United States Nuclear Regulatory Commission - Protecting People and the Environment

Information Notice No.80-04 - BWR Fuel Exposure in Excess of Limits

                                                            SSINS No.: 6870 
                                                            Accession No.:
                                                            7912190655 

                                UNITED STATES
                        NUCLEAR REGULATORY COMMISSION
                    OFFICE OF INSPECTION AND ENFORCEMENT
                           WASHINGTON, D.C. 20555 

                             February 4, 1980  

                                           Information Notice No. 80-04 

BWR FUEL EXPOSURE IN EXCESS OF LIMITS 

On November 1, 1979, and December 17, 1979, respectively, the licensees of 
the Quad Cities Unit No. 1 and Monticello Nuclear Power Plants informed the 
Nuclear Regulatory Commission that the actual peak average planar exposure 
of some fuel assemblies in the core was beyond the maximum average planar 
exposure value of the Maximum Average Planar Linear Heat Generation Rate 
(MAPLHGR) Limits specified in the plant Technical Specifications. 

In the case of Quad Cities, the licensee was aware that some fuel assemblies
would approach and exceed the exposures for which MAPLHGR limits had been 
analyzed. In the interim, the station process computer was used to calculate
higher exposure MAPLHGR limits via an extrapolation routine, while awaiting 
determination of the additional high exposure MAPLHGR limits using standard 
licensing analysis methods. When the actual limits were made available for 
comparison with the extrapolated values, it was determined that the process 
computer had extrapolated values non-conservatively. Although the new 
MAPLHGR limits extensions were immediately entered into the computer, the 
new limits had not yet been submitted for review and approval by the NRC. 

With regard to Monticello, the licensee became aware that the 30,000 MWD/T 
maximum exposure specified in the plant Technical Specifications were being 
exceeded after several months of operation had elapsed. Although the high 
burnup fuel assemblies had at no time exceeded the MAPLHGR value 
corresponding to 30,000 MWD/T, MAPLHGR limits calculated by standard 
licensing analysis methods showed that lower MAPLHGR values should have been
utilized at the higher exposures. Again although the new MAPLHGR limits were
promptly substituted, the new limits were not at the time formally approved 
by the NRC. 

In both cases, it was subsequently determined by the licensees that the 
actual operating MAPLHGR values had at no time exceeded the revised MAPLHGR 
limits at the higher exposures. The licensees subsequently requested 
amendments to their Technical Specifications, adding MAPLHGR limits for 
average planar exposures values beyond the actual peak average planar 
exposure projected for the present cycles. These changes have been reviewed 
and approved by the staff. 

Additionally, fuel rod thermal-mechanical design and safety analyses for the
subject fuel are dependent on local (peak pellet) exposure conditions. The 
peak pellet exposure basis for those analyses is 40,000 MWD/T. Since the 
peak pellet exposure exceeds the fuel assembly maximum average planar 
exposure as fuel assembly average planar exposure increases, the concern is 
raised that the 
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Information Notice No. 80-04                             February 4, 1980 
                                                            Page 2 of 2 

40,000 MWD/T fuel thermal-mechanical analysis basis exposure could also be 
approached or exceeded. Investigations conducted by the licensees showed 
that the peak pellet exposure had not nor would riot exceed the fuel 
thermal-mechanical design maximum basis during the current operating cycles.

The potential for occurrence of the above events can be decreased by (a) 
surveillance  procedures which require periodic comparison of actually peak 
average planar exposure and peak pellet exposure values to approved exposure
limits, and (b) use of the computer to provide an alarm or flag as an aid to
indicate when approved exposure limits are being approached. 

This Information Notice is provided to inform licensees of a significant 
safety matter. It is expected that recipients will review the information 
for possible applicability to their facilities. No specific action or 
response is requested at this time. IF you have any question regarding this 
matter, please contact the Director of the appropriate NRC Regional Office. 

Page Last Reviewed/Updated Tuesday, November 12, 2013