Analyses on the Thickness of the Bentonite Buffer in Deep Geological Disposal for Spent Nuclear Fuels

Jongyoul LEE^*, Heuijoo CHOI, Changsoo LEE, Seonghoon JI, Dongkeun CHO

Korea Atomic Energy Research Institute, 989-111, Daedeokdaero Yuseong-gu Daejeon-city,34057

Received 2024-08-29 ; Revised 2024-09-23 ; Approved 2024-10-24

Abstract

A multi-barrier can be applied for the deep geological disposal of high-level radioactive waste. The multi-barrier comprises an engineered barrier and the natural barrier of the host rock. In the engineered barrier, the bentonite buffer is the key component for the disposal container, and the bentonite buffer thickness is given important consideration when designing the engineered barrier. This study reviewed the safety functions of bentonite buffers. Subsequently, the requirements and factors necessary to determine the thickness of the bentonite buffer, including criteria for radiological safety and the thermal stability of the disposal system, were identified. Additionally, the bentonite buffer thicknesses required for the top, bottom, and side of the disposal container were calculated. A double-layered emplacement method is also proposed for the bentonite buffer to improve disposal efficiency in terms of thermal management. Based on radiological safety and thermal stability analyses, an optimal thickness of 0.36 m was found to be appropriate for the bentonite buffer surrounding the disposal container. The thickness of the bentonite buffer above the disposal container can be determined based on the excavation damaged zone depth. The study findings can be used as a reference when designing deep geological disposal systems.

Key Words : deep geological disposal, spent nuclear fuels, buffer thickness, engineered barrier, radiological safety, thermal stability