05000456/LER-2010-002

LER-2010-002, Limiting Condition for Operation Action Not Completed Within the Required Time

Docket Number
Event date:	08-16-2010
Report date:	10-15-2010
Reporting criterion:	10 CFR 50.73(a)(2)(i)(B), Prohibited by Technical Specifications
4562010002R00 - NRC Website

A. Plant Operating Conditions Before The Event:

Event Date:�August 16, 2010� Event Time: 0241 CDT Unit: 1� MODE: 3� Reactor Power: 0 percent Unit 1 Reactor Coolant System (RCS) [AB]: Temperature: 559 degrees F Pressure: 2230 psig

B. Description of Event:

On August 16, 2010, at 2019, the Unit 1 main turbine received an automatic trip on low condenser [AB] vacuum, resulting in an automatic reactor trip. This event is addressed under Unit 1 LER 2010-001-00.

At 0241, Unit 1 received a volume control tank (VCT) [CB] high level alarm (VCT level > 70%), causing a loss of the boron dilution protection system (BDPS) function. Entry into Technical Specification Limiting Condition for Operation (LCO) 3.3.9 Conditions A and C for BDPS were required, which includes in Condition C a one-hour Required Action to close non-borated water source isolation valves and a one hour Required Action to verify shutdown margin is within its limits. Due to post trip activities, the entry condition for LCO 3.3.9 was not recognized.

At 0341, while the shutdown margin had been verified, the one-hour Required Action of LCO 3.3.9 Condition C to verify non-borated water source isolation valves closed was not completed, which met the entry conditions for LCO 3.0.3.

At 0540, during a review of the main control board indications, the required entry into LCO 3.3.9 was identified. The unit operator was directed to lower the VCT level to clear the high level alarm and restore BDPS to operability.

At 0545, the VCT level was established below 70%, and the VCT alarms cleared. Late log entries were made to indicate entries into LCOs 3.3.9 and 3.0.3.

This event is reportable under 10 CFR 50.73(a)(2)(i)(B), any operation or condition which is prohibited by the plant's Technical Specifications.

C. Cause of Event

The root causes for this event were determined to be:

1. The Braidwood procedure for reactor trip response does not provide adequate guidance to alert operators to potential LCO 3.3.9 entry during plant transients.

• Emergency operating procedures do not reference Technical Specifications. Per the Westinghouse Owners Group writer's guide, Technical Specification entries are expected during plant transients. Only one-hour LCO action requirements are incorporated into the procedures as actual steps to be performed.

LCO 3.3.9 is a conditional action, the LCO is only entered after VCT level exceeds 70%, and is therefore not called out in the procedure. Other Operations procedures typically contain Technical Specification references.

2. The BDPS annunciators are not adequately human factored.

• Braidwood annunciators are not human factored to indicate a short-term or long-term LCO required action.

Windows are backlit red for first out, and three windows have a red border for pump trips to identify significant plant conditions requiring more operator attention. A different colored annunciator window or window border would alert the operator to a required LCO action requirement and draw attention to that annunciator when a large number of annunciator windows are lit during a transient. A human factored �NRC FORM 366A (9-2007) PRINTED ON RECYCLED PAPER annunciator window would alleviate some of the human performance reliance and more reliance on plant design factors to prevent events.

D. Safety Consequences:

There were no safety consequences impacting plant or public safety as a result of this event.

The significance of this event is minimal due to multiple methods of monitoring reactivity. The purpose of the BDPS is to provide a warning of a potential boron dilution event. LCO 3.3.9 is only applicable during reactor shutdown conditions (Modes 3, 4, and 5). An unexpected rise in VCT level could indicate non-borated water introduction to the RCS. The LCO actions require verification that a shutdown margin is within limits and all non-borated water sources with the ability to enter the RCS to be isolated within one-hour.

At the time of the Unit 1 reactor trip, the RCS boron concentration was 142 ppm. At this low concentration, several reactor operator borated the RCS with 100 gallons of 7 weight percent (w/o) boric acid to compensate for control rods inserting during a turbine runback below the minimum Technical Specification control rod height. After the reactor trip, all control rods fully inserted. Fission product poisons (xenon and samarium) were building up inside of the reactor core adding additional negative reactivity.

The intermediate range detectors [IG] monitored the neutron flux level until the source range instruments energized.

Once energized, the source range neutron detectors automatically turned on to monitor reactivity in the Unit 1 core.

reactivity conditions. If the Unit 1 operators heard a rise in source range count rate, the operators could immediately add a high concentration of boric acid to the Unit 1 RCS to raise the amount of negative reactivity in Unit 1 to maintain an adequate shutdown margin.

This event did not result in a safety system functional failure.

E. Corrective Actions:

The corrective action to prevent recurrence is to revise the reactor trip response procedure to check VCT level greater than 70% and initiate entry into LCO 3.3.9 and complete the appropriate actions to isolate all non-borated water sources into the RCS along with the shutdown margin calculation.

An additional corrective action is to evaluate human factors improvements for the plant annuniciator system.

F. Previous Occurrences:

There have been no previous, similar events identified at the Braidwood Station.

G. Component Failure Data:

Manufacturer Nomenclature Model MfQ. Part Number N/A N/A N/A N/A NRC FORM 366A (9-2007) PRINTED ON RECYCLED PAPER