NUREG/CR-5625 (ORNL-6698) - Oak Ridge National Laboratory

ABSTRACT
This report was prepared to provide support for major revisions to the current U.S. Nuclear Regulatory Commission decay
heat rate guide entitled "Regulatory Guide 3.54, Spent Fuel Heat Generation in an Independent Spent Fuel Storage
Installation," using a new data base produced by the SAS2H analysis sequence of the SCALE-4 system. The new data base
of heat generation rates provides a significant improvement by increasing the number and range of parameters that
generally characterize pressurized-water-reactor (PWR) and boiling-water-reactor (BWR) spent fuel assemblies. Using
generic PWR and BWR assembly models, calculations were performed with each model for six different burnups at each of
three separate specific powers to produce heat rates at 20 cooling times in the range of 1 to 110 y. A procedure that
includes proper interpolation formulae for the tabulated heat generation rates is specified. Adjustment formulae for the
235
interpolated values are provided to account for differences in initial U enrichment and changes in the specific power of a
cycle from the average value. Finally, safety factor formulae were derived as a function of burnup, cooling time, and type of
reactor. The procedure included in this report was developed with the intention of providing one that was easier to use than
that in the current Regulatory Guide. Also, the complete data base and procedure is incorporated into an interactive code
called LWRARC which can be executed on a personal computer.
The report shows adequate comparisons of heat rates computed by SAS2H/ORIGEN-S and measurements for 10 BWR and
10 PWR fuel assemblies. The average differences of the computed minus the measured heat rates of fuel assemblies were
–0.7 ± 2.6% for the BWR and 1.5 ± 1.3% for the PWR. In addition, a detailed analysis of the proposed procedure indicated
the method and equations to be valid.
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NUREG/CR-5625