ML20059E301

Forwards Safety Assessment of Yae 1735, Reactor Pressure... Evaluation Rept for Yankee Nuclear Power Station, Submitted w/900705 Ltr.Nrc Calculations Recognizing Uncertainties Conclude That Plant May Operate Until Feb 1992

ML20059E301
Person / Time
Site:	Yankee Rowe
Issue date:	08/31/1990
From:	Murley T Office of Nuclear Reactor Regulation
To:	Kadak A YANKEE ATOMIC ELECTRIC CO.
Shared Package
ML20059E305	List: ML20059E301 ML20059E307
References
NUDOCS 9009100134
Download: ML20059E301 (5)

Text

{{#Wiki_filter:N .r 3). -.3 i, , g* ; - kmou, Q q, UNITED STATES Og g g 3: NUCLEAR REGULATORY COMMISSION ""( - 7. ' S[ WASHING TON, 0. C. 20$$$ U ,' tt tuo n, -Docket No.-50-029 / r' 'Dr. Andrew C. Kadak President and Chief-Operating Officer

• 4 Yankee Atomic Electric Company 580 Main Street Bolton,-Massachusetts 01740-1398

Dear Dr. Kadak:

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SUBJECT:

YANKEE R0WE REACTOR VESSEL By letter of-July 5,1990, you sult.itted for staff review the report, " Reactor Pressure. Vessel Evaluation Report for Yankee Nuclear Power Station." This report was in response to our letters of May 1, 7, and 15, 1990. Because of. our concerns regarding reactor vessel integrity, we requested informations that was needed to assess the effect of vessel operating temperatures, beltline -material. chemical composition and material surveillance test results. These -concerns can affect the conclusions of previous NRC rev_iews of vessel integrity. .Those previous reviews considered postulated Low Temperature Over Pressurization -(LTOP) events, Pressurized Thermal Shock (PTS) events, and low irradiated W 'Charpy Upper Shelf Energy (USE). In your July 5,1990, submittal, you stated that the RTHDT values for~ reactor -_ vessel plate and weld metal for the years:1990_and-2000, are below the screening criteria of 270'F and only slightly above.the screening criteria for the year; 2020. AdditionalLinformation was provided to support your statements in ' numerous communications which are listed as' references in the-attached NRC-safety assessment: report. The staff, in its review of your submittal, has concluded that there are sub-stantial uncertainties ' associated with the weld chemistry and the effects of-

coarse grain plate material on the shift in the RTNDT reference-temperature.

These uncertainties could result in reference temperatures significantly higher than the screening criteria!specified in the regulations. However, staff . calculations, recognizing these uncertainties coupled with estimates of the likelihood of the occurrence of PTS events, lead us to conclude-that it is . acceptable to operate the Yankee Rowe plant until the end of fuel cycle 21 (approximately February 1992).

Although your July 5,1990 submittal did not consider LTOP events, the staff shas' evaluated this scenario based upon additional information provided by your staff. We consider that the systems and procedures implemented at Yankee Rowe, along with-estimates of vessel conditional probability of failure provide grumunne P

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~-. .-~- e-br. Andrew C. Kadak 'AUG s i 1990 i sufficient assurance that the probability of an LTOP event leading to brittle vessel failure _is-sufficiently low to permit continued operation for an additional

cycle, In your July 5,1990, submittal, you stated that after performing an additional analysis using the ASME Section XI methodology the USE calculated for the 3

Yankee irradiated plate and weld are 35 ft-lb and 40 ft-lb respectively. Paragraph IV.A.1 of Appendix G,10 CFR 50 states that reactor vessel beltline materials must have USE throughout the life of the vessel of no less than 50 ft-lb, unless it is demonstrated in a manner approved by the Director, i Office of Nuclear Reactor Regulation, that lower values of upper shelf energy will provide margins of safety against fracture equivalent to those required by Appendix G of the ASME Code. According to staff. calculations the USE for-the Yankee Rowe vessel could be as low as 35.5 ft-lb. Your USE analysis indicates that the reactor vessel with 35 ft-lb Charpy USE has margins of safety against fracture, equivalent to those in Appendix G of the ASME. Code as required by the regulations. The staff has reviewed your analysis-and considers that it is acceptable to operate the Yankee Rowe reactor vessel until the end of. fuel cycle 21 with 35 ft-lb Charpy USE. During a meeting on August 21, 1990 you agreed 'to provide us within 60 days 'of-the meeting date, a proposed plan to address the-uncertainties noted herein.. The enclosed staff safety assessment addresses these uncertainties in detail. For Yankee Rowe to continue to_ operate beyond the next operating cycle, we stress the.need for you.to. reduce the uncertainties in the various elements affecting reactor vessel. integrity. Your plan should: include any appropriate procedural changes, technical specification changes, and sampling and physical tests to ascertain the chemical and physical proporties of reactor vessel lower plates and welds. The staff concludes the following actions'should be included in your plan: Long Term Actions to.be. Completed Prior.to Cycle 22.Startup - 1. LDevelop inspection methods for the beltline welt.t and each beltline l plate from'the clad to 1 inch from the clad /stee interface to determine if-the metal contains flaws. 2. PerformtestsontypicalYankeeRowebasemetal(0.lg-)0.20%Cu)to ] determinetheeffectof-irradiation (f=1-5E19n/cm, austentizing temperature (1650*F-1800*F)-and nickel composition (0.18-0.70 percent) on embrittlement at 500*F and 550*F irradiation temperatures. l-3. Determine composition of the circumferential weld metal in beltline by L removing samples from the weld. In addition, prior to Cycle 22 startup, you-should install surveillance capsules in accelerated irradiation positions. The capsules are to include materials representing the beltline circumferential weld metal and upper and lower plates. l* 1 i

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g Br. Andrew C. Kadak. AUG 8 01900-d In addition,'you'also agreed to the following: I 1. Fluence: calculations prepared by Westinghouse will be provided by October 1,. 1990. -l 2. Results of peer evaluation of Yankee's July 5, 1990, submittal will be-i .provided within three months, h- - The results' of the-staff's review of your ' July 5,1990, submittal ere included j in the enclosed safety assessment, a D" ] Sincerely, ,. Y[ original cicned 4 + %., i 2tomanz. Murley p ' 3 "i, Thomas E. Murley, Director it+. 0ffice of Nuclear Reactor Regulation s., hb+i[

Enclosure:

As stated N w e 9.m i, ~ p' cc:..See attached mp 3 s i n ( i. i'it / G

• See previous concurrence

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L t j gUr.AndrewC.Kadak -- w, W, cc:_ S-Thomas.Dignan,. Esquire L Ropes and Gray' 225 Frcnklin Street L l Boston, Massc:husetts 02110 z; ^ Mr. T. K. Henderson Acting Plant Superintendent-X, Yankee Atomic Electric Company ' Star: Route Rowe, Massachusetts.01367 Resident-Inspector-Yankee Nuclear Power Station U.S.. Nuclear-Regulatory Commission Post Office Box 28 Monroe Bridge', Massachusetts 01350 RegionalAdmin'istrator,iRegionI. 'U.S. Nuclear Regulatory Commission 475 Allendale Road. King of Prussia',~ Pennsylvania 19406 Robert M. Hallisey, Director-Radiation Control-Program Massachusetts Department of Public' Health- -150 Tremont Street, 7th-Floor-Boston, Massachusetts 102111 . Mr.. George Sterzinger - ' Commissioner ' Vermont-Department of Public. Service i 120: State Street, 3rd Floor- -Montpelier,' Vermont:-05602' g Ms. Jane M. Grant: Senior Engineer - License Renewal Yankee Atomic Electric Company 580 Main Street 'Bolton, Massachusetts 01740-1398 j

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