With respect to spent nuclear fuels, disposal containers and bentonite buffer blocks in deep geological disposal systems are the primary engineered barrier elements that are required to isolate radioactive toxicity for a long period of time and delay the leakage of radio nuclides such that they do not affect human and natural environments. Therefore, the thermal stability of the bentonite buffer and structural integrity of the disposal container are essential factors for maintaining the safety of a deep geological disposal system. The most important requirement in the design of such a system involves ensuring that the temperature of the buffer does not exceed 100℃ because of the decay heat emitted from high-level wastes loaded in the disposal container. In addition, the disposal containers should maintain structural integrity under loads, such as hydraulic pressure, at an underground depth of 500 m and swelling pressure of the bentonite buffer. In this study, we analyzed the thermal stability and structural integrity in a deep geological disposal environment of the improved deep geological disposal systems for domestic light-water and heavy-water reactor types of spent nuclear fuels, which were considered to be subject to direct disposal. The results of the thermal stability and structural integrity assessments indicated that the improved disposal systems for each type of spent nuclear fuel satisfied the temperature limit requirement (< 100℃) of the disposal system, and the disposal containers were observed to maintain their integrity with a safety ratio of 2.0 or higher in the environment of deep disposal.

1. Introduction
2. Improved Geological Disposal Systemfor SNF
    2.1 Improved CANDU SNF disposal system
    2.2 Improved PWR SNF disposal system
3. Thermal Stability Analyses of the ImprovedDisposal Systems
    3.1 Thermal stability of improved CANDUSNFs disposal system
    3.2 Thermal stability of improved PWR typeSNFs disposal system
4. Structural Stability Analyses for the ImprovedDisposal Container
    4.1 Analyses model for the structural integrityof the improved disposal containers
    4.2 Results of the structural integrity analysesfor disposal containers
5. Conclusions and Future Plan
REFERENCES

• Jongyoul Lee(Korea Atomic Energy Research Institute) Corresponding Author
• Hyeona Kim(Korea Atomic Energy Research Institute)
• Inyoung Kim(Korea Atomic Energy Research Institute)
• Heuijoo Choi(Korea Atomic Energy Research Institute)
• Dongkeun Cho(Korea Atomic Energy Research Institute)