Event Notification Report for October 12, 2005

U.S. Nuclear Regulatory Commission
Operations Center

Event Reports For
10/11/2005 - 10/12/2005



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Power Reactor Event Number: 42050
Facility: PALO VERDE
Region: 4 State: AZ
Unit: [ ] [2] [3]
RX Type: [1] CE,[2] CE,[3] CE
Notification Date: 10/11/2005
Notification Time: 22:32 [ET]
Event Date: 10/11/2005
Event Time: 16:02 [MST]
Last Update Date: 10/11/2005
Emergency Class: NON EMERGENCY
10 CFR Section:
50.72(b)(2)(i) - PLANT S/D REQD BY TS
50.72(b)(3)(ii)(B) - UNANALYZED CONDITION
50.72(b)(3)(v)(B) - POT RHR INOP
50.72(b)(3)(v)(D) - ACCIDENT MITIGATION
Person (Organization):

Unit SCRAM Code RX CRIT Initial PWR Initial RX Mode Current PWR Current RX Mode
2 N Y 100 Power Operation 0 Hot Standby
3 N Y 100 Power Operation 0 Hot Standby

Event Text


"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 October 11, 2005 Palo Verde Nuclear Generating Station (PVNGS) Units 2 and 3 at approximately 1602 and 1655 Mountain Standard Time (MST), respectively commenced reactor shutdowns required by Technical Specification 3.0.3.

"Engineering personnel were unable to demonstrate that the original design of the Emergency Core Cooling System (ECCS) could perform its safety function for its mission time under certain postulated accident scenarios. Specifically, the Refueling Water Tank (RWT) is designed with baffles to prevent a vortex from developing and air binding the Safety Injection pumps during a Loss of Coolant Accident (LOCA). On a LOCA, the High Pressure Safety Injection pumps take a suction from the RWT and inject borated water into the Reactor Coolant System (RCS). At 7.4 percent RWT level, the source of borated water by design automatically shifts from the RWT to the containment sump. However, for small break LOCA there may be insufficient containment pressure to ensure inventory is not continuing to be drawn from the RWT. This may allow the baffles in the bottom of the RWT to uncover. With the RWT baffles uncovered, a vortex may develop, leading to potential air binding of the Safety Injection pumps before the operator manually isolates the RWT.

"At approximately 1333 Mountain Standard Time, based on the inability to demonstrate that the ECCS can perform its safety function under certain accident scenarios, Palo Verde Units 2 and 3 entered Technical Specification 3.0.3.

"Engineering continues to evaluate this condition.

"There were no RPS/ESF actuations, and none were required.

"There were no structures, systems or components that were inoperable at the start of event that contributed to the event.

"This condition 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. This condition did not adversely affect the safe operation of the plant or health and safety of the public.

"The NRC Resident Inspector has been notified of this condition and this ENS notification."

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