Information Notice No. 84-33: Main Steam Safety Valve Failures Caused by Failed Cotter Pins
SSINS No: 6835 IN 84-33 UNITED STATES NUCLEAR REGULATORY COMMISSION OFFICE OF INSPECTION AND ENFORCEMENT WASHINGTON, D.C. 20455 April 20, 1984 Information Notice No. 84-33: MAIN STEAM SAFETY VALVE FAILURES CAUSED BY FAILED COTTER PINS Addressees: All nuclear power reactor facilities holding an operating license (OL) or a construction permit (CP). Purpose: This information notice is provided as a notification of a potentially sig- nificant problem pertaining to a failure mode of safety and safety/relief valves caused by failed cotter pins. It is expected that recipients will review the information for applicability to their facilities and consider actions, if appropriate, to preclude a similar problem occurring at their facilities. However, suggestions contained in this information notice do not constitute NRC requirements and, therefore, no specific action or written response is required. Description of Circumstances: On February 9, 1984, St. Lucie Unit 2 Nuclear Power Station reported a main steam safety valve (MSSV) stuck partially open following a reactor trip with MSSV actuation (lifting). Approximately 40 minutes were required to reseat the MSSV. On March 2, 1984, Davis Besse Nuclear Power Station reported a MSSV stuck open following main steam isolation valve (MSIV) closure with MSSV lifting. This latter event caused the steam generator to empty. The MSSV was then replaced. Both the above events were caused by the release nut turning on the spindle to a lower position while the MSSV was lifted. When the main steam pressure was reduced to the reseat pressure, the MSSV could not reseat because the release nut was holding the spindle up. This turning of the release nut was apparently caused by the failure of the release,nut cotter pin and the vibration of the spindle while the MSSV was lifted. The pieces of the cotter pin at Davis Besse were later found and were observed to be rusted. These failures were on MSSVs supplied by different manufacturers. The St. Lucie Unit 2 MSSV was manufactured by Crosby. The Davis Besse MSSV was manufactured by Dresser-Consolidated. The NRC staff believes this failure can occur on any safety or safety/relief valve of similar design, but has no further information on valves from other manufacturers at this time. 8404160130 . IN 84-33 April 20, 1984 Page 2 of 2 Followup action for both these events included replacing the cotter pin and checking all other MSSV cotter pins. The Davis Besse procedures were revised to require stainless steel cotter pins and to prohibit reuse of these cotter pins after once removing them. St. Lucie Unit 2 has investigated removing parts of the manual lift mechanism from the MSSVs to preclude reoccurrence, but the NRC staff is not aware of any conclusions reached on this approach to the problem. If you have any questions regarding this matter, please contact the Regional Administrator of the appropriate NRC Regional Office or this office. Edward L. Jordan,Director Division of Emergency Preparedness and Engineering Response Office of Inspection and Enforcement Technical Contact: H. A. Bailey, IE (301) 492-7078 Attachments: 1. Davis Besse Main Steam Safety Valve 2. List of Recently Issued IE Information Notices
Page Last Reviewed/Updated Tuesday, March 09, 2021
Page Last Reviewed/Updated Tuesday, March 09, 2021