Effectiveness of source term optimization for higher disposal density of spent fuels in a deep geological repository

• In the past, a disposal system was developed using a conservative reference spent fuel.
• ASOURCE was used to exclude conservativeness in source terms of spent fuels.
• Respective source terms of spent fuels were considered in a disposal system design.
• Benefits were evaluated in terms of footprint reduction of a repository.
• As a result, the footprint was decreased up to a roughly 50%

Spent fuels to be disposed of have various initial 235U enrichments, discharge burnups, and cooling times, and consequently each type of spent fuel has a different decay heat. Because a disposal system design considering respective spent fuel characteristics was not previously possible in Korea, a system was developed based on a conservative reference spent fuel nominated through historical data analyses on the relation of spent fuel inventory with the initial 235U enrichment, discharge burnup, and cooling time. Recently, ASOURCE, an advanced source-term calculation system, was developed by the Korea Atomic Energy Research Institute, making it possible to design a disposal system considering the respective source terms of the spent fuels. In this study, the benefits resulting from a consideration of the individual decay heat for entire spent fuels were evaluated in terms of the footprint of a repository. As a result, it was seen that conservativeness in the disposal system design can be remarkably avoided, revealing a roughly 50% decrease in the footprint of the repository, considering the respective irradiation and cooling profile. It is therefore concluded that optimization of the source term is a viable option in a deep geological disposal system design.