United States Nuclear Regulatory Commission - Protecting People and the Environment

Information Notice No. 83-82: Failure of Safety/Relief Valves to Open at BWR - Final Report

                                                            SSINS No.: 6835 
                                                            IN 83-82       

                                UNITED STATES
                        NUCLEAR REGULATORY COMMISSION
                    OFFICE OF INSPECTION AND ENFORCEMENT
                           WASHINGTON, D.C. 20555
                                     
                              December 20, 1983

Information Notice No. 83-82:   FAILURE OF SAFETY/RELIEF VALVES TO OPEN 
                                   AT BWR - FINAL REPORT 

Addressees: 

All nuclear power reactor facilities holding an operating license (OL) or 
construction permit (CP). 

Purpose: 

This information is being provided as a final supplement and update to 
Information Notices 82-41 and 83-39. An update is provided on meetings, 
testing results, conclusions, and courses for future action involving the 
Target Rock two-stage safety/relief valves (SRVs). No specific action or 
response is required. 

Description of Circumstance: 

Synopsis of Triggering Event: On July 3, 1982, Georgia Power Company's Plant
Hatch was operating at 100% power when a spurious high-pressure signal 
caused a reactor scram. A Group 1 isolation occurred, high pressure coolant 
injection (HPCI) and reactor core isolation cooling (RCIC) turbines 
auto-started and injected, and the recirculation pumps tripped. HPCI, RCIC, 
and the feedwater pump turbines tripped at the high water level setpoint. 
Repressurization continued beyond the high-pressure scram setpoint without 
relief valve actuation until the system pressure reached 1180 psig, at which
point three of the eleven SRVs actuated, rapidly relieving pressure. 
Setpoints for the eleven SRVs were 1080, 1090, and 1100 psig. 

Synopsis of Industry Response to the Event: Georgia Power and a number of 
other utilities using the two-stage Target Rock SRVs formed an owners' group
and, together with General Electric and the Target Rock Company, began a 
testing program designed to learn the cause of the Hatch event and the cause
for the apparent setpoint drift upward in bench testing of SRVs from other 
plants. Test parameters and initial results are given in Information Notices
82-41 and 83-39. 

Recent Additional Information: A total of 34 valves were subjected to 
screening tests, establishing a data base from which it was concluded that 
labyrinth seal friction and disc-to-seat sticking were the causes for the 
setpoint drift phenomenon. A characteristic pop "signature" was plotted for 
each event. The labyrinth seal problem was found to have been caused by 
lower than design tolerance clearances. This may have been an "as-built" 
condition or the result of 


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                                                          IN 83-82         
                                                          December 20, 1983 
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creep during operation. The disc-to-seat sticking problem resulted from 
corrosion of the stellite material. The magnitude of the Hatch problem was 
likely to have been related to an earlier event in which there was an 
intrusion into the primary system of a nonionic chlorinated hydrocarbon 
which decomposed under reactor conditions and caused a conductivity of 21 
micromhos per centimeter and a pH of 4.6. The stellite material is 
susceptible to this type of corrosion. 

Based on discussions with General Electric Company representatives we 
understand that a program of revised maintenance procedures intended to 
minimize upward setpoint drift are in preparation for potential issuance as 
a Service Information Letter. 

If you have any question 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:  Mary S. Wegner, IE
                    (301) 492-4511

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