ENS 45748
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ENS Event | |
|---|---|
18:24 Mar 7, 2010 | |
| Title | Notification Of Unusual Event Due To Electrical Fault Causing Damage To Equipment |
| Event Description | The following event description is based on information currently available. If through subsequent reviews of this event, additional information is identified that is pertinent to this event or alters the information being provided at this time, a follow-up notification will be made via the ENS or under the reporting requirements of 10CFR50.73.
On March 7, 2010, at approximately 1124 MST Palo Verde Unit 1 declared a Notification of Unusual Event (NOUE) due to an electrical fault (explosion) experienced on the 13.8 KV Non-Class busses being supplied from the Unit Auxiliary Transformer. The fault resulted in a minor explosion and damage to the bus work leading from NAN S03 to NAN S01. The fault resulted in the loss of the NAN S01, which caused a reactor trip due to the loss of 2 of 4 reactor coolant pumps. There was no fire detected after the initial event. The reactor trip (RPS actuation at 1117 MST) was from 100% rated thermal power due to low departure from nucleate boiling (DNBR) trips on all four channels of the core protection calculators (CPCs). The unit was at normal temperature and pressure prior to the trip. All of the control rods fully inserted into the core. Four of eight steam bypass control valves quick opened, per design, directing steam flow to the condenser. No main steam or primary relief valves lifted and none were required. There was no loss of heat removal capability or loss of safety functions associated with the event. ESF Electrical buses remain energized from off-site power. The Shift Manager determined this event was an uncomplicated reactor trip. No significant LCOs have been entered as a result of this event. No major equipment was inoperable prior to the event nor contributed to the event. Unit 1 is stable at normal operating temperature and pressure in Mode 3. No ESF actuations [other than RPS] occurred and none were required. The event did not result in any challenges to the fission product barrier or result in any releases of radioactive materials. There were no adverse safety consequences or implications as a result of this event. The event did not adversely affect the safe operation of the plant or health and safety of the public. Decay heat is being removed via the steam bypass valves to the condenser. The plant is in its normal shutdown electrical lineup with the exception of powering the NAN S01 bus. Unit 2 and Unit 3 were not affected by the transient on Unit 1. The licensee has notified the NRC Resident Inspector.
Palo Verde Unit 1 has terminated the NOUE at 1516 MST. The termination criteria was that the plant is stable, the area around the fault has been inspected and no other conditions exist that would prevent termination of the event. Decay heat path has been changed from steam dumps to condenser to atmospheric dumps due to difficulty in maintaining temperature. There is no known primary to secondary leakage. The licensee has notified the NRC Resident Inspector. Notified R4DO (Cain), NRR EO (Holian), IRD (Gott), DHS (Roper) and FEMA (LaForte). |
| Where | |
|---|---|
Palo Verde  Arizona (NRC Region 4) | |
| Reporting | |
| Emergency class: | Unusual Event |
| 10 CFR 50.72(a) (1) (i), Emergency Class Declaration 10 CFR 50.72(b)(2)(iv)(B), RPS Actuation | |
| LER: | 05000528/LER-2010-001 |
| Time - Person (Reporting Time:+-4.02 h-0.168 days <br />-0.0239 weeks <br />-0.00551 months <br />) | |
| Opened: | Alfred Erdelji 14:23 Mar 7, 2010 |
| NRC Officer: | Howie Crouch |
| Last Updated: | Mar 7, 2010 |
| 45748 - NRC Website
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Unit 1 | |
|---|---|
| Reactor critical | Critical |
| Scram | A/R |
| Before | Power Operation (100 %) |
| After | Hot Standby (0 %) |
Palo Verde with 10 CFR 50.72(b)(2)(iv)(B), RPS System Actuation, 10 CFR 50.72(a)(1)(i), Emergency Class Declaration | |
WEEKMONTHYEARENS 570662024-04-04T23:18:0004 April 2024 23:18:00
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