NRC Generic Letter 79-58, ECCS Calculations on Fuel Cladding

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GL79058

(LETTER TO ALL OPERATING WATER REACTORS)

Gentlemen:

On November 1, 1979, the NRC met with representatives of the NSSS vendors and fuel suppliers to discuss those portions of their ECCS evaluation models dealing with fuel cladding swelling and the incidence of rupture. The staff indicated that as a result of its ongoing evaluation of data from confirmatory research programs concerning reactor fuel, it was uncertain that presently approved ECCS models conform to Section I.B. of Appendix K, 10 CFR Part 50. The staff discussed how these data were developed into new fuel cladding strain and fuel assembly flow blockage models. This issue received considerable media and other public attention during the week of October 29 and was addressed in the Commission's Press Announcement (see Attachment 1) dated October 31, 1979, and in a Commission briefing on November 2, 1979, that was attended by the public.

At the November 1, 1979 meeting each vendor or supplier was asked to show how, in view of these new models, the plants of their design continued to meet the limits of Section 50.45 of Part 50. Their presentations were documented and formally submitted to the staff on November 2, 1979 (see Attachment 2). The information presented demonstrates that, in general, for operating LWRs the calculated peak cladding temperature following a postulated LOCA would not exceed the 2200<deg>F limit in Section 50.46.

As you are aware, our preliminary evaluation, based on the information received from the fuel suppliers, caused us to conclude that there is no significant safety concern for your facility. There remains, however, a need for you to confirm that the representations made in your behalf are correct. Therefore, you are hereby requested to provide, within sixty

(60) days of the date of this letter, written statements, signed under oath or affirmation, which will enable the staff to determine, in light of the concerns described above, whether or not further action is necessary.

We are enclosing copies of the material relating to fuel cladding strain and fuel assembly flow blockage that was presented by the staff at the November 1 and 2, 1979 meetings. Also included is the documented response of each vendor or fuel supplier.

.You are requested to review the enclosed information on the new fuel cladding strain and fuel assembly flow blockage models, designated as Staff's Analysis on the enclosures. Where the models used by you for cladding stain and assembly blockage in your ECCS calculations are as conservative as the staff's new models, please confirm that this is the case. If your models are as conservative as the new models no further calculations are necessary. However, if regions exist where either of your models is less conservative than the staff's model, additional calculations must be performed to demonstrate compliance with the limits of 10 CFR 50.46. Appropriate sensitivity studies may also be submitted with your evaluations.

If you have any questions regarding this matter, please contact Mr. Paul Check, Chief, Reactor Safety Branch (301-492-8030)

Sincerely,

Darrell G. Eisenhut, Acting Director Division of Operating Reactors Office of Nuclear Reactor Regulation

Enclosures:

As Stated