United States Nuclear Regulatory Commission - Protecting People and the Environment

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 
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                                                            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, November 12, 2013