United States Nuclear Regulatory Commission - Protecting People and the Environment

Information Notice No. 88-24: Failures of Air-Operated Valves Affecting Safety-Related Systems

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

                                  May 13, 1988


Information Notice No. 88-24:  FAILURES OF AIR-OPERATED VALVES 
                                   AFFECTING SAFETY-RELATED SYSTEMS


Addressees:

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

Purpose:

This information notice is being provided to alert addressees to potential 
problems with air-operated valves in safety-related systems.  These problems 
result from overpressurization failures of solenoid valves caused by the in-
stallation of solenoid valves that may not operate against the supplied air 
pressure.  It is expected that recipients will review the information for ap-
plicability 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:

Kewaunee:  On February 8, 1988 the licensee, Wisconsin Public Service 
Corporation, notified the NRC in Licensee Event Report 50-305/87-12 of a 
potentially generic problem.  During a periodic inservice timing test required 
by technical specifications, the licensee observed that one of the redundant 
pressurizer relief tank makeup isolation valves and one of the redundant 
reactor coolant drain tank discharge header isolation valves failed to close 
on loss of electric power to their respective 3-way solenoid valves.  The 
isolation valves perform a containment isolation function and since their 
source of actuator power, the instrument air system, is not a safety-related 
system, they are designed to fail closed on loss of either air or electrical 
power.

For this application, when the solenoid valve is deenergized, its internal 
spring moves the valve core so that the inlet port from the instrument air 
system is blocked.  This action simultaneously opens a flow path connecting 
the solenoid valve outlet and exhaust ports, permitting the air pressure on 
the actuator diaphragm to decrease, and causing the isolation valve to close.






8805090186
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                                                                 May 13, 1988
                                                                 Page 2 of 4


Investigation revealed that the regulated inlet air pressure of 80 psi was 
forcing the solenoid valve core away from the inlet port seat; as a result the 
flow path to the actuator diaphragm was being maintained.  This happened 
because the supply pressure exceeded the rating for the internal spring (70 
psi).  This rating is called the design maximum operating pressure 
differential (MOPD).  

After the internal spring and core assembly were replaced in the failed sole-
noid valves and the supply air pressure was reduced to 60 psi, the solenoid 
valves and hence the containment isolation valves worked satisfactorily.  The 
licensee inspected ratings for other solenoid valves and did find instances 
where the solenoid valve had an MOPD less than the supplied air pressure.

In September 1987, the licensee had decided to replace a number of solenoid 
valves to upgrade their level of environmental qualification.  For both the 
failed solenoid valves discussed above, the licensee found that whereas the 
original valves had MOPD ratings greater than the supplied air pressure, the 
replacement valves had MOPD ratings less than the supplied air pressure.

The licensee's investigation disclosed the following data: 

     Original solenoid valves      ASCO Model No. LB83146
                                   Catalog 26 (late 1960s vintage) 
                                   General-purpose enclosure
                                   MOPD:  100 psi

     Replacement solenoid valves   ASCO Model No. NP8314C13E
                                   Catalog 30A (1980s vintage)
                                   Watertight and explosion-proof enclosure
                                   MOPD:  70 psi

According to the catalog, the letter "C" in the model number "indicates a 
major design change affecting spare parts kits, rebuild kits and coils."  
Apparently, one of the changes made by ASCO (the vendor) to the original Model 
No. 831413 valve, currently listed as a Model No. 8314C13 valve, involved the 
internal spring and core assembly and resulted in a reduced MOPD.  

On seeing the difference in MOPD between the original and replacement solenoid 
valves, the design engineer assigned the task of upgrading the environmental 
qualification of these valves contacted the vendor for advice on which model 
was a direct nuclear grade replacement for the LB83146 model.  The vendor 
recommended that model number NP8314C13E be used.  The design engineer ques-
tioned the vendor on the significance of the MOPD difference.  The vendor 
responded in writing essentially that if the supply pressure exceeded the MOPD 
rating, the solenoid valve would not operate correctly (in the way described 
above).

.                                                                 IN 88-24
                                                                 May 13, 1988
                                                                 Page 3 of 4


The design engineer and engineering supervisor discussed this letter and con-
cluded that if the solenoid valve were exposed to 100 psi instrument air 
pressure when deenergized, there would be some air leakage from the inlet to 
the outlet ports, but some venting to atmosphere through the exhaust port 
would also occur.  This would pressurize the control valve diaphragm, but 
equilibrium would occur at a pressure below that required for control valve 
actuation.  Their conclusion was heavily influenced by their belief that the 
original solenoid valves were actually rated for 70 psi and had been operating 
successfully for approximately 13 years.  

Based on this interpretation, the design review package made available to the 
second level reviewer did not include a reference to this correspondence with 
the vendor.  Thus, an independent assessment of the interpretation was not 
performed. 

To see if other safety-related control valves and damper actuators could be 
vulnerable to the same failure, the licensee inspected all the containment 
isolation solenoid valves and those solenoid valves included in the list of 
systems and components that prevent or mitigate the consequences of postulated 
accidents.  The licensee recorded the solenoid valve and air regulator name-
plate data and the air regulator settings.  For those valves with insufficient 
MOPD, the licensee determined the reason for the purchase and installation of 
incorrect solenoid valves.  They also reviewed the functional operability of 
the instrument air regulators to provide assurance they will not fail high and 
thus overpressurize the solenoid valves.

Calvert Cliffs Unit 2:  On April 14, 1988, the licensee, Baltimore Gas and 
Electric Company, notified the NRC in a 10 CFR 50.72 report that several 
safety systems were vulnerable to a single failure of the air supply pressure 
regulating system:  the auxiliary feedwater system, the safety injection fill 
and vent system, the containment isolation system, and the steam generator 
blowdown isolation system.  Investigation had shown that those air regulators 
located in a harsh environment after a postulated accident can fail in a way 
that applies high pressure to solenoid valves.   If such solenoid valves are 
not rated for sufficient MOPD, then the solenoid valves will affect the 
correct post accident alignment of the system valves they control.  To correct 
this problem, the licensee will expand emergency procedures to include local 
operation of affected valves and will replace the affected solenoid valves 
with valves rated for higher MOPD.

Discussion:

In many plants, the air supply systems for safety-related components are not 
designed as safety-related systems.  Hence, safety-related components that 
depend on the air system are designed to assume a fail safe condition on loss 
of air; however, the converse condition of air overpressurization may not 
always be considered.  Such a condition could render the affected 
safety-related components inoperable.  

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                                                                 May 13, 1988
                                                                 Page 4 of 4


Quality assurance requirements include procurement of materials, equipment, 
and services (10 CFR 50.34 and Appendix B).  The similarity of part numbers 
for components with different operating characteristics illustrates how a 
qualified component or system can be degraded if controls over the design and 
procurement of replacement parts are not adequate. 

Other events in which air system failures have affected safety-related systems
are discussed in Information Notice 87-28, "Air System Problems at U.S. Light 
Water Reactors," and Information Notice 87-28, Supplement 1, of the same 
title. The supplement notice transmitted copies of NUREG-1275, Vol. 2, 
"Operating Experience Feedback Report - Air Systems Problems." 

No specific action or written response is required by this information notice.
If you have any questions about this matter, please contact one of the techni-
cal contacts listed below or the Regional Administrator of the appropriate 
regional office.




                              Charles E. Rossi, Director
                              Division of Operational Events Assessment
                              Office of Nuclear Reactor Regulation

Technical Contacts:  Vern Hodge, NRR
                     (301) 492-1169

                     I. Villalva, Region III
                     (312) 790-5763

                     R. Nelson, Region III
                     (414) 388-3156

Attachment:  List of Recently Issued NRC Information Notices 
.                                                            Attachment
                                                            IN 88-24 
                                                            May 13, 1988 
                                                            Page 1 of 1

                             LIST OF RECENTLY ISSUED
                            NRC INFORMATION NOTICES 
_____________________________________________________________________________
Information                                  Date of 
Notice No._____Subject_______________________Issuance_______Issued to________

88-23          Potential for Gas Binding     5/12/88        All holders of OLs
               of High-Pressure Safety                      or CPs for PWRs. 
               Injection Pumps During a 
               Loss-of-Coolant Accident 

88-22          Disposal of Sludge from       5/12/88        All holders of OLs
               Onsite Sewage Treatment                      or CPs for nuclear
               Facilities at Nuclear                        power reactors. 
               Power Stations 

88-21          Inadvertent Criticality       5/9/88         All holders of OLs
               Events at Oskarshamn                         or CPs for nuclear
               and at U.S. Nuclear                          power reactors. 
               Power Plants 

88-20          Unauthorized Individuals      5/5/88         All holders of OLs
               Manipulating Controls and                    or CPs for nuclear
               Performing Control Room                      power, test and 
               Activities                                   research reactors,
                                                            and all licensed 
                                                            operators. 

88-19          Questionable Certification    4/26/88        All holders of OLs
               of Class 1E Components                       or CPs for nuclear
                                                            power reactors. 

88-18          Malfunction of Lockbox on     4/25/88        All NRC licensees 
               Radiography Device                           authorized to 
                                                            manufacture, 
                                                            distribute, and/or 
                                                            operate radio-
                                                            graphic exposure 
                                                            devices. 

88-17          Summary of Responses to NRC   4/22/88        All holders of OLs
               Bulletin 87-01, "Thinning of                 or CPs for nuclear
               Pipe Walls in Nuclear Power                  power reactors. 
               Plants" 
_____________________________________________________________________________
OL = Operating License
CP = Construction Permit 
Page Last Reviewed/Updated Tuesday, November 12, 2013