlled by the system assumed their respective fail positions. This resulted in a cool down of the RCS to 1635 psi and 530 degrees F. The operator, expecting this condition, started all makeup pumps and opened the associated high pressure injection valves to the RCS which limited the rate of RCS pressure reduction and associated reduction in pressurizer level. At 3:20:42 p.m., power was restored to the ICS and RCS conditions were restored. Although RCS cooldown limits were exceeded, the pressurizer and steam generators did not go dry, and at least 79 degrees F subcooling was maintained during this event. No engineered safety features actuation setpoints were reached, and, except for the components discussed above, no component malfunctions occurred. The licensee has installed a redundant electromechanical transfer switch between the loads and the regulated supply. This switch will actuate and power the loads from the regulated supply should the original static switch fail to transfer. Longer term resolution of the need or desirability to separate these instruments onto diverse electrical supplies or to provide redundant instrumentation display channels for operator use from essential power supplies are also under . Information Notice No. 79-29 November 16, 1979 Page 2 of 2 consideration. It is anticipated that further NRC evaluations will result in issuance of an IE Circular, Bulletin, or NRR Generic letter in the near future which will recommend or request specific applicant or licensee actions. This Information Notice is provided to inform licensees of a possibly significant matter. It is expected that recipients will disseminate the information to all operational personnel working at their licensed facilities. If you have questions regarding this matter, please contact the Director of the appropriate NRC Regional Office. No written response to this Information Notice is required.
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