ENS 47491
ENS Event | |
|---|---|
11:46 Nov 20, 2011 | |
| Title | Turbine Trip Protection Disabled While in Mode 3 |
| Event Description | On November 20, 2011 at 0546 hours0.00632 days <br />0.152 hours <br />9.027778e-4 weeks <br />2.07753e-4 months <br /> [CST], STP Unit 2 transitioned modes from Mode 4 to Mode 3. Prior to the mode change, all Solid State Protection System (SSPS) generated turbine trip signals were defeated by a maintenance work activity that installed a jumper in both channels (Train R and S) of non-class relays to the turbine trip circuit. The SSPS signals to the non-class relays that were defeated by the jumpers included the turbine trip from reactor trip breakers open (P4), turbine trip from a reactor trip signal (P-16), and the turbine trip from Steam Generator HI- HI (P-14). T.S. 3.3.2 Items 5a (P4) and 5b (P-14) are required in Modes 1, 2, and 3. The jumpers were removed around 0930 on November 20, 2011 with U2 still in Mode 3.
Both the UFSAR and TS bases identify that the turbine trip mitigates the consequences of an accident. The TS bases states that an ESFAS initiated turbine trip mitigates the consequences of a steam line break or loss of coolant accident. The accident analysis for SGTR also assumes a turbine trip on a reactor trip to isolate the steam path. Although Unit 2 was in Mode 3, with the reactor trip breakers open, and turbine throttle valves closed while the jumpers were installed, this condition is conservatively considered to be a safety system functional failure. If not corrected, this condition could have prevented the fulfillment of the accident mitigating and control of the release of radiation safety functions. A review of the performance of this activity in previous outages was conducted. It was identified that during 2RE14 in April of 2010, a work package for this activity was not closed until after Mode 3. The 60 day LER will address if the jumpers were installed in Mode 3 in April, 2010. This was determined to be reportable within 8 hours9.259259e-5 days <br />0.00222 hours <br />1.322751e-5 weeks <br />3.044e-6 months <br /> as required by 10 CFR 50.72(b)(3)(v) parts (C) and (D). The licensee did not determine the reportability of this event until 1415 CST on 11/30/11. The licensee has notified the NRC Resident Inspector. |
| Where | |
|---|---|
South Texas  Texas (NRC Region 4) | |
| Reporting | |
| 10 CFR 50.72(b)(3)(v)(C), Loss of Safety Function - Release of Radioactive Material 10 CFR 50.72(b)(3)(v)(D), Loss of Safety Function - Mitigate the Consequences of an Accident | |
| Time - Person (Reporting Time:+244.45 h10.185 days <br />1.455 weeks <br />0.335 months <br />) | |
| Opened: | Robert Brinkley 16:13 Nov 30, 2011 |
| NRC Officer: | Bill Huffman |
| Last Updated: | Nov 30, 2011 |
| 47491 - NRC Website
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Unit 2 | |
|---|---|
| Reactor critical | Not Critical |
| Scram | No |
| Before | Hot Shutdown (0 %) |
| After | Hot Standby (0 %) |