Abstract
Accurate neutron transport models for BWRs are needed to characterize neutron damage to the top guide, top guide cylinder, vessel nozzles, and to other upper internals. In the past, neutron transport calculations above top-of-active-fuel (TAF) have had large uncertainties (well in excess of ± 20%) mainly due to the fact that the steam density distribution in that region is not well known. An advanced three-dimensional (3D) neutron transport model, which incorporates computational fluid dynamics (CFD) in the code suite, has been developed. Retrospective dosimetry measurements were made to benchmark the transport results. Six fuel channel clips were removed from the top of the fuel bundles, and small disk-shaped dosimetry samples were cut from the clips. The cuts were made through the Inconel spring and through the stainless steel clip body. The clips were selected from bundles that cover regions of low, intermediate, and high steam density. The average C/M ratio for the 10 dosimeters is 1.06. It has been shown that all of the calculated dosimeter activities fall within ± 20% of the measurement. This meets the criterion set by RG 1.190 [1] for acceptability of the calculations.
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