SPATIAL DEPENDENCE OF REACTIVITY COEFFICIENTS

Abstract: The objective of this thesis is to study and understand the behavior of the reactivity coefficients (RCs) in a boiling water reactor (BWR) partially within 25 different segments with different void fractions, with enriched oxide fuel (UOX) core, as well as to evaluate the methodologies exposed in [10]. These two normalization  methods (described in chapter 3) are used to analyse the contribution of each segment of the core having different regions (fuel, clad, coolant, moderator and channel box) to the RCs. All the calculations in this work are performed using PSG2 / Serpent – a Continuous-energy Monte Carlo Reactor Physics Burnup Calculation Code. The overall reactivity coefficient's values are exactly the same for both methodologies, but the partial reactivity coefficients are totally differing from each other. Using the symmetric normalization methodology introduced in chapter 3 section 3.4.3 the partial reactivity coefficients become almost the same for both methodologies. Moreover, the overall reactivity coefficients are exactly the same as well. Methodologies for reducing the radiotoxicity of the actinides and fission products produced in nuclear fuels are presently under investigation. Therefore, currently the nuclear reactors are designed not only for power generation, but also are used as transmuters as well, by inserting, for example, the minor actinide to a reactor core the safety parameters can get worse. Moreover, it is wiser to study the partial reactivity coefficients of a reactor core.