United States Nuclear Regulatory Commission - Protecting People and the Environment

Information Notice No. 83-39: Failure of Safety/Relief Valves to Open at BWR - Interim Report

                                                           SSINS No. : 6835 
                                                           IN 83-39        

                                UNITED STATES
                        NUCLEAR REGULATORY COMMISSION
                    OFFICE OF INSPECTION AND ENFORCEMENT
                           WASHINGTON, D.C., 20555
                                     
                                June 17, 1983

Information Notice No. 83-39:   FAILURE OF SAFETY/RELIEF VALVES TO OPEN 
                                   AT BWR - INTERIM REPORT 

Addressees: 

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

Purpose: 

This information notice is provided as a supplement and update to 
Information Notice No. 82-41. An update is provided on testing results, 
meetings, and events involving Target-Rock two-stage safety/relief valves 
(SRVs). No specific action or response is required.  

Description of Circumstances: 

Georgia Power Co. (GPC) has been joined by five additional licensees in the 
formation of an owners' group to fund the General Electric (GE) test 
program, mentioned in IN 82-41, to find the cause of the high setpoint drift 
problem with SRVs. The SRVs are specified to open within +/- 1% of their 
setpoint. Valves that did not open at 103% of the setpoint were selected for 
additional testing to determine the cause of the failure to actuate. 

At the February 10, 1983 meeting with the owners' group, GE, and Target 
Rock, a report was given on the results of testing accomplished at that 
time. Eleven valves had been screened: six from Millstone 1, one from Browns 
Ferry, and four from Hatch 1 (licensees are Northeast Nuclear, TVA, and GPC,
respectively). Of these, seven failed to actuate at 103% of set pressure and
became candidates for additional testing. Five of the seven showed signs of 
labyrinth seal friction. The other two valves had indications that a stuck 
pilot disc/seat condition existed. One of these two valves was sent to the 
GE laboratory at Vallecitos, CA for metallurgical examination. Preliminary 
reports on this valve and two additional valves, subjected to metallurgical 
examination at other laboratories, indicate that the grey-black film on the 
discs is a corrosion product of the stellite disc. The principal 
constituents of the film are cobalt, chromium, and oxygen. Iron and silicon 
were identified in amounts consistent with the base metal of the disc. No 
elements that could not be found in the stellite alloy were detected in the 
film. 
.

                                                              IN 83-39     
                                                              June 17, 1983 
                                                              Page 2 of 2  

As a result of these and other tests, it was determined that leakage is 
unrelated to the problem of setpoint drift. (For more information on the 
leakage problem, see INPO SER 98-81 and LERS 50-293/81-62 and 
50-333/82-037.) 

On January 17, 1983, at he J. A. FitzPatrick Nuclear Plant, the reactor 
scrammed from 89% power, caused by main steam isolation valve closure and 
recirculation pump trip. During the ensuing transient conditions the relief,
valve (Target Rock two-stage; setpoint 1090 psig) did not lift. The reactor 
system pressure reached 1120 psig, as measured by the process computer, when
the relief valve (Target Rock two-stage; setpoint 1140 psig) lifted. Since 
the event resulted in a relatively rapid transient, the failure of the SRV 
to open tends to contradict the hypothesis that SRV sticking occurs only 
during slow pressure increases. 

The topworks (pilot section) of both valves were sent to Wyle Laboratories 
where both actuated within 103% of their setpoints. The valve was not 
exercised prior to shipment to Wyle (LER 50-333/83-006). The results 
obtained at Wyle are not inconsistent with the event observed at the 
FitzPatrick plant. 

Continuing tests on the disc-seat interface on non-leaking valves are being 
done to establish the magnitude of the disc-sticking and labyrinth seal 
contribution when the disc is stuck. Additional candidates for metallurgical
exam are being sought and the data base on time without actuation is being 
expanded. The testing program is expected to conclude in the late Fall of 
this year. 

Target Rock is investigating a modification of the valve internals which is 
expected to alleviate the sticking problems. The modifications will be bench
tested prior to offering them to the utilities for plant operational 
experience. A carbon bushing to reduce the labyrinth seal friction and a 
redesigned pilot disc are being considered. 

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:  Mary S. Wegner, IE
                    301-492-4511

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