ceptual design study includes the layout of the underground facilities, the engineered barrier system, and the dimensions of the major repository system components needed to support the reference repository system design. This study is not site specific, because there are no site characterization data requiring repository performance to a specific location. Many design parameters and criteria are necessarily general or assumed.

These design bases provide the information that identifies the specific functions to be performed by the repository system, as well as the specific values or ranges of values chosen as controlling parameters to bound the design. As a general guideline for this study² the conceptual repository will be located in granitic rock, the major rock type in Korea, at a depth nominally of 500 m between two large fault zones that extend from this depth to the surface. The rock quality varies from highly weathered surface deposits to competent rock at the repository horizon. For this conceptual design the distance between faults should be about 7 to 10 km. Therefore, the repository layout must be capable of fitting within these major structural features. The most stringent requirement for the base-case underground facility is that the temperature of the bentonite buffer material remains below 100°C throughout the lifetime of the repository.

The development of the underground repository system conceptual design requires specifications of (1) design constraints and criteria, (2) disposal canister design, and (3) waste form and throughput. Key design constraints are summarized in Box 1.