Information Notice No. 82-25: Failures of Hiller Actuators upon Gradual Loss of Air Pressure

                                                            SSINS No.: 6835 
                                                            IN 82-25 

                               UNITED STATES 
                          WASHINGTON, D. C. 20555 

                               July 20, 1982 

                                   LOSS OF AIR PRESSURE 


All holders of a nuclear power reactor operating license (OL) or 
construction permit (CP). 


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, 
     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. 


                                                           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 

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 

List of Recently IssUed IE Information Notices 


Page Last Reviewed/Updated Thursday, March 25, 2021