ML17037C202

Letter Regarding Steam Vent Clearing Phenomenon and Steam Quenching Vibration Phenomenon and a Request for the Development of a Program for Review Directed Toward Continuing Integrity of the Torus and Operating Procedures ..

ML17037C202
Person / Time
Site:	Nine Mile Point
Issue date:	02/15/1975
From:	Lear G Office of Nuclear Reactor Regulation
To:	Rhode G Niagara Mohawk Power Corp
References
Download: ML17037C202 (8)

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PDR Docket Pebruary 15, 1975 ~

.ORB83 Rdg KRGoller Docket Ho. 50-220 TJCarter GLear C JDeBevec SATeets Niagara t(ohawk Power Corporation SVarga ATTN: Hr, Gerald K. Rhode OELD Vice President Engineering OIM (3) 300 Erie Boulevard 'treat ACRS (12)

Syracuse, Hew York l3202 . , Gray file extra cps (5) /g a pat~~

Gentlemen:

Experiences at various B>tR plants. with tfark I Containmeots have shown that damage to the torus structure can occur from two different phenomena associated with relief valve operations. Damage can result from the-force exerted on the structure when, on first opening, relief valves discharge air and steam into the torus water. This phenomenon is referred to as steam vent clearing, Damage also can result fxom torus vibrations which accompany extended relief valve dischaxge into the torus water or the flow from the drywcll during a AVOCA if the pool water is at elevated temperatures.'his effect is kno~m's .the steam quenching vibration phenomenoh. These phenomena are discussed below.

Steam Vent Cleaving Phenomenon The Nark I torus structure of some boiling water reactor plants was found to be defective-following cycles of steam vent cleax'ing into the torus when primary system relief valves opened. Investigation indicated that

'some of these plants may not have been designed to withstand this phenomenon throughout the life of the plant when the torus pas subjected to 43 predicted number of xelief valve openings.

The quad Cities Unit 2 and the Hrowns Perry Uni.t 1 torus structures were subjected to tests when defects -or excessive noise and vibrations were discovered following thc above phenomenon. (1)(2) As a result of these tests, some modifications to the'orus structures pere made for these facilitieq and some similax facilities. Because of the apparent progressive nature of the material fatigue type of failure phenomenon, we do not believe that there is any immediate potential hasard; however, we presently do not 71WIIRRO 10559 steaci vent clearing phenomena and structural Response of the BfS Torus (Nark I Containment)", General Electric Company.

(2) "1973 Browne Perry Unit 1 Torus Expexience'" submitted by the Tennessee Valley Authority to the Office of Regulation, Hay 7, 1974, OFFICE% oRMZ ass&

SURNAME+

Selevec':' GLear Q DA'fEtp 2/ I W

/75 2/ ly /75 Form AEC-318 (Rov. 9-53) AECM 0240 '6 V.n. OOVKRNNRNT PIIINTINO OffrCNI 'lars~as 2ss

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have the necessary assurance that the torus structures wi11 maintain their integrity throughout the entire life of the facilities. ( )

Steam Quenching Vibration Phenomenon Elevated. torus pool temperatures during extended relief valve operation have become of concern in light of occurrences at two European reactors as reported to us by the General Electric Company. Hith local torus (4)(5) pool temperatures in excess of about 170F, due to prolonged relief valve operation, it w'as observed that severe torus structural vibrations occurred with moderate to high .relief valve flow rates. GE reported that these vibrations were caus'edby a .steam condensing mode characterized by periodic pulsation of the steam jet at the relief valve discharge point.

to continue, the vibrations could have resulted in structural damage to If allowed the torus due to material fatigue.

The probability for this vibration phenomenon from extended relief valve operation is considered to be low in view of operating limits imposed by current technical specifications. The existing technical specifications on torus pool temperatures generally limit normal power operations to 90-95F with a maximum short term limit of 120-, 130F. However, occasions have arisen when a relief valve remained open for extended periods resulting in elevated pool temperatures and creating the potential for the steam quenching vibration phenomenon.

Requested Action In view of the foregoing considerations,, we request that the following action be initiated.

1. For the Steam Vent Clearing Phenomenon, a program should be developed for our review that is directed toward establishing the continuing integrity of the torus of your plant. Sou should consider at least the following in developing your program:

(a) The need for verification tests.

(b) The need for physical modifications to improve capability of the torus structure.

H. Butler,'EC, dated September 12, 1974.

(4) Letter, E. G. Case, USAEC, from I. F. Stuart, GE Company dated November 7, 1974.

(5) Letter, E. G. Case, USAEC, from I. F. Stuart', GE Company dated December 20, 1974.

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0 (c) The torus fatigue characteristics when subjected to forces resulting from opening of relief valves.'d)

The predicted maximum number of relief valve openings, singly and collectively, during plant life.

(e) Surveillance requirements; including frequency of inspections, for verification of torus structural integrity.

2. For the steam quenching vibration phenomenon, operating procedures should be developed, and changes to the Technical Specifications should be proposed to preclude the development of elevated temperatures of the torus pool watex'nd p'rovide for inspection of the torus as appropriate to identify any damage in the event of an extended relief valve operation. In this effort, consider the results of your review required by Regulatory Operations Bulletin 74-14, "BUR Relief Valve Discharge to Suppression Pool", dated November l,l, 1974, and the interim recommendations of the General Electric Company to 1N/R owners (References 4 and 5).

3. Submit a description of your program and your proposed changes to the Technical Specifications. A, suggested review schedule with major milestones and dates is enclosed for your considerati'on; are not satisfactory, adjustments may be possible after discussion if these dates with us. If you do not intend to initiate a'program for verification of the torus and/or proposed surveillance 'requirements, we require that you submit appropriate justification.

Your submittals are requested in accordance with the proposed schedule.

Three signed and notarized originals and thirty-seven (37) copies of are needed for our review'. youx'ubmittals Sincerely, lS/

George Lear, Chief Operating Reactors Branch J3 Division of Reactor Licensing

Enclosure:

Proposed Schedule of Major Activities cc: See next page OFFiCE>

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Form AEC-318 (Rev. 9-53) AECM 0240 V. ~ . C 6<NNrNT PRINTIMC ICE> 197 9 R5$

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Niagara lfohawlc Power Corp.

cc: w/enclosure Arvin E. Upton, Esquire LeBoeuf, Lamb, Leiby &. MacRae 1757 N Street, N. M.

Qashington, D. C- 20036 Anthony Z. Roisman, Esquire Berlin, Roisman & Kessler 17l2 N Street, N. H.

washington, D. C. 20036 Hiss Juanita Kersey, Librarian Oswego City Library 120 E. Second Street Oswego, New York 13126 OFFICE+

SURNAME+

DATEtD Form AEC-318 (Rov. 9-53) AECM 0240

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