ENS 42527
ENS Event | |
|---|---|
17:30 Apr 25, 2006 | |
| Title | Unanalyzed Condition - Control Logic Error |
| Event Description | TMI Issue Report # 482679 identified an issue while performing reviews of fire abnormal operating procedures to assure compliance with the Fire Hazards Analysis Report (FHAR), in that a control logic error was identified in the circuitry elementary drawing for the isolation valves DH-V-6A and DH-V-6B between the Borated Water Storage Tank (BWST) and the Reactor Building (RB) sump. Plant circuitry was verified to be wired as per the elementary drawing. This circuitry design was to prevent a hot short, due to a fire, from opening the valve.
However, the identified control logic error could allow a spurious opening to occur on DH-V-6A or DH-V-6B due to a fire. The FHAR credits these valves as being protected from spuriously opening due to a fire in AB-FZ-5 (Auxiliary Building 281' general area). If this protection is not provided, then spurious opening could result in draining the BWST inventory to the RB sump. This hot short condition would result in the depletion of the BWST inventory and loss of the High Pressure Injection (HPI) makeup capability, resulting in an unanalyzed condition that significantly degrades plant safety. This condition is reportable under 10 CFR 50.72(b)(3)(ii)(B), 'Any event or condition that results in the nuclear power plant being in an unanalyzed condition that significantly degrades plant safety.' A 60-day LER is also required under 10 CFR 50.73(a)(2)(ii)(B) for the same degraded condition. An hourly fire-watch has been established in the affected fire zone in the 281' elevation Auxiliary Building as an interim compensatory measure. Additionally, the control circuitry at the 1A and 1B ES MCCs will be modified to prevent the RB sump isolation valves DH-V-6A and DH-V-6B from spuriously opening due to a hot short. The licensee notified the NRC Resident Inspector. |
| Where | |
|---|---|
Three Mile Island  Pennsylvania (NRC Region 1) | |
| Reporting | |
| 10 CFR 50.72(b)(3)(ii)(B), Unanalyzed Condition | |
| Time - Person (Reporting Time:+0.57 h0.0238 days <br />0.00339 weeks <br />7.80786e-4 months <br />) | |
| Opened: | Stuart Brantley 18:04 Apr 25, 2006 |
| NRC Officer: | Pete Snyder |
| Last Updated: | Apr 25, 2006 |
| 42527 - NRC Website | |
Unit 1 | |
|---|---|
| Reactor critical | Critical |
| Scram | No |
| Before | Power Operation (100 %) |
| After | Power Operation (100 %) |
WEEKMONTHYEARENS 531062017-12-06T14:58:0006 December 2017 14:58:00
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