United States Nuclear Regulatory Commission - Protecting People and the Environment

Information Notice No. 86-57: Operating Problems with Solenoid Operated Valves at Nuclear Power Plants

                                                            SSINS No.: 6835 
                                                            IN 86-57       

                                UNITED STATES
                           WASHINGTON, D.C. 20555

                                July 11, 1986

                                   VALVES AT NUCLEAR POWER PLANTS 


All nuclear power reactor facilities holding an operating license or a 
construction permit. 


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. 


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 


                                                              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

                    George A. Schnebli, Region II

1.   Examples of Solenoid-Operated Valve Failures at 
       Operating Nuclear Power Plants
2.   List of Recently Issued IE Information Notices

                                                              Attachment 1 
                                                              IN 86-57     
                                                              July 11, 1986 
                                                              Page 1 of 4  


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"


                                                              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. 

                                                              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 

     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 

                                                              Attachment 1 
                                                              IN 86-57     
                                                              July 11, 1986 
                                                              Page 4 of 4   

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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