05000362/LER-2006-005

LER-2006-005, Dilution error results in exceeding 20 percent power prior to completion of required surveillances

Docket Number
Event date:	12-11-2006
Report date:	03-07-2007
Reporting criterion:	10 CFR 50.73(a)(2)(i)(B), Prohibited by Technical Specifications
3622006005R01 - NRC Website

Description of Event:

On December 11, 2006, SONGS plant operators were in the process of starting up Unit 3 following a refueling outage. To support turbine testing, at approximately 1954 PST, operators began raising power from 15 +/- 0.5 percent to 18 +/- 0.5 percent using boron dilution. The two operators involved erred when determining the amount of demineralized water necessary. Consequently, at approximately 2017 PST, power briefly exceeded 20 percent, reaching 20.5 percent at about 2022 PST. Operations had not yet completed all the required surveillance testing for exceeding 20 percent power. Technical specification surveillance requirement (TSSR) 3.0.4 requires that all surveillance requirements be complete before entering a mode or other specified condition for which the LCO is applicable. Therefore, SCE is reporting this event in accordance with 10 CFR 50.73(a)(2)(i)(B).

SCE Operators returned power below 20 percent at approximately 2024 PST and subsequently completed the required surveillances. See the Additional Information section below for a list of the applicable surveillance requirements.

Cause of Event

The event occurred because plant operators estimated boron dilution based upon an extension of the dilutions for xenon control already in progress. Operators did not follow procedures which require that the amount of reactivity insertion to be obtained from a controlled source during planned load changes. Additionally, the Shift Manager and the Control Room Supervisor did not ensure that a reactivity pre-job brief was conducted prior to adding the dilution water for the power increase, which likely would have prevented the error. A contributing factor included using rolling average power (a lagging indicator) to monitor the power increase instead of the instantaneous power.

SCE's final cause evaluation will be contained in Action Report 061200640-6.

Corrective Actions

SCE has completed the following interim corrective actions:

1. The Operations Manager and the Manager of Plant Operations have conducted a Reactivity Control Focus Stand down with each crew.

2. SCE is adding more formality to the process for all reactor power changes greater than 1 percent.

3. SCE has taken appropriate disciplinary action for the individuals involved in this occurrence.

SCE may identify and implement additional corrective actions.

Safety Significance

The missed surveillances were related to the operability of the Core Operating Limits Supervisory System (COLSS). The COLSS system was confirmed operable when the missed surveillances were completed. As a result there was little or no safety consequence to this occurrence.

Additional Information

The unplanned power increase occurred prior to completing S023-3-3.41, "COLSS Operability and Computer Surveillances". This procedure includes the surveillances for TSSR 3.2.1.3, 3.2.3.2, 3.2.3.3 and 3.2.4.3, which had not been completed at the time of the occurrence. TSSR 3.2.3.1 and 3.2.5.1 are contingent surveillances required to be performed within 12 hours1.388889e-4 days <br />0.00333 hours <br />1.984127e-5 weeks <br />4.566e-6 months <br /> when COLSS is out of service. Since COLSS was not yet Operable, these would also have applied. After returning power to 18 +1- 0.5 percent, the required surveillances were completed satisfactorily.

Channel "A" results in Technical Specification Violations" reported a miscommunication between maintenance personnel that resulted in one channel placed in service for startup with the required surveillances incomplete. The cause of that event was miscommunication between personnel. The corrective actions for that event (training and proceduralizing the use of formal communication) would not have prevented this cause of this occurrence (failure to follow procedures and lack of a pre-job brief).