United States Nuclear Regulatory Commission - Protecting People and the Environment

Information Notice No. 88-30, Supplement 1: Target Rock Two-Stage SRV Setpoint Drift Update

                                UNITED STATES
                        NUCLEAR REGULATORY COMMISSION
                    OFFICE OF NUCLEAR REACTOR REGULATION
                           WASHINGTON, D.C.  20555

                              February 2, 1990


Information Notice No. 88-30, SUPPLEMENT 1:  TARGET ROCK TWO-STAGE SRV 
                                  SETPOINT DRIFT UPDATE


Addressees:

All holders of operating licenses or construction permits for nuclear power 
reactors.

Purpose:

This information notice supplement is intended to alert addressees to 
continuing problems associated with setpoint drift occurring in Target Rock 
two-stage safety/relief valves (SRVs) originally described in Information 
Notices (INs) 82-41, 83-39, 83-82, 86-12, and 88-30 (References 1 - 5).  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.

Background:

On July 2, 1982, at Hatch Unit 1, all 11 Target Rock two-stage SRVs failed 
to open at their setpoints of 1080 psig, 1090 psig, and 1100 psig.  Pressure 
in the reactor coolant system (RCS) rose to 1180 psig before three SRVs on 
one steamline opened and relieved RCS pressure rapidly.  This incident 
focused concern on a problem that was beginning to be seen in those SRVs 
called "setpoint drift."

The Georgia Power Company, the General Electric Company (GE), and the Target 
Rock Company initiated a study of the cause of the event at Hatch Unit 1.  
Other utilities that had installed two-stage Target Rock SRVs joined Georgia 
Power in an owners' group to look at the nature of the problem and its 
solutions.

Similar problems had been observed throughout the industry, and reports of 
these problems indicated that the number of valves affected and the extent 
of the observed setpoint drift had been increasing.  The problem was 
ultimately identified as one or both of two situations:  (1) binding in the 
labyrinth seal area caused by tolerance buildup during manufacturing, or (2) 
disc-to-seat bonding caused by oxides of the disc and seat material forming 
a continuous film and inhibiting disc movement.



9001290102
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                                                  IN 88-30, Supplement 1
                                                  February 2, 1990
                                                  Page 2 of 3


To address these problems, additional maintenance was performed to refurbish 
valves and to replace parts found to be out of tolerance in the labyrinth 
seal area.  This repair proved to be effective in some cases; however, 
problems caused by disc-to-seat bonding continued.  A material, PH13-8 Mo, 
whose oxide would not form a continuous film with the oxide of the seat 
material, was chosen for new discs.  Trial tests of valve performance, after 
installing the new discs on about 50 percent of the valves at a plant, has 
been conducted.

Test Results:

Initial results in 1987 and 1988, at Hatch 1, Brunswick 2, and Hatch 2 
showed that the performance of PH13-8 Mo had a marked improvement over the 
performance of Stellite discs.  However, in 1988, Fermi 2 results were less 
optimistic. 

     Plant          Year      Disc Material     Deviation Range

     Hatch 1        1987      Stellite          -2.50 - +6.11% 
                              PH13-8 Mo         -1.65 - +1.94% 
     Brunswick 2    1988      Stellite          -1.40 - +9.30% 
                              PH13-8 Mo         -0.10 - +4.00% 
     Hatch 2        1988      Stellite          +0.20 - +4.10% 
                              PH13-8 Mo         -1.10 - +2.90% 
     Fermi 2        1988      PH13-8 Mo         -0.20 - +4.28% 

Subsequently, the NRC was informed (in Licensee Event Report 50/366-89/007) 
that valves from Hatch 2 were tested, with the following results:

     Valve          Disc           Setpoint       As-found       Deviation 
     No             Material       (psig)         SP (psig)      (percent)

     F013A          PH13-8 Mo      1100           1077           - 2.09
     F013B          Stellite       1090           1199           +10.00
     F013C          PH13-8 Mo      1090           1129           + 3.58
     F013D          Stellite       1100           1115           + 1.36
     F013E          Stellite       1110           1135           + 2.25
     FO13F          Stellite       1090           1103           + 1.19
     F013G          Stellite       1090           1150           + 5.50
     F013H          PH13-8 Mo      1110           1227           +10.54
     F013K          PH13-8 Mo      1100           1201           + 9.18
     F013L          PH13-8 Mo      1110           1137           + 2.43
     F013M          Stellite       1100           1118           + 1.64

The range for new discs is -2.09 percent to +10.54 percent.  Of particular 
interest are valves H and K.  This range of deviation reflects a magnitude 
of bonding that had not been reported in valves with new discs before.

On November 1, 1989, the licensee for the Brunswick 2 plant reported by the 
Emergency Notification System that valve number F013L lifted 10.4 percent 
high at 1242 psig during testing.  The new disc had been installed on this 
valve.
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                                                  IN 88-30, Supplement 1
                                                  February 2, 1990
                                                  Page 3 of 3


The owners' group, GE, and Target Rock are evaluating this information and 
developing plans about future actions to resolve the disc-to-seat bonding.  
The NRC continues to monitor the issue.

This information notice requires no specific action or written response.  If 
you have any questions about this matter, please contact the technical 
contact listed below or the appropriate NRR project manager. 




                              Charles E. Rossi, Director
                              Division of Operational Events Assessment
                              Office of Nuclear Reactor Regulation

Technical Contact:  Mary S. Wegner, AEOD
                    (301) 492-7818

References

1.  Information Notice No. 82-41, "Failure of Safety/Relief Valves to Open 
    at a BWR"
2.  Information Notice No. 83-39, "Failure of Safety/Relief Valves to Open 
    at a BWR - Interim Report"
3.  Information Notice No. 83-82, "Failure of Safety/Relief Valves to Open 
    at a BWR - Final Report"
4.  Information Notice No. 86-12, "Target Rock Two-Stage SRV Setpoint Drift"
5.  Information Notice No. 88-30, "Target Rock Two-Stage SRV Setpoint Drift 
    Update"

Attachment:  List of Recently Issued NRC Information Notices
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Page Last Reviewed/Updated Tuesday, November 12, 2013