05000530/LER-2006-003
| Docket Numbersequential Revmonth Day Year Year Month Day Yearnumber No. None 05000 | |
| Event date: | 04-02-2006 |
|---|---|
| Report date: | 05-26-2006 |
| Reporting criterion: | 10 CFR 50.73(a)(2)(iv)(A), System Actuation 10 CFR 50.73(a)(2)(v), Loss of Safety Function |
| 5302006003R00 - NRC Website | |
All times in this report are approximate and Mountain Standard Time (MST) unless otherwise noted.
1. REPORTING REQUIREMENT(S):
This LER (50-530/2006-003-00) is being submitted pursuant to 10 CFR 50.73(a)(2)(iv)(A), to report an actuation of the B train emergency diesel generator in response to a valid loss of power event to one class bus (3EPBBSO4).
2. DESCRIPTION OF STRUCTURE(S), SYSTEM(S) AND COMPONENT(S):
Class lE AC System Safety-related equipment is divided into two load groups. Either one of the associated load groups is capable of providing power for safely shutting down the unit. Each ac load group consists of one 4.16 kV bus (EIIS: EB), three 480V load centers (EIIS: ED), four 480V motor control centers (MCCs)(EIIS: ED), and two non-Class lE MCCs (EIIS:
ED). The preferred power source for each load group is off-site ac power (EIIS: EK).
Standby Power Supply [EIIS Code: EK] The standby power supply for each safety-related load group consists of one emergency diesel generator (EDG)(EIIS: EK), complete with its accessories and fuel storage and transfer systems. The standby power supply functions as a source of alternating current (ac) power for safe plant shutdown in the event of loss of preferred power and for post-accident operation of engineered safety feature (ESF) loads.
3. INITIAL PLANT CONDITIONS:
Unit 3 was in Mode 5, Cold Shutdown, for a refueling outage at the time of the event.
Shutdown Cooling (SDC)(EIIS: BP) train A was in-service with an inlet temperature of approximately 135 F and outlet temperature of approximately 110 F. Off site power (preferred) was providing power to the A train components. Engineering and maintenance personnel were performing integrated safeguards (ISG) testing on the B train at the time of the event with the B train EDG providing power to the B train components.
4.�EVENT DESCRIPTION:
On April 2, 2006 at approximately 20:54 Mountain Standard Time, Unit 3 experienced a valid Loss of Power (LOP) actuation on the Train "B" 4.16 kV safety bus. The event occurred during performance of surveillance test 73ST-9DG02 (Class lE Diesel Generator and Integrated Safeguards Test Train B). EDG "B" had been started in Emergency Mode per the surveillance test by opening the normal supply breaker to the associated B train 4.16 kV bus and initiating simulated Safety Injection Actuation System (SIAS) and Containment Isolation Actuation System (CIAS) signals. A subsequent portion of the surveillance test was in progress which demonstrates that the EDG "test mode" trips are bypassed with the EDG operating in Emergency Mode. The step being performed was intended to simulate an overcurrent (test mode) trip by installing a jumper at the overcurrent relay. However, the jumper was inadvertently installed at the differential current relay, which generated an "Emergency Mode" trip of EDG "B". This resulted in the deenergization of the 4.16 KV bus. The operations staff (utility-licensed) entered Abnormal Operating Procedure (AOP) 40A0-9ZZ12 (Degraded Electrical) and reset EDG "B". Upon reset at 21:26, EDG "B" automatically started in response to a valid Loss of Power (LOP) signal from the deenergized 4.16 KV bus. The EDG "B" output breaker automatically closed to restore power to the Train "B" 4.16 KV and equipment was automatically sequenced onto the 4.16 kV bus. Due to the loss of power on the Train "B" 4.16 KV bus, the Train "B" Control Room Essential Filtration System (CREFS) and Control Room Emergency Air Temperature Control System (CREATCS) were rendered inoperable and LCOs 3.7.11 Condition 'A' and 3.7.12 Condition 'A' were entered. Operability of Train "B" CREFS and CREATCS was restored when the Train "B" 4.16 KV bus was reenergized and these LCO Conditions were exited.
5. ASSESSMENT OF SAFETY CONSEQUENCES:
There was no safety consequence related to this event. Offsite power remained available to the Train "A" 4.16 KV bus and EDG "A" remained operable throughout the event. SDC was unaffected since it was powered by the Train "A" safety train, which was supplied by offsite power. The Required Action and Completion Time for LCOs 3.7.11 and 3.7.12 require restoration of the inoperable train within 7 days and 30 days, respectively. Power to the B train 4.16 KV bus and the LCOs were exited within approximately 30 minutes.
No other ESF actuations occurred and none were required. There were no structures, systems, or components that were inoperable at the time of discovery that contributed to this condition. The event did not result in the release of radioactivity to the environment and did not adversely affect ttr safe operation of the plant or health and safety of the public.
The condition did not prevent the fulfillment of any safety function and did not result in a safety system functional failure as defined by 10CFR50.73(a)(2)(v). Note that safety functions are: reactor shutdown, heat removal, control of the release of radioactive material, and mitigation of the consequences of an accident.
6. CAUSE OF THE EVENT:
The investigation of the event has not been completed however, preliminary results indicate that human error on the part of engineering (utility non-licensed) and maintenance (utility non-licensed) personnel caused the event. The maintenance personnel were not properly briefed by the test engineer of their role during the evolution; the electricians did not see the procedural steps to be performed but were taking verbal direction from the engineer; there was inadequate communication from the engineer to the maintenance personnel as to which relay was to be jumpered during the ISG testing. A contributing cause of the event was the use of only one engineer to conduct the test. Previous performances of the test procedure required two engineers.
The engineer involved in the event indicated that there was some self-imposed time pressure to complete the testing. In addition, the relays involved in this event are located in the EDG control cabinet with limited space for personnel and the EDG B control room was noisy because the EDG was running and EDG alarm panel horn was actuated making communication difficult.
A supplement to this LER will be submitted if the completed investigation identifies information that significantly changes the course or consequences of the event presented in this LER.
7.�CORRECTIVE ACTIONS:
Operations personnel (utility-licensed) entered the Degraded Electrical AOP. The EDG was reset and automatically energized the bus.
Specific guidance was added to the ISG Test Log to require an engineering peer check of direction provided by the Lead Test Engineer to others. In addition, a formal prejob briefing, specifically for the engineering staff, that addresses the scope of testing, roles and responsibilities of personnel involved, critical parameters, standards, and lessons learned for performing the integrated safeguards test was implemented.
If the completed investigation results in substantial changes to the corrective actions a supplement to this LER will be submitted.
8.�PREVIOUS SIMILAR EVENTS:
There has been no similar event reported by Arizona Public Service to the NRC within the last three years in which personnel operated an incorrect component resulting in a reportable event.