Buffer retardation experiment for radionuclides under the elevated temperature conditions: Strategy and methodology development for the Korean Bentonite

KAERI has been investigating the long-term behaviors of the bentonite under the Korean granite environments. The spent nuclear fuels generate decay heats for a very long time. Thus, the thermal criteria for thehosting buffer materials must be set for the disposal repository. In most countries, it is set to below 100 .deg. C, due to the possible transformation of the smectite to illite which will result in the loss of their requested properties including the swelling capacity. Recently, some efforts (e.g., Grimsel Test Site (GTS) HotBENT Project) have been started to reconsider the thermal criteria for the buffer, because if the maximum temperature allowed for the disposal repository increases, the disposal density decreases dramatically. This will help certain nation with a high population density, especially from a viewpoint of the national economy, site availability, and public acceptance. We have developed a strategy and methodology for the Korean bentonite retardation experiments to rationally address the issues related to the thermal criteria. First, we have illustrated a scienario for the Korean bentonite in the disposalrepository with time. Second, the alteration of the Korean bentonite in the absence and/or presence of he groundwater at the elevated temperatures must be investigated due to the buffer saturation period, which will likely take several-hundred years up to one thousand years.