United States Nuclear Regulatory Commission - Protecting People and the Environment

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

                                  UNITED STATES
                          NUCLEAR REGULATORY COMMISSION
                      OFFICE OF NUCLEAR REACTOR REGULATION
                              WASHINGTON, DC  20555

                                  May 25, 1988


Information Notice No. 88-30:  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 is being provided to alert recipients 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, and 86-12 (References 1 - 4).  It is expected that re-
cipients will review the information for applicability to their facilities 
and consider actions, if appropriate, to avoid similar problems.  However, 
suggestions contained in this information notice do not constitute NRC require-
ments; 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 into the nature of the problem and its 
solutions. 

Similar problems had been observed throughout the industry and reports in-
dicat-ed 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. 




8805200030
.                                                                 IN 88-30
                                                                 May 25, 1988 
                                                                 Page 2 of 3 


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

Test Results:

Initial results of the test of the new discs were obtained in May of 1987 when 
the Hatch Unit 1 valves were tested.  Of the five valves that had new discs 
installed, four had pilot valves that leaked before the test.  Only one of 
these four pilot valves did not leak after the test.  The valve that did not 
leak before the steam test had first been tested with nitrogen gas (N 2) to 
determine if the disc was stuck.  It lifted at 5 psig N 2.  The remaining four 
valves lifted within 2% of setpoint.  The technical specification (TS) limit 
is � 1% of the setpoint.  One of these leaked so much that the bonnet pressure 
could not be stabilized and the delay time (time between lift of the pilot 
disc and the lift of the main disc) was excessive.  Subsequently, the 
remaining valves were tested.  Test values for all 11 valves are given in 
Table 1. 

Disc numbers 313 and 1186, which are new discs, showed a lighter-color oxide 
which was less-adherent and softer in the steam area than was seen on the old 
discs in previous tests.  Also, the seating area was bright and was not banded 
with the apparent cleft of the corrosion seen on the old discs in previous 
tests.  Discs 1189 and 1002 showed similar corrosion properties, but were 
obviously steam drawn around the entire circumference.  Disc 1189 showed signs 
that foreign material had been lodged between the disc and the seat.  A stabi-
lizer disc (Stellite) from one valve exhibited the same darker, harder, 
more-adherent corrosion as had been seen previously on the old (Stellite) 
discs.  The decision was made to turn the new disc over to GE for testing and 
to replace the new discs with other new discs, but not to replace the old 
discs at that time. 

Brunswick Unit 2 completed its testing for this cycle in early 1988.  Initial 
reports indicate that valves with the PH13-8Mo discs lifted at +1.9%, -0.1%*, 
-1.2%, +0.6%, and +4.0% of their setpoint.  One valve was not tested.  The 
old-style valves, with the Stellite 6 discs, lifted at +9.3%, -1.4%, -0.2%, 
+0.6%, and +2.6%*.  Details are shown in Table 2. 

Hatch Unit 2 test results were also recently received.  They show the valves 
with PH13-8Mo discs lifted at +2.9%, +1.8%, +0.7%, and -1.1%.  The valves with 
the Stellite discs lifted at +1.5%, +0.3%, +4.1%, +0.2%, +2.8%, and +1.6%.  
Details are shown in Table 3.

Based on available test results, the valves with new discs appear to perform 
better than valves with old discs, and valves with old discs appear to perform 
better than they did in the past.  


(*Second lift - the recorder was not running when the disc was first lifted).
.                                                                 IN 88-30
                                                                 May 25, 1988 
                                                                 Page 3 of 3 


If, when the analysis of the data is completed, the cause of the +4.0% drift 
on the Brunswick Unit 2 valve and the +2.9% drift on the Hatch Unit 2 valve 
can be determined, then PH13-8Mo may be proven to be an acceptable substitute 
for Stellite 6.  The NRC will continue to follow the testing program.  

No specific action or written response is required by this information notice.
If you have any questions about this matter, please contact the technical 
contact listed below or the Regional Administrator of the appropriate regional 
office. 




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

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

Attachments:
1.  Table 1, 1987 Test Results for Hatch Unit 1 Target Rock SRVs
2.  Table 2, 1988 Test Results for Brunswick Unit 2 Target Rock SRVs
3.  Table 3, Test Results for Hatch Unit 2 Target Rock SRVs
4.  List of Recently Issued NRC Information Notices

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 
     BWR - Interim Report."

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

4.   Information Notice No. 86-12, "Target Rock Two-Stage SRV Setpoint Drift."
.                                                                 Attachment 1 
                                                                 IN 88-30
                                                                 May 25, 1988 
                                                                 Page 1 of 1 


                                     TABLE 1

               1987 TEST RESULTS FOR HATCH UNIT 1 TARGET ROCK SRVs












  Valve Identifier                       Setpoint                   Leak[1]   
Disc             SN             TS       As-Found     Var        Prior    Post

New             1189           1090        1072      -1.65%       Yes     Yes
New              313           1080        1096      +1.48%       Yes     No
New             1002           1080        1101      +1.94%       Yes     Yes
New             1186           1100          5 (N2)   LT 1%       No      No
New             1190[2]        1100        1083      +1.55%       Yes     Yes
Old             1006           1090        1093       LT 1%       Yes     Yes
Old             1187           1090        1076      -1.28%       Yes     Yes
Old             1011           1080        1146[3]   +6.11%       No      No
Old             1009           1080        1053      -2.50%       Yes     Yes
Old             1004           1090        1101      +1.01%       Yes     Yes
Old             1003           1100        1116      +1.45%       Yes     Yes


                            

SN = Serial Number
TS = Technical Specifications

Notes: 

[1]  Pilot disc leakage.
[2]  Originally mounted on a Hatch body, but was removed due to leakage past 
     the main disc.  Remounted on a slave (Wyle) body.  Pilot leakage was so 
     great that the 30-minute stabilization of the bonnet temperature was 
     waived. 
[3]  Failed to lift when tested on 5 psig nitrogen.
.                                                                 Attachment 2
                                                                 IN 88-30
                                                                 May 25, 1988
                                                                 Page 1 of 1


                                     TABLE 2

             1988 TEST RESULTS FOR BRUNSWICK UNIT 2 TARGET ROCK SRVs












       Valve Identifier                    Setpoint         
Part Number   Disc   SN    SL       TS     As-Found   Var     Leak[1]   N2 Test

2B21-F013A    New   1109   A       1105      1126    +1.9%      Yes       No
2B21-F013B    Old   1103   A       1125      1230    +9.3%      Yes       No
2B21-F013C    Old   1099   B       1105      1090    -1.4%      No      Failed
2B21-F013D    New   1102   B       1115      1114[2] -0.1%
2B21-F013E    Old   1105   B       1115      1113    -0.2%      Yes       No
2B21-F013F    Old   1091   C       1105      1112    +0.6%      No      Failed
2B21-F013G    New   1106   C       1105      1092    -1.2%      Yes       No
2B21-F013H    New   1107   D       1115      1122    +0.6%      Yes       No
2B21-F013J    New   1108   D       1125      1170    +4.0%      Yes       No
2B21-F013K    Old   1101   C       1115      1144[2] +2.6%
2B21-F013L    New   1104   B[3]


                               

SN = Serial Number
SL = Steamline
TS = Technical Specifications


Notes: 

[1]  Pilot disc leakage.
[2]  Second lift, valve was inadvertently lifted without recorder running.
[3]  Retainer bolts removed, spring preload lost, no as-found test done.
.                                                                 Attachment 3
                                                                 IN 88-30
                                                                 May 25, 1988
                                                                 Page 1 of 1


                                     TABLE 3

                 TEST RESULTS FOR HATCH UNIT 2 TARGET ROCK SRVs












  Valve Identifier                       Setpoint           
Disc             SN             TS       As-Found     Var         Leak[1]      

Old              301           1100        1116      +1.5%         Yes
New              302           1100        1132      +2.9%         Yes
Old              303           1110        1114      +0.4%         Yes
New              306           1110        1130      +1.8%       Yes, badly
New              307           1110        1118      +0.7%       Yes, badly
New              308           1090        1078      -1.1%         Yes
Old              310           1090        1135      +4.1%         No
Old              312           1090        1092      +0.2%         Yes
Old              314           1090        1121      +2.8%         Yes
New              315           1100        1109      +0.8%         Yes
Old             1001           1100        1118      +1.6%         Yes


                

SN = Serial Number
TS = Technical Specifications


Notes:

[1]  Pilot disc leakage.
.                                                            Attachment 4
                                                            IN 88-30 
                                                            May 25, 1988 
                                                            Page 1 of 1

                             LIST OF RECENTLY ISSUED
                            NRC INFORMATION NOTICES 
_____________________________________________________________________________
Information                                  Date of 
Notice No._____Subject_______________________Issuance_______Issued to________

88-29          Deficiencies in Primary       5/24/88        All holders of OLs
               Containment Low-Voltage                      or CPs for nuclear
               Electrical Penetration                       power reactors.
               Assemblies

88-28          Potential for Loss of         5/19/88        All holders of OLs
               Post-LOCA Recirculation                      or CPs for nuclear
               Capability Due to                            power reactors.
               Insulation Debris Blockage

88-27          Deficient Electrical          5/18/88        All holders of OLs
               Terminations Identified                      or CPs for nuclear
               in Safety-Related                            power reactors.
               Components

85-35,         Failure of Air Check          5/17/88        All holders of OLs
Supplement 1   Valves to Seat                               or CPs for nuclear
                                                            power reactors.

88-26          Falsified Pre-Employment      5/16/88        All holders of OLs
               Screening Records                            or CPs for nuclear
                                                            power reactors and
                                                            all major fuel
                                                            facility 
                                                            licensees. 

88-25          Minimum Edge Distance for     5/16/88        All holders of OLs
               Expansion Anchor Bolts                       or CPs for nuclear
                                                            power reactors.

88-24          Failures of Air-Operated      5/13/88        All holders of OLs
               Valves Affecting Safety-                     or CPs for nuclear
               Related Systems                              power reactors.

88-23          Minimum Edge Distance for     5/16/88        All holders of OLs
               Expansion Anchor Bolts                       or CPs for PWRs.
_____________________________________________________________________________
OL = Operating License
CP = Construction Permit 
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