ML19289C223
| ML19289C223 | |
| Person / Time | |
|---|---|
| Site: | Browns Ferry  |
| Issue date: | 12/12/1978 |
| From: | Gossick L NRC OFFICE OF THE EXECUTIVE DIRECTOR FOR OPERATIONS (EDO) |
| To: | Lagomarsino R HOUSE OF REP. |
| References | |
| RTR-WASH-1400 NUDOCS 7812210336 | |
| Download: ML19289C223 (13) | |
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COMMENTS ON MR. HUGHES*
J SEPTEMSER 27, 1978 LETTER TO CONGRESSMAN LAG 0MARSIN0 l
The three concerns of Mr. Hughes' that fall within the responsibility of the NRC are:
(1) the validity of the Reactor Safety Study, (2) the fire at the Browns Ferry Nuclear Station, and (3) the operating perfor-mance of commercial nuclear power plants. The NRC comments on each of these concerns are provided below.
Concerning Mr. Hughes' comments on the Reactor Safety Study, we agree that there is a large uncertainty in the absolute values of probabil-ities presented in the Reactor Safety Study. However, subsequent to the publication of Tne Union of Concerned Scientists criticism, this report and peer comments on it have been reviewed by an independent group of eminent scientists and scholars established as the Risk Assessment Review Group. This critique was published a3 NUREG/CR-0400 in September 1978 (copyattached). During its extensive review, this group intereiewed members of The Union of Concerned Scientists about.their concents 'n '
o the RSS.
Nontheless, the Risk Assessre t Review Group concluded that, a
while absolute values of the risks in WASH-1400 "...should not be used...in the regulatory process or for public policy purposes.", the'
"...RSS has been most successful in the provision of a logical framework for the discussion of reactor safety, infomation about the relative probabilities of various accident sequences, and the beginning of an effort to provide absolute probabill:.ies."
The NRC is currently evaluating the implications of this independent review for the regulatory / licensing process with the intent of implement-ing policy changes where appropriate.
The NRC has and will continue to use the defense-in-depth approach to assure public health and safety. This approach provides for achieving the required high degree of safety assurance by echelons of safety systems.
The defense-in-depth afforded in this way does not depend on the achieve-ment of perfection in any single system or component and the overall level of safety achieved is high.
This approach has been shown to be effective in the past and particularly during the Browns Ferry fire that occurred on March 22,-1975. Contrary to Mr. Hughes' views concerning this incident, the defense-in-depth approach to plant design was responsible for the fact that this serious fire that involved the inoperability of many important systems resulted in no adverse effect on the public health and safety.
It was clear from our investigation that the fission process was terminated (the reactor was scrammed) shortly after the start of the fire. The capability to
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. e scram the reactor was not affected by the fire. Subsequent to the scram of the reactor, the reactor fuel was cooled (decay heat removal) by using available methods not routinely used during shutdown situations.
While some difficulty was encountered before the normal means of decay heat renoval was permanently established, danger that the cooling water would boil-off thus subjecting the fuel to possible meltdown was small.
In f act, had the method chosen by the operator not functioned, there were a number of other means available to effect removal of decay heat.
These alternate methods are discussed on pages 73 and 74 of the JCAE hearing print.* We believe that this unfortun;.. and serious occurrence has shown that the reliance on the defense-in-depth concept for reactor safety is sound for the protection of public health and safety.
The last item of concern expressed by Mr. Hughes regarded nuclear plant operating capacities. Operating statistics are published by the NRC in a report titled " Operating Units Status Report, NUREG-0020". The average nuclear unit capacity factor for the
~ year-to-date through September,.1978 is listed as 67.1%.in the October,1978 issue of NUREG.0020 (copy attached). For the calendar year 1977 nuclear pTants represented 8.9% of the nation's electrical capacity and produced 11.8% of the power consumed.
?^'1 284
- Hearing before the Joint Committee on Atomic Energy Congress of the United States; September 16, 1975 (copy attached).
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[The Joint Conunittee reconvened at 2 p.ni., Repars:.tative John o"",
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OPEUING REMARKS OF REFEZ3ENTATIVE YOUNG
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In h-Representative Young [prvsiding' The committee will com onler.
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Thi.s morning we heani fnem tiv chainnan. Mr. Andert. and rug D lir. Do:.ald Knuth, both of titt N R C.
/) O that Thi.e aftenioon we are runnh.g a little lat.. We have first Mr.
U U nard Rusehe and Dr. Stephen 11ananer. In deference to the time M
,I Ltre two witnesse.< :oteht sumnnoize their statements for us and then w!ose
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and the obvion problem that we have.I am gone to sugee-t that t!
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.uses ont objection we will enter theit written stateme:cs in the record.
ora-With that then, would you proceed. Mr. Rusche.
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'?:r-STATEMENT OF EENARD C. RUSCHI, DIRECTOR OTTICE OF NUCLEAR REACTOE REGULATION. NRC nn.
udi-Mr. Rtwin:.Thank rou Mr. Chairman.
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] would like to outlihe the events both durine and inunediatelv fob v as lowing the event and then IV.ll discuss briifir the actions that 'NRC n c-reMaratiott activitics and then the with a brief outline vi our enrrent
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ha< taken and plans to talte in connection with TV.D recovery and hoy thinkin~g nith re pect to the fire itself.
th" Fir _st let me di ens, plant safety during the fire. Yoa recall thi.s morning that we had a consiilerable inaount of discusm,n in resp.n=e J.!
to que.tions of tide sort so I wili saove fairly rapidly with your Pen"u-ion.
A detailed disenuinn of the means by which the TVA operators i !1 achieved and innintained n..-afe shutdowh condition of the plants and
.Le one nnalysis of the availahi!ity of abenmte means that exi.ted for achievinit t':e same-goal are de.:rrihed in.\\ttachnunt I t" my written is statement. I would like to.< unnuarize the<e resuhs very briefh nnd note partienlarly that they apply to Unit I and note thlit in ali caces
-the situation in Unit 2 wa= more favoral,le.
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.\\ l.ou t IT minutes after the fire staited. the n--ion proces was al-stopped by the operator's action to rapidly intert n!! control rods. In our jargon, such a rod insertion is cahed a manual scram. The efreets of of the lite damage on protection circuitry wouhl have subsequently can:cd un automatic scram had thn operator no: eheted to take action vs at the time that he did. That is, the rod sv-teni w.i< fail sa fe. I woubl like to emp!.asize that this is a key and inipouant..etior. in converting h.
the time respun requi:vd from the oper-uona froni that of a im mt:.i.tes to.-crend hours and we had come dien :o: on tha; point is 11A ruorning.
Fo!!owingshutdown of the finion process.a reart..r mnrt continne to he cooled to renpele b.ent prmluced'by r.DlI3! ion IlMon P:Uductde'ay.
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Heat iemoval is required for an extendcd perio.1 of time after plant r
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74 shutdown in on!cr to prevent fuel damage. Immediately following the shutdown of I' nit 1. the reartor co: dant sv.-tem was being maintained ct. a pressme near that of imr:nal ope'r:nie-that i.<, ninut.1,100 t,sig-by operation of relief vaives. Ikcansn of fire dam.:; e nt this p
une, there wa:. no automatically available high pre.-ure source of watc r that was rei sullicient capacity to lunintidn the cote c.ncred with wa t er.
In light of this situation, the Browns Ferry operatore de,ided to depre.-mrize the prinuiry eminut syrtem by opening irlief valves. As noted in the detailed -Inti analv8i< in Attnehmen* l nlternate methods for depressurizing the inimar'y ey.-tem were avaihble and there was j
niso availnble mannat method; for supplying co, ling water at high 1
plPisnit.
The o the. rena*perator< depire:nrized the reactm hv discharging 5. team from
- r to the enpinession imol through the four relief valves that cou'-
2 operated from the co6 trol room. The discharged steam he., red up ti water in the snppreuion pm1 na inten.!ed. Because of the large volume of water in tho ponh al.ont 12 hours1.388889e-4 days <br />0.00333 hours <br />1.984127e-5 weeks <br />4.566e-6 months <br /> of sneh discharm conid he necommodated before the pool water wonhl boih even without the cooling sysicm for the supprc<sion pel whi-h was not avniinide at the time beennen of fhe damage to its control syst.:m. Once the-reactor,
pressure was redneed. low pressure pump < weic used to provide un ndeqnnte source of. Tvater for cooling the fueh Lny low prescurc l
pon pu capable of sunnlyine more than enom.:h weter to keep the core -
covered were available 'o the operators at low rea< tor presure.
Some. hours latei. ns was broncht ont in the qn,tionine t!h morn-ing. the rupply of compreerd air that artuntes I;e relief valves was lo<t owing to continnim: fire damare experienced in I nit I nnd the valves closed. Since the deeny heat in ilm fuel continned to boil the water in Ihe renetor ves-el and the relief valves were elesed, the reactor pressure increased ngain to the point that additional water could not he inj.vted hv the low pirsnre innnp<.
At this point two courses of action were pursued. The first involved restorine the air innpir to t:ie relief va es so that n low reactor pres-sure could he reestablished. The second murse of action pursned was to establish a depressurization path throm_a the main steam line drain with water iniection from com tol rod drive pmup (I' nit 1) and from control rod drive pump Wnit 2).
l As de-cribed in AttacInnent 1.the depres-nrization path through thn drain line was established in nhout I hour. Analvses show that n satisfactory conline condition was beine achieved'nt that time In nl.m 3M. honr3 the operator.: restored th nir snpply to the relief valves and again ieduce.1 reactor prc:3nre suf9 iertiv to permit opera-tinn of the low pers-nre pinnic-nuain. From ihis point.on 1he prmure wr.s maintained low ynough for t.he low pivnnte p.nnps to be etiective
. in injectine water.
I would like ta confirm Chairman.\\nderiim mer statement that the -
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core cooling was innintained with mnhiple sy.-ti rs nvailable.1 inicht,
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if yen would poimit me to interject. say in icip'nse to Senator htoyn question thi.4 morning we do have nn ently e.cilmnte of the
}!bfl boiH1 of surb un event nS citimated by our Unsmus.ced bimly I
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