Abstract
A quantitative assay of isotopic fissile materials (U235, Pu239, Pu241) was done at Korea Atomic Energy Research Institute (KAERI), using lead slowing down spectrometer (LSDS). The optimum design of LSDS was performed based on economics, easy maintenance and assay effectiveness. LSDS system consists of spectrometer, neutron source, detection and control. LSDS system induces fissile fission and fast neutrons are collected at fission chamber. The detected signal has a direct relation to the mass of existing fissile isotopes. Many current commercial assay technologies have a limitation in direct application on isotopic fissile assay of spent fuel, except chemical analysis. In the designed system, the fissile assay model was setup and the correction factor for self-shield was obtained. The isotopic fissile content assay was performed by changing the content of Pu239. Based on the fuel rod, the isotopic content was consistent with ~2% uncertainty for Pu239. By applying the covering (neutron absorber), the effective shielding was obtained and the activation was calculated on the target. From the assay evaluation, LSDS technique is very powerful and direct to analyze the isotopic fissile content. LSDS is applicable for nuclear fuel cycle and spent fuel management for safety and economics. Additionally, an accurate fissile content will contribute to the international transparency and credibility on spent fuel.
Highlights
An isotopic fissile content assay is very important for the reuse of fissile materials through nuclear fuel cycle and the management of spent fuel
The accurate fissile content is a key point to be verified for increased safety and economics in the reuse and management
For the U235 assay, the results show good agreement to the actual mass
Summary
An isotopic fissile content assay is very important for the reuse of fissile materials through nuclear fuel cycle and the management of spent fuel. The pyro process produces the source material including trans-uranium to fabricate a fuel rod for sodium fast reactor (SFR). The fissile content is one of the factors to be given for the optimum design of spent fuel storage site. An accurate fissile material content can makes it possible for a maximum burnup credit on spent fuel storage site. LSDS is under development to analyze the isotopic fissile content in spent fuel. In the designed LSDS device[1], the source neutron is slowed down in the lead medium and produces continuously slowed down energy. The effective shielding calculation was performed at the outside wall by applying the neutron absorber surrounding the spectrometer
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