ENS 45754
ENS Event | |
|---|---|
03:16 Mar 10, 2010 | |
| Title | Potential Loss of 1E Pumps Due to Degraded Voltage During Postulated Accidents |
| Event Description | While attempting to analyze the consequences of scenarios (loss of coolant accident (LOCA) and loss of offsite power (LOOP)) postulated during the Component Design Basis Inspection (CDBI), PG&E concluded both units were in an Unanalyzed Condition that significantly degrades plant safety, and therefore, reportable under 10 CFR 50.72(b)(3)(ii)(B).
The postulated scenario could result in permanently connected class 1E pump motors tripping over current relays due to sustained degraded voltage on the startup offsite power source. The scenario starts with a safety injection (SI) signal transferring 4160 volt vital buses from auxiliary power to the startup offsite power source. Following bus transfer, the startup source is postulated to degrade to a level above the first level under voltage relay (FLUR) setting of equal to or greater than 2583 volts and below the second level under voltage relay (SLUR) setting of equal to or greater than 3785 volts. Permanently connected class 1E pump motors would experience this degraded voltage for up to the SLUR time delay relay setting of equal to or less than 20 seconds. Prior to reaching the SLUR time delay relay setpoint and transferring loads to the onsite emergency diesel generators (EDGs), operating motors (e.g. auxiliary saltwater (ASW) pump and component cooling water (CCW) pumps) could trip on over current. Operators would be directed by procedures to re-start these motors on an operable power source (EDG). However, since this scenario has not been previously analyzed and could reasonably challenge containment pressure or peak clad temperature limits, it is considered unanalyzed. The postulated scenario had previously been considered non-credible, and therefore, had not been analyzed. PG&E considers this a nonconservative technical specification (TS) since the values in TS surveillance requirement (SR) 3.3.5.3 would not protect permanently connected class 1E loads from damage during degraded voltage conditions." The licensee has notified the NRC Resident Inspector. The condition was discovered by NRC inspectors while performing a CDBI inspection. |
| Where | |
|---|---|
Diablo Canyon  California (NRC Region 4) | |
| Reporting | |
| 10 CFR 50.72(b)(3)(ii)(B), Unanalyzed Condition | |
| LER: | 05000275/LER-2010-002 |
| Time - Person (Reporting Time:+-3.62 h-0.151 days <br />-0.0215 weeks <br />-0.00496 months <br />) | |
| Opened: | John Whetsler 23:39 Mar 9, 2010 |
| NRC Officer: | Charles Teal |
| Last Updated: | Mar 9, 2010 |
| 45754 - NRC Website | |
Unit 1 | |
|---|---|
| Reactor critical | Critical |
| Scram | No |
| Before | Power Operation (100 %) |
| After | Power Operation (100 %) |
Unit 2 | |
|---|---|
| Reactor critical | Critical |
| Scram | No |
| Before | Power Operation (100 %) |
| After | Power Operation (100 %) |
WEEKMONTHYEARENS 544172019-11-30T19:00:00030 November 2019 19:00:00
[Table view]10 CFR 50.72(b)(3)(v)(D), Loss of Safety Function - Mitigate the Consequences of an Accident, 10 CFR 50.72(b)(3)(ii)(B), Unanalyzed Condition Both Trains of Containment Spray Removed from Service ENS 522602016-09-21T03:47:00021 September 2016 03:47:00 10 CFR 50.72(b)(3)(ii)(B), Unanalyzed Condition Steam Line Pipe Whip Restraint Coupling Sleeve Found Not Engaged ENS 503342014-08-01T00:29:0001 August 2014 00:29:00 10 CFR 50.72(b)(3)(v)(A), Loss of Safety Function - Shutdown the Reactor, 10 CFR 50.72(b)(3)(v)(B), Loss of Safety Function - Remove Residual Heat, 10 CFR 50.72(b)(3)(ii)(B), Unanalyzed Condition, 10 CFR 50.72(b)(3)(v)(C), Loss of Safety Function - Release of Radioactive Material Unanalyzed Condition ENS 498792014-03-06T17:06:0006 March 2014 17:06:00 10 CFR 50.72(b)(3)(v)(A), Loss of Safety Function - Shutdown the Reactor, 10 CFR 50.72(b)(3)(ii)(B), Unanalyzed Condition Unanalyzed Condition Regarding Potential Tornado Missile Damage to Emergency Diesel Exhaust Plenum ENS 496632013-12-19T15:52:00019 December 2013 15:52:00 10 CFR 50.72(b)(3)(v)(D), Loss of Safety Function - Mitigate the Consequences of an Accident, 10 CFR 50.72(b)(3)(ii)(B), Unanalyzed Condition Two of Three Emergencey Diesel Generators Inoperable at the Same Time ENS 496342013-12-14T23:03:00014 December 2013 23:03:00 10 CFR 50.72(b)(3)(ii)(B), Unanalyzed Condition Unanalyzed Condition Affecting Unit 1 Emergency Diesel Generator ENS 491482013-06-26T04:58:00026 June 2013 04:58:00 10 CFR 50.72(b)(2)(xi), Notification to Government Agency or News Release, 10 CFR 50.72(b)(3)(v)(D), Loss of Safety Function - Mitigate the Consequences of an Accident, 10 CFR 50.72(b)(3)(ii)(B), Unanalyzed Condition, 10 CFR 50.72(b)(2)(i), Tech Spec Required Shutdown Plant Shutdown Required Due to Rhr System Socket Weld Leak ENS 491472013-06-24T23:15:00024 June 2013 23:15:00 10 CFR 50.72(b)(3)(ii)(B), Unanalyzed Condition Emergency Diesel Generators Unavailable for Auto-Start ENS 487262013-02-06T23:24:0006 February 2013 23:24:00 10 CFR 50.72(b)(3)(ii)(B), Unanalyzed Condition Unanalyzed Condition for Control Room Ventilation ENS 483952012-10-04T01:15:0004 October 2012 01:15:00 10 CFR 50.72(b)(3)(ii)(B), Unanalyzed Condition Unanalyzed Fire Protection Deficiencies ENS 482462012-08-29T00:00:00029 August 2012 00:00:00 10 CFR 50.72(b)(3)(v)(D), Loss of Safety Function - Mitigate the Consequences of an Accident, 10 CFR 50.72(b)(3)(ii)(B), Unanalyzed Condition Mitigating Actions Implemented for Inoperable Control Room Envelope ENS 475642011-12-31T10:00:00031 December 2011 10:00:00 10 CFR 50.72(b)(3)(ii)(B), Unanalyzed Condition Fire Barrier Rating of Vital Swtichgear Walls May Not Meet Standards ENS 474142011-11-03T22:50:0003 November 2011 22:50:00 10 CFR 50.72(b)(3)(ii)(B), Unanalyzed Condition Unanalyzed Condition - Control Room Ventilation Single Point Vulnerability ENS 472582011-09-13T00:45:00013 September 2011 00:45:00 10 CFR 50.72(b)(3)(ii)(B), Unanalyzed Condition Control Room Envelope Declared Inoperable ENS 472232011-08-30T00:24:00030 August 2011 00:24:00 10 CFR 50.72(b)(3)(ii)(B), Unanalyzed Condition Maintenance Inadvertently Renders Control Room Ventilation System Inoperable ENS 465312011-01-10T21:21:00010 January 2011 21:21:00 10 CFR 50.72(b)(3)(v)(D), Loss of Safety Function - Mitigate the Consequences of an Accident, 10 CFR 50.72(b)(3)(ii)(B), Unanalyzed Condition Both Trains of Auxiliary Building Ventilation Became Inoperable ENS 457542010-03-10T03:16:00010 March 2010 03:16:00 10 CFR 50.72(b)(3)(ii)(B), Unanalyzed Condition Potential Loss of 1E Pumps Due to Degraded Voltage During Postulated Accidents ENS 454612009-10-23T15:00:00023 October 2009 15:00:00 10 CFR 50.72(b)(3)(ii)(B), Unanalyzed Condition Post Loca Recirculation Valve Position Interlocks ENS 449272009-03-22T20:34:00022 March 2009 20:34:00 10 CFR 50.72(b)(3)(ii)(B), Unanalyzed Condition Unit 1 Steam Generator Found in an Unanalyzed Condition Related to Gaps on Seismic Washer Plates 2019-11-30T19:00:00 | |