NRC Bulletin 80-25
text
Bulletin 80-25: Operating Problems with Target Rock Safety-Relief Valves at BWRs
SSINS No.: 6820
Accession No.
8012170482
UNITED STATES
NUCLEAR REGULATORY COMMISSION
OFFICE OF INSPECTION AND ENFORCEMENT
WASHINGTON, D.C. 20555
December 19, 1980
IE Bulletin No. 80-25: OPERATING PROBLEMS WITH TARGET ROCK SAFETY-RELIEF
VALVES AT BWRs
Description of Circumstances:
Five events have occurred over a three-month period involving two types of
malfunctions of the Target Rock (TR) safety-relief (S/R) valves at Boston
Edison Company's Pilgrim Nuclear Power Station Unit 1. On two occasions
(July 25 and August 1, 1980), the "D" S/R valve failed to open in response
to manual demand. This same "D" valve failed to reclose in response to
manual control actions on October 1, 1980. On October 7 and 31, 1980, the
"A" S/R valve opened spuriously while the reactor was operating at power and
did not reclose in response to repeated attempts until the reactor was shut
down and the reactor coolant system depressurized. The first three events
represented failures of the S/R valve, whereas the last two events resulted
from failures of the nitrogen supply system pressure regulation.
The S/R valves at Pilgrim are two-stage, pilot-operated, dual-purpose valves
designed by Target Rock Corporation in accordance with GE criteria for
service application in the GE BWR main steam system. The two-stage S/R valve
has been designed to replace the TR three-stage S/R valve that had a
tendency to leak at the pilot valve and thereby keep the main disk from
reseating. The replacement of the three-stage valves at Pilgrim was
accomplished during the refueling outage that was completed in May 1980. The
Pilgrim reactor has four of the two-stage S/R valves installed plus two
spring-loaded safety valves.
When the "D" S/R valve failed to open on July 25, 1980, this event was
determined to be caused by a failure of its solenoid actuator to function.
During fabrication, the excessive use of Loc-tite (i.e., a trademark
adhesive for nuts and bolts) caused the solenoid plunger to adhere to the
bonnet, thus preventing pneumatic pressure from entering the pneumatic
operator.
When the second failure of the "D" valve to open on August 1, 1980 was
investigated, no discrete cause was found. The investigation involved the
removal, disassembly, inspection and testing of only the top-works of the
valve. It did not include, however, a corresponding inspection and testing
of the main-stage internals including the piston and guide.
The October 1, 1980 failure of the "D" valve to reclose was concluded to be
caused by foreign material being lodged between piston and guide of the main
stage of the valve. This conclusion was reached when scoring marks on the
surfaces of the piston and guide were found, although no foreign material
was recovered.
.
December 19, 1980
Page 2 of 3
The two remaining events of October 7 and 31, 1980 involved the "A" S/R
valve that spuriously opened and depressurized the reactor coolant system.
These events represented failures of the pneumatic system when excessive
pressure in the nitrogen supply system caused the "A" valve to open and then
to stay open. The events were addressed in IE Information Notice No. 80-40,
"Excessive Nitrogen Supply Pressure Actuates Safety-Relief Valve Operation
to Cause Reactor Depressurization," that was issued on November 7, 1980.
General Electric recently provided recommendations with regard to these two
events caused by high pneumatic supply pressure.
Action to be Taken by Utilities with BWR Plants with Operating Licenses or
Near-Term Operating Licenses:
1. If your facility has not yet installed or changed or is presently in
the process of changing to the two-stage S/R valves, initiate
appropriate quality control procedures to assure inspection of the
solenoid actuators for excess Loc-tite prior to operation. If the
solenoid actuator manufactured by Target Rock Corporation is already
installed in your facility, confirm its operability either by its
operational performance (i.e., it has functioned as designed following
an aging period of about 3 months in the higher temperature environment
of power operating conditions) or by functional testing at full
pressure during the next refueling shutdown of the facility. Include in
your report the results of all attempts to operate the two-stage S/R
valve(s).
2. In the event that a S/R valve, regardless of make or model (e.g., both
two or three stage), fails to function as designed, excepting for
pressure setpoint requirements, and the cause of the malfunction is not
clearly determined, understood, and therefore corrected, standard
operating procedures shall require that the entire valve be removed
from service, disassembled, inspected, adjusted, and pressure setpoint
tested with steam for proper operation prior to returning the valve to
service. These overhaul requirements shall be at least equivalent to
those applicable to periodic surveillance rehabilitation requirements.
Appropriate revisions to your operating procedures shall be made to
include these requirements.
3. A review of your S/R valve pneumatic supply systems shall be performed
to determine the potential for and magnitude of an overpressure
condition. The determined overpressure potential of the pneumatic
supply shall be compared with the maximum operating pressure
capabilities of the solenoid actuator valves serving the S/R valves, so
as to determine whether supply pressure could result in valve
malfunction. Protective devices (such as relief valves) shall be
installed in the proximity of the S/R valves and set to protect against
supply pressure in excess of the operating pressure capabilities of the
solenoid actuator device. In addition, consideration should be given to
modification or replacement to reduce the sensitivity of the solenoid
actuator to pneumatic supply overpressure. Further, the failure, either
high or low, of the pneumatic supply system shall be annunciated to the
control room operator. The annunciated supply pressure should be
measured at a location as close as practical to the S/R
.
December 19, 1980
Page 3 of 3
valves and downstream of any check valve connecting two or more
pneumatic sources. Appropriate operating procedures shall be provided
to guide operator response to such an occurrence of high or low supply
pressure.
4. The results of your review in response to each of the three items above
shall be provided within 90 days of the date of this bulletin. The
system upgrading identified in Item 3 shall be completed within 6
months of the time that you conclude a replacement or modification
would be made and the necessary parts are available; this upgrading
shall be reported when completed.
Provide written reports as required above, signed under oath or affirmation,
under the provisions of Section 182a of the Atomic Energy Act of 1954.
Reports shall be submitted to the Director of the appropriate Regional
Office and a copy forwarded to the Director, Office of Inspection and
Enforcement, NRC, Washington, D.C. 20555.
This request for information was approved by GAO under a blanket clearance
number R0072 which expires November 30, 1983. Comments on burden and
duplication should be directed to U. S. General Accounting Office,
Regulatory Reports Review, Room 5106, 441 Eighth Street, N. W., Washington,
D. C. 20548