2009 Winter NHUG MeetingJanuary 16, 2009

Chris BoozerV.C. Summer Station – SCE&G

• Background/Significance

• Design Function/Configuration

• Testing

• Inspection Findings/Challenges

• Restoration

• Causes/Preventative measures

• Conclusion/Questions

• During Cycle 17 (July 2007), the Control Room received an alarm on ‘A’ train Reactor Building Cooling Unit (RBCU) Condensate Flow.

• The flow switches provide an alarm on RBCU condensate flow increase of 0.5 gpm indicating an RCS primary or secondary leak inside containment. They are tested/calibrated every 18 months (every refueling outage).

• The RBCUs provide cooling and filtration of Reactor Building air during normal and post accident operation.

• The NRC Resident Inspector questioned the adequacy of the testing and maintenance of the RBCU Condensate Flow Detection Switches (IFS01900A/B).

• Attempts to calibrate the switch (at power) were unsuccessful. IFS01900A was declared inoperable.

• Video inspection revealed a debris field in the p-trap of the drain line connecting to IFS01900A.

• IFS01900B was assumed to be in a similar condition and both trains of condensate flow detection were declared inoperable.

• A plan was developed to inspect, clean and retest IFS01900A/B during Refuel 17 (RF-17).

• Inspections during RF-17 found significant amounts of debris collected in the drain line p-trap of both trains. This debris in effect blocked the flow path from the condensate drain line to the flow switches, thus defeating their design function of providing high condensate flow alarm to warn of RCS leakage.

• Maintenance Rule Function, “Provide RBCU drain flow high alarms indicative of primary or secondary leakage inside containment.” (Instrument Loops: IFS01900A, IFS01900B)

• Tech Spec Requirements, RBCU Condensate Flow Detection is one of three RCS leakage detection systems required to be operable during Operating Modes 1,2,3 and 4.

Location of the drain p-trap and Leak Detection

Switch

XAA-2A XAA-1AELEV. RB-514

ELEV. RB -463

IFS01900A-TV1-LD

IFS01900A-TV2-LD

IFS01900A-LD

TEST CONNECTION

DRAIN CLEANOUT NOT ADJACENT AT IFS1900B

LOCATION

FLOW FROM RBCU’S

• Original Method • Tested on an 18 month frequency (every refueling outage).• Apply 0.5 gpm water flow at the test connection.

•Problem - This method bypassed flow to the p-trap

Water flow applied here.

• New Method •Tested on an 18 month frequency (every refueling outage).• Isolate the 1” tap line by IFS01900A/B-TV1. • Apply 0.5 gal. water in the p-trap.• Open the isolation valve and observe switch response.

IFA01900A/B-TV1

IFS01900A• Initially inspected/cleaned online through the clean-out port.• Borescope inspection of the p-trap area revealed a debris field covering the 1” tap line to IFS01900A.•Initial cleaning efforts (plumbing snake, water flush, etc.) were believed to be successful. They were not! Debris still remained in the p-trap

IFS01900B• Inspected by removal of the upper elbow of the p-trap (no adjacent cleanout).• Debris field found to be much worse than expected. Also found other debris (tape, zip ties, paper shreds)• Removal of the p-trap elbow facilitated cleaning.• The ‘A’ train was eventually cleaned by the same method.

BEFORE AFTER

• Drain lines had not been cleaned/inspected in 30+ years. • Original test method bypassed the p-trap. Did not identify blockage in the drain line. • Mechanics wash debris from coil cleaning down the 4 drain taps in each plenum.

• Mechanics now use FME covers and filtration media in the drain entrances to the plenum during coil cleaning. • Coil cleaning is followed by 200 gallon water flush (50 gal./drain). • Testing procedures revised to apply water to the p-trap for switch testing/calibration.

• Evaluating alternative designs to facilitate inspection and cleaning that do not involve cutting the drain pipe.

• Adequacy of testing and maintenance of RBCU condensate flow detections switches IFS01900A/B was challenged by the NRC.

• The original test method only tested the switch function and not the system operation as a whole (RBCU drain + switch).

• Debris field blocked the 1” tap line to the flow detection switch rendering it inoperable. Original testing method was not adequate to identify this condition. • Drain lines were cleaned and new testing procedure was developed that utilized the actual flow path through the p-trap.

• Debris in the RBCU condensate drain lines was the result of years of build-up and inadequate cleaning.

• Drain lines were cleaned during the outage and switches were restored operable.

Chris BoozerPhone – (803) 345-4163Email – cdboozer@scana.com

For additional information on the switches, Jack Bonnette - Leak Detection System EngineerPhone – (803) 345-4023Email - JACK.BONNETTE@scana.com