05000454/LER-2001-003
| Byron Station, Unit 1 | |
| Event date: | |
|---|---|
| Report date: | |
| Reporting criterion: | 10 CFR 50.73(a)(2)(i)(b) 10 CFR 50.73(a)(2)(v), Loss of Safety Function |
| 4542001003R01 - NRC Website | |
LICENSEE EVENT REPORT (LER) estimate to the information and Records Management Branch (t-6 f33), U.S.
Paperwork Reduction Project (3150-0104), Office Of Management And Budget, Washington, DC 20503. If an information collection does not display a currently valid OMB control number, the NRC may not conduct or sponsor, and a person is not required to respond to, the information collection.
FACILITY NAME (1) DOCKET NUMBER (2) LER NUMBER (6) PAGE (3) Byron Station, Unit 1 STN 05000454 NUMBER NUMBER _ (If more space is required, use additional copies of NRC Form 366A)(17)
A. Plant Conditions Prior to Event:
Event Date / Time: September 27, 2001 / 1330 hours0.0154 days <br />0.369 hours <br />0.0022 weeks <br />5.06065e-4 months <br /> Unit 1 — Mode 1 — Power Operations, Reactor Power — 100% Reactor Coolant System [AB]: Normal operating temperature and pressure No structures, systems or components were inoperable at the start of the event that contributed to the event.
B. Description of Event:
An equipment modification package was developed addressing the Safety Injection [BQ] (SI) venting system on May 31, 2001. The purpose of this modification was to add an additional valve and piping downstream of the 1S1081 vent valve so that the Operators would not have to climb on ladders to vent the SI system. The work was scheduled for the week of September 24, 2001.
Upon reviewing the Design Change Package (DCP) for this modification, the maintenance department non-licensed Work Planner (WP) believed it would be prudent to enhance the sock-o-let weld on the 1SI081 vent valve during this design change. The Site Welding Administrator and Design Engineer had indicated to the WP that this improvement to the weld is not required but would be considered a good practice. On July 6, 2001, the WP added this work to the scope of the planned modification work. This additional work included a weld buildup from the current one-to-one leg length ratio to a two-to-one ratio on the sock-o-let weld for the 1SI081 valve.
This change to the work scope was not made via the formal Field Change Request (FCR) process utilized for making revisions to DCPs. The WP believed it was acceptable not to use the FCR process since this weld upgrade was not considered a critical design parameter. In addition, the WP did not include this part of the work in the request for removal from service (i.e., Clearance Request (CR)) because he knew this line could not be isolated and that "water back" welding of this nature is usually performed on in-service systems.
(k:byrdocs 11ers1454-2001-003-01.doc) LICENSEE EVENT REPORT (LER) estimate to the information and Records Management Branch (t-6 f33), U.S.
Paperwork Reduction Project (3150-0104), Office Of Management And Budget, Washington, DC 20503. If an information collection does not display a currently valid OMB control number, the NRC may not conduct or sponsor, and a person is not required to respond to, the information collection.
FACILITY NAME (1) DOCKET NUMBER (2) LER NUMBER (6) PAGE (3) Byron Station, Unit 1 STN 05000454 NUMBER NUMBER (If more space is required, use additional copies of NRC Form 366/)(17) B. � Description of Event (continued):
On August 10, 2001, the work package preparation began. During the preparation, a work package hold point for an Operations Department Clearance Order (CO) Coordinator review should have been identified but it was not included in the work package. The Operations CO Coordinator prepares the method of removing the appropriate parts of the system from service in order to perform the work.
Additionally, a production risk evaluation was not completed by the WP for this work. It was later determined during the investigation that even if a production risk evaluation was performed it would have screened out due to a flaw in the procedure. The Production Risk System matrix for Byron Station did not include the SI system.
On September 6, 2001, the three-week prior to the scheduled work walkdown was performed by a maintenance senior mechanic. The CO was not reviewed during this walkdown as it was not yet available. On September 21, 2001, this work package was received by the maintenance supervisor assigned to the work. This maintenance supervisor was different than the one responsible for the three- week walkdown and did not receive a detailed turnover from the supervisor performing the three-week walkdown nor did he review the work package in sufficient detail. Additionally, no maintenance risk evaluation was performed as required by the Conduct of Maintenance Manual.
On September 26, 2001, the CO was hung on the 1S1081 valve, denoting it as an isolation point. The work was scheduled to begin the next day. The maintenance supervisor still had not recognized that the weld buildup on the 1S1081 valve was outside the boundaries of the CO. On September 27, 2001, the appropriate pre-job briefings were conducted. After the pre-job briefings, the crew went directly to the field to begin work. The supervisor mistakenly assumed all work would be performed within the CO boundaries and therefore, marked "NA" in the step for Operations Department authorization.
The welding process on the 1S1081 valve was started at 1300 hours0.015 days <br />0.361 hours <br />0.00215 weeks <br />4.9465e-4 months <br /> on September 27, 2001. The SI system pressure was at approximately 50 pounds per square inch. After building up the weld approximately two thirds of the way around the pipe, the existing weld started to leak a small amount of water. The leak was characterized as a small stream about the size of a needle. The maintenance crew notified their supervisor at 1345 hours0.0156 days <br />0.374 hours <br />0.00222 weeks <br />5.117725e-4 months <br />; he in turn notified the Work Execution Center (WEC). An Operations representative investigated and determined that the leak was on the upstream side of the valve, which is part of the SI pumps' common suction line. The Operations representative reviewed the CO with the WEC supervisor and determined that the leak was outside the CO boundary. The Shift Manager was then notified at approximately 1530 hours0.0177 days <br />0.425 hours <br />0.00253 weeks <br />5.82165e-4 months <br />.
(k:byrdocs1011ers1454-2001-003-01.doc) LICENSEE EVENT REPORT (LER) estimate to the information and Records Management Branch (t-6 f33), U.S.
Paperwork Reduction Project (3150-0104), Office Of Management And Budget, Washington, DC 20503. If an information collection does not display a currently valid OMB control number, the NRC may not conduct or sponsor, and a person is not required to respond to, the information collection.
FACILITY NAME (1) DOCKET NUMBER (2) LER NUMBER (6) PAGE (3) Byron Station, Unit 1 STN 05000454 NUMBER NUMBER (If more space is required, use additional copies of NRC Form 366A)(17) B. Description of Event (continued):
The Regulatory Assurance, Engineering, and Operations Departments were consulted regarding the operability status of the piping given this small leak. The conclusion was that the piping subsystem was inoperable. Both trains of SI were declared inoperable at 1630 hours0.0189 days <br />0.453 hours <br />0.0027 weeks <br />6.20215e-4 months <br /> and Technical Specification (TS) Limiting Condition for Operations (LCO) 3.0.3 was entered. A controlled shutdown of Unit 1 began at 1834 hours0.0212 days <br />0.509 hours <br />0.00303 weeks <br />6.97837e-4 months <br />. At 1839 hours0.0213 days <br />0.511 hours <br />0.00304 weeks <br />6.997395e-4 months <br /> both SI pumps were removed from service and the common suction header was drained to allow an American Society of Mechanical Engineers Code repair of the weld. The repair was executed at 2117 hours0.0245 days <br />0.588 hours <br />0.0035 weeks <br />8.055185e-4 months <br /> and was successfully tested. Unit 1 was at approximately 25% power. LCO 3.0.3 was exited at 2308 hours0.0267 days <br />0.641 hours <br />0.00382 weeks <br />8.78194e-4 months <br /> and the Unit subsequently returned to full power. Entry into LCO 3.0.3 and the initiation of a unit shutdown is considered a condition reportable to the NRC in accordance with 10 CFR 50.73(a)(2)(i)(b). The repair of the common SI pump suction line is considered a condition that could have prevented the fulfillment of a safety system and is also reportable to the NRC in accordance with 10 CFR 50.73(a)(2)(v).
C. Cause of Event:
The following root causes of this event were identified:
The existing sock-o-let weld on the 1S1081 valve had a pre-existing defect that, when coupled with the decision to reinforce this weld on-line, resulted in a leakage path from the SI system common pump suction header to the Auxiliary Building general area. The internal weld defect was determined to be porosity. Since the weld was performed during original plant construction, the exact cause of the porosity is unknown.
The WP mistakenly believed this additional work could be added to the work scope without using the FCR process or creating a separate work task. Had one of these processes been used, a more rigorous review of the work would have taken place and the work would have likely not been approved.
Other contributing causes identified:
A recent change to the electronic work preparation software did not carryover the ability to automatically assist the WP to insert work hold points. The WP must remember to manually insert hold points. Due to inattention to detail, the WP did not manually insert a hold point for this work for the Operations CO Coordinator.
(k:byrdocs 101 lers1454-2001-003-01.doc) LICENSEE EVENT REPORT (LER) estimate to the information and Records Management Branch (t-6 f33), U.S.
Paperwork Reduction Project (3150-0104), Office Of Management And Budget, Washington, DC 20503. If an information collection does not display a currently valid OMB control number, the NRC may not conduct or sponsor, and a person is not required to respond to, the information collection.
FACILITY NAME (1) DOCKET NUMBER (2) LER NUMBER (6) PAGE (3) Byron Station, Unit 1 STN 05000454 NUMBER NUMBER (If more space is required, use additional copies of NRC Form 366A)(17) C. Cause of Event (continued):
The Conduct of Maintenance Manual expectation to perform a maintenance risk evaluation was not conducted by the executing work supervisor due to poor implementation and communication of this process to maintenance supervisors.
No formal turnover is required between supervisors when the three-week walkdown supervisor and the work supervisor are different. This contributed to the work supervisor being unfamiliar with the details of the work scope and his inappropriate decision to mark "NA" the Operations Department Authorization step in the work package.
D. Safety Analysis:
The small leak would not have prevented the ability of the SI pumps to perform their function; therefore, the pumps were available and there was no increase in the risk of core damage or large early release from containment. However, during the time from 1839 hours0.0213 days <br />0.511 hours <br />0.00304 weeks <br />6.997395e-4 months <br />, when both SI pumps were disabled by placing their control switches in the pull to lock position and the suction header drained for the weld repair, to 2239 hours0.0259 days <br />0.622 hours <br />0.0037 weeks <br />8.519395e-4 months <br /> when the header was re-pressurized, the online station risk status was determined to be "Yellow". This event constitutes a safety system functional failure.
E. Corrective Actions:
1. � Immediate Corrective Actions:
A Maintenance Memorandum to the Mechanical Maintenance Department was issued stating that any welding to be completed outside of a CO boundary on an operable system would require a review by the Maintenance Manager or his designee prior to starting work.
All existing welding packages for the remainder of the SI venting modifications were reviewed and revised to remove any weld re-enforcements to existing welds. All work in the packages were verified to be downstream of the CO isolation boundary.
(k:byrdocs1011ers1454-2001-003-01.doc) LICENSEE EVENT REPORT (LER) estimate to the information and Records Management Branch (t-6 f33), U.S.
Paperwork Reduction Project (3150-0104), Office Of Management And Budget, Washington, DC 20503. If an information collection does not display a currently valid OMB control number, the NRC may not conduct or sponsor, and a person is not required to respond to, the information collection.
FACILITY NAME (1) DOCKET NUMBER (2) LER NUMBER (6) PAGE (3) Byron Station, Unit 1 STN 05000454 NUMBER NUMBER (If more space is required, use additional copies of NRC Form 366A)(17) E. C Corrective Actions (continued):
2. Corrective Action to Prevent Recurrence:
Byron Station has stopped the practice of reinforcing existing welds unless directed by Engineering using the DCP process.
The Work Planning Department will issue a Maintenance Directive instructing the Work Planners to create an additional task for any work that is in addition to a Design Change Modification if not already covered by a FCR.
Training will be provided to the Work Planning Department personnel on the requirements of the FCR and DCP processes.
3. Additional Corrective Actions:
The Work Planning Department has initiated an enhanced electronic software hold point feature for Work Planners.
The Mechanical Maintenance Department will develop and evaluate a formal process, similar to the other maintenance departments, for work turnover for which the walkdown supervisor and the executing supervisor are different.
The Mechanical Maintenance Department will develop supervisor continuing training on the Maintenance Risk Program to ensure compliance to the Maintenance Risk Program similar to the other Maintenance Departments and will use this event as a case study.
The involved work planners and supervisors have been counseled on their work performance.
The Corporate Welding Administrator will add appropriate cautions to the Water-back welding procedure.
Awareness sessions will be given on the Production Risk and Maintenance Risk Programs to all Maintenance Departments.
(k:byrdocs1011ers1454-2001-003-01.doc) LICENSEE EVENT REPORT (LER) estimate to the information and Records Management Branch (t-6 f33), U.S.
Paperwork Reduction Project (3150-0104), Office Of Management And Budget, Washington, DC 20503. If an information collection does not display a currently valid OMB control number, the NRC may not conduct or sponsor, and a person is not required to respond to, the information collection.
FACILITY NAME (1) DOCKET NUMBER (2) LER NUMBER (6) PAGE (3) Byron Station, Unit 1 STN 05000454 NUMBER NUMBER (If more space is required, use additional copies of NRC Form 366A)(17) E. Corrective Actions (continued):
The Maintenance Departments will include a module in their continuing training program on the Production Risk and Maintenance Risk Programs.
The Site Engineering Department will present a review of this event and the consequences to the department during a Site Engineering Monthly Communication Meeting.
The Site Engineering Department will issue a document outlining expectations concerning the method of issuing and controlling recommendations or good practices to Maintenance.
The Production Risk matrix was re-evaluated and determined not to be flawed. The SI system was determined not to be a Production Risk system.
F. Previous Occurrences:
Condition Report B1998-02239, "2CV01PB Vent Line Cut In," May 2, 1998.
(k:byrdocs101lers1454-2001-003-01.doc)