ML19253A087

Forwards Review of 770924 Event Re Depressurization of Primary Sys.Similarities to 790328 Incident at TMI-2 Noted

ML19253A087
Person / Time
Site:	Davis Besse
Issue date:	05/18/1979
From:	Roe L TOLEDO EDISON CO.
To:	Reid R Office of Nuclear Reactor Regulation
References
503, NUDOCS 7905230371
Download: ML19253A087 (3)

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Fac:1.t.es Or<etes. teas Docket No. 50-346 ,us, ,3,.3,,,

License No. NPF-3 Serial No. 503 .

May 18, 1979 -

Director of Nuclear Reactor Regulation Attentien: Mr. Robert N. Reid, Chief Operating Reactors 3 ranch No. 4 Division of Operating Reactors United States Nuclear Regulatory Cccnission

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. D. C. 20555

Dear.Mr. PeId:

t-In accordance with Toledo Edison's letter of May 4, 1979 (Serial No. 500),

a reviau of the Septe:ber 24, 1977 avent at the Davis-3 esse Nuclear Power Statica Unit 1 is attached.

Yours very truly, y ;-? fdA LIR:TJM Attach ant ec:

J. 2 atzig Operating Reactors Srcach No. 4 Diiisica of Operattag Eaactors U. S. Nuclear ?e;ulatory Ccanission

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Serial : o. 503 May 13, 1979 Scotenber 24, 1977 Event Review A transient with some similarities to the Three Mile Island (TMI) incident of March 23, 1979 occurred at DB-1 during the early phases of the testing program. .

A cc=plete description of the September 24, 1977 event concerning the depressufi-zation of the primary system was presented in the supplement to Reportable Occurrence NP-32-77-16 dated November 14, 1977.

This event was similar to the TMI incident in that the event uas initiated by a loss of feedwater resulting in a reactor coolant system (RCS) pressure surge .

which opened the power cperated relief valve (PORV). The FORV failed open, causing loss of coolant and coolant pressure with sc=e voiding in the RCS, and a subsequent increase in indicated pressurizer level (characteristic of a leak in the top of the pressurizer). As at TMI, the opera,t; ors initially failed to reccgnize the open. _FORV and whenAressurizer _l_evel started increasing as voids cave Ep"'e~~c~~in tne .wS, the operators ; hut off the high pressure injection pumps.

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Unlike Three Mile Island, however, the Davis-Besse 1 operators recognized the open FORV in a relatively Ebp.rtJige (approximately by 21 minutes and responded properly by closing the block valve and sj! ,s,e_gygn,tJy.,nasuid..hi;h-,p.t%wr.

b l3 g. In the DB-1 incident, two reactor coolant pumps were tripped to inj,ec,t;,i_,c.n,fi reduce the system heat . input t and en_e . _ r,e_

.__. actor coolant pu.,m_pe~c.er l._o.op was maintained in,,,c,;$r,31icn throughout the incij.nt. . _ _

Ihe Icss of feedwater was caused by a spurious trip of the steam and feedwater rupture ccntrol system (SFRCS) resulting in a loss of feed to cne steam generator with a subsequent full"STRCS tri;f on low steam generator level. The full SFRCS trip stcpped normal feed to both generators and initiated the auxiliary feedwater J (AFW) system. Both trains of the AFV started,J ut,,,gnj L one,,, fed its associate,(

sy g ge,ner,alor. The other experienced a malfunction of the governor which kept the at: ciliary feedwater pump turbine at a speed insufficient to pump water to its asscciated steam generator.

) f As a r+sult of the incident at D3-1, all licenrad operators and the station 71 '

( cn3f -. earing staff were ginn detailed trainin, cn the event 11th special attention

,, ], to the hanards of relying en pressurizer level instru- entation as todication of

,.rf- .ry systas inventory +.cn a lcak in tha top of the pre ssurizer cxists. The error in cacuring high pressure injection becauce of increasing pressuriner icvel irficatica tas also discussed. Modifications to the mergency precedures vere drc tic p ed. Base required the operator to verify that no leak exists at the top of .'.e pres.turizer before the pressurizer level is relied upca, and high acc-ssure hjecticn flov is secured.

As a direct result of the incident, several system cdificaticus ware nade. The au ciliary feed punp turbine gcvernors were ccdified to pravent any further binding calfunctic.s. The centrol reca annunciatica of SFRCS trip status was modified to provide additional infc=atica to the crerators. Thasa :di ficaticas are dcscribed in tha s aplement to Rapert:ble Cccurrance 5?-32-77-16 dated Move...ber 14, 1977.

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.:::-ket W. 50-346

", License No. N?F-3 Sarial No. 503 May 18, 1977 .

Further nodifications were cade to i= prove the reliability of the SFRCS and AFW as a result of experience gained during the test prograa; these changes included ,

the fellcwing: the high pressure taps of the SFRCS pressure differential switches

-cre :cved to reduce spurious trips of the SFRCS caused by perturbations in nain feedvater line pressure (see Monthly Report of October, 1978, su : ary of ccapleted Facility Change Requests,77-424). A spring was installed in each auxiliary feedvater governor to prevent the closing of the governor valves due to vibration dur"ng plant operation (see Annual Report for 1977, su:. mary of ceapleted Facil.ty .

Change Pequests,77-450). The relays used in the auxiliary feed pump turbine speed centrol circuitry were replaced with better relays because of repeated failures of the original relays (see Monthly Report of March,1978, summary of cen;1eted Facility Change Requests,77-221). Indication on the mechanical linkage

, of the pilot valve for the ?ORV was added to provide the operator better status

' of the ;csition of the ?ORV. (. Facility Change Raquest 77-351).

i The Septanter 24, 1977 event has again been reviewed to determine if any additional c:ncerns exist which would not be covered by the changes currently being prepared to satisfy the require ents of SRC Bulletins 79-05,79-05A, and 79-053. No additional items of ccncern were identified. Along with the procedural and equip-

snt :cdifications already rade as a result of the Davis-3 esse Nuclear Pcwer Statica, Unit 1 transient, the additional guidelines, including instructions for maintaining proper RCS pressure / temperature cenditiens and for stopping high -

pressure injectien, provided all the procedural guidance necessary for coping with

/ tha cenditicas of the September 24, 1977 event.

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