Actinide Separation from HLLW

Abstract

Spent nuclear fuel can either be incapsulated and stored permanently in a deep underground repository or reprocessed to recover valuable U and Pu. The high level liquid waste (HLLW) solution resulting from PUREX reprocessing contains the fission products, small fractions of the U and Pu, and most of the Np, Am and higher actinides originally present in the spent fuel. The α-activity in the HLLW amounts to more than 99% of all such activity in wastes from the nuclear fuel cycle (1). This solution can be vitrified and stored as high active glass in deep underground repositories in a similar way as the unprocessed fuel. The Swedish KBS study (2, 3) shows that such repositories can be placed in granite bedrock at 500 m depth. Careful analysis of the possible releases from a repository of this kind shows that U and Np isotopes, with daughters, are responsible for the main radiation doses generated by the repository (2, 4). Because of the enormous time scale, a remedy seems to be a reduction of actinide content by about a factor 100 before solidification of the waste. In anticipation that a separation process might eventually be required or at least had to be considered as an option, we began development work on an actinide separation process in 1974. The general philosophy and a broad outline of our flowsheet was presented in 1976 at the Symposium on Waste Management in Tucson (5).