Protecting People and the EnvironmentUNITED STATES NUCLEAR REGULATORY COMMISSION
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.
