Abstract
This paper presents calculation studies towards validation of a methodology for estimations of the mass of tramp uranium in a boiling water reactor (BWR) core from water chemistry measurements. The computational studies are carried out for a typical BWR fuel assembly with CASMO-5M and MCNPX. By approximating the evolution of fissile nuclides and the fraction of 235U fissions to total fissions in different zones of a fuel rod, including tramp uranium on the clad surface, it is found that Pu gives the dominant contribution to fissions for tramp uranium after an irradiation on the outer clad surface of at least one cycle. Thus, the use of the so-called “Pu-based model” for the determination of the tramp uranium mass (this means in particular using the yields for 239Pu fission) appears justified in the cases considered. On that basis, replacing the older “U-based model” by the “Pu-based model” is recommended.
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