ML19296B776
| ML19296B776 | |
| Person / Time | |
|---|---|
| Site: | Haddam Neck File:Connecticut Yankee Atomic Power Co icon.png |
| Issue date: | 02/14/1980 |
| From: | Counsil W, Fee W CONNECTICUT YANKEE ATOMIC POWER CO. |
| To: | Ziemann D Office of Nuclear Reactor Regulation |
| References | |
| TASK-03-08.D, TASK-3-8.D, TASK-RR NUDOCS 8002210490 | |
| Download: ML19296B776 (3) | |
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CONNECTICUT YANKEE ATOMIC POWER COMPANY BERLIN. CO N N ECTIC U T P.O. BOX 270 H ARTFORD. CONN ECTICUT 0610t Tat appose s 203-6 66 69f f February 14, 1980 Docket No. 50-213 Director of Nuclear Reactor Regulation Attn:
Mr. D. L. Ziemann, Chief Operating Reactors Branch #2 U. S. Nuclear Regulatory Commission Washington, D. C.
20555
References:
(1)
V. Stello, Jr., letter to All PWR Licensees dated January 25, 1978.
(2) WCAP-9570
" Mechanistic Fracture Evaluation of Reactor Coolant Pipe Containing a Postulated Circumferential Through-Wall Crack.", August,1979.
(3) WCAP-9628
" Westinghouse Owners' Group Asymmetric LOCA Loads Evaluating Phase B", November,1979.
Gentlemen:
Haddam Neck Plant Asymmetric LOCA Loads Since 1976, Connecticut Yankee Atomic Power Company (CYAPCO) has been a member of the Westinghouse Owners' Group organized to assess the dynamic effects of postulated double-ended guillotine breaks of reactor coolant system piping. During May, 1976, the utility group proposed Laplementation of an augmented inservice inspection program to the NRC in response to this concern.
Subsequent to that proposal, during January,1978, the NRC transmitted Reference (1) to all PWR licensees.
Reference (1) required an assessment of the potential for damage to NSSS component supports, the reactor vessel fuel and internals, etc., for effects of postulated RCS pipe breaks.
Attachment (1) to Reference (1) recognized the value of probabilistic studies performed throughout the industry supporting the conclusion that catastrophic Reactor Coolant System pipe breaks have an extremely low probability of occurrence.
The NRC concluded therein that these studies provided sufficient basis to justify operation of PWR facilities during the interim period urtil analyses are completed.
Attachment (1) to Reference (1) concluded that modifications shown necessary to preclude damage to required NSSS components following postulated RCS guillotine pipe breaks is the preferred resolution of the issue. Also recognized were cases where, " modifications may be judged to be unwarranted based on the consideration of overall risk".
It was further concluded that in those cases the NRC Staff would be prepared to consider alternative approaches such as probability or ISl.
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. Subsequent to receipt of Reference (1), during January,1978, the Westinghouse owners' Group developed a two-year program consistent with the requirements specified in Reference (1). The program developed by the Owners' Group consisted of two major objectives. The first objective was to analytically asaess the capa-bility of each plant to withstand the loadings caused by hypothetical double-ended guillotine breaks of RCS piping at the locations specified in Reference (1).
The second objective was to demonstrate mechanistically using f o'eture mechanics in conjunction with experimental test programs that the concept of evaluating effects of a guillotine rupture is an overly conservative design basis.
The basic conclusion or the Mechanistic Pipe Break Program was that guillotine ruptures could not occur under any of the loadings achieved by or specified for RCS piping, including the design basis seismic event.
The results of this program have been documented in Reference (2).
The analytical program developed to assess the capability of participating Westinghouse plants to withstand postulated guillotine RCS pipe breaks is summarized in Reference (3).
The position of CYAPCO is consistent with that expressed in Reference (3). Namely, that the inservice inspection program presently required by ASME Section XI, coupled with results of the Mechanistic Pipe Break Program and other industry studies based on fracture mechanics and probability considera-tions, justify continued long-term operation of the Haddam Neck Plant without installation of physical plant modifications for ef fects of hypothetical guillotine pipe breaks.
In accordance with the verbal Staff request, CYAPCO has evaluated the economic and radiologic impact associated with installation of modifications required to mitigate consequences of postulated guillotine RCS pipe breaks. The evaluation performed indicated that the modifications would involve costs of at least $10 million and personnel exposures in the order of 2800 man-rem.
These costs and exposures are based upon preliminary conceptual modifications which may be escalated if detailed modifications are finalized. CYAPCO has concluded that intensified engineering evaluations would be required to assess the feasibility of incorporating these modifications. Depending upon the timing of installation of these potential modifications, significant replacement power costs could also be incurred. The costs to customers in the northeast are estimated to be on the order of $500,000 per day, merely to purchase the oil required to produce an equal amount of elec-tricity. The financial and radiological estimates presented above could, therefore, be escalated considerably based upon a more rigorous evaluation of a specific set of circumstances. This additional level of detail is not necessary to support CYAPCO's conclusion regarding the appropriateness of these modifications.
CYAPCO has determined that the incorporation of physical modifications to mitigate consequences of the hypothetical RCS pipe breaks would not result in an appreciable increase in plant safety. CYAPCO will evaluate, following NRC concurrence with this approach, the consequences of limited area pipe cracks determined mechanistically using the Westinghouse analysit - " Mechanistic Fracture Evaluation of Reactor Coolant Pipe Containing a Postulated Circumf erential Through-W'all Crack".
Should any design modifications be demonstrated to be necessary by that evaluation, they would be incorporated into the plant design expeditiously.
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- In light of the numerous technical issues which have evolved from evaluations of the accident at TMI-2, it would be an inappropriate diversion of engineering resources to design and implement major plant modifications to mitigate the ef f ects of a purely hypothetical evcat. CYAPCO has also been informally advised of ongoing discussions within the NRC Staff and the industry regarding a more rational treatment of LOCA and scismic events, that being de-coupling. Resolution of the coupling question in this manner would lend further support to CYAPCO's proposed course of action.
In summary, CYAPCO's position is supported by:
(1) The results of the Mechanistic Pipe Break Program (2) Probabilistic considerations (3) The presence of the ISI program, and (4) Over 13 years of plant operation without detection of any service-related defects in the welds in question.
We, therefore, conclude that the above considerations constitute an acceptable resolution to the Asymmetric LOCA Loads issue at the Haddam Neck Plant.
Very truly yours, CONNECTICUT YANKEE ATOMIC POWER COMPANY r
0 9
W. G. Younsil Vice President 90s
" -~ -
By:
W. F. Fee Vice President
.