ML19346A041

Discusses Turbine Missile Evidence Re Disk 1 Containment in Event of Turbine Casing Burst.Westinghouse Topical Repts W/ Conclusions to Be Submitted by 810615.Related Correspondence

ML19346A041
Person / Time
Site:	North Anna
Issue date:	05/29/1981
From:	Christman J HUNTON & WILLIAMS
To:	Buck J, Quarles L, Rosenthal A NRC ATOMIC SAFETY & LICENSING APPEAL PANEL (ASLAP)
References
ISSUANCES-OL, NUDOCS 8106040427
Download: ML19346A041 (4)

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May 29, 1981 Alan S. Rosenthal, Esquire Atomic Safety and Licensing Appeal Board U.S. Nuclear Regulatory Commission ,

Washing ton, D.C. 20555 ,.' ,

Dr. John H. Buck ,, coc,*.UC \

Atomic Safety and Licensing Appeal (*'N Board '- er" g'$'6M ' &d

-7 U.S. Nuclear Regulatory Commission

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5::a:h Dr. Lawrence R. Quarles A d Atomic Safety and' Licensing Appeal '.q,s. p Board . ,

U.S. Nuclear Regulatory Commission Washing ton, D.C. 20555 0"'\ 8 D ,-

Virginia Electric and Power Company ( e\

(North Anna Power Station, Units 1 and 2) 9 6'\h'.g'S

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Docket Nos. 50-338 OL and 50-339 OL M d' J

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Gentlemen: 'w

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This will update and expand on my letter to you of May 8,' which was somewhat abbreviated because of the press of time 1 and my uncertainty about when and how some of the technical issues about turbine missile risk analysis will be resolved by Westinghouse and the NRC Staff.

First, let me advise you of what I may not have made i clear before: Vepco has every intention of submitting to you, as part of its final package of evidence on turbine missiles, evidence that the number 1 disk would be contained by the turbine casing and would never reach vital plant equipment even 6

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f if it should burst. The methods of analysis that were used.to l reach that conclusion I expect to be contained in one.of the i

. two Westinghouse " topical reports" that we have told you about. u

. -I am informed by Westinghouse that the topical reports should l be provided to the NRC Staff by about.. June 15, but I can make i no guarantees, because the preparationy of the reports is beyond l Vepco's control, and the schedule depends in part on what demands for information are made upon Westinghouse by the NRC Staff.

You should be aware, however, that I am not going to be ,

able to ' prove to you that all turbine disk missiles, should they be generated, will be contained, because the calculations simply do not show that to be the case. That is why Tables 9 .3 of the " Turbine Missile Report" (enclosed with my January

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14 ' etter to you). indicate that only missiles from the No. 1 disk and not Noc. 2-5, are " contained." I understand that the Westinghouse topical repo,rt to which I have referred above will explain how the results in Tables 9-13 were derived.-

Because there is some probability, however small, that missiles from Disks 2-5 may be generate 3 and will escape the casing, it will be necessary to go beyond the exit energy analysis contained in the Turbine Missile Report and the topical report.' That is why Vepco (and other' utilities) have ,

been concentrating on the calculation of safe inspection

intervals. Because of the recent disk cracking experience, i Vepco believes it will be necessary to* adopt a schedule of-I periodic inspections, snd the important question now, it seems to us, is how frequently those inspections will need to be done. That is why we think that the ongoing discussions between Westinghouse and the NRC Staff about the methods to use for calculating inspection intervals are important, and we are attempting, through Westinghouse, to keep informed about.the.

progress of those discussions. Information on the' appropriate inspection intervals for North Anna will be part of Vepco's final information package, along with the information about turbine missile exit energies and the containment of Disk No. 1

-fragments . Vepco does not believe the Appeal Board can reach a sound decision without the former, as well as the latter, evidence.

In short, Vepco expects to submit to you two lines of ev id ence . One, consisting of a reference to the Westinghouse

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topical report on exit energies and the " Turbine Missile Report" that I sent you January 14, plus any additional I

material that seems necessary to clarify the analysis, will 2,

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e show that fragments from Disk No. I would be contained (except for the 90' . fragment destructive overspeed case) . .The second, consisting of a new calculation of inspection intervals based on the current methods acceptable to the NRC Staf f, plus any necessary explanatory material, will show how frequently the turbines should be ultrasonically inspected in order to provide reasonable assurance that turbine missiles should not be generated from Disks 2 through 5 between inspections. This at least is my present plan; since I haven' t seen much of the evidence that I hope to submit, I can' t say for certain whether any additional evidence will need to be included in the package. .

- The schedule I foresee is this: The first line of evidence (containment of Disk No. 1) depends on the Westinghouse topical report on exit energies that is planned to reach the NRC Staff by about June 15. I will be in touch with the NRC Staff counsel to arrange to provide you with the.

necessary information on this subject. The second line of evidence (inspection intervals) depends on the outcome of current NRC Staf f-Westinghouse discussions of methodology.

Once the calculation methods are approved in writing by the 4

Staff, the inspection intervals for North Anna 1 and 2 can be recalculated, using those approved methods, in about three weeks.

There is also a third line of evidence, consisting of the calculations of the probability of unacceptable missile d amag e P . These calculations, like the inspection intervals, dependodtheoutcomeofthecurrentStaff-Westinghouse discussions insofar as they are affected by the determination of the missile generation probability P With my letter of November 6, 1980, I enclosed a Stone & he.bster " Summary Report" of the P 4 calculations using the then-accepted, but now somewhat outdated, analytical methods. Stone & Webster have done work on updating the " Summary Report" already. In light of the new approach of periodic inspections at calculated

,, intervals, however , it may not prove necessary to recalculate the P 4 numbers at all.

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I hope this letter clarifies Vepco's plans, insof ar as we are able to make plans at this stage. I will try to keep you informed from time 'to time as I learn more.

Yours very truly,

?2.0ds ai % w James N. Christman 126/586 cc: Stuart Treby, Esq.

Anthoriy' J. Gambardella, Esq.

Chief, Docketing and Service Section /

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