Effect of Cs and Sr separation on occupied area reduction in current nuclear energy system and its evaluation by CAERA index

ABSTRACT

Separation of Cs and Sr from high-level liquid waste (HLLW) contributes to reducing heat generation and correspondingly to minimizing the required use of space in geological disposal repositories for high-level radioactive waste. To maximize the impact of Cs and Sr separation on reducing the occupied area of a repository, it is necessary to consider both the front-end and back-end stages of the nuclear energy system. Therefore, we quantitatively surveyed factors that potentially affect the reduction in the occupied area – that is, the area required for disposal of one waste package – when introducing Cs and Sr separation. From an evaluation using the Comprehensive Analysis of Effects on Reduction of Disposal Area (CAERA) index, we found that in case of a 15-year cooling period of spent nuclear fuel (SNF) after discharge, which is the current operational condition at the Rokkasho Reprocessing Plant, a maximum reduction of 30% in occupied area was achieved for 25 and 30 wt% waste-loaded vitrified waste with Cs and Sr separation. In that case, separation of more than 70% of Cs and Sr was required based on the current reference case for the Japanese geological disposal concept (the so-called H12 Report). In addition, the effectiveness of Cs and Sr separation for reducing the occupied area was drastically decreased if the cooling period after discharge was extended beyond 15 years; for instance, vitrified waste with a more than 40-year cooling period showed almost no reduction in occupied area. This was because the amount of ²⁴¹Am, which is generated from the beta decay of ²⁴¹Pu, and the contribution of ²⁴¹Am to heat generation in vitrified waste increased as the cooling period became longer. The results suggested that the cooling period of the SNF, the waste loading of the vitrified waste, the Cs and Sr separation ratio and the occupied area of the waste were key factors governing the effectiveness of Cs and Sr separation for geological disposal area reductions.

KEYWORDS:

• Reprocessing
• partitioning
• vitrification
• waste management
• geological disposal
• nuclear fuel cycle

Additional information

Funding

This research was supported by the Radioactive Waste Management Funding and Research Center (RWMC) and some of the results of this study were obtained as part of the RWMC’s research program “Study on the effects of advanced nuclear fuel cycle technology to the geological disposal concept”.