Neutronic investigation of a VVER-1200 (Th-233U)O2 fuel assembly with protactinium oxide as a burnable absorber coated on the outer surface of the fuel rods

ABSTRACT

Due to the obvious excess reactivity associated with using ²³³U as a fissile material, fresh fuel must include a burnable absorber (BA) to reduce excess reactivity. As a result, the objective of this study is to look into the use of protactinium oxide (PaO₂) as a thin BA layer coating on the outer surface of the fuel rod for the VVER-1200 assembly, which is fueled by (Th-²³³U)O₂. Through neutronic calculation, the thicknesses of PaO₂ as a BA were determined using the Monte Carlo code MCNP6. For comparison, UO₂ and (Th-²³³U)O₂ assemblies without absorbers were used as references. The study suggests that using PaO₂ with a thickness ranging from 0.11 to 0.13 mm can reduce the early excess reactivity of the (Th-²³³U)O₂ assembly while also increasing the discharge burnup by an average of 2.1 GWd/ton when compared to the UO₂ assembly. Furthermore, it was found that the selected (Th-²³³U)O₂ + PaO₂ assemblies exhibit negative fuel temperature and boron worth coefficients. However, these assemblies exhibit positive moderator temperature coefficients. Neutron spectra, radial power distribution, and fission product poisons were also evaluated to understand the viability of using PaO₂ as a BA for reactivity control in the VVER-1200 assembly under consideration.

KEYWORDS:

• VVER-1200 assembly
• (th-²³³U)O₂ fuel
• protactinium oxide
• reactivity control
• discharge burnup

Disclosure statement

The authors declare that they have no known competing financial interests or personal relationships that could appear to have influenced the work described in this paper.

Data availability

The data used in this study, which may be required to reproduce these findings, are presented in the paper and the references cited.