Neutron sources in spent nuclear fuel of RBMK-1500 type reactor

Abstract

The main part of residual power of spent nuclear fuel depends on fission product radiation. The impact of neutron radiation on man and environment can be very significant, because the dosimetrical values from neutron sources become equivalent to those of photon irradiation when nuclear fuel is transported or stored for a long time in casks as in the case of Ignalina NPP. Mechanisms of neutron emission are discussed in the present paper and the results of calculations of spent nuclear fuel nuclide inventory using the codes APOLLO1 and REFACTN for the RBMK-1500 type reactor are presented. Results of calculations are used for the evaluation and assessment of neutron sources. It is shown that the main neutron sources in the spent nuclear fuel of the RBMK-1500 type reactor are 242,243,244 Cm, 236,238,240 Pu, 232 U, and 241 Am. It is determined that the emission of neutrons does not decrease with the time uniformly. Neutron emission due to the (�, n) reaction of 228 Th becomes significant after 50 years of cooling. The cooling time and burn-up of the nuclear fuel are the most important parameters that affect build-up of neutron sources.