Abstract
The steam void effect on core reactivity and flux distribution was experimentally studied on cores loaded with fuel assemblies of various void fractions. The voids were simulated by hollow polyethylene tubes. The local flux distributions within the assembly cells of various void frac-tions have already been discussed in Part (I) of the present series of papers.
The study proved that the reactivity calculation can be improved by considering the double heterogeneity that characterizes an assembly lattice simulating the BWR core, by means of the following treatments: (a) Consideration of the spatial variation of the thermal neutron spectrum around water gaps. This gave good results for the analyses of local flux distributions, (b) Adoption of the effective Dancoff factor, which evaluates the difference in the resonance neutron shielding effect between fuel rods lining the water gap and those others closed in by similar rods.
