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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