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Information Notice No. 92-67: Deficiency in Design Modifications to Address Failures of Hiller Actuators Upon a Gradual Loss of Air Pressure
UNITED STATES NUCLEAR REGULATORY COMMISSION OFFICE OF NUCLEAR REACTOR REGULATION WASHINGTON, D.C. 20555 September 10, 1992 NRC INFORMATION NOTICE 92-67: DEFICIENCY IN DESIGN MODIFICATIONS TO ADDRESS FAILURES OF HILLER ACTUATORS UPON A GRADUAL LOSS OF AIR PRESSURE Addressees All holders of operating licenses or construction permits for nuclear power reactors. Purpose The U.S. Nuclear Regulatory Commission (NRC) is issuing this information notice to alert addressees to a potentially significant problem pertaining to modifications made to address failures of Hiller valve actuators upon a gradual loss of air pressure, as discussed in NRC Information Notice (IN) 82- 25, "Failures of Hiller Actuators upon Gradual Loss of Air Pressure." It is expected that recipients will review the information for applicability to their facilities and consider actions, as appropriate, to avoid similar problems. However, suggestions contained in this information notice are not NRC requirements; therefore, no specific action or written response is required. Description of Circumstances Valve assemblies for three Shearon Harris main feedwater preheater bypass isolation valves were specified, procured, and installed for Q Class application. The Anchor Darling Valve Company supplied the valves and the associated Hiller actuators. On January 7, 1992, Carolina Power and Light Company discovered several components associated with the air supply to the actuators of the three main feedwater preheater bypass isolation valves were not qualified for a Q Class application. Specifically, the failure of the air pump in the non-Q Class, non-seismic instrument air supply to the valve actuator accumulator could prevent pressure switches upstream of the air pump from detecting slow leakage in the Q Class, seismic portion of the actuator air lines. The pressure switches were installed to ensure valve closure by sending an automatic close signal if the instrument air system pressure (upstream of the actuator air pump) dropped to 66 psig as discussed in IN 82-25. The main feedwater preheater bypass isolation valves function as containment isolation valves upon receipt of a feedwater isolation signal. The function of the air pump is to raise the normal instrument air supply pressure from 70 to 100 psig to approximately 150 psig. If accumulator pressure drops from 9209030017. IN 92-67 September 10, 1992 Page 2 of 2 150 psig to 122 psig, the main feedwater preheater bypass isolation valve may not close within 10 seconds. If pressure drops to a value as low as 20 psig, it may not be sufficient to close the main feedwater preheater bypass isolation valve and keep it closed against the maximum differential pressure across the valve seat. Upon discovery of this condition, Shearon Harris established a surveillance interval for verifying that the actuators' components were functioning properly and that the accumulators were fully pressurized. On January 12, 1992, non-Q components were replaced with suitable components and testing was completed satisfactorily. On January 15, 1992, the Shearon Harris Safety Committee determined that the deficiency in the Hiller actuator for the main feedwater preheater bypass isolation valves was reportable under 10 CFR Part 21 (Attachment 1), because of the possibility that these valves might not be able to meet their safety- related function to close within 10 seconds of a feedwater isolation signal for containment isolation. Other air-operated valves may be susceptible to similar failure mechanisms. This information notice requires no specific action or written response. If you have any questions about the information in this notice, please contact the technical contact listed below or the appropriate Office of Nuclear Reactor Regulation (NRR) project manager. ORIGINAL SIGNED BY Charles E. Rossi, Director Division of Operational Events Assessment Office of Nuclear Reactor Regulation Technical contact: Patricia Campbell, NRR (301) 504-1311 Attachments: 1. Carolina Power and Light Company Shearon Harris Nuclear Power Plant Part 21 2. List of Recently Issued NRC Information Notices .
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