ML19322C290
| ML19322C290 | |
| Person / Time | |
|---|---|
| Site: | Crane, Davis Besse  |
| Issue date: | 05/19/1979 |
| From: | Mattson R Office of Nuclear Reactor Regulation |
| To: | Jennifer Davis NRC OFFICE OF INSPECTION & ENFORCEMENT (IE) |
| References | |
| TASK-TF, TASK-TMR NUDOCS 8001160808 | |
| Download: ML19322C290 (3) | |
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!! Ell 0RNiDU?! FOR Joh:1 C. D;vis, Acting Director-Offico of Inspection _and Enforcement 4"
1 FROM Roger J. l4ttson, Directorf Divisica of Systens Safety'.y
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J SUBJECT TMI-2 INVESTIGATION'
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.e The attached copy of an August 9,1978 letter.from B&W to the Davis-Besse licensee was handed to me by a reporter at last Friday's ACRS meeting. At page two it indicates that B&W
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. advised at least one of Its.ouners'yone_ months ago of thi'niedh.
[lto'olis fysitioth jiressurtzerlieve1PandlRCS~pisssure;:t o
e tha circ;umstances surrcunding the THI-2' accident
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'.' night be of use,to_ your people in their investigatory activities.:
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RogerJ.Matbon. '-
.,RogerJ.;Mattson, Director ~
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Enclosure:
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.: j l',r. T. D. Mrray, Station Supt:rintendent
. Davis-Sesse Nuclear power Station g.k 5501 North State Route 82 k..[}-
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Subject:
SMUD Rapid Cooldown Transient
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Dear Terry:
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'On March 20, 1978, Bancho Seco experienced a severe thercal transient in'iti,
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by the loss of electrical pcuer to a substantial portion of the Non-N :elear i@4-jh. h Instrumentation (NNI).
Tne loss of power directly caused the loss of Contr-Roon indication of nany plant pc.re=eters, the loss of input of these paru-
=eters to the plant co=puter, end erroneous input signals (=idrange,2.ero, or othervise incorrect) to the Integrated Control Syste: (ICS).
9 Tne plant response vas not the usual transient in that the ICS responded te k{fj the erroneous input signals rather than actuel plant conditions, end restGtt in a Benctor Protection System (R?S) trip on high pressure.
Subsequent to
,.,y the Reactor Trip, the erroneous signals to the ICS contributed to the rapid cooldown of the BCS.
Plant operators had extrene di,fficulty in deter =ining
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, tg the truu status of some of the plant part:neters and in controlling the pler d
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tecsuse of the erroneous indications in T.he Control Ecom.
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An investigation of the events following this loss of power points out a ne.
for a close look at operator training and energency operating procedu--es fe.
.i'y any 1 css of UNI power (or portion thereof}.
td The follo. ring recon =endaticus b
are cade to essist your staff in a review of training and procedures. to ass-.
proper operator action for events of this nature.
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Operators should be trained to recognize a loss of pover to all or a bajority of their UNI (e.g. indicators fail to rid-range, auto =rstic or eenual transfer to alternate instrqent strings brings no response).
($g Tae loss of power is e=phe. sized here rather than the failure of any one
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instn::ent or con' trol signal which are adequately covered in current si=ulator training courses.
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2' Given thst the oparator cas deternine that electrical prver hcs been s
$ y; lost to all or pa t of the miI, he should knov the location of tha
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povar supply breakers, end htde a procedure available to quickly r.:.-
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gnin pouer.
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If the fault cannot be clee. red (i.e. the breakers to the pcVer cupplies reopch), the operator should hcVe a' list of alt'ernate instrunentation
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available to-hi=, and he should be thoroughly trained in its use.
Ex-j]
l caples are:
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ESFAS panels b.
?.PS penels
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- c..ECI (Essential Centrols and Instr :=entation) l]
SRCI (Safety Related Controls,end Instru=entation) d.
Feco'te shutdcr n panels c.
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Local gases j
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Plant computer
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Recognizing that no procedure can cover all possible co=binations' of MiI l
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failures, the operator's respense should be keyed to certain variables.
p If the operator realizes that be has an instru=entation proble= (es op-l 5
posed to a LOCA or steam line break, for exe=ple), he can linit the l
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transient by controlling a few critical variables:
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Pressurizer level {.via EPI or no_eal Nakeup Pu=psl h
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RCS pressure (via Pressu-izer heaters, spray, E/M relief valves, etc.)
j Stec= Generator level ( ein feed flo *, feedvater valves, etc. )
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Stea= Generator pressure (via turbine bypass system) f I
'Ihe pressurizer level end RCS pressure assure that 1be Reactor Coolant
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Syste= is filled; the Stean Generator level end pressure assure adecuate 3
decay heat re=cval.
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Attach ents 1 and 2 are provided to give a brief description of the events fo11ovic6 this loss of miI power at Rancho Seco.
As een be seen by this 7
transient,' prompt precise operator action and the ability to recognize a loss of MiI po cr are critical factors in limiting the severity of a trans-1 ient such as this.
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If,you have any que,stio.,s or ev_ents, ple,ase advise.
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Yours truly, D _- 9 k we. -_
p Site Operations (<Managerjrf) 6] f N Y Ivan D. Green p
IDC: TIS:nif I
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