05000324/LER-1980-106-01, /01T-0:on 801226,HPCI Sys Tripped Immediately After Low Level 2 auto-initiation on High Steam Line Exhaust Pressure Signal.Caused by Water Hammer Event in Exhaust Line.Hpci Sys Trip Reset

/01T-0:on 801226,HPCI Sys Tripped Immediately After Low Level 2 auto-initiation on High Steam Line Exhaust Pressure Signal.Caused by Water Hammer Event in Exhaust Line.Hpci Sys Trip Reset

ML19340E727
Person / Time
Site:	Brunswick
Issue date:	01/09/1981
From:	Poulk R CAROLINA POWER & LIGHT CO.
To:	NRC OFFICE OF INSPECTION & ENFORCEMENT (IE REGION II)
Shared Package
ML19340E722	List: 05000324/LER-1980-106, Forwards LER 80-106/01T-0 05000324/LER-1980-106-01, /01T-0:on 801226,HPCI Sys Tripped Immediately After Low Level 2 auto-initiation on High Steam Line Exhaust Pressure Signal.Caused by Water Hammer Event in Exhaust Line.Hpci Sys Trip Reset
References
LER-80-106-01T, LER-80-106-1T, NUDOCS 8101150538
Download: ML19340E727 (2)

LER-1980-106, /01T-0:on 801226,HPCI Sys Tripped Immediately After Low Level 2 auto-initiation on High Steam Line Exhaust Pressure Signal.Caused by Water Hammer Event in Exhaust Line.Hpci Sys Trip Reset

Event date:
Report date:
3241980106R01 - NRC Website

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EVE *.T.0ESCRIPTION AND PRO 8 A8LE CONSF.M,'ENCES h i

! [TT q l Following a reactor scram on low water level, the. HPCI system trioned irrediateiv 4

,after a Low Level 2 auto-initiation on a high steam line exhaust pressure signal.

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3J 35 36 37 40 el 42 43 44 47 CAUSE DESCRIPTION AND CORRECTIVE ACTIONS h (TTTI IThe HPCI system trip was i= mediately reset and the system started to return vessel l

g l level to normal. An investigation determined that a water hammer event in the exhaust l A plant modifiedtion 1

l m ;line caused the.high pressure signal which tripped the system.

lhas been writen to correct the problem which allowed water to enter this line.

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i LER ATTACHMINT - RO # 2-80-106 Facility: BSEP Unit No.

2 Event Date:

12-26-80 Following a low level reactor scram caused by the loss of the operating feed pump, the HPCI and RCIC Systems received an auto-initiation signal at Low Level 2 (-38").

Both systems started; however, the HPCI System immediately tripped due to a high exhaust steam line pressure signal.

The HPCI System was immedi-ately reset and system started to restore vessel level.

i While investigating the cause for the high exhaust steam line pressure trip, three snubbers on the steam exhaust line were found to be physically damaged.

The remaining snubbers on this line were functionally tested and four were found inoperable. The inoperable snubbers and their problems were as follows:

1) 2E41-6SS35 and 2E41-6SS37 were found to have all four mounting bolts broken;

2) 2E41-6SS64 had a broken piston rod; 3) 2E41-6SS32, 2E41-6SS33, 2E41-6SS36 and 2E41-6SS38 all failed to lock-up on the functional test.

The damaged snubbers were removed and new snubbers were functionally tested and installed in their place. All four snubbers which failed to lock-up were disassembled,-

rebuilt using new seal kits, puppets, and springr, functionally tested, and returned to service. No reason for the snubber lock-up failures could be found during the inspection. The three broken snubbers were damaged during a water hammer event in the steam exhaust line.

Further investigation of the high steam line exhaust pressure and the water hammer event determined that the HPCI inlet steam line drain pot had become filled and allowed condensate to back up into the inlet steam line. When the system was scarted, this water was carried through the turbine and into the exhaast line causing a momentary high pr2ssure and a water hammer event.

Due to failures of the drain pot level switch, 2E41-LSH-N014, to function and open the drain valve, 2E41-F054, a plant modification was written to replace this switch with an analog type instrument. Due to hardware problems with the new instrumentation and unreliability of the installed switch, the automatic drain function of the switch was recoved from the drain valve in February 1980, and a requirement was placed on the control operator's Daily Surveillance Report (DSR) to require that the inlet drain pot be manually drained for 10-15 seconds twice per shift.

Apparently, in this case, this amount of draining was not sufficient to assure that the drain pot was drained. To prevent a recur-rence of this problem, the control operator's DSR has been revised to require draining the inlet drain pot twice per shif t, and to drain until a temperature increase is noted in the Reactor Building Equipment Drain Tank (RBEDT).

This j

temperature increase will indicate that the drain pot is empty., We plan to complete the instrumentation modification at the next long-term scheduled outage for each unit.

l The HPCI turbine and associated piping were inspected and no problems were noted. Before the unit was returned to power, operational and vibration surveillance tests were performed on the HPCI System and all tests were satisfactory.

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