ENS 48811
ENS Event | |
|---|---|
06:35 Mar 7, 2013 | |
| Title | |
| Event Description | At 0135 EST, Unit 2 High Pressure Coolant Injection (HPCI) system was declared inoperable, and LCO 3.5.1 entered, due to its turbine steam exhaust valve failing in the closed position during the quarterly valve exercising surveillance. The supply breaker tripped when the opening stroke was attempted. The valve was verified to have remained fully closed via the manual operator. HPCI will not automatically start with this valve closed.
HPCI is a single train Emergency Core Cooling Safety [ECCS] system. This event results in the loss of an entire safety function which requires an 8 hour9.259259e-5 days <br />0.00222 hours <br />1.322751e-5 weeks <br />3.044e-6 months <br /> ENS notification in accordance with 10CFR50.72(b)(3)(v) and the guidance provided under NUREG-1022, rev. 2. There are no other ECCS systems presently out of service. The licensee has notified the NRC Resident Inspector.
The reported condition, described above, was further evaluated by PPL Susquehanna, LLC (PPL). The following is additional information concerning the condition: The HPCI Turbine Exhaust valve (HV255F066): 1) is a DC motor operated valve with no design features which cause automatic valve actuation, 2) is manipulated by remote Operator action to open or close the valve, 3) is designed as a normally open valve to support the HPCI function, and 4) is manually closed for long-term containment isolation. When the HPCI turbine exhaust valve was stroked, the valve successfully closed; however, position indication was lost when attempting to re-open the valve. Troubleshooting identified a faulty relay contact that in conjunction with the operator repositioning the key lock switch from CLOSE to OPEN caused a direct short in the circuit. NUREG-1022, Revision 2, Section 3.2.7, provides the following example of a condition that is not reportable under 10 CFR 50.72(b)(3)(v): 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). When the failure of the HV255F066 occurred, HPCI was properly removed from service for planned quarterly valve exercising in accordance with an approved surveillance procedure and LCO 3.5.1. Since HV255F066 is a normally open valve, a failure to open does not impact the safety function to provide a flow path for HPCI exhaust since routine valve stroking or maintenance that might close the valve would not be conducted in an accident scenario where HPCI would be required to start and closure associated with long-term containment isolation would only occur after the HPCI function is complete (i.e., the failure to open was introduced by the testing activity and would not occur in a scenario in which the valve is required to perform its safety function to open). With regard to the long-term containment isolation function, the faulty relay contact failed in a manner that prevented the valve from opening but did not prevent the valve from closing. Based on closure of the valve during the test, there was no pre-existing operability issue associated with its safety function to close. Furthermore, even without credit for HV255F066, the containment isolation safety function would be maintained by Check Valve 255F049 and Drain Isolation Valve 255F013. Based on the above additional information, PPL is retracting this report. Susquehanna was in a planned evolution and did not discover a condition that could have prevented performing a safety function. The licensee will notify the NRC Resident Inspector. Notified R1DO (Hunegs). |
| 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:+-2.98 h-0.124 days <br />-0.0177 weeks <br />-0.00408 months <br />) | |
| Opened: | Dave Borger 03:36 Mar 7, 2013 |
| NRC Officer: | Bill Huffman |
| Last Updated: | May 3, 2013 |
| 48811 - NRC Website
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Unit 2 | |
|---|---|
| Reactor critical | Critical |
| Scram | No |
| Before | Power Operation (99 %) |
| After | Power Operation (99 %) |