ML20155F875
| ML20155F875 | |
| Person / Time | |
|---|---|
| Issue date: | 04/22/1986 |
| From: | Baer R NRC OFFICE OF INSPECTION & ENFORCEMENT (IE) |
| To: | Shank J AUTOMATIC SWITCH CO. |
| Shared Package | |
| ML20155F880 | List: |
| References | |
| NUDOCS 8604250261 | |
| Download: ML20155F875 (9) | |
Text
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L f!DR 2 21986 l.
Mr. John-Shank l
Valve Engineering Department Automatic Switch Company l
Hanover Road Florham Park, New Jersey 07932
Dear Mr. Shank:
Subject:
Draft Information Notice 86-XX, " Operating Problems With Solenoid l
Pilot Valves at Nuclear Power Plants" The enclosed draft information notice is being considered for issuance to all-nuclear power reactor facilities holding an operatir.g license or construction l
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e l
. permit. Because your company is specifically identified in the notice, we l
wou?d appreciate your review of the facts presented.
If the information presented is incorrect or there is additional information pertinent to the i
discussion, we would appreciate your comments. Any comments received prior to j.
May 16, 1986 will be considered in preparation of the final version.
Thank you, in advance, for your time and effort in this matter.
Sincerel,
d Robert L. Baer, Chief l
Engineering and Generic Contnunications Branch Division of Emergency Preparedness and Engineering Response Office of Inspection and Enforcement
Enclosure:
. Draft Information Notice l
. DISTRIBUTION.
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GENERAL PDR i
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.1 SSINS No.: 6835 IN 86-XX UNITED STATES NUCLEAR REGULATORY COMMISSION OFFICE OF INSPECTION AND ENFORCEMENT WASHINGTON, D.C.
20555 April
, 1986 IE INFORMATION NOTICE NO. 86-XX: OPERATING. PROBLEMS WITH SOLEN 0ID PILOT VALVES AT NUCLEAR POWER PLANTS Addressees:
All nuclear power reactor facilities holding an operating license (0L) or a construction permit (CP).
Purpose:
This notice is to advise recipients of a series of reported valve failures that have occurred recently at several nuclear power plants.
It is expected that recipients will review the events discussed below and determine 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:
Brunswick Station On September 27, 1985 at Brunswick Unit 2, during the performance of a periodic f
l test to demonstrate operability of the main steam isolation valves (MSIVs),
l three out of eight isolation valves failed to fast-close as designed. The l
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-fast-clos 2 t:st ns requir:d before rsturning Unit 2 to full-power operation after the plant had been 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 significcnt 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 solenoid air pilot valves that supply operating air to the MSIV operators to open or close the MSIVs. The faulty solenoid-operated valves (S0Vs) were identified as Automatic Switch Company (ASCO) Model 8323A36E. A more detailed review of the problems determined that the causes for failure were attributed to valve disc-to-seat sticking of the S0V and portions of the elastomer disc material plugging the SOV exhaust port. These failures prevent-ed closing the associated MSIV. Ethylene propylene (EP) was the elastomer substance used for seals and valve disc material in this model S0V.
The licensee's failure analysis of the S0Vs included technical assessments of the problems from the valve manufacturer, ASC0; the supplier of the EP materi-al, Minnesota Rubber; and CP&L's research center, Harris Energy and Environmen-tal Center, Raleigh, North Carolina. The findings resulting from this joint effort indicated that the 50V failures could have been caused by a combination of hydrocarbon contamination of the air system which plated-out on the inter-nals of the valve; the internal geometry of valve; high ambient temperature conditions; and the use of EP valve seating and seal material under poor air quality and/or high ambient temperature conditions.
The ASCO Model 8323A36E S0V,s were installed in Brunswick Unit 1 in June 1983 l
and in Unit 2 in August 1984 to meet the Environmental Qualification (EQ) i Program requirements. The Unit 1 SOVs were subsequently replaced during the l
e 1985 out:ga wh:n modifications wera b;ing mad 2 to th2 MSIVs. The new S0Vs w;re 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 that:
Ethylene Propylene is rated for service to 300*F, is resistant to higher levels of radiation than Viton, and is, therefore, the materi-al of choice for EQ applications. However, EP absorbs hydrocarbons and swells.
This exposure also lowers its melting point.
It is undesirable in applications where the air system is not designed to
" oil-free" specifications.
Viton is rated for use to 400*F 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.
On the basis of a licensee review of the Brunswick Station maintenance history on ASCO valves and the available literature and industry experience, the licensee replaced all Unit 2 dual solenoid valves wits valves having Viton seats and seals. The licensee also is initiating a replacement program for all Viton discs and seals within the recommended radiation-limiting 3.3-year life span.
After replacement with valves having Viton disc and seal material, the licensee experienced several SOV failures resulting from open circuits of the de coils on Unit 2.
(Brunswick Station employs a design that uses one ac coil and one dc coil in applications using the subject dual solenoid valve.)
l
On October 5, 1985, tha de coils of two MSIVs failed during the p2rformanca of.
post-maintenance testing of the MSIVs.
Investigation into the failures indi-cated an opening in the de 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% full power. Closure of the MSIV occurred when the ac solenoid coil portion of the MSIV associated 50V was de-energized in accordance with a periodic test procedure.
It was not known then that there was an open circuit in the associated de solenoid coil portion of the dual S0V. Consequently, when the ac coil was de-energized, closure of the MSIV resulted. The failed de coil was replaced and then retested satisfactorily.
Investigation into the failures of-the de 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 connec-tion point is a soldered connection which is then taped and lacquered.
l Further analysis of the coils (2 failed de coils plus 5 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 l
the source of the chloride.
However, followup investigation by the NRC re-vealed that ASCO bad previously experienced dimilar dc coil open circuit anomalies during a shipment of SOVs overseas to Japan. At that time, ASCO l
believed that the salt water ambient conditions during shipping may
'e been l
the source of the chlorine induced failures. ASCO recommends maintaining good l
l handling and storage conditions for spare parts and valves at facilities that 7
7 could be exposed to salt water ambient conditions.
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l 9
e Th2 lic;nsee_initiat;d a temp:rary survaillanco prograa to moniter 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 3; voltage drop across the resistor. According to the licensee, until the cause for failure can be determined, plans are to check the coil circuity for continuity on a daily basis.
Similar S0V failures have been experienced at other nuclear power plants also.
Haddam Neck Power Plant
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On September 10, 1985, the Haddam Neck Power Plant was operating at 100% power
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when one of the six SOVs in the auxiliary feedwater sys,t4m (AFW) failed to change state when de-energized.
This failure was d ected during the perfor-mance of a pretentive maintenance procedure deve'oped to periodically cycle each of the six S0Vs to prevent a sticking e oblem similar to S0V failures previously experienced on November 2,1 ' 4.
In that earlier event two feedwater bypass valves failed to r en automatically and the cause was deter-mined to be sticking 50Vs. TF faulty 50V was ASCO Model NP8320A-185E and the licensee has been unable o determine the cause of the malfunction. The licensee plans are, o periodically cycle the 50Vs until they are either re-
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placed with, ani upgraded model or the specific cause of the existing sticking probica is determined and corrected.
Millstone Nuclear Power Station, Unit 1,
Chi December.24,1985, whilo parfcrming a control r:d scram time t:st at Mill-stone Unit 1, three control rods failed to insert during the performance of single rod scram time test'ng.
In all cases, the control rod was immediately l:
inserted and electrically disabled.
i Investigation into the failures revealed that in first case the cause for failure of ona sticking 50V was attributed to deterioration of the BUNA-N valve disc material within the valve. According to the. licensee, this type of failura 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 othar two control rod drop failures failed
-to reveal the causes for failure othar than a misalignment problem of one 50V's internals which prevented proper movement. However, in each case the S0Vs were disassembled, overhauled, retested satisfactorily, and returned to service.
Grand Gulf Unit 1
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Another f ailure of sticking S0Vs occurred at Grand Gulf Unit 1 on February 10, 1985 and was the subject of IE Information Notice No. 85-17 entitled, "Possible Sticking of ASCO Solenoid Valves."
Discussion:
In each case mentioned above the cause for triggering the event was attributed i
to a malfunctioning 50V which in turn resulted in the malfunction of the associated main valve Hogever, failures of the SOVs can be attributed to the following different causes:
(1) questionable receiving, handling, and storage procedures associated with the 50Vs; (2) potentially high temperature ambient 4
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conditions not being continuously monitored in areas wh;ra SOVs are installed e
and operating in a continuously energized state; (3) periodic use of backup cir systems (e.g., service air, shop air) that are not designed to " oil-free" specifications, as required for Class 1E service; and (4) the lack of maintain-ing an active replacement narts program associated with the elastomers and other recommended short-lived subcomponents used in the suspect SOVs.
The information herein is being provided as an early notification of a possible significant matter that is still being pursued by the NRC staff. For more specific d.! tails concerning the causes for failures, it is suggested that the valve manufacturer ASCO be contacted for an update of preventive maintenance procedures or other corrective measures.
Because of the recurring 50V failures discussed above, NRC's evaluation of the protdem ts continuing. Depending on the results, specific actions may be requested.
i 4
m
o IN 86-XX e
April, 1986 Page of 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 Contacts:
Vincent D. Thomas, IE (301)492-4755 George A. Schnebli, Region II (404)331-4875
Attachment:
List of Recently Issued IE Information Notices
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