05000461/LER-2013-005
| Clinton Power Station, Unit 1 | |
| Event date: | 09-20-2013 |
|---|---|
| Report date: | 11-18-2013 |
| Reporting criterion: | 10 CFR 50.73(a)(2)(ii)(B), Unanalyzed Condition |
| Initial Reporting | |
| ENS 49373 | 10 CFR 50.72(b)(3)(ii)(B), Unanalyzed Condition |
| 4612013005R00 - NRC Website | |
PLANT AND SYSTEM IDENTIFICATION
General Electric — Boiling Water Reactor, 3473 Megawatts Thermal Rated Core Power Energy Industry Identification System (EllS) codes are identified in text as [XX].
EVENT IDENTIFICATION
Safe Shutdown Analysis Noncompliance for Diesel Generator Room Ventilation
A. CONDITION PRIOR TO EVENT:
Unit: 1 Event Date: 9/20/13 Event Time: 0917 hours0.0106 days <br />0.255 hours <br />0.00152 weeks <br />3.489185e-4 months <br /> CDT Mode: 1 Mode Name: Power Operation Reactor Power: 97 percent
B. DESCRIPTION OF EVENT:
On 9/20/13, a self assessment of the Clinton Power Station (CPS) fire protection program identified a potential noncompliance with License Condition 2.F due to the inability to achieve safe shutdown in the event of a fire. Circuit failure analysis and post-fire recovery guidance for the diesel generator [DG] ventilation [VJ] system and DG room carbon dioxide (CO2) system [Ka] were found to be technically incorrect, rendering the DG room ventilation systems unable to be restored for certain fire safe shutdown scenarios where the ventilation system was credited (i.e., Fire Zones CB-1e, CB-1f, CB-2, and CB-4). Fire-induced circuit failures can inadvertently actuate CO2 discharge in credited DG rooms, which also generates a maintained-trip signal to credited trains of DG ventilation. The CPS Safe Shutdown Analysis for these scenarios directs operators to restart the fans [FAN] using the main control room (MCR) handswitches [HS], however, this action will not bypass the maintained-trip signal generated by the CO2 system, and thus the affected DG ventilation unit(s) would be unavailable to restart.
This event was determined to be reportable under the provisions of 10 CFR 50.73(a)(2)(ii)(B), as an unanalyzed condition that significantly degraded plant safety. The station notified the NRC of this event via Event Notification 49373 at 1800 hours0.0208 days <br />0.5 hours <br />0.00298 weeks <br />6.849e-4 months <br /> (ET) on 9/20/13.
C. CAUSE OF EVENT:
An apparent cause analysis was performed under Issue Report 1561495. The analysis determined the cause of this event to be an error that occurred during an Appendix R validation project in the 1997-1998 timeframe. Limited details are available to validate the reasons behind the flawed analysis. However, it appears that the logic analysis was focused on the CO2 relaying that initiated the trip and did not sufficiently identify that the trip signal would remain sealed in.
D. SAFETY ANALYSIS:
This event had no actual safety consequences. The CPS Safe Shutdown Analysis (Updated Safety Analysis Report (USAR) Appendix F) for this scenario directs operators to take manual control of the DG room ventilation fans from the MCR to enable the CO2 trip to be bypassed. Tripping the DG room ventilation fans when the CO2 protection initiates prevents the CO2 from being exhausted from the room before the fire is extinguished. This condition would not cause an immediate loss of the DG(s). The potential consequence of this event is that the temperature in the DG rooms could increase beyond design limits, eventually exceeding the environmental limits of sensitive equipment in the DG rooms, and cause failure of the DG prior to completion of its mission time. At the time of this event there was insufficient guidance for DG room ventilation fan restoration. The USAR and Safe Shutdown Analyses describe this fire event; however, inaccurate operator actions were specified to achieve safe shutdown.
E. CORRECTIVE ACTIONS:
Operations revised procedure 1893.04, Fire Fighting, direct operators to remove the fuse in the MCR panel 1H13-P839, and restart the diesel generator room fans, to prevent interruption of or recovery of the DG room ventilation system.
Associated calculations and documents, including USAR Appendix F, will be updated to reflect the final disposition.
F. PREVIOUS OCCURRENCES:
None.
G. COMPONENT FAILURE DATA:
Not applicable.