The radiation characteristics analysis code system for geological disposal is developed to study the radiation influence of high-level waste on an engineered barrier system for the various conditions from a reactor burnup through geological disposal. The verification of the code system is performed by the comparisons with the data in the previous study which analyzed the radioactivity, the radiation emission rate, the radiation energy spectrum, and the radiation flux for the vitrified waste fabricated from spent UO2 fuel with 45 GWd/t discharge burnup. The calculation of neutron emission rate and energy spectrum shows the improvement by the introduction of updated data, and the calculation results of the code system show the good agreement with the reported data, considering the calculation conditions. The effect of the burnup condition of spent nuclear fuel in a light water reactor (LWR) on the radiation characteristics of vitrified waste is surveyed by the application of the code system. The numerical analyses are performed on the basis of the burnup conditions of two types of fuels (UO2 and MOX) and two burnup levels of current standard (45 GWd/t) and high burnup (70 GWd/t). The ratio of high-level liquid waste in vitrified waste is 20 wt% for all cases. The analysis results indicate that the utilization of MOX fuel increases the MA radioactivity drastically, thereby increasing the neutron emission rate of waste and the neutron flux on the inner surface of the overpack by a factor of over nine in comparison to the UO2 fuel waste disposal, whereas the utilization of high burnup fuel increases the emission rate and flux of neutron and γ-ray by 20 – 170 %. The radiation fluence is sufficiently small even by the change of burnup condition compared to the lifetime fluence of reactor pressure vessel employed in LWR.
- Engineered barrier system
- Geological disposal
- Vitrified waste
ASJC Scopus subject areas
- Nuclear Energy and Engineering