Calculation of correction factors for neutron multiplication in spent fuel

not registered; Takagi, Shunji*

The responses have been calculated for the burnup measurement equipment placed in the spent fuel storage facility beside JOYO by using the Monte Carlo code "MCNP-4A". These responses are influenced by the neutron multiplication depending to the burnup of the fuel to be measured. In this work, the dependence of calculated responses to the burnup of fuel was ivestigated using the composition of the irradiated fuels obtained from the burnup calculation with MAGI. These responses were compared to the responses without multiplication. The following relationship between burnup and detector response became clear as the results of these calculations. (1)The burnup of fuel influence to the detector response from the neutron source near the detector, but does not significantly influence to the detector apart from the neutron source. (2)The response from the neutron source near the detector decrease with burnup, and the decrease is proportional to the multiplication; 1/(1-k), except for the case that the neutron source is at the end of fuel region. The burnup dose not significantly influence to the detector response from the neutron source at the end of fuel. The detector responses from the neutron from a spent fuel of arbitrary burnup can be corrected by the hear interpolation for neutron multiplication; 1/(1-k), when the detector closes to neutron source, and no corrections are required when the detector is apart from neutron source. It was also investigated that the effect of considering the gas plenum at the top of fuel and considering fission products in irradiated fuels. The multiplication factor of fuel and detector response were decreased with the model considering gas plenum because of neutron leakage from the void in gas plennum. The axial distribution of the detector response was not influenced by this modeling. The fission products in irradiated fuel cause great negative reactivity, about 6%k for the burnup of 62,540MWd/t, and decrease ...