05000266/LER-2013-002

LER-2013-002, Condition Prohibited by Technical Specifications

Point Beach Nuclear Plant Unit 1
Event date:	04-14-2013
Report date:	06-13-2013
Reporting criterion:	10 CFR 50.73(a)(2)(i)(B), Prohibited by Technical Specifications 10 CFR 50.73(a)(2)(v)(D), Loss of Safety Function - Mitigate the Consequences of an Accident
2662013002R00 - NRC Website

Description of the Event:

On April 13, 2013 at 23:39 PBNP Unit 1 entered Mode 4 during start up from a refueling outage. On April 14, 2013 at 0620, approximately 6 hours6.944444e-5 days <br />0.00167 hours <br />9.920635e-6 weeks <br />2.283e-6 months <br /> after entering into MODE 4, the Unit1 sodium hydroxide tank outlet valve (1SI-831A) valve was found to be closed. This valve isolated the flow path for both trains of spray additive equipment and resulted in not meeting LCO 3.6/, Spray Additive System. That mode change resulted in a violation of LCO 3.0.4.

The incorrect 1SI-831A valve position was discovered when the tagging senior reactor operator (SRO) was validating tags in the field for PBNP Unit 1. The SRO noticed the caution tag hanging on the 1SI-831A valve and discovered the tag was hung the day before to support an interim configuration for a containment spray test. Operators were sent to investigate the unexpected condition and then immediately placed the valve in its proper position to meet the Technical Specification requirements.

The spray additive system consists of one spray additive tank that supports both trains of spray additive equipment, resulting in both trains being inoperable. Therefore this event is being reported as a safety system functional failure.

Cause of the Event:

The cold shutdown to hot standby procedure is for maneuvering the plant from Mode 5 to Mode 4. It is also the procedure that positions 1SI-831A valve to the correct position for the mode change. The procedure that performs surveillance of the containment spray pumps and valves during cold shutdown requires the valve to be tagged shut to perform the surveillance.

Normally the surveillance procedure is completed prior to Mode 5 to Mode 4 procedure. However, during the outage the steps in the Mode change procedure that aligns 1SI-831A valve were completed prior to the surveillance procedure. The change in the sequence of the procedures did not ensure that the 1SI-831A valve was in its proper position prior to entering into Mode 4. The root cause was identified to be inadequate procedural ties within procedures to ensure that the 1SI-831A valve is placed in the locked open position prior to changing from Mode 5 to Mode 4.

Analysis of the Event

The spray additive system, supported by the containment spray system, assists in reducing the iodine fission product inventory in the containment atmosphere following a design basis accident (DBA). Radioiodine in its various forms is the fission product of primary concern in the evaluation of a DBA. It is absorbed by the spray from the containment atmosphere. To enhance the iodine absorption capacity of the spray, the spray solution is adjusted to an alkaline pH that promotes iodine hydrolysis, in which iodine is converted to nonvolatile forms. The NaOH added to the spray also ensure a pH value in the acceptable range of 7.0 to 10.5. The minimum pH in the containment sump needed to keep iodine in the iodate form is 7.0. The maximum pH is based on equipment qualification considerations to minimize the occurrence of chloride and caustic stress corrosion on mechanical systems and components and is set to 10.5. The spray additive system consists of one spray additive tank that is shared by the two trains of spray additive equipment. Each train of equipment provides a flow path from the spray additive tank to a containment spray pump and consists of an educator for each containment spray pump, valves, instrumentation, and connecting piping recirculation phase of spray operation and also minimizes the occurrence of chloride induced stress corrosion cracking of the stainless steel recirculation piping.

During Modes 1, 2, 3, and 4, valve 1S1-831A is locked open. While shutdown in Modes 5 and 6, the valve is administratively required to be tagged shut to prevent inadvertent sodium hydroxide contamination in RCS/RWST during the outage.

Safety Analysis

The 1S1-831A valve being in the closed position had low risk with respect to nuclear and radiological safety.

Any design basis accident that could have occurred during the period that the 1S1-831A was closed would not have exceeded design containment pressure or temperature limits because of the relatively low reactor coolant system temperature and pressure. The function of 1S1-831A is to deliver sodium hydroxide into the containment spray flowpath to aid in reducing the iodine fission product inventory in the containment atmosphere following a DBA. PBNP Unit 1 reactor coolant samples taken on April 2, 2013, and April 10, 2013 indicated less than detectable iodine concentrations. Additionally, the iodine inventory in the reactor core was much lower than the inventory assumed in the accident analyses because the reactor had been shut down for approximately 26 days and one third of the core was new fuel.

Corrective Actions

Procedures were revised to add procedural ties to ensure that the 1S1-831A valve is placed in the locked open position prior to changing from Mode 5 to Mode 4.

Similar Events There were no similar events identified within the last five years.