Information Notice No. 86-57: Operating Problems with Solenoid Operated Valves at Nuclear Power Plants
SSINS No.: 6835
IN 86-57
UNITED STATES
NUCLEAR REGULATORY COMMISSION
OFFICE OF INSPECTION AND ENFORCEMENT
WASHINGTON, D.C. 20555
July 11, 1986
Information Notice No. 86-57: OPERATING PROBLEMS WITH SOLENOID OPERATED
VALVES AT NUCLEAR POWER PLANTS
Addressees:
All nuclear power reactor facilities holding an operating license or a
construction permit.
Purpose:
This notice is to advise recipients of a series of valve failures that have
occurred recently at several nuclear power plants. It is expected that
recipients will review the events discussed below for applicability to their
facilities and consider actions, if appropriate, to preclude similar-valve
failures occurring at their facilities. However, suggestions contained in
this notice do not constitute NRC requirements; therefore, no specific
action or written response is required.
Description of Circumstances:
The NRC has received reports from licensees of operating nuclear power
plants involving failures of certain valves that are actuated by solenoid
operated valves (SOVs) to operate properly. These failures have adversely
affected the intended functions of the main steam isolation system, pressure
relief and fluid control systems. Attachment 1 to this information notice
describes the failure events and the corrective actions taken.
Discussion:
In most of the cases described in Attachment 1, the cause for triggering the
event was attributed to a malfunctioning SOV that served as a pilot valve.
This in turn resulted in the malfunction of the associated main valve. The
failures of the SOVs can be traced to the following different causes: (1)
potentially high-temperature ambient conditions are not being continuously
monitored in areas where SOVs are installed and operating in an energized
state, (2) hydrocarbon contaminants, probably because backup air systems
(e.g., plant service or shop air systems) are being used periodically and
are not designed to "oil-free" specifications as required for Class IE
service, (3) chloride contaminants causing open circuits in coils of the
SOVs, possibly as a result of questionable handling, packaging, and storage
procedures, (4) an active replacement parts program associated with the
elastomers and other short-lived subcomponents used in SOVs has not been
adequately maintained, and (5) lubricants have been used excessively during
maintenance. ASCO provides installation and maintenance
8607090425
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IN 86-57
July 11, 1986
Page 2 of 2
sheets with all its valves and rebuild kits. For additional information ASCO
should be contacted.
Because of the recurring SOV failures discussed above, NRC's evaluation of
the problem is continuing. Depending on the results of the evaluation,
specific actions may be requested.
No specific action or written response is required by this information
notice. If you have any questions about this matter, please contact the
Regional Administrator of the appropriate regional office or this office.
Edward L. Jordan Director
Division of Emergency Preparedness
and Engineering Response
Office of Inspection and Enforcement
Technical Contact: Vincent D. Thomas, IE
(301)492-4755
George A. Schnebli, Region II
(404)331-4875
Attachments:
1. Examples of Solenoid-Operated Valve Failures at
Operating Nuclear Power Plants
2. List of Recently Issued IE Information Notices
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Attachment 1
IN 86-57
July 11, 1986
Page 1 of 4
EXAMPLES OF SOLENOID-OPERATED VALVE FAILURES
AT OPERATING NUCLEAR POWER PLANTS
Brunswick Station
1. Main Steam Isolation Valve (MSIV) Solenoid Failures
On September 27, 1985 at Brunswick Unit 2, during the performance of a
periodic test to demonstrate operability of the MSIVs, three out of
eight isolation valves failed to fast close as designed. The fast-close
test was required before returning Unit 2 to full-power operation after
the plant had been placed in cold shutdown on September 26, 1985. Two
of the three affected valves were installed as 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 steam line.
The licensee's initial investigation isolated the cause for the MSIV
failures to the dual SOVs that serve as pilot valves that supply
operating air to the MSIV operators to open or close the MSIVs. The
faulty SOVs were identified as Automatic Switch Company (ASCO) Model
NPL8323A36E. A more detailed review of the problems determined that the
causes for failure were attributed to valve disc-to-seat sticking of
the SOV and portions of the elastomer disc material plugging the SOV
exhaust port. These failures prevented closing the associated MSIV.
Ethylene propylene (EP) was the elastomer substance used for seals and
valve disc material in this model SOV.
The licensee's failure analysis of the SOVs included technical
assessments of the problems from the valve manufacturer (ASCO), the
supplier of the EP material (Minnesota Rubber), and Carolina Power and
Light's (CP&L's) research center (Harris Energy and Environmental
Center, Raleigh, North Carolina). The findings resulting from this
joint effort indicated that the SOV failures could have been caused by
a combination of hydrocarbon contamination of the air system and high
ambient temperature conditions, causing degradation of the EP valve
seating and seal material.
The ASCO Model NPL8323A36E SOVs were installed in Brunswick Unit 1 in
June 1983 and in Unit 2 in August 1984 to meet the Environmental
Qualification (EQ) Program requirements. The Unit 1 SOVs were
subsequently replaced during the 1985 outage when modifications were
being made to the MSIVs. The new SOVs (NP8323A36V) were identical to
the old ones except the valves contained Viton seats and seal materials
in lieu of EP. Additionally, the information provided from ASCO shows
the following:
a. Ethylene propylene is resistant to higher levels of radiation (200
megarads) than Viton. However, EP absorbs hydrocarbons that can
cause swelling and loss of mechanical properties. It is unsuitable
in applications where the air system is not designed to "oil-free"
specifications.
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Attachment 1
IN 86-57
July 11, 1986
Page 2 of 4
b. Viton has superior high-temperature performance when compared to
EP and is impervious to hydrocarbons. Its major disadvantage is
that it is less resistant to radiation than EP by a factor of ten.
ASCO recommends Viton for applications that are not oil-free and
where radiation levels do not exceed 20 megarads.
On the basis of a licensee review of the Brunswick Station maintenance
history, which showed the performance of Viton to be satisfactory in
ASCO valves, and the available literature and industry experience, the
licensee replaced all Unit 2 dual solenoid valves with valves having
Viton seats and seals. Because Viton has a 20-megarad limit, the
licensee plans to replace these elastomers every 3.3 years to meet
environmental qualification requirements for the MSIV application.
After replacing the faulty valves with valves having Viton disc and
seal material, the licensee experienced several SOV failures resulting
from open circuits of the dc coils on Unit 2. (Brunswick Station
employs ASCO NP8323A36V valves that use one ac coil and one dc coil in
applications using the subject dual solenoid valve.) On October 5,
1985, the dc coils of two MSIVs failed during the performance of
post-maintenance testing of the MSIVs. Investigation into the failures
indicated an open circuit in the dc coils. The coils were replaced and
the valves subsequently retested satisfactorily.
On October 15, 1985, an unplanned closure of an MSIV occurred while
Unit 2 was operating at 99 percent full power. Closure of the MSIV
occurred when the ac solenoid coil portion of the MSIV associated SOV
was de-energized in accordance with a periodic test procedure. It was
not known then that there was an open circuit in the associated dc
solenoid coil portion of the dual SOV. Consequently, when the ac coil
was de-energized, closure of the MSIV resulted. The failed dc coil was
replaced and then retested satisfactorily.
Investigation into the failures of the dc coil by the licensee
determined that the failures appeared to be separation of the very fine
coil wire at the junction point where it connects to the much larger
field lead. This connection point is a soldered connection that is then
taped and lacquered.
Further analysis of the coils (two failed dc coils plus five spares
from storage) by the CP&L Research Center indicated the separation
might be corrosion induced by chloride contaminants. To date, the
licensee and ASCO are unable to determine the source of the chloride.
However, followup investigation by the NRC revealed that ASCO had
previously experienced similar dc coil open circuit anomalies after a
surface shipment of SOVs overseas to Japan. At that time, ASCO believed
that the salt water ambient conditions during shipping may have been
the source of the chlorine-induced failures. ASCO recommends specific
handling, packaging, and storage conditions for spare parts and valves
at facilities.
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Attachment 1
IN 86-57
July 11, 1986
Page 3 of 4
The licensee initiated a temporary surveillance program to monitor
operability of the solenoid coils on October 16, 1985. A modification
was performed to install a voltage dropping resistor in the individual
coil circuits so that they can be monitored directly from cabinets in
the control room. This allows continuity of the coil circuitry to be
verified by measuring a voltage drop across the resistor. According to
the licensee, until the cause for failure can be determined, plans are
to check the coil circuitry for continuity on a daily basis.
2. Scram Discharge Solenoid Valve Failure In November 1985, Carolina Power
and Light's Brunswick facility experienced problems with several scram
discharge SOVs. The problems were identified during periodic
surveillance testing to determine the single rod insertion times and
resulted in several rods with slow insertion times. Initial
troubleshooting isolated the problem to the SOVs in the scram discharge
line for two of the control rods, which were subsequently replaced and
tested satisfactorily.
The licensee disassembled the failed SOVs, which were manufactured by
ASCO (Model HV-90-405-2A), for failure analysis. When the valves were
disassembled, it was noted that copious amounts of silicone lubricant
had been applied by the licensee to all gaskets, seals, and diaphragms
internal to the valves during previous routine maintenance. The
licensee believes that the excessive amount of lubricant may have
blocked some of the valves' internal passages or caused sticking of the
diaphragms, thereby contributing to the slow insertion times. The
technical manual for the subject valves states that body passage
gaskets should be lubricated with moderate amounts of Dow Corning's
Valve Seal Silicone Lubricant or an equivalent high-grade silicone
grease.
The licensee conducted successful scram tests on all other rods. A
periodic retest of 10 percent of the control rods every 120 days as
required by the Technical Specifications provides sufficient assurance
that this problem does not exist in other SOVs. In addition, the
licensee stated that maintenance procedures and practices would be
reviewed and modified, as required, to prevent the application of
excessive amounts of lubricant during repair or overhaul of components.
Haddam Neck Nuclear Power Plant
On September 10, 1985, the Haddam Neck Nuclear Power Plant was operating at
100 percent power when one of the six SOVs in the auxiliary feedwater system
(AFW) failed to change state when de-energized. This failure was detected
during the performance of a preventive maintenance procedure developed to
periodically cycle each of the six SOVs to prevent a sticking problem
similar to SOV failures previously experienced on November 2, 1984. In that
earlier event, two feedwater bypass valves failed to open automatically and
the cause was determined to be sticking SOVs. The faulty SOV was ASCO Model
NP8320A-185E and the licensee has been unable to determine the cause of the
malfunction. The
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Attachment 1
IN 86-57
July 11, 1986
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licensee's plans are to periodically cycle the SOVs until they are either
replaced with an upgraded model or the specific cause of the existing
sticking problem is determined and corrected.
Millstone Nuclear Power Station, Unit 1
On December 24, 1985, while performing a control rod scram time test at
Millstone Unit 1, three control rods failed to insert during the performance
of single rod scram time testing. In all cases, the control rod was
immediately inserted and electrically disabled.
Investigation into the failures revealed that in the first case the cause
for failure of one sticking SOV was attributed to deterioration of the
BUNA-N valve disc material within the valve. According to the licensee, this
type of failure had been identified by General Electric in their Service
Information Letter No. 128, Revision 1, dated March 2, 1984.
The licensee's investigation of the other two control rod drop failures
failed to reveal the causes for failure other than a misalignment problem of
one SOV's internals, which prevented proper movement. However, in each case,
the SOVs were disassembled, overhauled, retested satisfactorily, and
returned to service.
Grand Gulf Nuclear Station, Unit 1
Another failure of sticking SOVs occurred at Grand Gulf Unit 1 on February
10, 1985, and was the subject of Information Notice No. 85-17, entitled
"Possible Sticking of ASCO Solenoid Valves."
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