United States Nuclear Regulatory Commission - Protecting People and the Environment

Information Notice No. 95-34: Air Actuator and Supply Air Regulator Problems in Copes-Vulcan Pressurizer Power-Operated Relief Valves

                                 UNITED STATES
                         NUCLEAR REGULATORY COMMISSION
                     OFFICE OF NUCLEAR REACTOR REGULATION
                            WASHINGTON, D.C. 20555

                                August 25, 1995


NRC INFORMATION NOTICE 95-34:  AIR ACTUATOR AND SUPPLY AIR REGULATOR PROBLEMS
                               IN COPES-VULCAN PRESSURIZER POWER-OPERATED
                               RELIEF VALVES

Addressees

All holders of operating license or construction permits for nuclear power
reactors.

Purpose

The U.S. Nuclear Regulatory Commission (NRC) is issuing this information
notice to alert addressees to problems caused by actuator degradation in
Copes-Vulcan pressurizer power-operated relief valves (PORVs).  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 do not constitute
NRC requirements; therefore, no specific action or written response is
required.

Description of Circumstances

During an inservice testing surveillance at the Haddam Neck nuclear power
plant on February 19, 1994, both pressurizer PORVs failed to open fully on
demand.  At the time of the event, the plant was in cold shutdown and the
valves were not required to be operable.  The cause was leaks in the air
actuator assemblies of both PORVs.  Reduced pressure output of the control air
regulators compounded the problem.

Discussion

The Haddam Neck PORVs are 2-inch nominal size, air-operated plug valves
manufactured by Copes-Vulcan (Model D-100-160).  The portion of the control
air system that supplies air to the PORVs serves a safety-related function.
It is isolated from the remainder of the control air system by two safety-
related check valves.  It also includes a 405 liter [107-gallon] emergency air
accumulator to support PORV operation in the event of a loss of the normal
control air supply.  Each of the air supply lines leading to the PORVs (see
Attachment 1) is equipped with a pressure regulator that reduces the air
pressure being supplied from 931 kPa [120 psig] to 690 kPa [85 psig].  An air
relief valve on each PORV actuator will protect it from overpressurization if
the supply line regulator fails open.  These relief valves are set to open at
793 kPa [100 psig], which is the maximum design pressure of the PORV
diaphragms.

9508210169
                                                            IN 95-34
                                                            August 25, 1995
                                                            Page 2 of 4

The licensee determined that the primary cause of the unacceptable valve
stroke performance was air leakage from the PORV air actuators caused by
improper installation of the diaphragms.  Both PORV diaphragms had been
replaced by a new style during a 1993 refueling outage.  The principal
difference in the replacement diaphragms was a change in the material
composition.  The replacement diaphragm was made of EPDM (Part #264331); the
old style diaphragm was made of BUNA-N (Part #080815).  The licensee switched
to the EPDM diaphragms because of a vendor recommendation that EPDM would
provide enhanced performance under the temperature and radiation conditions
experienced by the PORV.  In addition, the EPDM diaphragms have a 24-bolt-hole
configuration while the old style BUNA-N diaphragms only have a 12-bolt-hole
configuration.  The diaphragms also have slightly different shapes.

The licensee apparently had some difficulty installing the EPDM diaphragms
because of the bolt hole pattern and shape differences between the EPDM and
BUNA-N style diaphragms.  The licensee believes that the sealing surfaces of
the diaphragms were damaged as a consequence of the installation difficulties.
Extrusion of the diaphragm from between the base and cover and away from the
bolt holes led to small tears at several diaphragm bolt holes locations which
ultimately resulted in the air leakage.  The licensee has chosen to use the
BUNA-N diaphragms to avoid the installation difficulties encountered with the
EPDM diaphragms.  A Copes-Vulcan representative indicated that they have no
reports from other users on installation difficulties of either type of
diaphragm.

A search of the Nuclear Plant Reliability Data System (NPRDS) in regard to the
historical performance of the type of PORVs used at Haddam Neck revealed
numerous air-actuator related problems affecting this model of Copes-Vulcan
valves.  The problems can be grouped into three categories:

(1)   Actuator air leaks resulting from in-place diaphragm failures (e.g.,
      holes, rips, and tears)

      The plant-specific historical failure rates of these diaphragms should
      be readily ascertainable from an empirical analysis of the maintenance
      records.  Recent failures of installed diaphragms may have implications
      for the preventive maintenance or refurbishment program for these valves
      at a particular licensee.  Discussions with the Copes-Vulcan
      representative indicate that replacement frequency depends on service
      conditions such as temperature and valve usage.  Diaphragm lifespan can
      range from 1 year to more than 10 years.

      Regarding the specific diaphragm failure which occurred at Haddam Neck,
      no data was available to support any correlation between diaphragm
      failure and the type of diaphragm in use (EPDM versus BUNA-N).
.                                                            IN 95-34
                                                            August 25, 1995
                                                            Page 3 of 4


(2)   Actuator air leaks resulting from loose actuator cover bolts

      Air leakage because of the loosening of air actuator cover bolts may
      reflect the effect of environmental conditions on the valves.
      Temperature variations can result in the thermal loosening of bolts.
      Routine maintenance can also contribute to this problem if the cover
      bolts are not tightened to manufacturer specifications whenever the
      valve actuators are serviced.

(3)   Valve stroke malfunctions resulting from improper supply of air pressure
      from the air regulating valves

      The air pressure regulators used at Haddam Neck are ITT Conoflow (Model
      GFH25XT2365G) and have contributed to the PORV problems on three
      separate occasions over the last several years.  In 1993, one of the air
      pressure regulators failed high, subjecting one of the PORV diaphragms
      to the full air supply line pressure of 931 kPa [120 psig] which is
      greater than the diaphragm design pressure of 793 kPa [100 psig].
      Although the PORV actuators are equipped with relief valves to protect
      the diaphragms from overpressurization, it is believed that the high
      pressure contributed to or caused premature failure of the diaphragm.
      In the other two instances, the air supply regulators had drifted low,
      resulting in inadequate stroke performance of the valves.  The air
      pressure regulator setpoints for the Haddam Neck configuration are 690
      kPa [85 psig].  The PORVs need 552 kPa [65 psig] to start opening and
      690 kPa [85 psig] to open fully.  An engineering evaluation by the
      licensee showed that the valves will come to the full open position with
      control air pressure reduced to 586 kPa [70 psig] and reactor coolant
      system pressure as low as 5895 kPa [840 psig].

      Several causes of the air pressure regulator setpoint drift have been
      postulated: one is that moisture intrusion from the control air system
      can cause corrosion of the regulating mechanism, and the other is that
      the drift may be configuration related.  At Haddam Neck, the air
      regulating valve is upstream of the (normally closed) solenoid operated
      valve, meaning that the air regulating valve is constantly subjected to
      system pressure.  The air regulating valve vendor has indicated that
      this configuration may cause setpoint drift.

Related Generic Communications

The issue of pressurizer PORV reliability has been addressed in Generic Letter
90-06, "Resolution of Generic Issue 70, .Power-Operated Relief Valve and
Block
Valve Reliability,' and Generic Issue 94, .Additional Low-Temperature
Overpressure Protection for Light-Water Reactors,'" in which the staff
requested licensees to include the PORVs and PORV control air system in their
American Society of Mechanical Engineers Section XI inservice testing program..                                                            IN 95-34
                                                            August 25, 1995
                                                            Page 4 of 4


This information notice requires no specific action or written response.  If
you have any questions about the information in this notice, please contact
one of the technical contacts listed below or the appropriate Office of
Nuclear Reactor Regulation (NRR) project manager.

                                    /s/'d by DMCrutchfield

                                   Dennis M. Crutchfield, Director
                                   Division of Reactor Program Management
                                   Office of Nuclear Reactor Regulation

Technical contacts:  William C. Huffman, NRR          Eric J. Benner, NRR
                     (301) 415-2766                   (301) 415-1171

                     Charles G. Hammer, NRR
                     (301) 415-2791

Attachments:
1.  PORV Actuation System
2.  List of Recently Issued NRC Information Notices

Page Last Reviewed/Updated Monday, November 18, 2013