United States Nuclear Regulatory Commission - Protecting People and the Environment

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
                            WASHINGTON, D.C.  20555

                              September 10, 1992

                               FAILURES OF HILLER ACTUATORS UPON A GRADUAL
                               LOSS OF AIR PRESSURE


All holders of operating licenses or construction permits for nuclear power


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 

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 


                                                            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

1.  Carolina Power and Light Company
      Shearon Harris Nuclear Power Plant Part 21
2.  List of Recently Issued NRC Information Notices
Page Last Reviewed/Updated Tuesday, November 12, 2013