05000334/LER-2006-005
| Beaver Valley Power Station | |
| Event date: | 08-25-2006 |
|---|---|
| Report date: | 11-06-2006 |
| Reporting criterion: | 10 CFR 50.73(a)(2)(i)(B), Prohibited by Technical Specifications |
| 3342006005R00 - NRC Website | |
PLANT AND SYSTEM IDENTIFICATION
Westinghouse-Pressurized Water Reactor {PWR} High Pressure Safety Injection System {BQ}
CONDITIONS PRIOR TO OCCURRENCE
Unit 1: Mode 3 at 0 percent power (An unexpected reactor trip occurred on September 7. See BVPS Unit 1 LER 2006-004.) There were no systems, structures, or components that were inoperable at the start of the event that contributed to the event other than as described below.
DESCRIPTION OF EVENT
Beaver Valley Power Station (BVPS) Unit 1 performed a scheduled plant shutdown on August 25, 2006 to perform a foreign object search and retrieval action (FOSAR) on a steam generator. The plant returned to full power on August 29, 2006.
On September 8, 2006, as a follow-up action to address some minor procedure issues encountered during this recent plant shutdown, an Operations Unit Supervisor at BVPS Unit 1 contacted a station procedure writer concerning an apparent discrepancy between the plant shutdown procedure and the BVPS Unit 1 Technical Specification (TS) Bases 3.5.4. During the plant shutdown that occurred on August 25, 2006, four applicable Emergency Core Cooling System (ECCS) High Head Safety Injection (HHSI) flow path valves were closed in accordance with the current plant shutdown procedure. On September 8, 2006, the Unit Supervisor presumed that the part of the TS Bases 3.5.4 regarding de-energizing the ECCS HHSI flow path valves during Modes 4, 5 and 6 was incorrect. Further review determined that the TS Bases was correct and the shutdown procedure was in error.
BVPS TS 3.5.4 Limiting Condition for Operation (LCO) requires that "The ECCS automatic high head safety injection flow path shall be isolated" during Mode 4 (when any Reactor Coolant System cold leg temperature is less than or equal to the enable temperature), Mode 5 or Mode 6. TS Bases 3.5.4 states "Isolation of the ECCS automatic HHSI flow path is achieved by closing and de-energizing the flow path isolation valves." However, the plant shutdown procedure was recently revised to (incorrectly) remove the instruction to de-energize the applicable two of the four HHSI flow path isolation valves. These valves need to be closed and de-energized to prevent a potential unanalyzed cold overpressure condition which could be caused by an inadvertent safety injection event. Thus, during the DESCRIPTION OF EVENT (Continued) plant shutdown that occurred on August 25, 2006, the four applicable HHSI flow path valves were closed in accordance with the current plant shutdown procedure, but were not required by the procedure to de-energize these valves. Therefore, during the time that TS 3.5.4 was applicable during August 25-29, the plant did not comply with TS 3.5.4 to have the HHSI flow path isolated.
REPORTABILITY
TS 3.5.4 became applicable at 10:35 on August 25, 2006 as BVPS Unit 1 entered Mode 4.
The HHSI flow path isolation valves were closed but not de-energized, which is not in compliance with TS 3.5.4 Limiting Condition for Operation. TS 3.5.4 Action requires that the flow path be isolated within one hour, which did not occur. The plant stayed in this non-compliant condition until the applicability for TS 3.5.4 was exited at 02:31 on August 29 when the plant entered Mode 3 as it returned to full power. This condition was discovered on September 8, 2006.
Since two of the four applicable HHSI isolation valves in the flow path were closed but not de-energized, the HHSI flow path was not isolated as required by TS 3.5.4 LCO and Action between August 25 and 29. This was a condition prohibited by the plant's Technical Specifications within the last three years, and is reportable pursuant to 10 CFR 50.73(a)(2)(i)(B).
EVENT ANALYSIS
The BVPS Unit 1 Extended Power Uprate (EPU) License Amendment Request (LAR) was submitted to the NRC for approval in October, 2004. This LAR proposed 23 Technical Specification changes. TS 3.5.4 was being revised with a new title and a new number. In addition, the previous TS LCO criterion for the HHSI flow path to be "isolated and de energized" was being revised for the HHSI flow path to be "isolated" with the criterion to de-energize the two of the four HHSI flow path valves being re-located to the TS Bases, similar to other current Improved Standard Technical Specification LCO text. There was no intended change to the station since the need to de-energize two of the four HHSI flow path valves during Modes 4, 5 and 6 was being retained in the TS Bases.
In preparation for ultimate NRC approval of this EPU LAR, a procedure writer in January 2005 incorrectly identified that the TS 3.5.4 LCO criteria to de-energize valves was being (completely) deleted, due to his failure to read and understand the LAR and TS Bases.
Thus, 10 procedures were listed as needing to be revised to delete the instruction to EVENT ANALYSIS (Continued) de-energize the HHSI flow path valves in the applicable plant procedures. In June 2006 with NRC approval of the EPU LAR imminent, another procedure writer incorrectly drafted 10 plant procedures changes to remove the instruction to de-energize the four HHSI flow path valves when TS 3.5.4 was applicable, as listed in the procedure-change matrix developed in January 2005. NRC approval of the EPU LAR was then obtained in July, 2006. Three additional subsequent procedure reviewers did not identify the discrepancy, and the (incorrectly) revised procedures were issued on August 11, 2006. Training provided to the licensed Operators by three different means and times identified TS 3.5.4 as revised, but was silent on whether the criteria to de-energize valves was altered in any fashion. The control room Operations crew halted the shutdown on August 25, 2006 at the point that the newly missing procedure step to de-energize the flow path valves was reached during the plant shutdown. A brief crew peer check identified that this shutdown procedure was recently revised to explicitly remove the instruction to de-energize these valves and that TS 3.5.4 LCO was recently revised by the EPU license amendment to remove the criteria to de-energize these valves. Then the plant shutdown was re-started with these valves only being closed, but not de-energized. TS Bases 3.5.4 was not reviewed at that time (which correctly identified the need for these valves to be de-energized). Thus, there were multiple barriers that were broken to allow this human performance event to occur.
CAUSE OF EVENT
There were two root causes for this event.
Human performance errors occurred during the implementation of procedure changes associated with the Extended Power Uprate License Amendment Request (LAR) 1A-302 and the resulting BVPS Unit 1 License Amendment 275. Procedures that ensure compliance with TS 3.5.4 were incorrectly changed due to a failure to read and understand the LAR and the revised TS Bases. Personnel involved with each step of the development of this group of procedures that incorrectly removed the instruction to de-energize the HHSI valves had an incorrect mindset as to why the proposed changes were acceptable. This limited their perceived need to further research the original basis for the change.
The Technical Specification end users, primarily Operations shift personnel, were not aware of the need to refer to current TS Bases when applying recent Technical Specifications changes. Therefore, change management was not totally effective regarding the BVPS Licensing philosophy over the last few years of expanding the content of the current Technical Specification Bases. This situation was exacerbated by the fact that this recent Technical Specification change appeared to only delete a known previous LCO requirement for the HHSI valves to be de-energized, not giving the personnel involved plausible doubt to further research the reason for the change.
SAFETY IMPLICATIONS
The risk significance of BVPS-1 violating Tech Spec 3.5.4 by closing, but not de-energizing, the ECCS high head safety injection flow path isolation valve is considered to be of very low risk significance, given that the automatic Safety Injection (SI) signals were blocked and 2 out of 3 HHSI/charging pumps were made inoperable, during the period that the TS Limiting Condition for Operation was applicable.
This is based on an Engineering evaluation of the mass injection consequences of having an inadvertent safety injection while the Overpressure Protection System (OPPS) is in service. This evaluation determined the RCS pressure overshoot for a Safety Injection condition and compared it to the current design basis analysis of record. In this evaluation it was shown that the pressure overshoot attributed to one HHSI pump injecting through the Boron Injection Tank (BIT) with 2 Power Operated Relief Valves (PORVs) available, is bounded by the current Low Temperature Overpressure (LTOPS) design basis analysis, which assumes one HHSI pump injecting with one PORV available.
It also determined that with 1 HHSI pump injecting through the BIT with only 1 PORV available, the additional overshoot of the RCS pressure would only be about 14 psi higher than the current design basis analysis.
When OPPS is placed in service, the PORV actuation setpoint is set at 395 psig to ensure that the PORVs would open at less than the minimum calculated required pressure limit of 403 psig. This pressure limit of 403 psig is based on having reactor vessel flange restriction limits and all three RCPs running, and staying under the minimum required 10CFR50 Appendix G pressure limit of 621 psig when instrument uncertainties, pressure losses, and PORV opening pressure overshoot are addressed. While the assumption that all three RCPs are in service provides Operations the greatest flexibility in operating the RCPs, it also provides additional margin in the allowable overshoot if less than three RCPS are in service. Based on the current design basis analysis, if only 1 RCP is operating during the time that OPPS is in service, the minimum calculated required OPPS pressure setpoint should be 435 psig. Therefore, by having only 1 RCP operating an additional 32 psi would be available in the pressure overshoot margin. Likewise, if only 2 RCPs were in service, the OPPS pressure setpoint should be 422 psig, which would provide an additional 19 psi in the pressure overshoot margin.
At the time when TS 3.5.4 was applicable (entered on August 25,2006 at 10:35 and exited on August 29, 2006 at 02:31), OPPS was in service with 2 PORVs and only 1 charging pump available. In addition, only 1 RCP was in operation (except for a brief time of about 10 minutes when 2 RCPs were running during the plant heatup), which would provide an additional 32 psi of overshoot pressure available and still be below the Appendix G limits.
Since the Engineering evaluation determined that there would only be an additional 14 psi of overshoot with 1 HHSI pump injecting through the BIT and 1 PORV operable, the SAFETY IMPLICATIONS (Continued) maximum RCS pressure during an inadvertent SI would still be below the Appendix G limits. This would also be true for the brief period that 2 RCPs were running, albeit, less margin would be available.
Based on the above, the maximum RCS pressure during this event, given an inadvertent SI and assuming a single PORV failure, would remain below the 10CFR 50 Appendix G limits. Therefore, the safety significance from this event is considered to be very low.
CORRECTIVE ACTIONS
1. The need to review Technical Specification Bases in the current Technical Specifications (CTS) will be reinforced. Training has already been provided which emphasizes the need to review Improved Standard Technical Specifications (ISTS) Technical Specification Bases information when ISTS is implemented at BVPS in place of CTS (expected in early 2007).
2. Human performance aspects of this event were reinforced through the actions taken to reset the site human performance clock.
3. An independent review by a Senior Reactor Operator will be performed for Technical Specification compliance on procedure changes made or being planned pursuant to the Extended Power Uprate License Amendment.
Completion of the above and other corrective actions are being tracked through the BVPS corrective action program.
PREVIOUS SIMILAR EVENTS
A review found no prior BVPS Unit 1 or BVPS Unit 2 Licensee Event Report within the last five years for an event involving a license amendment implementation concern.
COMMITMENTS
There are no new commitments made by FirstEnergy Nuclear Operating Company for BVPS Unit 1 in this document.