Characteristics of Effective Delayed Neutron Fraction in Heterogeneous Fuel Solution Systems

Abstract

The particular characteristics of an effective delayed neutron fraction are found in a heterogeneous fuel solution system in the present study. Those are against a conventional systematic understanding successfully employed in a homogeneous system. Therefore, the characteristics in a heterogeneous fuel solution systems should be validated by a new systematic understanding. For the conventional systematic understanding, the effective delayed neutron fraction is described by the geometrical buckling based on the Fermi age theory of a relation between an effective delayed neutron fraction and a fuel concentration of a fuel solution in a fuel solution system. To establish the new systematic understanding, the effective delayed neutron fraction in the heterogeneous system is numerically evaluated with its distribution in the system. As a result, it is found that the effective delayed neutron fraction in the heterogeneous system becomes small while that in the homogeneous system becomes large, as the fuel concentration in the fuel solution increase and the fuel solution level decreases. It is concluded that the change of neutron leakage effect due to the fuel concentration for horizontal direction causes the particular characteristics in a heterogeneous systems against the characteristics in a homogeneous system. As described above, the characteristics in a heterogeneous fuel solution systems have been validated and it is concluded that the characteristics varies depending on the heterogeneity. This result will contribute to the systematic understanding for the critical safety on fuel solution systems.