Protecting People and the EnvironmentUNITED STATES NUCLEAR REGULATORY COMMISSION
UNITED STATES
NUCLEAR REGULATORY COMMISSION
OFFICE OF NUCLEAR REACTOR REGULATION
WASHINGTON, D.C. 20555
February 28, 1990
Information Notice No. 90-11: MAINTENANCE DEFICIENCY ASSOCIATED
WITH SOLENOID-OPERATED VALVES
Addressees:
All holders of operating licenses or construction permits for nuclear power
reactors.
Purpose:
This information notice is intended to alert addressees to a potential
problem resulting from improper maintenance that may affect the operability
of main steamline isolation valves (MSIVs), main steamline relief valves
(MSRVs) or similarly designed components. The problem relates to
solenoid-operated valves (SOVs) that may not have been properly maintained
or tested after maintenance. 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 inspection at Automatic Valve Corporation (AVC) in Novi, Michigan,
the NRC staff learned that a nuclear power plant licensee may have performed
improper maintenance on SOVs, possibly by using an obsolete set of
instructions. AVC manufactures pneumatic control assemblies (PCAs) that are
assembled on actuators (manufactured by others) which in turn operate
safety-related valves. An evaluation of this situation led to the discovery
of a failure mechanism for SOVs that had not been considered previously.
The NRC staff determined that updated maintenance instructions consistent
with current replacement parts design were not provided to all users of
these SOVs. As a result, AVC sent a letter dated February 1, 1990, to
utilities known to use SOVs supplied directly by AVC, Atwood & Morrill and
Target Rock (valve manufacturers that use solenoids supplied by AVC), and
General Electric (a nuclear steam system supplier that supplied original
equipment or subsequent parts for MSIVs and MSRVs). This letter alerted
organizations that received SOVs from AVC of the design change and potential
problem which could be caused by not using the proper tool; the letter also
provided a copy of the current maintenance instructions. AVC obtains SOVs
from a subtier supplier and may either incorporate them in an AVC PCA, or
provide only the SOVs.
9002230283
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IN 90-11
February 28, 1990
Page 2 of 3
Discussion:
The PCA directs air to the actuator to operate MSIVs and MSRVs. Multiple
SOVs in the PCA are arranged in a design such that with a single failure
involving one of the SOVs, the MSIVs and MSRVs are to go to or remain in the
preferred position following the single failure. However, a single failure
was discovered that could prevent an MSIV from achieving the preferred
position; an MSRV would remain closed, but would not be able to be opened.
Even though the following discussion is limited to MSIVs, it applies in an
analogous manner to the MSRVs. Therefore, the problem should not be
considered to be limited to MSIVs.
In one design arrangement for an MSIV, the PCA has two SOVs controlling air
to and from a four-way air valve which in turn directs motive air under a
piston operator to open the MSIV or on top of the piston to drive the MSIV
closed. Should one of the two SOVs mechanically bind in the energized
position, the four-way air valve cannot be moved; therefore, the MSIV would
fail to close when required, even though the other SOV was in the proper
(de-energized) position.
Mechanical binding was found to be a reasonable and potential possibility
because interchangeable parts with a different design were provided to
licensees without concurrent notification that a revised installation and
maintenance procedure should be followed. In the original design, "flats"
were used as a means of exerting a force to screw two metal pieces together.
The new design required a spanner wrench. Use of pliers or vise-grips (as
designated in the earlier procedure) on a thin walled guide tube could
deform the tube and prevent a plunger actuated by the solenoid from moving
freely inside the tube. It was reported that pliers or vise-grips may have
been used at one utility during either disassembly or assembly of an SOV.
Sticking of the plunger within the guide tube (another binding mechanism)
can also occur without deformation of the tube if an improper lubricant is
used. Lubricants, as well as other materials, have been known to become
sticky, cause other problems and prevent proper operation of an SOV after
extended time in a high-temperature or excessive radiation environment. For
example, Super O Lube, which is usually used by AVC in their valves, as well
as by Ralph A. Hiller in their pneumatic/hydraulic operators, will begin to
solidify after exposure to a radiation dose of about 1.9 MegaRads. Another
lubricant, Houghton 620, used in qualification testing, has been
subsequently identified by the manufacturer as "Non-compatible" with
unanodized aluminum, the material used in AVC PCAs. There has been no
unanimity as to which lubricant to use or its service life. Lubricant and
some of its effects are discussed in Information Notice 88-43, "Solenoid
Valve Problems," dated June 23, 1988.
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IN 90-11
February 28, 1990
Page 3 of 3
Gross damage or failures caused by the use of improper maintenance
procedures should be detected during post maintenance testing. However,
less than gross damage might only cause the SOV to operate in a sporadic and
unpredictable manner. This is particularly true because not all PCAs are
installed with the same orientation (e.g., vertical versus horizontal) or in
the same environment (e.g., temperature, radiation field, and humidity). A
review by the NRC staff of plant equipment failure and maintenance records
shows that not all licensees adequately evaluate or compare actual service
conditions with those intended or used to qualify these components.
A review may be required of the purchase documentation for MSIVs and MSRVs,
along with any replacement parts, to establish whether licensees have the
potential for the above-described failure mechanism. Because of the nature
of the control assembly used on MSIVs and MSRVs, several different vendors
and suppliers are involved in the manufacture, assembly, and procurement of
the PCA. Therefore, licensees may not readily recognize the vendor
mentioned in this information notice as a supplier of a portion of one of
their safety-related components.
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 NRR project
manager.
Charles E. Rossi, Director
Division of Operational Events Assessment
Office of Nuclear Reactor Regulation
Technical Contacts: J. Carter, NRR
(301) 492-1194
H. Ornstein, AEOD
(301) 492-4439
K. Naidu, NRR
(301) 492-0980
Attachment: List of Recently Issued NRC Information Notices
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