FSRUG Presentation – January 2014

Tennessee Valley Authority Browns Ferry Nuclear Plant

Unit 3 Reactor Feed Water (FW) Clean Up Piping Break

TVA – BFN – FW Long Cycle Piping

On February 11, 2013, Unit 3 was taken off-line for Component Cooling Water (CCW)

tunnel repairs. During shut-down a gradual loss of condenser vacuum prompted a

Manual SCRAM of the reactor. The investigation discovered the failed temporary patch

in the FW Long Cycle (FWLC) piping.

The FWLC piping hole was caused by flashing and impingement due to leaking FWLC

solid-disk gate valves (FCV-3-71/-72/-73). There is a history of leaking valves starting in

1998. Units 2 and 3 had Furmanite boxes on piping downstream of the FCV-3-073 valve

installed during the operating cycle. Maintenance history shows repeated repair of the

valves every outage between approximately 1993 to 2005. Work Orders were written to

replace the valves in 2005 with improved valves; however, the WO was cancelled in

2010. Due to the temperature and pressure conditions of these valves rather than solid-

disk gate valves a better application may have been flex-disc or a double-disc gate valve.

TVA – BFN – FW Long Cycle Piping24E – DSX Thru Wall Leak

TVA – BFN – FW Long Cycle PipingThru Wall Leak Downstream of 003-0073 Valve

Furmanite Box

Stanchion / Pipe SupportDamage

TVA – BFN – FW Long Cycle PipingThru Wall Leak Downstream of 003-0073 Valve

Furmanite Box

Stanchion / Pipe SupportDamage

TVA – BFN – FW Long Cycle Piping

TVA – BFN – FW Long Cycle Piping

The FWLC piping is used to clean up FW for all three trains of Feedwater Heaters (FWHs)

after refueling outages to primarily scrub clean the Secondary side of the plant (Balance

of Plant ) and secondarily to keep debris out of the reactor core. It is a bypass from the

feedwater piping to the main condenser.

The piping is Low Carbon-steel 8” - Schedule 40, 0.322” nominal wall thickness. The

piping may see pressures as high as 350 psi with 6000 - 8000 gpm flow for short periods

of time. Flow velocities at or above 16 fps start to deteriorate piping through erosion. A

flow rate of 6000 - 8000 gpm equates to velocities of 35 - 45 fps. The elbow with the

hole was worn smooth. There were no indications of FAC wear or impingement at the

hole.

TVA – BFN – FW Long Cycle Piping

During the CCW tunnel repair shutdown, the immediate action taken was to replace fifty

feet of the Long Cycle piping with chrome-moly steel pipe, but not replace the weld-o-

let at the 24” Misc. Drain tank. Although parts to repair the FWLC valves were in stock a

decision was made to not repair the FWLC valves.

TVA – BFN – FW Long Cycle Piping

TVA – BFN – FW Long Cycle Piping

Unit 3 was restarted, when on February 25, 2013, three days after the restart from the

CCW repairs, a very loud bang was heard in the Turbine Building, coincident with a

signification loss of Main Condenser vacuum then a subsequent Automatic SCRAM. The

8” FWLC piping broke at the 24” miscellaneous drain tank connection, which connects to

the Main Condenser.

Valves leaking past the seats cause vibration due to water hammer, impingement, and

flashing when going from a 300°F temperature at 1,100 psig to condenser vacuum at

100°F. The pipe break at the 24” miscellaneous drain tank appeared to be a brittle

fracture due to vibration related to water hammer from valve seat leakage. The weld

was intact indicating it did not fail.

The immediate action was to cut the FWLC piping, cap the FWLC valves FCV-3-071, 072,

and 073 valves, plus cut and cap the 8” connection to the 24” miscellaneous drain tank.

TVA – BFN – FW Long Cycle PipingPiping Break at 24” Miscellaneous Drain Tank

Pipe Break

Water

TVA – BFN – FW Long Cycle Piping

TVA – BFN – FW Long Cycle Piping

TVA – BFN – FW Long Cycle PipingPiping Break at 24” Miscellaneous Drain Tank

Pipe Break

Water

TVA – BFN – FW Long Cycle Piping

• Extent of Condition

– Unit 2 and Unit 3 have similar issues with valves leaking by the seats.

– The elbows downstream of the FCV-3-071/-072/-073 valve have been

replaced on both units.

– The 24E – DSX pipe measured 0.070” on Unit 2 during recent U2 RFO

– The same elbow at the Unit 3 - 24” Misc. tank broke off in 2003

– Both Unit 2 and Unit 3 had Furmanite boxes on the elbow

downstream of the FCV-3-073 valve during their respective operating

cycles

TVA – BFN – FW Long Cycle Piping

• Short-Term Corrective Action Plan

– Cut-n-Capped the U3 FWLC valves at the discharge of each 8” valve.

– Cut-n-Capped the U3 Misc. Drain Header 8” to 24” connection.

– During Spring 2013 U2 RFO Cut-n-Capped the FWLC & Misc. connections.

– Installed temporary thermocouples at the U1 FWLC valves, upstream and

downstream, and weekly monitor the temperature to evaluate if the

temperature gradient indicates grossly leaking U1 FWLC valves.

– Visually inspect other similar configured Misc. Drain Headers connected to

the Main Condenser to identify piping movement, vibration and/or leaks

similar to U3’s event.

TVA – BFN – FW Long Cycle Piping

TVA – BFN – FW Long Cycle Piping

• Long-Term Corrective Action Plan

– Replace FWLC valves with ValvTechnologies “Zero Leakage” Ball valves.

– Add a new manual valve just before the 24” Misc. Drain Tank

connection for dual isolation.

– Upgrade the piping from the three FWLC valves from 100 psig

(schedule 40) to 1,200 psig (schedule 80) to the new manual valve.

– Add follow up inspections to the Unit’s future outages after piping

replacements are made.

TVA – BFN – FW Long Cycle Piping

Pipe Break

Water

TVA – BFN – FW Long Cycle Piping

Pipe Break

Water

VALVTECHNOLGIES™ – “Zero Leakage” Metal Seat Ball Valve

TVA – BFN – FW Long Cycle Piping

• Lessons learned, changes that could have been done to prevent the issue from recurring, any monitoring or testing that could have been performed to have been able to detect the issue before a failure occurred?

– Thermography inspection of the FWLC valves identified the problem and the FAC engineer was working to repair the valves• Lesson: Never give up ownership of your System to another engineering group

– Management made a decision to not repair the valves• Lesson: Always be demanding with management to repair your System