United States Nuclear Regulatory Commission - Protecting People and the Environment

Bulletin 80-25: Operating Problems with Target Rock Safety-Relief Valves at BWRs

                                                       SSINS No.: 6820 
                                                       Accession No. 
                                                       8012170482 
                                                       IEB 80-25 

                                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. 
.

                                                       IEB 80-25 
                                                       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 
.

                                                       IEB 80-25 
                                                       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 
Page Last Reviewed/Updated Tuesday, July 23, 2013