Optioneering in nuclear ion exchange resin disposal

Abstract

Spent ion exchange resins from nuclear facilities make up 4 % of all solid waste from that industry, and with no current disposal pathway, represent an orphan waste stream. Currently spent ion exchange resins are stored in vaults where they slowly degrade, producing dangerous secondary waste that is harder to dispose of.

In this work the most viable disposal options have been assessed using Multi Criteria Decision Analysis (MCDA). Several methodologies were appraised, and a modified version of the Analytical Hierarchy Process (AHP) was chosen. Disposal options identified were shortlisted by the application of threshold criteria. Using AHP, eight Key Performance Indicators (KPIs) were defined and grouped into three overarching criteria: Engineering, Economics and Environmental. The KPIs and criteria were subjected to a ‘pairwise rating process’ to assess their relative importance, which was then used to calculate weightings. These weightings were used to prioritise the raw scores each disposal route had received for the KPIs giving rankings for each disposal option. These were analysed using an uncertainty assessment, employing additional indicators to give an uncertainty percentage. A sensitivity analysis was conducted which changed the weightings to assess the impact this could have on the final rankings.

Vitrification was found to be the most viable option, achieving good scores in all categories. Cementation and Plastic Solidification were also found to be promising, offering a more cost-effective option. A control disposal option, designed to emulate the current UK strategy of storage pending treatment, was included in the analysis. As expected, this disposal option scored poorly, ranking 11th out of 14 demonstrating that the current approach is unsustainable. Several viable alternatives are suggested with further laboratory and economic studies that would allow for deployment of the chosen disposal options.