| Summary: | 博士 === 國立清華大學 === 工程與系統科學系 === 99 === Taiwan Research Reactor (TRR) spent fuel rods contain weapons-grade plutonium. For the nuclear safeguard purpose, this work aims to determine the plutonium content in the TRR spent fuel rods by using the nondestructive neutron measurement before and after the fuel stabilization process, by which the metallic spent fuel rods will be transformed to oxide power for interim storage.
We established two neutron detection systems, namely, the SPent-fuel Neutron Counter (SPNC) system and the Neutron Coincidence Counter (NCC) system for determining the Pu-240 content in the TRR spent fuel rod and in the transformed oxide powder, respectively. The measured Pu-240 contents in the TRR spent fuel were then converted into total plutonium contents by using the MCNPX-calculated Pu-to-240Pu mass ratio. The detection efficiency of the SPNC system was calibrated by the measurement of a TRR fresh fuel in a water trench filled with clean water and verified by the MCNPX simulation calculation. Seven TRR spent fuel rods were measured in the nearby water trench connected to the spent fuel storage pool. The measured plutonium contents agree well with the MCNPX-calculated values based on the burnup history of each spent fuel rod, except for the broken rods with fuel oxidation. The detection efficiencies consisting of singles rate and doubles rate efficiencies of the NCC system were determined by using measurements using U3O8 powder in couple with MCNPX calculations. Canisters filled with oxide powder converted from three TRR spent fuel rods were measured by the NCC system in the hot cell. The measured plutonium contents of the oxide powder from the spent fuel rods agree well (<18%) with the measured value before the fuel stabilization process.
In conclusion, our nondestructive neutron detection systems can accurately determine the plutonium content in TRR spent fuel. Furthermore, the two measurements for each TRR spent fuel prove that there is no obvious process and artificial loss of plutonium contents during the fuel stabilization process.
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