05000318/LER-2001-001
| Docket Number | |
| Event date: | |
|---|---|
| Report date: | |
| Reporting criterion: | 10 CFR 50.73(a)(2)(v)(A), Loss of Safety Function - Shutdown the Reactor |
| 3182001001R00 - NRC Website | |
I. DESCRIPTION OF EVENT
On February 13, 2001, while performing scheduled preventative maintenance, an additional wire was found installed on the starter auxiliary contacts for 22 Saltwater Air Compressor (SWAC) feeder breaker. The additional wire was not identified on the design drawing. A station issue report (IR3-050-935) was initiated recommending removal of the wire and for a visual inspection of the other SWACs' feeder breakers. The additional wire was removed from the 22 SWAC feeder breaker and visual inspection confirmed that similar wires were not installed in the others.
On February 26, 2001, during station issue report review for maintenance rule functional failures, the maintenance rule coordinator identified that a causal analysis should be performed for the event described in IR3-050-935. Station issue report number IR3-052-763 was initiated requesting a causal analysis to address the effects of the additional wire found in 22 SWAC feeder breaker.
On May 16, 2001 during performance of the causal analysis, it was determined that the described scenario did not affect the design safety function of 22 SWAC [to start and operate upon receipt of a safety injection actuation signal (SIAS)]. However, it could affect the Appendix R function of the 22 SWAC (safely shut down the plant and maintain in a safe shutdown condition in the event of a severe control room fire). As a result, the Shift Manager- Nuclear Plant Operations was notified and informed to initiate an RM-1-101 Attachment 1, "Calvert Cliffs Nuclear Operations' Checklist For Timely Notification" to document this potentially reportable event. And, on June 8, 2001, station issue report IR3-052-763 was elevated from a Category II issue (causal analysis required) to a Category I issue (root cause analysis required).
II. CAUSE OF EVENT
The extra wire had been installed since original installation of the feeder breaker cubicles. It was a spare wire or "jumper" installed off the starter motor auxiliary contacts wired back to the terminal block. This extra wire originally had no impact on the function of the 22 SWAC. However, on February 25, 1999 a plant modification (dual fuse modification) was completed requiring removal of the spare wire as identified on the design change notice, but the wire was inadvertently left installed. With the spare wire installed post-modification, the condition was created (protective fuses shunted) for potential failure of 22 SWAC in the event of a Control Room fire. Subsequent inspection identified that the spare wire had been removed from the other SWACs (11, 12, and 21) as required during the dual fuse modification.
III. ANALYSIS OF EVENT
The compressed air system at Calvert Cliffs includes safety-related air compressors; the SWACs that provide redundant air supply to safety-related components when the normal air compressors are lost. The SWACs are independently powered from the stations emergency diesel generators, seismically qualified, air-cooled, and oil-free. The instrument air portion of the compressed air system is primarily used for valve actuation and is not used in any reactor indication, control, or protective circuitry. The valve actuators are designed to fail in the safe position after loss of the instrument air supply. The SWACs are normally not running, but will start automatically on receipt of a SIAS, or may be manually started from the Control Room. Upon evacuation of the Control Room, remote manual control may be shifted to local manual control, and SIAS input to the compressors is overridden.
As described above, the additional wire affects the Appendix R function of the 22 SWAC only and would not prevent it from starting and operating upon receipt of a SIAS. The Appendix R function specifically affected involves recovery in the event of a severe Control Room fire. Specifically, in the event of a severe Control Room fire, coincident with a loss-of-offsite power, a loss of all instrument air compressors is assumed. For this scenario, with evacuation of the Control Room, the only available diesel generator is the station blackout (OC) diesel. In the event of a Control Room fire, the OC diesel generator is aligned to the 11 (Unit 1) and 24 (Unit 2) 4 kV buses. So for Unit 2, the only available source of instrument air is provided by the 22 SWAC (it is electrically aligned to the 24 4 kV bus). With evacuation of the Control Room, the 22 SWAC must be operated from the local manual control (Appendix R) handswitch. However, with the additional wire installed, the protective fuses are shunted out and a short circuit could result in failure of the 22 SWAC transformer. A short circuit is possible during a Control Room fire since the cables associated with the 22 SWAC feeder breaker run through the postulated fire area. Calvert Cliffs analysis for safe shutdown of the plant as a result of a severe Control Room fire relies on the 22 SWAC being available. Without the 22 SWAC, manual action would be required, however, that manual action is not documented in Abnormal Operating Procedure 9A "Control Room Evacuation and Safe Shutdown Due to a Severe Control Room Fire".
Therefore, this event is reportable pursuant to 10 CFR 50.73(a)(2)(v)(A) as an event that could have prevented the fulfillment of the safety function of a system needed to shut down the reactor and maintain it in a safe shutdown condition.
A significance determination process assessment was performed to evaluate this issue. Based on a bounding qualitative analysis, the delta increase in core damage frequency was estimated to be less than 10-6 and the delta increase for large early release frequency was estimated to be less than 10-7. Therefore, this issue is considered "Green," very low safety significance as per Calvert Cliffs Nuclear Power Plant procedure QL-2-100, "Issue Reporting and Assessment.
IV. � CORRECTIVE ACTIONS A. � The extra wire was removed from the 22 SWAC and the SWAC tested satisfactorily.
B. Maintenance activities were performed to inspect the other SWAC feeder breakers for the additional wire. The 22 SWAC feeder breaker was the only one with the wire installed.
C. An Issue Report was initiated requesting a causal analysis. A formal root cause assessment is in progress to determine the causal factors, evaluate generic implications, and establish additional corrective actions as required.
V. � ADDITIONAL INFORMATION A. � Affected Component Identification:
Component or System Compressed (Instrument) Air Breaker B. � Previous similar events:
IEEE 803 � IEEE 805 EIIS Funct � System ID CMP � LD BKR � LD A review of Calvert Cliffs' licensee event reports over the past several years was performed. The review did not identify any similar reportable events where the operability of the instrument air system was challenged by Appendix R circuit failures.