05000445/LER-2003-001
| Event date: | |
|---|---|
| Report date: | |
| Reporting criterion: | 10 CFR 50.73(a)(2)(i)(B), Prohibited by Technical Specifications |
| 4452003001R00 - NRC Website | |
I. DESCRIPTION OF REPORTABLE EVENT
A. REPORTABLE EVENT CLASSIFICATION
Any operation or condition prohibited by the plant's Technical Specifications.
B. PLANT OPERATING CONDITIONS PRIOR TO THE EVENT
On October 5, 2002, Comanche Peak Steam Electric Station (CPSES) Unit 1 was in Mode 6 during the ninth refueling outage.
C. STATUS OF STRUCTURES, SYSTEMS, OR COMPONENTS THAT WERE
INOPERABLE AT THE START OF THE EVENT AND THAT CONTRIBUTED TO
THE EVENT
There were no inoperable structures, systems, or components that contributed to the event.
D. NARRATIVE SUMMARY OF THE EVENT, INCLUDING DATES AND
APPROXIMATE TIMES
At 10:00 a.m. on October 5, 2002, Unit 1 was in Mode 6 during the ninth refueling outage with the reactor vessel [EIIS:(RPV)] head removed. The reactor core contained all of the spent fuel assemblies and the upper internals were in place. Core cooling was being provided by RHR [EIIS:(BP)] Train A and RHR Train B was aligned to the Refueling Water Storage Tank (RWST) [EIIS:(BE)(TK)] for refueling cavity fill. Operations personnel (Utility, Licensed) were preparing for Safety Injection (SI) Accumulator discharge check valve [EIIS:(BQ)(CKV)] testing which followed a plan whereby the two accumulators [ElIS:(BQ)(ACC)] associated with the RHR Train providing cavity fill would be discharged first and the remaining two would be discharged following realignment of the other RHR Train to provide cavity fill.
Simultaneous to the SI check valve testing preparations, Maintenance personnel (Utility, Non- Licensed) began Technical Specification required channel calibration testing on one of the two Low Temperature Overpressure Protection (LTOP) System channels. Permission to commence this testing was granted by both the Surveillance Work Window Manager (Utility, Licensed) and the Unit Supervisor (Utility, Licensed) based on the schedule predecessor logic tie (reactor vessel head removal) being met. Maintenance personnel were approved to commence the LTOP channel calibration at 10:02 a.m. with the Reactor Coolant System (RCS) [EIIS:(AB)] level just above the reactor vessel flange. It should be noted here that the LTOP channel calibration testing renders the Train B RHR Pump Hot Leg Recirculation Isolation Valve [EIIS:(BP)(ISV)] interlocked closed to prevent RHR overpressurization.
At 11:45 a.m., the Unit 1 Reactor Operator (Utility, Licensed) attempted to open the Train B RHR Pump Hot Leg Recirculation Isolation Valve from the main control board [EIIS:(MCBD)] as a part of aligning RHR Train B for shutdown cooling. Attempts to open the valve were unsuccessful and Train B of the RHR system was declared inoperable. The Surveillance Work Window Manager then contacted the Maintenance personnel performing the LTOP channel calibration and requested them to terminate the test. The Maintenance personnel initially misinterpreted the request to attempt to restore the interlock and efforts to pursue that activity added to the delay. As a result, restoration of the inoperable RHR Train took a total of about forty minutes to perform. Following the successful restoration of RHR Train B to operable status, the Maintenance personnel involved reviewed the subject calibration with the Surveillance Work Window Manager to determine the specific cause of RHR Train B inoperability. Once it was determined that re-entry into the test procedure would not cause further inoperability conditions, the subject testing was resumed and completed satisfactorily.
Technical Specification Section 3.9.6 requires that, in Mode 6 with the water level less than 23 feet above the reactor vessel flange, both RHR Trains must be operable with one of the two trains in operation providing decay heat removal. With less than the required number of RHR Trains operable, the Technical Specification required action is to immediately initiate actions to restore the required RHR Trains to operable status or initiate actions to establish at least 23 feet of water above the top of reactor vessel flange. At 11:30 a.m. on January 6, 2003, this condition was determined to have been a reportable violation of Technical Specifications because Train B of the RHR system was unintentionally made inoperable.
E. THE METHOD OF DISCOVERY OF EACH COMPONENT OR SYSTEM
FAILURE, OR PROCEDURAL OR PERSONNEL ERROR
On October 5, 2002, Operations personnel (Utility, Licensed) determined that Train B of the Unit 1 RHR system was inoperable when attempting to open the Train B RHR Pump Hot Leg Recirculation Isolation Valve from the main control board as a part of aligning RHR Train B for shutdown cooling.
II. COMPONENT OR SYSTEM FAILURES
A. FAILURE MODE, MECHANISM, AND EFFECTS OF EACH FAILED COMPONENT
Not applicable — No component or system failures were identified during this event.
B. CAUSE OF EACH COMPONENT OR SYSTEM FAILURE
Not applicable — No component or system failures were identified during this event.
C. SYSTEMS OR SECONDARY FUNCTIONS THAT WERE AFFECTED BY FAILURE
OF COMPONENTS WITH MULTIPLE FUNCTIONS
Not applicable — No component or system failures were identified during this event.
D. FAILED COMPONENT INFORMATION
Not applicable — No component or system failures were identified during this event.
III. ANALYSIS OF THE EVENT
A. SAFETY SYSTEM RESPONSES THAT OCCURRED
Not applicable - No safety system responses occurred as a result of this event.
B. DURATION OF SAFETY SYSTEM TRAIN INOPERABILITY
After discovery of the condition, Train B of the Unit 1 RHR system was declared inoperable for shutdown cooling service for approximately 40 minutes until the train was returned to an Operable status. Review of the Unit 1 Plant Computer data from October 5, 2002, indicates that the maximum amount of time that Train B of the Unit 1 RHR system could have been inoperable was approximately 98 minutes.
C. SAFETY CONSEQUENCES AND IMPLICATIONS
Throughout the actual event, Train A of the RHR system was providing continuous heat removal and RCS circulation. The standby RHR Train, Train B, was providing reactor cavity fill from the RWST and was determined to be inoperable for shutdown cooling when Operations personnel were attempting to align Train B to provide shutdown cooling such that the two trains of RHR could trade responsibilities. RHR Train B was declared inoperable when Operations personnel could not open the Train B RHR Pump Hot Leg Recirculation Isolation Valve. It was determined that the subject valve was being kept closed by the high- pressure interlock bistable, which was being tested as part of an LTOP channel calibration test.
Immediate actions to restore RHR Train B to operable status were initiated upon the request of the Unit 1 Control Room Operators, and the Train B of the RHR system was restored to operable status approximately 40 minutes after discovery.
During the time frame from approval to commence work until restoration of RHR Train B to an Operable condition, RHR Train A was providing shutdown cooling, RCS temperature was approximately 100 degrees F, RCS charging was in service at 200 gpm to the cold legs, the refuel cavity level ranged from just above the reactor vessel flange to 10 feet above the reactor vessel flange, and the reactor upper internals were in-place. At no time was the Train A RHR shutdown cooling system challenged by this event; therefore, this event did not adversely affect the safe operation of CPSES Unit 1 or the health and safety of the public.
IV. CAUSE OF THE EVENT
TXU Energy believes that the cause of the event was the Outage Work Schedule Report did not contain the necessary predecessor logic tie to ensure that the LTOP channel calibration would be performed in a timeframe that would ensure the operability of both RHR Trains in compliance with the Technical Specification requirements. Also, the LTOP channel calibration test did not contain specific references to the Refueling Operations Technical Specification requirements relevant to the conditions under which the testing was to be performed.
V. CORRECTIVE ACTIONS
As a part of the CPSES Corrective Action Program, the following actions will be taken to address this event:
The Outage Work Schedule Report will be changed to contain the necessary predecessor logic tie to ensure that future LTOP channel calibration tests will be performed in a timeframe that will ensure the operability of the necessary RHR Trains in compliance with the Technical Specification requirements.
LTOP channel calibration test procedures will be clarified to note that the RHR Pump Hot Leg Recirculation Isolation Valves, if closed, cannot be opened from the Control Room, during performance of the test. References to the applicable Technical Specifications (3.9.5 and 3.9.6) will also be added to the procedures.
Other potentially impacted procedures will be reviewed to ensure that future LTOP channel calibration tests are not impactive to plant operations or system operability. A lessons learned regarding this event will be issued to Outage Scheduling and Operations personnel.
W. PREVIOUS SIMILAR EVENTS
There have been no previous similar events in the last three years.