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Information Notice No. 81-10: Inadvertent Containment Spray Due to Personnel Error
SSINS No.: 6835 Accession No.: 8011040273 IN 81-10 UNITED STATES NUCLEAR REGULATORY COMMISSION OFFICE OF INSPECTION AND ENFORCEMENT WASHINGTON, D.C. 20555 March 25, 1981 Information Notice No. 81-10: INADVERTENT CONTAINMENT SPRAY DUE TO PERSONNEL ERROR Description of Circumstances: On February 11, 1981 while in mode 5 (cold shutdown), an auxiliary unit operator at Sequoyah Unit 1 misunderstood a verbal instruction and opened a single valve in the residual heat removal (RHR) system. The opened valve created direct flow path through the RHR system from the primary coolant system to the RHR containment spray header. A rapid primary system depressurization to the atmospheric pressure resulted, and a total of about 110,000 gallons of water was sprayed into the containment from the primary system and from the refueling water storage tank (RWST). Licensees and applicants should be aware of the following aspects of this event and should take appropriate steps to prevent a recurrence a their plant. The auxiliary unit operator did not have adequate training or orientation at the particular duty station involved. A single valve at that station is part of the primary coolant system pressure boundary when using the residual heat removal (RHR) system for shutdown cooling. Thus, personnel/administrative problems and a plant design feature combined to cause the event. Design of the control room annunciators contributed to prolonging the event. The panel indicating emergency core cooling system (ECCS) valve positions is designed to warn when the ECCS is not properly aligned for the injection (safety) mode. When the first valve misalignment occurs, one light comes on in an otherwise dark field of indicators, and an alarm sounds and flashes. However, in the shutdown cooling mode, several valves are not in their injection mode position. Therefore, in the event at Sequoyah, the alarm light had already been on continuously for some time, the annunciator was not supposed to operate, and one more light coming "on" in a valve-position- indicating field with several lights already "on" was easily missed. The operators thus failed to detect the presence of the inadvertently opened valve for at least 35 minutes. Lack of an ECCS initiation procedure for use in the shutdown cooling mode did not significantly delay recovery from this event, but potentially could have done so had the primary system been at a higher pressure. To provide injection flow for pressurizer level recovery, the operators opened the RHR system suction valve from the RWST, but they neglected to close the RHR system suction valves from the reactor coolant system (RCS). A proper procedure would require those latter valves to be closed to prevent reactor pressure . IN 81-10 March 25, 1981 Page 2 of 2 from seating a check valve in the RWST suction line, which would prevent the injection mode for the low-pressure (RHR) pumps from being effective and delay recovery from the event. A similar problem with the borated water storage tank (BWST) check valve occurred at Crystal River 3 on July 16, 1980 while the unit was in Mode 5 with the decay heat system in use for shutdown cooling. Improper valve alignment on the decay heat system heat exchangers caused a rapid cooldown of the RCS which resulted in a loss of pressurizer level. When recovery was attempted by realigning the decay heat system suction to the BWST, injection flow could not be established until RCS pressure approached atmospheric conditions since the RCS suction valves remained open. This problem would be particularly significant under a LOCA condition with the RCS temperature above boiling (Mode 4). The information herein is being provided as an early notification of a possibly significant matter that is still under review by the NRC staff. Recipients should review the information for possible applicability to their facilities. If NRC evaluation so indicates, further licensee actions may be requested. No written response to this information notice is required. If you need additional information regarding is matter, contact the Director of the appropriate NRC Regional Office. Attachment: Recently issued IE Information Notices.
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