United States Nuclear Regulatory Commission - Protecting People and the Environment

Information Notice No. 89-66: Qualification Life of Solenoid Valves

                                  UNITED STATES
                          NUCLEAR REGULATORY COMMISSION
                      OFFICE OF NUCLEAR REACTOR REGULATION
                             WASHINGTON, D.C.  20555

                               September 11, 1989


Information Notice No. 89-66:  QUALIFICATION LIFE OF SOLENOID VALVES 

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 potential 
problem, resulting from a common-mode failure, that may affect the operability 
of main steam line isolation valves or similarly designed components.  The 
problem relates to control solenoid valves whose elastomer discs (seats) are 
exposed to temperatures higher than originally assumed in calculating their 
qualified life and which may be presently in service beyond their actual 
qualified service life.  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: 

Following a reactor trip in August 1989, the operators of Grand Gulf Unit 1 
closed the main steam line isolation valves (MSIVs) manually.  However, they 
observed that one outboard MSIV did not close until more than 15 minutes after 
a subsequent automatic closure set point (low vacuum) was reached.  Upon 
investigating the event, the licensee found a piece of the elastomer seat from 
the solenoid valve used for control of that MSIV on an outlet screen.  The 
licensee concluded that the piece had been lodged in the solenoid valve 
internals, thereby keeping the solenoid valve from venting control air and 
hence keeping the MSIV from closing.  It is believed that after the piece of 
elastomer became dislodged from the internals, the MSIV closed. 

Subsequent inspections by the licensee of all eight dual-coil solenoid valves 
piloting the MSIVs disclosed that all eight solenoid valves had degraded 
seats. Initial visual inspection did not reveal the degradations.  However, 
the degradations became apparent under microscopic examination.  The EPDM 
(ethylene propylene dimer) seats of all eight solenoid operated valves had 
cracking.  However, on six of them, the raised portion of the seat formed by 
the annular 






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                                                            September 11, 1989
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impression made in the seat by the exhaust port was missing.  Thus, it appears 
as if six of the eight solenoid valves had experienced similar sloughing of 
material from the seat.  This had been sufficient to prevent one of the 
solenoid valves from operating properly, thereby preventing the MSIV from 
operating properly. 

The solenoid valves in question are dual-coil solenoid valves manufactured by 
Automatic Switch Co. (ASCO Model NP8323).  In 1985, the Grand Gulf licensee 
calculated the qualified life of these valves with EPDM seats using 
single-coil heatup data.  The resultant qualified life was calculated at 5.9 
years on inboard MSIVs.  After the recent event, the licensee repeated the 
qualification calculations using heatup data for dual-coil solenoids (which 
became available in 1987) and estimated the life to be about 2.9 years.  These 
solenoid valves had been in service for about 4.5 years.

Recent qualification calculations by the Perry licensee for their solenoid 
valves, which have operating conditions similar to those at Grand Gulf, found 
that NP8323 solenoid valves with Viton seats on the inboard MSIVs have an 
estimated service life of about two years.  These solenoid operated valves are 
routinely changed every refueling outage at Perry. 

Discussion: 

A number of operability problems have been associated with the dual-coil 
solenoid valve Model NP8323 manufactured by ASCO.  Information Notice No. 
88-43, "Solenoid Valve Problems," dated June 23, 1988, identifies older 
generic communications and describes potential common-mode failure mechanisms, 
for example, contamination, thermal degradation of the elastomer, sticky 
material, and deficient maintenance.  ASCO issued a service bulletin dated May 
23, 1989, which stated that rebuilding kits for the "NP" series valves were 
being discontinued.  ASCO has also recently indicated that it plans to phase 
out the NP8323 solenoid valve and that two NP8320 nuclear qualified 
single-coil solenoid operated valves connected in series may be an acceptable 
substitute. 

Since better and more recent temperature information is now available, it is 
important to note that the calculated maximum service period data supplied 
with solenoid valves used at both boiling water reactors and pressurized water 
reactors may be based on temperatures at the elastomer seat that are too low.  
Therefore, the calculated service life may be in error.  Temperatures in the 
vicinity of the elastomer seat are dependent upon the plant-specific ambient 
temperatures, localized hot spot heat sources, and heat input from the 
solenoid coils during the time the solenoids are energized.  A temperature 
rise of about 100 F above ambient temperature could be expected in the 
vicinity of the seat with the dual solenoid coils energized.  ASCO has 
temperature profile data available for various solenoid valve designs.  The 
temperature profile data vary for different solenoid valves under different 
operating conditions.
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                                                            September 11, 1989
                                                            Page 3 of 3 


In a service bulletin dated April 12, 1988, ASCO stated that it had no 
evidence of elastomer degradation when Viton was used.  General Electric 
Company issued SIL No. 481, dated February 14, 1989, which recommended that 
the elastomer be changed from EPDM to Viton.  Regardless of the material used, 
the qualified life will be adversely affected by higher temperatures and may 
be significantly less than the initially determined qualified life and 
possibly even less than the actual operating time.

MSIVs are subject to different testing and surveillance requirements.  Some 
licensees test MSIVs for operability once each quarter and others may use 
special slow-closing testing techniques such as that described in IN 88-43.  
Regardless of the testing or frequency, the MSIVs may be susceptible to a 
common mode of failure which could disable both MSIVs in a steam line.  This 
failure, in itself, would not cause a significant accident; however, should 
the MSIV failures occur in conjunction with a steam line break, radioactivity 
released to the public could result in doses in excess of the guidelines of 
10 CFR Part 100. 

This information notice requires no specific action or written response.  If 
you have any questions about the information in this notice, please contact 
one of the technical contacts listed below or the appropriate NRR project 
manager. 




                              Charles E. Rossi, Director 
                              Division of Operational Events Assessment 
                              Office of Nuclear Reactor Regulation 

Technical Contacts:  J. Carter, NRR
                     (301) 492-1194

                     H. Ornstein, AEOD
                     (301) 492-4439

Attachment:  List of Recently Issued NRC Information Notices
.                                                            Attachment 
                                                            IN 89-66 
                                                            September 11, 1989
                                                            Page 1 of 1

                             LIST OF RECENTLY ISSUED
                             NRC INFORMATION NOTICES
______________________________________________________________________________
Information                                  Date of 
Notice No._____Subject_______________________Issuance_______Issued to_________

88-46,         Licensee Report of            9/11/89        All holders of OLs
Supp. 4        Defective Refurbished                        or CPs for nuclear
               Circuit Breakers                             power reactors. 

89-65          Potential for Stress          9/8/89         All holders of OLs
               Corrosion Cracking in                        or CPs for PWRs. 
               Steam Generator Tube 
               Plugs Supplied by 
               Babcock and Wilcox 

89-64          Electrical Bus Bar Failures   9/7/89         All holders of OLs
                                                            or CPs for nuclear
                                                            power reactors. 

89-63          Possible Submergence of       9/5/89         All holders of OLs
               Electrical Circuits Located                  or CPs for nuclear
               Above the Flood Level Because                power reactors. 
               of Water Intrusion and Lack 
               of Drainage 

89-62          Malfunction of Borg-Warner    8/31/89        All holders of OLs
               Pressure Seal Bonnet Check                   or CPs for nuclear
               Valves Caused By Vertical                    power reactors. 
               Misalignment of Disk 

89-61          Failure of Borg-Warner Gate   8/30/89        All holders of OLs
               Valves to Close Against                      or CPs for nuclear
               Differential Pressure                        power reactors. 

88-48,         Licensee Report of Defective  8/22/89        All holders of OLs
Supp. 2        Refurbished Valves                           or CPs for nuclear
                                                            power reactors. 

89-60          Maintenance of Teletherapy    8/18/89        All NRC Medical 
               Units                                        Teletherapy 
                                                            Licensees. 

89-59          Suppliers of Potentially      8/16/89        All holders of OLs
               Misrepresented Fasteners                     or CPs for nuclear
                                                            power reactors. 
______________________________________________________________________________
OL = Operating License
CP = Construction Permit 
..
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