05000362/LER-2009-002, Regarding Emergency Diesel Start Failure Results in Unusual Event
| ML100470689 | |
| Person / Time | |
|---|---|
| Site: | San Onofre  |
| Issue date: | 02/10/2010 |
| From: | Hochevar A Southern California Edison Co |
| To: | Document Control Desk, Office of Nuclear Reactor Regulation |
| References | |
| LER 09-002-00 | |
| Download: ML100470689 (5) | |
| Event date: | |
|---|---|
| Report date: | |
| Reporting criterion: | 10 CFR 50.73(a)(2)(v), Loss of Safety Function |
| 3622009002R00 - NRC Website | |
text
~d SOUTHERN CALIFORNIA 5
EDISON An EDISON INTERNATIONAL Company February 10, 2010 u.s. Nuclear Regulatory Commission Document Control Desk Washington, D.C. 20555-0001
Subject:
Docket No. 50-362 Licensee Event Report No. 2009-002 San Onofre Nuclear Generating Station, Unit 3
Dear Sir or Madam:
This submittal provides Licensee Event Report (LER) 2009-002 to report a loss of on-site emergency power sources as a loss of safety function under 10 CFR 50.73(a)(2)(v)(D), based on the results of the root cause analysis.
The event reports a failure of an Emergency Diesel Generator (EDG) to start during a period when the alternate train was considered inoperable.
The safety significance is considered low, as the alternate train was available for automatic start during the reported period. This event did not affect the health and safety of either plant personnel or the public.
If you require any additional information, please contact me.
Sincerely, t:2U~~
Albert R. Hochevar Station Manager Unit 3 LER No. 2009-002 cc:
E. E. Collins, NRC Regional Administrator, Region IV G. G. Warnick, NRC Senior Resident Inspector, San Onofre Units 2 &3 P.O. Box 128 San Clemente, CA 92672
Abstract
On 12/11/09 the Train B Emergency Diesel Generator (EDG) was declared inoperable when a technician grounded a wire, opening a fuse, and causing alarms in the control room. Technical Specification (TS) 3.8.1 Action B required a common cause evaluation or starting the alternate train EDG within 24 hours2.777778e-4 days <br />0.00667 hours <br />3.968254e-5 weeks <br />9.132e-6 months <br />.
On 12/12/09 at 00:25 PST, TS Condition 3.8.1.F was entered when the 24 hour2.777778e-4 days <br />0.00667 hours <br />3.968254e-5 weeks <br />9.132e-6 months <br /> period expired. At 01:05 PST Train A EDG 3G002 failed to start to comply with Condition B.3.2. Unit 3 entered a TS required shutdown from 96% power at 01:26 PST and declared an Unusual Event as required by the SONGS Emergency Plan. The condition exited at 05:11 and 40% power when the Train B EDG became operable.
The Train A EDG failure was caused by an open capacitor in a power supply. The resulting voltage spikes caused a speed switch malfunction, locking out the start signal to the air motors.
The Train B EDG had a pre-existing ground on one side of the circuit that caused the fuse to open when the other side was grounded, actuating the control room annunciators.
Corrective actions included troubleshooting, which located the pre-existing ground, and installing new power supplies with recently manufactured capacitors.
The safety significance was low as the Train B EDG was fully functional during the event for either manual or automatic start.
FORM 366A U.S. NUCLEAR REGULATORY COMMISSION (7-2001)
LICENSEE EVENT REPORT (LER)
TEXT CONTINUATION
- 6. LER NUMBER PAGE (3)
YEAR SEQUENTIAL NUMBER REV NO San Onofre Nuclear Generating Station (SONGS) Unit 3 05000-362 2009
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00 2 of 4
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Background===
On December 11, 2009 at 00:25 PST, Operators declared Unit 3 Train B Emergency Diesel Generator (EDG) 3G003 [DG] inoperable due to multiple control room alarms. The alarms occurred when a technician performing maintenance grounded a wire, causing the fuse to open and the annunciator relays to actuate. Technical Specification (TS) Limiting Condition for Operation (LCO) 3.8.1 B was entered for one EDG inoperable. The TS Required Actions include completing a common cause evaluation or testing the operable (opposite train) Train A EDG 3G002 within 24 hours2.777778e-4 days <br />0.00667 hours <br />3.968254e-5 weeks <br />9.132e-6 months <br />.
Event On December 12, 2009 [Event Date], at 00:25 PST, TS Condition 3.8.1.F was entered since the Required Actions were not completed within 24 hours2.777778e-4 days <br />0.00667 hours <br />3.968254e-5 weeks <br />9.132e-6 months <br />. At 01:05 PST Train A EDG 3G002 failed to start in compliance with the TS Required Action. As a result, Unit 3 entered a TS required shutdown. A shutdown of Unit 3 from 96% power was initiated on December 12, 2009 at 01:26 PST. Reactor power was reduced to 40% before Train B EDG 3G003 was declared operable at 05:11 PST. Unit 3 was returned to 95% power by 02:10 PST on December 13, 2009. Unit 2 was in the Cycle 16 refueling outage and was not affected by the event.
The initiation of a TS required shutdown of Unit 3 under TS 3.8.1 required declaration of an Unusual Event (UE) under the SONGS Emergency Plan. The report of the UE and a 10 CFR 50.72 (b)(3)(v) eight-hour report were made under NRC Operations Log #45564.
SCE is reporting this occurrence as a loss of safety function (on-site emergency power) under 10 CFR 50.73(a)(2)(v)(D).
Cause of the Event
Train A EDG 3G002 The cause of the Train A EDG 3G002 failure to start on December 12, was found to be a failed open capacitor [CAP] in one of the two power supplies for the local panel annunciator (Panalarm model 70B-PCD-100 DC-DC converter). The failed capacitor caused excessive ripple voltage and spiking on the speed switch power supply circuit, causing the speed switch to malfunction. The voltage spikes caused the speed switch to change state prematurely, preventing the engine start. There was no direct indication to the control room that the speed switch was blocking a start signal.
The annunciator power supplies [RJX] of Train A EDG 3G002 had previously shown signs of age related degradation in June 2009, producing noise in the speed switch and also preventing a start of Train A EDG 3G002. These power supplies are continually energized and the capacitors normally degrade slowly over time. The power supply noise was caused by capacitors which had failed open-circuit. Two replacement power supplies were obtained and installed in the Train A EDG Plant:
San Onofre Nuclear Generating Station (SONGS) Unit 3 Event Date:
December 12, 2009 Reactor Vendor:
Combustion Engineering Mode:
Mode 1 Power:
96 percent
FORM 366A U.S. NUCLEAR REGULATORY COMMISSION (7-2001)
LICENSEE EVENT REPORT (LER)
TEXT CONTINUATION
- 6. LER NUMBER PAGE (3)
YEAR SEQUENTIAL NUMBER REV NO San Onofre Nuclear Generating Station (SONGS) Unit 3 05000-362 2009
--002 --
00 3 of 4 3G002 control panel. As part of the pre-installation testing of the power supplies, the capacitor in the power supply that subsequently failed on December 12, 2009 had been removed, tested, and reinstalled. Following the June 2009 power supply replacement, corrective action was initiated to replace all of the annunciator power supplies with newer units, containing capacitors which were no more than two years old at the time of receipt.
After the December 12, 2009 event, the power supply from Train A EDG 3G002 was removed for failure analysis testing. The failed capacitor was found to be in contact with an adjacent power resistor. Testing determined the amount of heat generated by the contact with the power resistor was not sufficient to account for the premature failure of the capacitor, and suggests it may have been caused by a latent manufacturing defect. There was no prior evidence of the capacitor failure until Train A EDG 3G002 failed to start. The failed capacitor was manufactured by Illinois Capacitor, part number TTAM 220uf/160 VDC.
Train B EDG 3G003 The direct cause of the fuse opening in the Train B EDG 3G003 local panel, was poor work practices by a maintenance technician, coincident with a pre-existing ground condition.
On December 11, a technician was working to correct a failure of a lube oil low temperature sensing switch on Train B EDG 3G003. While performing the work, the technician dropped an energized wire, grounding the circuit, opening the fuse, and activating the alarm panel relays.
On May 3, 2009 the same fuse had opened in the Train B EDG 3G003 panel and the cause was not found at that time. After the December 11 event, it was concluded a pre-existing ground condition caused the alarm when the technician dropped the energized wire. Troubleshooting located a ground in one of the power supplies where the diode mounting screw contacted a wire.
Corrective Action
Trouble shooting located the pre-existing ground in the Train B EDG 3G003 local panel power supply.
The preventative maintenance program will be revised to include a check of the ground detection circuit in the local EDG panels.
All of the EDG annunciator power supplies on all the EDGs in both Units 2 and 3, have been replaced with more recently manufactured units as a result of the December 12, 2009 failure.
Voltage readings were taken on these power supplies at the time of installation to confirm acceptable performance.
Safety Significance
The event was of low safety significance. At the time the Train A EDG 3G002 failed to start, the Train B EDG 3G003 remained fully functional during the event and was not prevented from receiving an automatic start signal, or being manually started to provide on-site AC power.
FORM 366A U.S. NUCLEAR REGULATORY COMMISSION (7-2001)
LICENSEE EVENT REPORT (LER)
TEXT CONTINUATION
- 6. LER NUMBER PAGE (3)
YEAR SEQUENTIAL NUMBER REV NO San Onofre Nuclear Generating Station (SONGS) Unit 3 05000-362 2009
--002 --
00 4 of 4 Operating Experience SONGS LER 3-2007-001 reported an EDG failure caused by a defective soldered connection on the engine speed probe. The failure was not similar to the December 12, 2009 event, other than it was associated with a speed sensing circuit.
OE29575 - Diesel Trip due to Excessive Voltage Noise from Refurbished Power Supply to Speed Switch (San Onofre). This June 2009 event was discussed in the Cause section.
The annunciator power supplies for the EDGs have caused events at other plants, refer to the OE below:
LER 2009-005 Wolf Creek described a similar failure in the annunciator power supplies that occurred on October 22, 2009 and was reported on December 21, 2009, after the SONGS event had occurred.
OE27329, Power Supply Failure From Blown Fuse Affected Main Control Board EDG Annunciators (Summer)
OE18444, Emergency Diesel Generator Locked-Out due to Speed Switch Actuation caused by Electrical Noise from Failed Power Supply Capacitor (Turkey Point)
OE16045, Diesel Speed Switch Erratic Operation (Summer)
OE17548, Update to OE 16119 - DC Voltage Spikes (Summer)