ML20148J249

Order for Mod of License DPR-3,reducing Tech Specs Limit for Allowable Peak Linear Heat Generation Rate

ML20148J249
Person / Time
Site:	Yankee Rowe
Issue date:	08/27/1976
From:	Rusche B Office of Nuclear Reactor Regulation
To:
Shared Package
ML20148J247	List: ML20148J241 ML20148J249
References
NUDOCS 8011210639
Download: ML20148J249 (5)

Text

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, ( ., j 916 s)NITED STATES OF AMERICA G

NUCLEAR REGULATORY CorNISSION In the Matter of

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Tankee Atomic Electric Comoary Docket No. 50-29 .

Yankee Nuclear Power station 9.

(Yankee-Rowe)

ORDER FOR M3DIFICATION OF LICENSE I.

Yankee Atomic Electric Company, is the holder of Facility Operating License No. DPR-3 which authorizes the operation of a nuclear power reactor known as Yankee Nuclear Power Station [ Yankee-Rowe] (the  !

y fa 'lity) at steady state reactor power levels not in excess of  ;

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600 themal megawatts (rated power). The facility is a pressurized water reactor (PWR) located at the Licensee's site in Rowe, Franklin County, Massachusetts. U h <

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In confomance with evaluations of the perfomance of the Emergency Core Cooling System (ECCS) of the facility submitted by the Licensee on b February 20, 1976, the Technical Specifications issued on June 2,1976 (Amanir,ent No. 26), for the facility limit the allowable peak linear R heat generation rate (LHGR) as set forth in Figure 8-1 of the Technical Specifications. The ECCS perfomance evaluation submitted by the Licensee ,j

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was based upon a previously approved ECCS evaluation model developed by 1

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- r Exxon Nuclear Corporation (Exxon), the nuclear fuel vendor, to confonn y, ;:: :;

to the requirements of the Commission's ECCS Acceptance Criteria,10 CFR Part 50. E50.46 and Appendix K. The evaluation indicated that with the peak LHGR limited as set forth above, and with the other limits set forth in the facility's Technical Specifications, the ECCS cooling performance for the facility would conform to the criteria contained in i:

10 CFR 550.46(b) which govern calculated peak clad temperature, maximum cladding oxidation, maximum hydrogen generation, coolable geonetry and long tenn cooling.

Due to the configuration of the reactor vessel design, a small portion of relatively cooler reactor inlet water is directed through a bypass gap in the inlet nozzles to cool the upper portion of the head. Accordingly,  ;

upper head temperatures were assumed in evaluating ECCS performance to be equal to the reactor inlet water temperature. However, recent operating data gathered at the Connecticut Yankee facility has indicated that,  ; ,

contrary to this expectation, the temperature of the water in the upper head is warmer than the reactor inlet water temperature, by about some  ;-

60" of the reactor inlet - reactor outlet temperature differential.

This increase in upper head water temperature over that used in ECCS performance calculations would have the effect of increasing the .

c61culated peak clad temperature. This higher upper head water .

temperature would have the effect of increasing the calculated peak 9 clad temperature in the event of a loss of coolent accident.

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In a meeting with the staff on August 9,19h6, Westinghouse, the reactor rc designer, presented generic evaluationsof the effect on calculated peak clad temperature for the worst break identified in previous calculations

• f for several types of Westinghouse reactnr designs using an upper head '!

4 water' temperature exceeding reactor inlet water temperature by an amount equal ~ to 75% of the reactor inlet - reactor outlet differential. On

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August 12, 1976, the staff directed the licensee to submit an analysis with the clearly conservative assumption of upper head water temperature equal to reactor outlet temperature (100% of the reactor inlet - reactor outlet differential) and to operate the facility in accordance with the results of this analysis. The results of the evaluation submitted for _

the Yankee-Rowe reactor indicated that with this modification of the

. upper head water temperature the calculated peak clad temperature for the q previously established worst case break would not exceed the Comission's ECCS perfont.ance criteria if the peak LHGR were reduced by 0.35 Kw/ft.

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This evaluation was performed using the approved Exxon ECCS evaluation model.

However, since a revised evaluation for the entire break spectrum for the facility using such an approved evaluation model with the properly corrected upper head temperature cannot be completed for sometime, the ,

I staff believes that it is prudent to impose an interim penal,ty on allowable '

! I peak LHGR to account for uncertainties that may exist. The staff concludes that a further limitation on peak LHGR, in addition to that originally y proposed by the Licensee will eliminate uncertainties resulting from the preliminary calculations thus far performed, and will assure that ECCS performance at the facility will conform to all the criteria set forth in 10 CFR 650.46(b).

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After discussions with the NRC staff on August 26, 1976, the licensee amended his previous submission, to account for these u.ncertainties, by h d

reducing the peak LHGR by another 0.5 kw/ft for a total reduction of h

0.85 kw/ft. The NRC. staff beliercs that the licensee's actions, under  !

j the circumstances, are appropriate and should be confirmed by NRC Order, a

The staff expects that, when revised calculations for the facility are submitted using an approved evaluation model with correct input for upper head water temperature, or assuming that the upper head water' temperature equals reactor vessel outlet water temperature, such cal-culations will demonstrate that operation at the reduced peak LHGR would conform to the criteria of 10 CFR 550.46(b). Such revised calculations fully conforming to the requirements of 10 CFR 950.46 are to be provided for the facility as soon as possible. The additional limitations set forth in this Order will provide reasonable assurance that the public health and safety will not be endangered.

Copies of the following documents are available for public inspection in the Ccmission's public Document Room,1717 H Street, NW., Washington, D.C. 20555 and are being placed in the Commission's Local public Document Room, Greenfield public Library, 402 Main Street, Greenfield, Massachusetts 01581 , (1) Licensee letter dated February 20, 1976, (2)

NRC letter dated June 2,1976, and (3) This Order for Modification of License, In the Matter of 'cnkee Nuclear power Station (Yankee-Rowe),

Docket No. 50-29.

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ill gII, R Accordingly, pursuant to the Atomic Energy Act of 1954, as amended, and

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the Comission's Rules and Regulations in 10 CFR Parts 2 and 50, IT IS ORDERED THAT Facility Operating License No. OPR-3 is hereby amended by adding the following new provisions: .

1. As soon as possible, the Licensee shall submit a re-evaluation of 5 ECCS cooling perfont.ance calculated in accordance with an approved ECCS Evaluation Model, with appropriate correction for upper head water temperature.

2. Until further authorization by the Comission, the Technical Specification limit for allowable peak LHGR (Table 8-1 in the Technical Specifications) shall be reduced by 0.85 Kw/ft. r FOR THE NUCLEAR REGULATORY CO HISSION

\ < 4vh 8en C. Rusche, Director Office of Nuclear Reactor Regulation Dated ir. Esthesda, Maryland this AUG 2 7 1975 r

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