ECCS Calculations On Fuel Cladding (Generic Letter 79-58)




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 2200F 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. 

                                    - 2 -

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) 


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

As Stated


Page Last Reviewed/Updated Thursday, March 25, 2021