ENS 47816
ENS Event | |
|---|---|
05:02 Apr 9, 2012 | |
| Title | Both Control Structure Chillers Declared Inoperable While Switching Power Supplies |
| Event Description | On 4/9/2012, starting at 0102 EDT, the 'A' and 'C' Emergency Diesel Generators (EDG) were sequentially and briefly declared inoperable to switch their DC control power back to their normal supplies. Switching power to the normal supply is required by Unit 2 technical specification 3.8.4 following maintenance work on the U1 power supplies. Previously, at 18:35 EDT on 4/4/2012, the 'B' Control Structure Chiller was declared inoperable due to an unrelated problem. With the 'B' Control Structure Chiller inoperable coincident with the 'A' EDG or 'C' EDG inoperable, neither Control Structure Chiller would be available to perform its design function on a loss of offsite power. This is a condition that, at the time of discovery, could have prevented fulfillment of a Safety Function and is reportable under 50.72(b)(3)(v)(D) as an 8 hour9.259259e-5 days <br />0.00222 hours <br />1.322751e-5 weeks <br />3.044e-6 months <br /> notification.
Switching the power supplies was a planned evolution. The duration of the loss of safety function was a total of eight minutes. As a mitigating action, operators were continuously available with communication to the control room. The associated diesel generator could have been returned to an operable condition promptly if required. Note that Technical Specifications allows four hours to correct the condition before further actions are required, i.e. declare the features ('A' Control Structure Chiller) supported by the inoperable diesel inoperable. The licensee notified the NRC Resident Inspector.
The licensee is retracting this report based on the following: On April 9, 2012, Susquehanna reported that the 'A' and 'C' Emergency Diesel Generators (EDGs) were sequentially and briefly declared inoperable to switch their DC control power back to their normal supplies while the 'B' Control Structure Chiller was inoperable. The basis for the 8 hour9.259259e-5 days <br />0.00222 hours <br />1.322751e-5 weeks <br />3.044e-6 months <br /> notification, which was reported under Reporting Requirement 50.72(b)(3)(v)(D), was the conclusion that neither Control Structure Chiller would be available to perform its design function on a loss of offsite power. The reporting guidance in NUREG-1022, Revision 2 identifies events or conditions that are generally not reportable in accordance with 50.72(b)(3)(v). One of the identified conditions is 'removal of a system or part of a system from service as part of a planned evolution for maintenance or surveillance testing when done in accordance with an approved procedure and the plant's TS (unless a condition is discovered that could have prevented the system from performing its function).' After further review, Susquehanna has determined that an ENS report was not required for this event since the EDGs and the associated 'A' Chiller were removed from service as part of a planned evolution in accordance with approved procedures and the plant Technical Specifications and no condition was discovered that could have prevented the EDGs and associated 'A' chiller from performing their function. Based on the above information, this ENS report is retracted. The licensee informed the NRC Resident Inspector. Notified R1DO(Cahill). |
| 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:+-2.92 h-0.122 days <br />-0.0174 weeks <br />-0.004 months <br />) | |
| Opened: | Alex Mclellan 02:07 Apr 9, 2012 |
| NRC Officer: | Mark Abramovitz |
| Last Updated: | Jun 7, 2012 |
| 47816 - NRC Website | |
Unit 2 | |
|---|---|
| Reactor critical | Critical |
| Scram | No |
| Before | Power Operation (100 %) |
| After | Power Operation (100 %) |