ENS 48293
ENS Event | |
|---|---|
14:25 Sep 10, 2012 | |
| Title | Both Units Entered Technical Specification 3.0.3 Due to Inoperable Control Structure Chillers |
| Event Description | Unit 1 and Unit 2 entered LCO 3.0.3 due to both Control Structure (CS) chillers 'A & B' concurrently inoperable.
At 1025 [EDT], the control room was notified that the 'B' CS Chiller was not running. There were no control room alarms due to this condition. Review of indications on control room panel 0C681 noted that the loop circ pump and all three CS fans remained in service. Indication of CS loop flow and loop temperature remained normal, approximately 600 gpm and 44 degrees. The 'B' CS Chiller restarted at 1027 [EDT] and normal system parameters were observed. Work on the 'A' CS Chiller was released at 0928 [EDT] on 9/10/2012 for scheduled maintenance, LCO's 3.7.3 and 3.7.4 were entered, however no work had actually commenced or was performed. The 'A' CS Chiller remained available and in standby during the entire evolution. Since the cause of the 'B' CS Chiller to shutdown has not been determined, the 'B' CS Chiller was declared inoperable. Inoperability of both CS chillers 'A & B' required immediate entry into LCO 3.0.3 per TS 3.7.4 Condition D. Both chillers were inoperable from 1025 [EDT] until 1042 [EDT] (17 minutes), when the 'A' CS Chiller was restored to operable status. This condition is being reported as an event or condition that could have prevented fulfillment of a safety function per 10CFR 50.72(b)(3)(v)(D). The licensee informed the NRC Resident Inspector.
This event was reported as a condition that could have prevented fulfillment of a safety function per 10 CFR 50.72(b)(3)(v)(D) because the 'A' Control Structure (CS) chiller was released for scheduled maintenance (LCO's 3.7.3 and 3.7.4 were entered), although no physical work had begun on the 'A' CS chiller. Concurrent with the 'A' chiller being in the aforementioned status, the 'B' CS chiller shutdown for approximately 2.5 minutes before automatically restarting. Following the ENS report, Susquehanna determined that although it had shutdown, the 'B' CS chiller remained operable and capable of fulfilling all its design functions. The chiller shutdown was not due to operation of a safety trip. Under safety trip conditions, automatic restart of the chiller would have been prevented and alarms would have been received in the control room. Rather, the event was due to chiller load recycle operation during which the chiller is designed to shutdown at approximately 5 degrees F below the normal operating chilled water temperature and automatically restart. Troubleshooting did not detect any faulty components and the chiller has remained in operation for greater than 48 hours5.555556e-4 days <br />0.0133 hours <br />7.936508e-5 weeks <br />1.8264e-5 months <br /> since the shutdown, without a repeat event. Additionally, although the 'A' CS chiller was declared inoperable due to entry into LCO's 3.7.3 and 3.7.4 to perform routine maintenance, no physical action had been taken to disable the 'A' chiller. Therefore, the 'A' CS chiller was capable of auto-starting and performing its safety function for all design conditions while in the LCO's. Based on the above information, Susquehanna has determined that since both the 'A' and the 'B' CS chillers were available and capable of performing their design safety functions, there was no loss of safety function therefore this ENS report is retracted. The licensee has notified the NRC Resident Inspector. Notified R1DO (Trapp). |
| Where | |
|---|---|
Susquehanna  Pennsylvania (NRC Region 1) | |
| Reporting | |
| 10 CFR 50.72(b)(3)(v)(D), Loss of Safety Function - Mitigate the Consequences of an Accident | |
| Time - Person (Reporting Time:+2.83 h0.118 days <br />0.0168 weeks <br />0.00388 months <br />) | |
| Opened: | David Walsh 17:15 Sep 10, 2012 |
| NRC Officer: | Steve Sandin |
| Last Updated: | Oct 8, 2012 |
| 48293 - NRC Website
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Unit 1 | |
|---|---|
| Reactor critical | Critical |
| Scram | No |
| Before | Power Operation (100 %) |
| After | Power Operation (100 %) |
Unit 2 | |
|---|---|
| Reactor critical | Critical |
| Scram | No |
| Before | Power Operation (100 %) |
| After | Power Operation (100 %) |