Volume 3, Issue 8 (September 2006)
Characterization of Neutron Fields Using MCNP in the Experimental Fast Reactor JOYO
An extensive set of neutron dosimeters ranging from the core center to beyond the reactor vessel were irradiated during the first two operating cycles of the MK-III core to allow a detailed characterization of the neutron spectra and flux distributions for this new core configuration. New analysis methods for predicting the reaction rates for comparison with the dosimetry measurements based on the MCNP code were developed. Analysis of previous MK-II cycle 34-35 dosimetry tests was used to verify the methods. Core models were developed for the different types and locations of dosimetry test subassemblies and biasing schemes were developed. MCNP optimization techniques and the C/E differences were explored. Most of the important parameters that affect the reaction rate calculations and measurements were investigated. In most cases, MCNP provides more accurate estimations of reaction rates and neutron flux than DORT. This indicates that treatment of heterogeneous structure is needed in the predictions for the irradiation test subassembly with no fuel and the irradiation field with large flux gradients.