Information Notice No. 82-25: Failures of Hiller Actuators upon Gradual Loss of Air Pressure
SSINS No.: 6835 IN 82-25 UNITED STATES NUCLEAR REGULATORY COMMISSION OFFICE OF INSPECTION AND ENFORCEMENT WASHINGTON, D. C. 20555 July 20, 1982 Information Notice No. 82-25: FAILURES OF HILLER ACTUATORS UPON GRADUAL LOSS OF AIR PRESSURE Addressees: All holders of a nuclear power reactor operating license (OL) or construction permit (CP). Purpose: This information notice is provided as an early notification of a potentially significant problem pertaining to Hiller actuators which could prevent failsafe closure of air-operated isolation valves. It is expected that addressees will review the information for applicability to their facilities. No specific action or response is required at this time. Description of Circumstances: Mississippi Power and Light Company has reported that a large number of isolation valves in the instrument air system at Grand Gulf Nuclear Station (GGNS) failed to pass test requirements. The valves were supplied by the, William Powell Company and equipped with actuators supplied by the Ralph A. Hiller Company. Various plant systems were affected, primarily those associated with containment isolation. During preoperational testing designed to simulate a slow loss of air in accordance with position C.9 of Regulatory Guide 1.80, a large number of pneumatically operated valves failed to go to their fail-safe condition when the instrument air header was slowly depressurized. Additional testing to simulate an air-line break in accordance wi th position C.8 was accomplished by depressurizing the instrument header supplying the containment, drywell, and auxiliary building from operating pressure (110 psig) to atmospheric pressure in one minute. Forty-eight valves failed this test. Hiller model numbers for the actuators used on these valves are as follows: 10 SA - A012, A014, A015, A016, A017, A018, A021, A022, A023, A024, A044 12 SA - A013, A014, A015, A019 14 SA - A004, A008, A010 16 SA - A007, A008, A012, A014 20 SA - A009, A010, A011 The specifications for the Grand Gulf actuators required the valve to fail to a specified position upon a loss of instrument air but did not specify the rate of depressurization. The Hiller actuators will operate in the specified manner only if the actuator itself is promptly depressurized. 8204210396 . IN 82-25 July 20, 1982 Page 2 of 2 The pneumatic actuators consist of an accumulator with stored air which is transferred to the actuator cylinder to stroke the valve by means of pneumatic-operated selector valves controlled by instrument air. Upon a gradual loss of instrument air pressure, the selector valves will bleed the accumulator air to the atmosphere rather than to the actuator cylinder. This occurs near 20 psi when the selector valve plunger is in an intermediate position. Mississippi Power and Light Company will add safety-related pressure switches to sense air supply pressure to the valves. When the supply air pressure drops to a point slightly above that at which the actuator selector valve would begin to move and bleed off the accumulator, the pressure switch will de-energize the solenoid pilot and immediately cause the valve to go to the fail-safe position. The instrument air system is not seismic Category 1; therefore, a line break causing a rapid loss of instrument air is a realistic concern. Had the condition simulated (instrument air-line break) occurred coincident with a postulated loss-of-coolant accident, then the failure of the pneumatic valves to go to their fail-safe position could have resulted in a loss of containment integrity. Site accident doses could have exceeded the limits specified in 10 CFR 100. If you have any questions regarding this matter, please contact the Regional Administrator of the appropriate regional office or this office. Edward L. Jordan, Director Division of Engineering and Quality Assurance Office of Inspection and Enforcement Technical Contact: M. S. Wegner 301-492-4205 Attachment: List of Recently IssUed IE Information Notices
Page Last Reviewed/Updated Tuesday, March 09, 2021
Page Last Reviewed/Updated Tuesday, March 09, 2021