Physics studies on BWR void simulated cores, (1)

In an attempt to obtain more information concerning steam void effects on the physical behavior of BWR cores, voids ranging from zero to 24% volume fractions were statically simulated by inserting polyethylene tubes between fuel rods of simulated BWR core, and measurements were made of local flux distribution, neutron spectrum, reactivity, reactivity coefficient of void and so forth. The results were compared with calculations. Improved methods of calculation were developed, which assured better agreement with measured results. While this paper only deals with local distributions of the thermal neutron flux and spectrum within the assembly cells, it has been shown that spectrum variation near water gaps could be well described by an overlapping model which provided an improvement on the analysis. An additional improvement was obtained by the incorporation of an approximate transport correction. (author)