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
. IN 88-24
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.
. IN 88-24
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, March 09, 2021