05000389/LER-2011-001

LER-2011-001, 1 OF 5

St. Lucie Unit 2
Event date:	12-02-2010
Report date:	01-29-2011
Reporting criterion:	10 CFR 50.73(a)(2)(i)(B), Prohibited by Technical Specifications
3892011001R00 - NRC Website

Description of the Event

On December 2, 2010 at 2320 during the performance of Plant Operator daily rounds, it was discovered that the Unit 2 CCW [EIIS:HX] train A and B headers were cross- connected though control room air conditioning [EIIS:ACU] unit HVA/ACC-3C via CCW cooling flow being supplied to the cooler from the A Header and returning to the B Header. The Control Room and Shift Manager were immediately notified and the misalignment corrected. Cross-connecting CCW trains by opening the supply or return valves [EIIS:FCV] to both trains violates the CCW system design criteria for independent trains and the independence requirement of TS 3.7.3 resulting in a condition prohibited by Technical Specifications.

Cause

On November 8, 2010, an equipment clearance order (ECO) was issued to establish conditions necessary to remove and to replace a vent valve on CCW supply header A to the control room HVA/ACC-3C. At that time CCW to ACC-3C was lined up to its alternate source, Train B. The ECO closed both Train A and Train B CCW supply valves (V14510 and V14506) and the combined discharger header isolation valve 5H14265, which isolates both Train A and Train B return lines. During restoration from the ECO on November 10, 2010, CCW supply valves were inadvertently returned to their default position from Train A. However the return valves from Train A and B were not part of the ECO and remained aligned to alternate Train B. This resulted in cross- connecting Train A and B of CCW.

Operations Department Policy OPS-531, "Configuration Control Methods," allows use of a procedure for configuration control if the procedure has steps for restoration; however 2-NOP-52.02 does not have restoration steps. The Root Cause of this event is the Operations Procedure 2-NOP-52.02, "Alignment of 2AB Buses and Components", had been inappropriately used as the sole configuration control method for CCW valves to Control Room Air Conditioning Unit HVA/ACC-3C when CCW to ACC-3C was previously aligned to alternate Train B on May 18, 2010. This procedure was closed out after the re-alignment and a record of the change using an active plant database to track the change in CCW valve positions to the alternate lineup was not made. As a result, the current lineup was not understood when the ECO was subsequently released on November 10, 2010.

The Root Cause of this event is that Operations Procedure 2-NOP-52.02, "Alignment of 2AB Buses and Components", was inappropriately used as the sole configuration control method for CCW valves to Control Room Air Conditioning Unit HVA/ACC-3C. An active plant database should have been used to track the change in CCW valve positions to the alternate lineup. An active plant database should have been used to track the change in CCW valve positions to the alternate lineup.

A contributing cause is inadequate instructions for verifying the position of CCW valves to Control Room Air Conditioning Unit HVA/ACC-3C in Administrative Procedure 2-0010123, "Administrative Control of Valves, Locks and Switches".

Analysis of the Event

The inadvertent cross-tie of A and B CCW headers to the control room HVA/ACC-3C found during Plant Operator daily rounds violated the independence requirement of the TS 3.7.3 for two independent CCW headers, which is a condition prohibited by Technical Specifications and reportable under 10CFR50.73(a)(2)(i)(B), and 10CFR50.73 (a) (2) (vii), a common cause of inoperability of independent trains.

The CCW system is a closed loop cooling water system configured with two redundant essential supply header systems (designated 'A' and 'B') each with a pump and heat exchanger and the capability to supply the minimum safety requirements during plant shutdown or design basis accident conditions. The non-essential supply header which is connected to both essential headers during normal operation is automatically isolated from the essential headers by valve closure on a safety injection actuation signal (SIAS). Each essential header alone has the heat removal capacity to safely shutdown the reactor or to mitigate the effects of a design basis accident and is separated from the other essential and non-essential header during accident conditions.

During normal operation, the CCW system provides cooling to components important to safety such as reactor coolant pumps, containment fan coolers, and spent fuel pool heat exchangers. During accident conditions, the CCW system provides cooling for safety related components associated with reactor decay heat removal, containment cooling, and control room habitability.

The three control room air conditioning units are supplied by an essential CCW header. Each essential CCW header is capable of supplying all three A/C units.

In order to maintain train separation, essential header 'A' is lined up to supply A/C Unit 3A, which is powered by Train A electrical power, and essential header 'B' is lined up to supply A/C Unit 3B, which is powered by Train B electrical power. A/C Unit 3C is a swing component that can have CCW and electrical power supplied from either Train A or B. In order to maintain train separation, electrical power and CCW must be aligned to the same train. Cross- connecting CCW trains by opening the supply or return valves to both trains violates the CCW system design criteria for independent trains. All valves associated with CCW to the A/C units are manually operated. No indications of CCW alignment to the A/C units are provided in the Control Room or other location.

The normal CCW supply arrangement for A/C 3C is Train A supply valves open, Train B return valves closed. In this event, an ECO was issued to establish the conditions to cut out and replace a vent valve for the CCW supply header A to control room HVA/ACC-3C. This valve was found to have a slow seat leak in July 2002 when upstream isolation valve V14510 was open. The ECO shut CCW supply valves V14510 and V14506 and combined discharger header isolation valve SH14265. However, during restoration of the ECO on November 10, 2010, CCW supply valves were returned to their default position, Train B to Train A. The Train A and B return valves were not part of the ECO and remained aligned to alternate Train B resulting in cross-tying the two trains.

Analysis of Safety. Significance The inadvertent cross-tie of A and B CCW headers to the control room HVA/ACC-3C found during Plant Operator daily rounds violated the independence requirement of the TS 3.7.3 for two independent CCW headers whiCh is a condition prohibited by Technical Specifications.

An Engineering assessment was performed too determine if any additional risk of core damage exists as a result of Cross connecting the essential trains of CCW in this event. The risk was evaluated for both normal operation, from a seismic event causing total loss of CCW due to a breakfin the cross-tied non-essential header, and during accident conditions from two concurrent initiating events where a postulated LOCA occurs in seismic qualified piping at the same time a seismic event occurs which causes a break in the cross connected non-essential header piping. In both cases the . calculated value for incremental core damage probability (ICCDP) was determined to be non-risk significant and below the threshold established in RG-1.174 for risk significance.

Corrective Actions

The corrective actions and supporting actions listed below are entered into the site corrective action program. Any changes to the actions will be managed under the commitment management change program.

Immediate corrective actions taken:

1. The checklist for Operations Policy 520, check sheet 4, "ECO Release Review.

and Authorization Check List" was modified to ensure the release is consistent with AB buses alignment.(Complete) 2. Station Clock Reset brief was communicated site wide.(Complete) The following actions will be tracked within the St. Lucie Corrective Action Program:

1. Revise Operations Procedure 2-NOP-52.02 to ensure CCW and ICW valves (including.

V14510, V14518, V14514, V14506, MV-14-1, MV-14-2, MV-14-3, MV-14-4, SB21165 and SB21211) have positions tracked in electronic shift operations management system (eSOMS) when transferring 2AB buses and components from A side to B side and from B

• side to A side.

2. Revise AP-1[2]-0010123 to remove the default positions of CCW valves V14510, V14518, V14514, V14506 and the other valves marked with an asterisk (*) that have the note similar to, "The position of these valves may change due to plant conditions.

3. Revise the following procedures to 4ighlight the required configuration control method for the identified swing components:

• 1[2]-NOP-14.02 o V14510 (Unit 2 only), V114518 (Unit 2 only), V14514 (Unit 2 only) o V14506 (Unit 2 only), M4-14-1, MV-14-2, MV-14-3, MV-14-4

• 1[2]-NOP-21.01A, B, C, o 5H21165, SH21211

• 1-NOP-52.02, o MV-14-1, MV-14-2, MV-14-3, MV-14-4, SH21165, o SH21211 4. Perform a "training needs analysis" to determine what additional SRO and SNPO training is needed to address AB bus swing components and configuration control related to this event.

Similar Events A review of external operating experience (OE) was completed. Several examples were identified including significant operating event report (SOER), SOER 98-1, "Safety System Status Control" Corrective actions taken or planned for this SOER are currently in our corrective action program (CAP) and will be reviewed to ensure they are effectively implemented and will prevent recurrence of similar problems.

A review of the St. Lucie CAP data base for similar events found there were no significant PSL events during the past 3 years where an equipment clearance was released as prescribed but in conflict with the existing system lineup which could have resulted in system inoperability.