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

摘要

Spent fuels to be disposed of have various initial ~(235)U 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 ~(235)U 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.