United States Nuclear Regulatory Commission - Protecting People and the Environment

Maintenance Deficiency Associated with Solenoid-Operated Valves

                                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
.

                                                       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 
.ENDEND
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