ML19347A830

Forwards ACRS to J Ahearne Re Ice Condenser Containments

ML19347A830
Person / Time
Site:	Sequoyah
Issue date:	09/18/1980
From:	Schwencer A Office of Nuclear Reactor Regulation
To:	Parris H TENNESSEE VALLEY AUTHORITY
References
NUDOCS 8009300329
Download: ML19347A830 (2)

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g UNITED STATES

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NUCLEAR REGULATORY COMMISSION

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WASHINGTON, O. C. 20655 t

o September 18, 1980 Docket Nos. 50-327 j

and 50-328

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Mr. H. G. Parris 2

Manager of Power Tennessee Valley Authority 500A Chestnut Street Tower II Chattanooga, Tennessee 37201 Dear Mr. Parrisk

SUBJECT:

ACRS REPORT ON SEQUOYAH NUCLEAR PLANT, UNITS 1 AND 2 A copy of a letter to Chairman Ahearne dated September 8,1980 concerning the Advisory Comittee on Reactor Safeguards' review of your application for authorization to operate the Sequoyah Nuclear Plant, Units 1 and 2, is enclosed for your information.

Also enclosed is a copy of letter dated September 8,1980 from the ACRS to the Commission on hydrogen control and containment capability.

Sincerely, A. Schwencer, Chief Licensing Branch No. 2 Division of Li, censing

Enclosure:

As stated cc:

See next page l

80098G0329

i Mr. H. G. Parris Manager of Power e

Tennessee Valley Authority 500A Chestnut Street Tower II Chattanooga, Tennessee 37401 i

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cc:

Herbert S. Sanger, Jr., Esq.

General Counsel c

Tennessee Valley Authority 400 Cmunerce Avenue E 118 33 Knoxville, Tennessee 37902

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Mr. H. N. Culver Tennessee Valley Authority 400 Commerce Avenue, 249A HBB Knoxville, Tennessee 37902 e

Mr. Bob Faas

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Westinghouse Electric Corporation P. O. Box 355 Pittsburgh, Pennsylvania 15230 l

Mr. Mark Burzynski Tennessee Valley Authority 400 Chestnut Street Tower II Chattanooga, Tennessee 37401 Mr. J. F. Cox Tennessee Valley Authority 400 Commerce Avenue, W10Cl31C Knoxville, Tennessee 37902 Resident Inspector /Sequoyah NPS c/o U.S. Nuclear Regulatory Commission P. O. Box 699 Hixson, Tennessee 37343

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NUCLEAR REGULATORY COMMISSION g

ADVISORY COMMITTEE ON REACTOR SAFEGUARDS ja e WASHINGTON, O. C. 20555 0, f,

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September 8, 1980 Honorable John F. thearne Chai rman Nuclear Regulatory Commission Mashington, D.C. 20555

SUBJECT:

SEQU0YAH NUCLEAR POWER PLANT, UNITS 1 AND 2 In connection with the Committee's review of the Sequoyah Nuclear Plant, Commissioner Gilinsky has addressed specific questions to the ACRS regard-ing ice condenser containments.

This is in response to your request for the Committee's comments on the questions raised by Commissioner Gilinsky in his letter of August 7, 1.980.

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"Does the Commi ttee believe additional hydrogen control measures are necessary for ice condenser containments?"

An intensive review of the capability of the Sequoyah containment has recently been completed.

Independent estimates have been made by the Applicant, the NRC Staff, various consultants, and the ACRS Subcommittee on Structural Engineering.

As a result, it has been concluded that the Sequoyah contain-ment is capable of sustaining a pressure of at least 45 psig without stru -

tural f ailure.

On this basis, the containment structure could tolerate burning of all the hydrogen evolved from the oxidation of 20%, or so, of the zirconium in the reactor, assuming the hydrogen was uniformly distributed in the containment atmosphere.

Hence, there is a range of accidents involving

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severe core damage for which additional hydregen control measures are not neces sary.

Of course, it would alsa be necessary to ascertain that all the essential equipment in the containment could withstand such an event.

TVA has stated that they are conducting a thorough review of this matter.

For a full scale core meltdown there is no assurance that failure of the

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containment could be avoided merely by the use of hydrogen centrol measures.

For events involving more than about 30% oxidation of the zirconium, hydrogen e

control measures may be necessary to avoid containment failure.

E A simil'ar situation, though not identical in detail, woulc be expectec to apply to ice condenser plants other than Sequoyah.

5 The Committee believes that it would be prudent to provide additional hydrogen Ei control measures for ice condenser containments, and that studies to demon-9 strate the effectiveness, reliability, and absence of significant adverse f

5 effects of candidate measures snould be pursued actively on a time scale that would ' permit thei r application before more than a few additional reactor F$$9lT01M

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f Honorable John F. Ahearne l September 8,1980 h.

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years of operation of ice condenser containment plants have elapsed.

As i

statad in our Sequoyah Report of July 15, 1980, in the Committee's cpinion, there is no need to delay the issuance of a full power operating license for Sequoyah until these studies have been ccmpleted.

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"Is the Committee reasonably persuaded of the effectiveness of distrib-uted igniters in ice concenser containcents?

Can such igniters be coun-ted on to keep pressure increases caused by hydrogen burns at suitaoly low values -- which I would define as design pressures -- during acci-dent sequences involving TMI-like quantities of hydrogen?"

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On the basis of the preliminary information available, it appears that a cistributed ignition system of the type considered for Sequoyah may provide

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a good capability of controlling the burning of a large amount of hydrogen.

It is yet to be established at just what hydrogen concentration a particular

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style of igniter will provide ignition with high reliability under the con-

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ditions anticipated.

With the assumption that it can be shown that this concentration is little, if any, higher than the average when the burn oc-curred at TMI-2, the pressure levels induced by iterated ignition would be well within the 45 psig capability of the Sequoyah containment.

There is no present basis for assurance that the pressure increases can be held below the design pressure -- nor would there seem to be any need to do so under the circumstances considered.

The hoped for, and expected, performance would be capable of disposing of all the hydrogen that might present itself, up to the

oint (about 800 kg burned) at which the oxygen level in the containment atmcsphere should drop to about 5"., after which no further hydrogen could

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curn.

This, of course, would depend on the continuing operation of the containment heat removal systems.

~he action of the igniters will probably reduce the risk, since there will

.be at least as many ignition events with them in use as if only unintended ignition sources were present.

The average amount of hydrogen per burning event should therefore be smaller, and the chance that a large pocket of j

2 ignitable or detonable hydrogen could survive without ignition (while waiting i

for a random source to act) will be reduced.

The results of the present testing program will, of course, be necessary before concluding that the ignition system being studied meets.all the neces-sary objectives.

Si ncerely,

l Milton S. Plesset Chai rman

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1 Honorable John F.

hearne September 8, 1980 References 1.

U.S. Nuclear Regulatory Commission, " Safety Evaluation Report Related to the Operation of Sequoyah Nuclear Plant, Units 1 and 2 " USNRC Report

!fJREG-0011, Supplement No. 2, August 1980 2.

U.S. Nuclear Regulatory Commission, " Safety Evaluation Report Related

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to the Operation of Sequoyah Nuclear Plant, Units 1 and 2," USNRC Report NUREG-0011, Supplement No. 3, September 1980 3.

Letter from Commissioner V. Gilinsky to M. Plesset, Chairman, Advisory Committee on Reactor Safeguards, dated August 7,1980 E-8 I

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WASHINGTCN, D. C. 20555 c

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September 8, 1980 Hencrable John F. Ahearne Chai rean U.S. Nuclear Regula: cry Commission

'< ashing:cn, D.C. 20555

Dear Dr. Ahearne:

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SU3 JECT: ADDITICNAL ACRS COMPENTS ON HYDR 0 GEN CONTROL AND IMPROVDiENT OF CON-TAINMENT CAPABILITY tie have responded in a letter of this date to your request for ccmments on the questions raised by Com.nissicner Gilinsky in his letter of August 7,

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In cur discussions acccmpanying the preparation of that response, it became evident that Ccmmissioner Gilinsky's questions need to be con-j sidered within a broader context.

In cur letter to you dated Decemcer 13, 1979, entitled, " Report on TMI-2

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Lessons Learned Task Force Final Report," we stated the following concerning "reliacility assessments":

"The ACRS strongly supports the application of reliabili:y assess-ments to final designs.

The Ccemittee supports the Integrated Reliability Evaluation Program (IREP) whicn is being ini:iatec oy

ne Office of Nuclear Regulatory Research.

However, :ne Committee coes not agree tha: the proposec IRE? will fully satisfy the need.

The ACRS recommends that tne NRC cevelop a program in which licen-sees actir.g individually or jointly develop reliability assessments of :neir plants, in addition :c tne NRC IREP, wnica should be performed concurrently.

"If the reliaoility assessments were performed in :he manner pro-pesed anove, it would accelerate obtaining potentially significant safe:y information and expedite the cevelopment of the basis for changes, should they be necessary.

It would also provide the Operating crganizations with cetter technical insight int: the safe y of their plants and would provide the benefits to be derived by separate studies cf system reliacility."

Ih acci:icn., concerning the :opic en:itled, " Design Features for Core-Damage an: Cere-Mel:, Accicents," we stated :ne folicwing:

"The ACRS supports :nis recommendation.

However, One Committee el i eves na: tne rec =menda:icn should be augmented :: require c ncurrent cesign studies by each licensee of possible hycrogen

n:rci and filtered venting systems which nave :ne poten;ial for mi:igati:n of accicents involving large scale core damage or core el:S;, inclucing an estima:e Of the cost, :ne possible schecule, anc :ne pc:ential for recuction in -isk."

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Honorable John F. Ahearne September 8, 1980

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i The NRC Staff appeared to supper: this latter rec:ccenda-fon in Task I:.5 cf tne Action Plan.

However, in the interim rule en degraced core cooling prcposec by the NRC Staff in Aug;s: 1930 and ap; roved for cualic comment on Septemoer ?, 1980, only the s:scy of measures for hydrogen c:ntr:1 are re-quested, leaving c:ner questiens of pcssible improvemen;s in centainmen; i

cesign for a.rulemaking which appears likely to take s:me years.

With regard to the reliability assessment of plan:s in Operaticn er under construction, the NRC Staff ap; ears to ce satisfied.vi:n an IREP whien is moving much more s10wly than was being cr jec:ec in Decemoer 1979, wnen we recommended a major acceleration cf such effer:s.

If one considers :he poten:ial fcr improving :ne safety Of lish water reac-

rs, we believe such c:nsiderati:n will nc: :rovide a basis for :ne rather cifferent priori:y and empnasis tha: the NRC is placing en hycrogen control in contrast to the priority and e phasis it is giving Oc reliability assess-of final design anc to a : re general approach to improving containment men:

capability.

For many reasons, we :elieve it is cifficult :: demonstrate with a hign degree of confidence th:: the frecuency Of severe core damage or core mel: for reactors in cperatica cr under ccnstruction is so 1:w tha: i is net pruden:

o a95ressively pursue measures c:h to prevent sericus accidents' and c

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mitigate them.

We believe :na: :he reccamenda icns qu :ec above fr = cur le-er dated December 13, 1979 secula be ace;:ed and given priority ay the nR,.

v Sincerely, i

Milton S. plesset Chairman References 1.

Le: 'r from Cc:missioner V. Giiinsky :: M. piesset, Chairman, Adviscr/

Cc=:.nt:ee on. Reactor Safeguarcs, ca:ed Augus: 7, 1980 2.

Le::er from P.. Car: n, Chair an, Acvisory C:=mi :ce on Reactor Safe-guards,

Subject:

Re:or: en TM:-2 Less ns Learnec Task F:rce Final Recor:, ca:ed Decaccer 13, 1979 4

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