Operating Experience Feedback Report, Solenoid-Operated Valve Problems at U.S. Reactors (Generic Letter 91-15)

				                 UNITED STATES 
                         NUCLEAR REGULATORY COMMISSION 
                              WASHINGTON D.C. 20555

                               September 23, 1991 


               (GENERIC LETTER 91-15)

This generic letter informs addressees of a case study report of operating 
experience problems with solenoid-operated valves (SOVs) prepared by the 
Office for Analysis and Evaluation of Operational Data AEOD) and published 
as NUREG-1275, Volume 6, "Operating Experience Feedback 
Report--Solenoid-Operated Valve Problems," February 1991 (copy enclosed).  
The case study integrates what has been learned over the past several years 
and provides an extensive assessment of SOV operating experience.  The study 
describes deficiencies in design and application, manufacture, maintenance, 
surveillance testing and feedback of failure data, and concluded that 
problems with SOVs need additional attention by the industry.  While the 
recommendations in the case study are not intended to establish regulatory 
requirements, many of the problems described in the report already are 
addressed by current environmental qualification and quality assurance 

In the study, several events are described in which SOV failures affected 
redundant safety components, multiple trains of safety systems or multiple 
safety systems.  Three of the most significant events were isolated 
occurrences involving the failure to close of both main steam isolation 
valves (MSIVs) in the same line, the inability to start two redundant 
emergency diesel generators, and simultaneous failure of several BWR control 
rods to insert.  The examples illustrate the vulnerability of safety-related 
equipment to common mode failure or degradation of SOVs.  The NRC is 
concerned about the reliability of SOVs used in safety applications. As part 
of NRC's ongoing regulatory activities, inspections such as Safety System 
Functional Inspections (SSFIs) include the reliability of SOVs as well as 
other components required by safety related applications.  The NRC also is 
providing technical advice to the Electric Power Research Institute's (EPRI) 
Nuclear Maintenance Application Center (NMAC) to assist in preparing an SOV 
maintenance guide.  The first draft of the SOV maintenance guide is 
anticipated to be available towards the end of 1991.  

It has been estimated that many hundreds of SOVs are in wide-spread use in 
each nuclear power facility.  They are used in safety-related systems 
indirectly as pilot operators working with control system fluid (such as 
pneumatic or hydraulically operated isolation valves) and directly in fluid 
systems (such as to vent the reactor vessel head or to supply air to the 
starting system for emergency diesel generators).  Many SOVs are also used 
in nonsafety-related systems that can significantly affect safety systems 
(such as plant instrument air drier systems).  Over the years, many failures 
of plant systems and components have been attributed to SOV problems.  To 
address specific SOV failures, the Nuclear Regulatory Commission (NRC) has 
issued numerous information notices 

Generic Letter 91-15                -2- 

and bulletins that provide the immediately attributed root cause for the 
failure.  Because these communications frequently were focused on a specific 
failure, licensees may have made assessments and taken corrective actions 
that were focused on the specific failures and not on broader issues. 

In the case study, the staff reviewed many SOV failures and degradations and 
discussed those having a similar failure mechanism, thereby showing how only 
slight differences frequently are all that separate operation from failure.  
Correcting only one obvious and specific deficiency at a time without 
awareness of other mechanisms for degradation may permit another problem in 
a short time to lead to unnecessary recurrent SOV failures.  In addition, 
correcting problems only in SOVs used in the specific application in which 
the problem was found can allow similar SOV degradation to develop in other 
No specific action or written response is required by this generic letter. 
However, it is expected that recipients will review the information 
presented in the case study for applicability to their facilities and 
consider actions, as appropriate, to avoid similar problems.  Since this 
generic letter and enclosure do not contain new or revised regulatory 
requirements, the Backfit Rule, 10 CFR 50.109, does not apply.  If you have 
any questions about this matter, please contact one of the technical 
contacts listed below or the appropriate NRR project manager. 


                                        James G. Partlow
                                        Associate Director for Projects
                                        Office of Nuclear Reactor Regulation

NUREG-1275, Volume 6

Technical Contacts:  H. Ornstein, AEOD
                     (301) 492-4439

                     J. Carter, NRR
                     (301) 492-1153

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