Protecting People and the EnvironmentUNITED STATES NUCLEAR REGULATORY COMMISSION
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
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June 23, 1988
Page 2 of 5
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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June 23, 1988
Page 3 of 5
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 200øC. 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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June 23, 1988
Page 4 of 5
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
284øF). 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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June 23, 1988
Page 5 of 5
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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