United States Nuclear Regulatory Commission - Protecting People and the Environment

Information Notice No. 86-12: Target Rock Two-Stage SRV Setpoint Drift

                                                            SSINS No: 6835 
                                                            IN 86-12       

                                UNITED STATES
                        NUCLEAR REGULATORY COMMISSION
                    OFFICE OF INSPECTION AND ENFORCEMENT
                           WASHINGTON, DC 20555

                              February 25, 1986

Information Notice No. NO 86-12:   TARGET ROCK TWO-STAGE SRV SETPOINT DRIFT 


Addressees: 

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

Purpose: 

This notice is provided to inform recipients of the continuing problem of 
setpoint drift occurring in the two-stage Target Rock safety/relief valve 
(SRV) which was originally described in Information Notice (IN) 82-41 and 
follow-up INs 83-39 and 83-82 It is expected that recipients will review 
the information for applicability to their facilities and consider actions, 
if appropriate, to preclude similar problems from occurring at their 
facilities However, suggestions contained in this notice do not constitute 
NRC requirements; therefore, no specific action or written response is 
required 

Background: 

The two-stage Target Rock SRV was designed to solve the problems of spurious
opening and failure to reseat that had been experienced with the three-stage
valve The two-stage valve exhibited some setpoint drift during testing and 
became a major concern in July of 1982, when 11 of 11 of the Hatch 1 valves 
failed to open at pressures that significantly exceeded their set pressures 
following a scram and isolation (Three valves subsequently opened at 1180 
psig and further response to the transient was normal) The owners' group 
that formed after this event, General Electric Company (GE), and the Target 
Rock Company investigated the causes of setpoint drift and developed 
recommended solutions The principal causes were determined to be galling in
the labyrinth seal area and corrosion-induced seat-to-disc bonding The 
recommended solutions were: (1) an enhanced maintenance program to ensure 
that adequate clearances were maintained in the labyrinth seal area and (2) 
a replacement disc of a material whose oxide film would be less likely to 
bond to the oxide film of the seat 

The enhanced maintenance program has been in effect for at least one fuel 
cycle in most plants Since the issuance of IN 83-82 in December 1983, 
testing results for a typical plant showed that a small number of valves 
were within the technical specification tolerance band of +/-l percent, the 
majority were within 5 percent of the setpoint, and a single valve was 
stuck 



8602200400 


                                                          IN 86-12         
                                                          February 25, 1986 
                                                          Page 2 of 3      

As the data base grew, it became apparent that setpoint drift had not gone 
away The Director, Division of Licensing, Nuclear Reactor Regulation (NRR) 
sent a letter to the owners' group in March 1985 recognizing the benefits of
enhanced maintenance, but concluding that maintenance alone was inadequate 
to solve the problem The next step taken by the owners' group was the 
selection of a replacement material for the disc which would have less 
tendency to develop a strong oxide bond with the Stellite alloy seat A 
precipitation hardenable stainless steel disc material was selected to 
replace the Stellite alloy currently used in the disc 

Description of Circumstances: 

Following the 1982 Hatch event, the tests performed at Wyle had consisted of
a steam pressure test to determine the setpoint, followed by diagnostic 
tests to determine the cause of the setpoint drift on those valves which did 
not lift within 3 percent (initially 5 percent) of the setpoint To 
determine the amount to which the disc is stuck, the test of the Brunswick 
valves, and the current test procedure, calls for determining if the disc is 
stuck before the steam pop This is done by backing the stem off the seat 
and pressurizing below the seat with nitrogen Because the disc is 
unrestrained, it is expected to lift within 5 psi-nitrogen pressure The 
nitrogen pressure indicates the extent of seat-to-disc bonding while the 
labyrinth seal problem is indicated by the characteristically large drop in 
steam pop pressure on repeated tests 

On January 7, 1986, Carolina Power and Light (CP&L) reported that 6 of-the 
11 Brunswick Unit 2 Target Rock two-stage SRVs being tested at Wyle 
Laboratories had failed to lift at a nitrogen pressure of 200 psi, 4 others 
lifted outside the tolerance band, and 1 lifted satisfactorily The nitrogen
tests on those valves were terminated at that time and CP&L directed that 4 
of the stuck valves be opened using the solenoid actuator to demonstrate 
operability in the automatic depressurization system (ADS) and manual modes
The valves operated properly A fifth valve, having a setpoint of 1105 psig,
was steam popped, lifting at 1219 psig-steam The sixth valve was 
disassembled before further testing Brunswick Unit 2 had completed 2 cycles
with the enhanced valve internals maintenance program, but the disc 
replacement was yet to be done These test results were significantly 
different from other licensees' results reported to the NRC recently NRC's 
concern was heightened because of the number of valves affected and the 
extent to which the discs appeared to be stuck 

The 5 stuck valves as well as the remaining 5 were successfully steam popped
the required number of times before being disassembled and refurbished This
demonstrated that the clearances in the labyrinth seal area were 
satisfactory Four of the stuck valves and 2 of the others are to have discs
of the new material retrofitted 

On January 9, 1986, the internals of the valve which was steam popped at 
1219 psig were examined by an NRC inspector, who reported no differences in 
appearance of this disc from previously observed discs The disc area 
exposed to steam appeared to be covered with a light gray film There was a 
reasonably narrow, bright seating band with no evidence of other problems 
The labyrinth seal showed very light wear CP&L personnel could not identify
any significant 


                                                          IN 86-12         
                                                          February 25, 1986 
                                                          Page 3 of 3      

conditions that may have contributed to the severity of the sticking such as
the primary water chemistry transient that Hatch had experienced in 1982 
The licensee noted that the three valves on the C-steamline exhibited the 
least amount of drift and that they were located in the same drywell 
quadrant The main steam line isolation valves in this line had been closed 
for about a six-week period, just prior to the end of the fuel cycle and 
there was a minor primary water chemistry transient during that time The 
licensee, also mentioned drywell temperature problems and steam leaks from 
the high-pressure coolant injection (HPCI) system as possible contributors 

Results of recent testing of the 11 Hatch Unit 1 valves identified two 
valves outside the tolerance band for the nitrogen test that determines 
disc-to-seat sticking Two valves lifted outside the tolerance band, 1 was 
leaking too much to test on nitrogen, and the remaining valves opened at 
less than 6 percent over setpoint The tests of the Brunswick and Hatch 
valves followed the same procedures and the results for both reactors are 
detailed in Attachment 1 for comparison 

Discs made of precipitation hardenable stainless steel will be installed in 
50 percent of the SRVs in each plant as they become available Hatch 1 and 
Brunswick 2 have just had the new discs installed Experience data will 
begin to be received in 12 to 18 months 

The NRC investigation of the Brunswick problem in particular and the Target 
Rock two-stage setpoint drift problem in general will continue until 
resolved satisfactorily As additional information is obtained, it will be 
disseminated to the industry 

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

Attachments:
1   Wyle Lab Test Results: Brunswick 2/Hatch 1
2   List of Recently Issued IE Information Notices


                                                          Attachment 1     
                                                          IN 86-12         
                                                          February 25, 1986 
                                                          Page 1 of 1      

                1986 WYLE LAB TEST RESULTS: BRUNSWICK 2/HATCH

                                 BRUNSWICK 2

VALVE #        SET PRESS (psig)    N2 PRESS (psig)     STEAM PRESS (psig)
               +/-1 percent        DISC LIFT           FIRST POP (1) 

1091           1105                11                  1131 
1099           1105                200+                1107 (2) 
1101           1115                11                  1134 
1102           1115                82                  1134 
1103           1125                48                  1134 
1104           1125                200+                1153 (2) 
1105           1115                200+                (DISASSEMBLED) 
1106           1105                5                   1116 
1107           1115                200+                (INSTRUMENT  FAILURE) 
1108           1125                200+                1176 (2) 
1109           1105                200+                1219 (3) 


                                   HATCH 1

VALVE#         SET PRESS (psig)    N2 PRESS (Psig)     STEAM PRESS (Psig)
               +/-1 percent        DISC LIFT           FIRST POP (1)

313            1080                42                  1092 
1002           1080                5                   1092 
1003           1100                31                  1132 
1004           1090                5                   1084 
1006           1090                5                   1119 
1009           1080                5                   1095 
1011           1080                5                   1086 
1186           1100                5                   1104 
1187           1090                5                   1101 
1189           1090                (LEAKING)           1102 
1190           1100                5                   1127


(1)  The steam pressure "first pop test" is performed after the nitrogen 
     pressure disc lift Therefore, except for the Brunswick 2 valves that 
     failed to lift with a nitrogen pressure of 200 psig, any corrosion bond
     that existed between the pilot disc and seat had been broken by the 
     nitrogen test 

(2)  These valves were opened by using the solenoid actuator before the 
     steam pressure "first pop test", thus breaking any corrosion bond that 
     existed between the pilot disc and seat 

(3)  Since this valve was not opened by nitrogen pressure or by the solenoid
     actuator, this pressure approximates the "as-found" valve condition 

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