Neutron field measurement in reactor cores with simulated fuel assembly structure and bundle configuration of absorption rods

The results are presented of the measurement of the macroscopic distribution of neutron flux density in the horizontal plane of the reactor core. The core contained fuel elements of a different enrichment and absorbers in a cluster configuration. A comparison of the experimental results and theoretical calculations of the neutron flux density distribution using boron carbide absorbers showed a difference in the values obtained, especially on the fuel element surfaces in the vicinity of irregularities. It is shown that a change in a single correction coefficient for all fuel elements with 3.6% 235U enrichment is not justifiable and it is therefore necessary to introduce a new correction characterizing the change in the relation of neutron flux density on the fuel element surface to the mean cell size as a result of depression close to the absorber and a neutron spectrum change. The results of measurement were processed using the BPLOT program and are shown in tables and graphs. (J.B.)