United States Nuclear Regulatory Commission - Protecting People and the Environment

Information Notice No. 88-43: Solenoid Valve Problems

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

                                  June 23, 1988


Information Notice No. 88-43:  SOLENOID VALVE PROBLEMS

Addressees:

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

Purpose:

This information notice is being provided to alert addressees to a series of 
solenoid valve failures that have occurred at several nuclear power plants.  
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:

On October 29, 1987, at Perry Unit 1, during performance of stroke time 
testing, three of eight MSIVs failed to fast close as designed.  The stroke 
time testing was being performed in accordance with a startup test procedure.  
Two of the three affected valves were inboard and outboard MSIVs in the same 
main steam line, which would be a significant safety problem in the event of a 
failure of that main steam line.  Subsequently, on November 3, 1987, at Perry 
Unit 1, during performance of stroke time testing, two out of eight MSIVs 
again failed to fast close as designed.  The stroke time testing was being 
performed as the result of the previous failures in preparation for performing 
the full reactor isolation startup test.  The affected valves were the inboard 
and outboard MSIVs in the same main steam line and were the same valves that 
had failed on October 29. Details may be found in Augmented Inspection Team 
(AIT) Report No. 50-440/87024. 

The licensee's investigation isolated the cause for the MSIV failures to the 
Automatic Switch Company (ASCO) Model NP-8323A20E dual solenoid operated 
valves (SOVs) that serve them.  The failure mechanism could not be positively 
identified, but the most likely cause was determined to be degradation of the 
Ethylene Propylene Diene Monomer (EPDM) elastomer seats due to exposure to a 
high temperature environment.  The high temperature environment was the result 
of several 








8806200306 
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steam leaks in the vicinity of the failed SOVs.  Although the degradation of 
the EPDM seat also was considered to have been possibly caused by hydrocarbon 
contamination, this possibility was later discounted (see "Discussion").  In-
spection of the SOVs indicated that an annular impression had been cut in the 
exhaust port seat material resulting in part of the seat material being 
extruded into the exhaust orifice.  This, together with the deteriorated state 
of the seat material, indicated that the exhaust seat could be held in an 
"energized" position, even though the solenoids had de-energized.  This would 
prevent the control air from being exhausted to atmosphere and thus prevent 
the MSIV from closing.  The licensee subsequently replaced three of the SOVs 
and rebuilt the remaining five SOVs.  

The third event also occurred at Perry.  On November 29, 1987, the licensee 
was performing a MSIV special operability check when it was found that one 
inboard MSIV did not function properly.  The licensee was performing the 
special operability checks as the result of commitments made in response to 
the previously discussed problems with MSIV closure.  The operability check 
consisted of depressing the slow closure "test" pushbutton and allowing the 
MSIV to fully close.  The control switch was then placed in the "close" 
position and the "test" push-button released.  During this operability check, 
one MSIV did not remain shut when the test pushbutton was released.  If the 
fast closure SOV shifts state per design, the MSIV will remain closed; if it 
fails to shift state, the MSIV will reopen.  Subsequent attempts to close the 
MSIV by placing the control switch in the "close" position also failed.  
Following plant shutdown, licensee personnel and the Senior Resident Inspector 
made a drywell entry to observe the MSIV during a closure attempt.  During 
this test, the valve stayed in the open position until the SOV was gently 
tapped.  The MSIV responded by closing with a normal stroke time.  Details may 
be found in Augmented Inspection Team (AIT) Report No. 50-440/87027.


The licensee's investigation isolated the cause for the MSIV failure to the 
ASCO Model NP-8323A20E SOV.  Inspection of the SOV revealed the presence of a 
sliver of foreign material and two smaller particles of foreign material in 
the "B" solenoid housing assembly.  The material was later identified as EPDM 
from one of the O-rings in the SOV that was replaced as part of the corrective 
action to the event of November 3, 1987.  No other signs of SOV degradation 
were evident.  The licensee concluded that the root cause of the failure of 
the MSIV to close was mechanical binding of the ASCO SOV by the sliver of EPDM 
material.  The mechanical binding resulted in the exhaust seat being held in 
an "energized" position even though the solenoids had been de-energized.  This 
prevented the control air from being exhausted to atmosphere and prevented the 
MSIV from closing.  Subsequently, the licensee replaced all eight MSIV SOVs. 

A fourth event involving an MSIV failure occurred at LaSalle Unit 1 on 
December 17, 1987.  The plant was in hot shutdown following a reactor scram 
resulting from a feedwater transient.  The licensee was in the process of 
closing the MSIVs to allow repair work on balance-of-plant equipment.  The 


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method being used to close the MSIVs was the same as discussed above for 
Perry's fast closure operability check.  During the course of closing the 
MSIVs, one of the outboard MSIVs reopened.  Examination of the SOV internals 
revealed that the interfacing surfaces of the core assembly and the plugnut 
assembly of the "B" solenoid had a thin layer of a yellowish/amber, sticky 
substance coating them.  When the interfacing surfaces of these components 
were pressed together (as they would be when energized) and then released, the 
core assembly would hang from the plugnut assembly with no support.  The 
licensee concluded that the film between the core assembly and the plugnut 
assembly acted like an adhesive and prevented the core assembly from shifting 
to the de-energized position.  This failure mode is very similar to MSIV 
failures that occurred at Grand Gulf in 1985 (reported in Information Notices 
85-17 and 85-17, Supplement 1, "Possible Sticking of ASCO Solenoid Valves") in 
which a similar appearing substance was found in the same locations. 

In response to the failure, the licensee and ASCO inspected the other SOVs.  A
thin layer of a similar appearing substance to that found in the failed SOV 
was found on the interfacing surfaces of the "B" solenoid core assembly and 
plugnut assembly in all cases.  The licensee collected samples of the 
substance and had it analyzed.  This analysis determined that the substance 
was primarily silicon in nature.  Further investigation by the licensee 
revealed that ASCO routinely lubricates the core assembly/plugnut assembly 
interfaces with Dow Corning 550 silicon based lubricant to reduce noise and 
wear associated with 60 Hz hum (the SOVs environmental qualification did not 
explicitly consider the use or non-use of the lubricant).  Their analysis 
stated that the thin film substance closely resembled the Dow 550 lubricant.  
Additional investigation by the licensee found that the Dow Corning product 
literature indicated that Dow 550 begins to gel after 14 months at 200�C.  The 
time for Dow 550 to gel appears to lessen exponentially as the temperature 
increases.  A Dow Corning Technical Service representative also indicated 
that, while Dow 550 is clear when new, it turns an amber color and becomes 
tacky when baked long enough. 

The adverse effect of a solenoid valve failure is not limited to MSIV failure, 
even though this IN focuses on MSIVs.  For example, on January 2, 1988, two 
redundant containment isolation valves on the drywell drain systems line at 
Brunswick Unit 2 failed to close; these isolation valves utilize solenoid 
valve design ASCO Model 206-832.  Even though the licensee was not able to 
determine the root cause of failure with certainty, there appears to have been 
a mechanical sticking problem.  The solenoid valve was in a closed position 
for an extended period of time, and would not vent when first called upon to 
open.  Details may be found in Augmented Inspection Team (AIT) Report Nos. 
50-325/8803, 50-324/8803. 

Discussion:

As a result of the failure at Perry on November 3, 1987, the licensee began a 
detailed physical and chemical testing program in an attempt to pinpoint the 


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failure mechanism.  In conjunction with this, the licensee instituted an envi-
ronmental testing program.  The environmental testing program consisted of 
baking ASCO Model NP-8323A20 SOVs (both with Viton and EPDM elastomers) in 
three ovens with each oven at a different temperature.  SOVs within each oven 
were cycled at varied frequencies.  The purpose of this environmental testing 
was to further confirm the root cause of the failures experienced, to 
establish a threshold temperature of EPDM degradation and to perform a 
comparison with Viton material.  Results of the physical and chemical testing 
substantiated the previous conclusion of heat degradation as the root cause of 
the failures and eliminated hydrocarbon degradation of the EPDM as a possible 
cause.  In addition, the chemical analyses revealed the presence of stearate 
compounds on the surface of the EPDM material.  

The independent laboratory retained by the licensee to perform the analyses 
indicated that the stearate had migrated from the EPDM as a result of heat 
degradation.  They postulated that the presence of the stearate compounds on 
the surface would probably act like glue and further increase the force 
necessary to separate the seat and exhaust port during SOV deenergization.  
Results to date from the environmental testing program have been several 
failures of the SOVs to cycle per design with less than 30 days in the highest 
temperature oven (temperature high enough to obtain a SOV body temperature of 
284�F).  The SOVs that have failed have had both EPDM and Viton elastomers.  
The analysis of the failed SOVs is not yet complete; however, evidence from 
this testing and from other failures that have occurred, as discussed in this 
IN, indicates that the failure mechanism for some failures is temperature 
dependent. 

There have been a multitude of solenoid valve failures at U.S. nuclear power 
plants over the past 15 to 20 years, especially with regard to solenoid valves 
used for MSIV closure, where there have been several dozen failures.  At 
various times the NRC has issued several forms of communications to alert the 
industry to these potentially significant failures.  A selection of these 
include:  IE Circular 81-14, "Main Steam Isolation Valve Failures to Close," 
November 5, 1981, which described 17 different PWR and BWR units that have 
experienced anywhere from one to nine fast closure solenoid valve failures on 
MSIVs; IN 85-17, "Possible Sticking of ASCO Solenoid Valves," March 1, 1985, 
which described a February 10, 1985 event at Grand Gulf in which three MSIV 
fast closure solenoid valves failed; and IN 86-57, "Operating Problems With 
Solenoid Operated Valves at Nuclear Power Plants," July 11, 1986, which 
described a September 27, 1985 event at Brunswick 2 in which three MSIVs (2 in 
1 line) failed to close due to failure of their ASCO fast closure valves. 

Addressees may wish to review past NRC generic communications as well as 
vendor and other industry information concerning solenoid valve problems to 
ensure that their maintenance, repair, and replacement practices have 
effectively utilized available knowledge from solenoid valve operating 
experience. 

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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: Roger D. Lanksbury, RIII
                    (815) 357-8611 

                    T. Jerrell Carter, Jr., NRR
                    (301) 492-1194 


Attachment:  List of Recently Issued NRC Information Notices 

.                                                            Attachment
                                                            IN 88-43 
                                                            June 23, 1988 
                                                            Page 1 of 1

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

88-42          Circuit Breaker Failures      6/23/88        All holders of OLs
               Due to Loose Charging                        or CPs for nuclear
               Spring Motor Mounting Bolts                  power reactors. 

88-41          Physical Protection           6/22/88        All holders of OLs
               Weaknesses Identified                        or CPs for nuclear
               Through Regulatory Ef-                       power reactors. 
               fectiveness Reviews (RERs) 

88-40          Examiners' Handbook for       6/22/88        All holders of OLs
               Developing Operator                          or CPs for nuclear
               Licensing Examinations                       power reactors. 

88-39          LaSalle Unit 2 Loss of        6/15/88        All holders of OLs
               Recirculation Pumps With                     or CPs for BWRs. 
               Power Oscillation Event 

88-38          Failure of Undervoltage       6/15/88        All holders of OLs
               Trip Attachment on General                   or CPs for nuclear
               Electric Circuit Breakers                    power reactors. 

88-37          Flow Blockage of Cooling      6/14/88        All holders of OLs
               Water to Safety System                       or CPs for nuclear
               Components                                   power reactors. 

88-36          Possible Sudden Loss of RCS   6/8/88         All holders of OLs
               Inventory During Low Coolant                 or CPs for PWRs. 
               Level Operation                              

88-35          Inadequate Licensee Performed 6/3/88         All holders of OLs
               Vendor Audits                                or CPs for nuclear
                                                            power reactors. 

88-34          Nuclear Material Control      5/31/88        All holders of OLs
               and Accountability of                        or CPs for nuclear
               Non-Fuel Special Nuclear                     power reactors. 
               Material at Power Reactors 

87-61,         Failure of Westinghouse       5/31/88        All holders of OLs
Supplement 1   W-2-Type Circuit Breaker                     or CPs for nuclear
               Cell Switches                                power reactors. 
_____________________________________________________________________________
OL = Operating License
CP = Construction Permit 
..
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