Information Notice 1988-43, Solenoid Valve Problems
UNITED STATES
NUCLEAR REGULATORY COMMISSION..
OFFICE OF NUCLEAR REACTOR REGULATION
WASHINGTON, D.C. 20555
June 23, 1988
NRC 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 identi- fied, 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 temper- ature environment. The high temperature environment was the result of several
8862036ZA
IN 88-43 June 23, 1988 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 SOYs and rebuilt the
remaining five SOVs.
The third event also occurred at Perrv. 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 opera- bility checks as the result of commitments made in response to the previously
discussed problems with MSIV closure. The operability check consisted of de- pressing 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 person- nel 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
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 SOY.
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 0-rings in the SOV that was replaced as part of the cor- rective action to the event of November 3, 1987.
No other signs of SOV degra- dation 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
IN 88-43 June 23, 1988 method being used to close the MSIVs was the same as \\diccussed above for
Perry's fast closure operability check.
During the course of closing the
MSIVs, one of the outboard MSIVs reopened.
Examination of the SOY 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 SOY 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 2001C.
The time for Dow 550 to gel appears to lessen ex- ponentially 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 mechani- cal 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
IN 88-43 June 23, 1988 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. SOYs 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 con- clusion 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
2840F). The SOYs 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:
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.
IN 88-43 June 23, 1988 No specific action or written response is required bylthis 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.
harles
~E.
RoSS, 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
June 23, 1988
- -1. Page 1 of I
LIST OF RECENTLY ISSUED
NRC INFORMATION NOTICES
Information
Date of
Notice No.
Subject
Issuance
Issued to
88-42
88-41
88-40
88-39
Circuit Breaker Failures
Due to Loose Charging
Spring Motor Mounting Bolts
Weaknesses Identified
Through Regulatory Ef- fectiveness Reviews (RERs)
Examiners' Handbook for
Developing Operator
Licensing Examinations
LaSalle Unit 2 Loss of
Recirculation Pumps With
Power Oscillation Event
Failure of Undervoltage
Trip Attachment on General
Electric Circuit Breakers
Flow Blockage of Cooling
Water to Safety System
Components
Possible Sudden Loss of RCS
Inventory During Low Coolant
Level Operation
6/23/88
6/22/88
6/22/88
6/15/88
6/15/88
6/14/88
6/8/88
88-38
All holders of OLs
or CPs for nuclear
power reactors.
All holders of OLs
or CPs for nuclear
power reactors.
All holders of OLs
or CPs for nuclear
power reactors.
All holders of OLs
All holders of OLs
or CPs for nuclear
power reactors.
All holders of OLs
or CPs for nuclear
power reactors.
All holders of OLs
All holders of OLs
or CPs for nuclear
power reactors.
All holders of OLs
or CPs for nuclear
power reactors.
88-37
88-36
88-35 Inadequate Licensee Performed 6/3/88
Vendor Audits
88-34
Nuclear Material Control
and Accountability of
Non-Fuel Special Nuclear
Material at Power Reactors
5/31/88
87-61,
Supplement 1
Failure of Westinghouse
W-2-Type Circuit Breaker
Cell Switches
5/31/88
All holders of OLs
or CPs for nuclear
power reactors.
OL = Operating License
CP = Construction Permit
IN 88-43 June 23, 1988 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
Transmitted by memo from Edward G. Greenman to C. E. Rossi, "Proposed NRC Infor- mation Notice on ASCO Solenoid Operated Valve Failures," dated March 22, 1988.
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IN 88- April
, 1988 Specific items to be inspected to determine the root cause should include, but
not be limited to:
hardening of the elastomer material; distortions such as
annular impressions being cut into the seat elastomer (note - minor seat im- pressions are normal); swelling and softening of the elastomer material; flaking
of the body gaskets (o-rings); a yellowish/amber, tacky substance on the core
assembly/plugnut assembly interface; and/or deposits of foreign materials on
valve internals.
In addition to the above, the air from the air system feeding
the SOV should be analyzed for dew point, particulate matter and hydrocarbons.
The rebuild should be complete (i.e., use of all components included in the
rebuild kit).
Care should be taken to ensure that no foreign material is in- troduced into the SOV and that all portions of the SOV internals not being re- placed are thoroughly cleaned.
Since one of the failure mechanisms postulated by licensees indicated that
use of the ASCO supplied lubricant (Dow 550) may be involved in causing the
SOV to fail, licensees may not which to use it during the rebuild except for
judicial use on the body gaskets (o-rings).
If a new SOV is installed, cleaning
the internal moving parts to remove the lubricant may be beneficial.
No specific action or written response is required by this information notice.
If you have any questions about this matter, please contact the technical
contact 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 Contact:
Roger D. Lanksbury, RIII
(312) 790-5579 Attachment:
List of Recently Issued
NRC Information Notices
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