ML20024H324

LER 91-001-01:on 910110,electro-hydraulic Control Sys Failure Occurred,Causing Reactor Trip.Caused by Turbine Trip.Both EHC Pump Discharge Filters Changed Out & Pump B Replaced W/Spare pump.W/910524 Ltr

ML20024H324
Person / Time
Site:	Millstone
Issue date:	05/24/1991
From:	Baumann P, Scace S NORTHEAST NUCLEAR ENERGY CO., NORTHEAST UTILITIES
To:	NRC OFFICE OF INFORMATION RESOURCES MANAGEMENT (IRM)
References
LER-91-001, MP-91-435, NUDOCS 9105310195
Download: ML20024H324 (4)

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NIRYHEAGT UTILITIES co- o"m san snee sean caoxu 3 Yne cwertcut uri Aw w cc%am ZIM.',0'T27"&k7.'s """"> po eox m

> Ncetr$ast i. names servee compa r, HARTFORD; CONNECTICUT 06414-C070 l ' ' ' Potteasi Ncea, Ene*gv Compey (203)665-6000 Re 10CFR5L.73(a)(2 Hiv)

May 24 1991 MP-91-435 U.S. Nuclear Reculatory Commission Document Control Desk ,

Washington, D.C. 20555 i

Reference:

Facility Operating License No. DPR-65 l Dod.et No. 50-336

! Licensee Event Report 91-001-01 Gentlemen:

This letter forwards update I icensee Event Report 91-001-01.

Very truly yours, NORTHEAST NUCLEAR ENERGY COMPANY Sthp f d ce # b Director, Millstone Station i

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Attachment:

LER 91-001-01 ,

cc: T. T. Martin, Recion 1 '

ir- ator W. J. Raymond.- Senior ' ee at laspector, Millstone Unit Nos,1, 2 and 3 G. S. Vissing NRC Project Manager, Mi:lstene Unit No. 2

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1. Dewof of Esem On January 10 lW1 with the unit operaung at 4." < pow e r the 'C E HC pump was in operanon and the T EHC purnp wa* m standhs The 'A pump dncharge hher prewure alarm annurasatea, mdicaung that the dncharge hher uas pluggmg At 1430 the 'N purup dnchat ge prewute dropped to 1350 psig.

causmp the T pump to autontan. When staned. the T purnp could not mamtam stable dncharge prewure due to sesere sibranon, and would onh maintam miem pn wure at 1400 psig t nonnal mit m prewure n inHO psig n both pumps were required to operate to mai nam miem prewure at 14 50 psig.

A!!er sest'ral adfu4 menti Aert made to the comptinator control on .E T pump. Plem preware W stabihred at 14' pug At 1500 hrs a decnion was made to lease the mh m operatmp m ns exnung conhguranon (T pump runnmg, ' A purnp m auto-stati; for a nurumum of I hour to prose rehabilns of the T pump, so that the dncharge hher of the 'N pump could be changed out. At !!!O his the T pumps performance showed conunuou, satntacton dncharge preuure of 14"' psig At 15 hrsthe mb supennor completed ho pre-job bnehng and eenhed that the rnecharua uere reads to bepm the change out of the 'N pump dacharge hher. The mechanics nustakenk behesed that thes had authonranon to begm work on the pump When the job supervnor lett the inb sne. the mechama began dnawembhng the 'N pump hher. At 1605 tht B pump expenenced a vihrauonal tranueru and miem maruloid pressure decrebed to 13f o pug. The auto-suin f uncuan of the 'N pump picked up and the 'N pump auto-started. The operator at the EHC skid called the control room to uor the 'N pump. ulule the mecharucs reawemnled the hlter houung. The EHC miem prewure conunued to drop causmp a turbme trip and correspondmg reactor inp, before the 'N hher and pum;, could be restmed to service.

!!. Cause of Es en' The Reactor tnp wat caused bs a turbme inp The root cause of the turbme tnp was the tailure of the Elecuo-H)draubc Control (EHC) system pumpt The EHC w(tem could not mamtam adequait u stem pressure unh the T pump m operanon, due to high vibranon and preNre fluctuanons h was necessan to change out the drcharge hher of the 'N pump because the 'C pump docharge prewure was decreasmg below the T pump auto-stan setpomt The T pump had been operaung erraucalk but after a one hour rtm. n was obsened that the pump was able to maintain adequate system prewure Aher the 'N pump had been remosed from semce the T pump subsequenth expenenced erranc operauon and the system prewure degraded sigmficanth enough to cause the lou EHC prewure turbme tnp There were 2 maior tactors coninbuung to the f ailure of the pump cavnauon and taiture of the holddown spnng retamer sleeve awembh. Wlule the pump was operaunc. air m-leakage past the o-nnp seaung surf aces on the sucuan stramer caused the cavuation. Coincidemally there was hean cortouonicxidauon unhm the holddown mnng awembh retamer bore. Thn oxidauon him would not allow the awembh to operate properk The combmauon o' .hese two factors eventualk led to the complete ladure of the pump. Addnional corarinuung f actors to the plant top were: li Work was l pertonned on the 'N hher u th an errancalh operaung T pump 2) A mnunderstandmp between the j mechanics and the job supervnot led to the premature dnassernbh of the 'N pump dncharge hiter 3)

The f aiird pump was m storage f or approumaich two 3 ears. The lack of Omd in the pump caung l allowed the oxidura him to build up on the reiamer bore t

Hl. Anah+ of Es ent Tho repon n bemg suhmated pursuant to the reqmrernenh of 10CFR 50 ~3(aH 2 H n !. ' Any esent or condluon that resuhed in the manual or automanc actuauon of ans Engmeered halen Feature (L5Fh mcludmg the Reactor Protecuon S\ stem GPD" There were no safets cornequernes resulung Irom thn esem smce normal post inp pacedures were followed 1

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\lillstone Nudear Power hianon U "', s 0l5loj0l0l3l3l0 ul1 o l ol 1 ol1 ol 0 OF ol3 ue n ny e u. m ,, ,,,n , ,,, e.> v,e mie ,u.50- xtm s l\L Drr e cth e -\ ct P +n I)uring the shutdow n f ollowing the inn. hotii EHC punip dNharge hher utre channd out and the 'li' punip uils replaced With a %paf t pu!Ilp l Ist (" rl!!p' ('Il tht 'U st l( 711 %I r a int f u tic repla(ed illld the pufnp um conipleteh oserhauled All worn or darnaped parts ut f e replaced, the pornp uas reinstalled and then returned to serace. To present oudauon. all haute pornps udl he mired unh their purup casirips blied unh EHC 11uid

\' Addinon:d Informanon Strinlar LEir5: None .

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