Information Notice No. 82-25: Failures of Hiller Actuators upon Gradual Loss of Air Pressure
SSINS No.: 6835
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
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.
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
Office of Inspection and Enforcement
Technical Contact: M. S. Wegner
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