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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 8909060284 . IN 89-66 September 11, 1989 Page 2 of 3 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. . IN 89-66 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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