Thermal treatment of PCM and ILW

The projected UK plutonium contaminated material (PCM) waste volume is >30000 m3 with 70% arising at Sellafield. The current baseline treatment is supercompaction / cement encapsulation. However, a BPEO study for Sellafield Ltd. highlighted “concerns regarding the composition of the conditioned wasteform and… stability during long term storage”. Thermal treatment, i.e. in-container or plasma vitrification, was identified as “the main alternative technology” with “advantages in terms of… stability of final product and improved volume reduction”. Although proof of concept studies by Sheffield University and others have demonstrated PCM compatibility with thermal processes, a fundamental understanding of waste incorporation reactions and the impact of waste inventory on product quality remains to be established. This generic understanding is clearly critical to successful technology deployment.

Laboratory scale experiments using mock ups of PCM waste (using Ce as a Pu surrogate) and glass forming additives have been performed in order to understand the reactions / processes of waste digestion and incorporation during thermal treatment.

The focus of this project is thermal treatment of PCM wastes relevant to four sites across the NDA estate. Since the aim is to develop a fundamental mechanistic understanding of waste incorporation reactions during thermal treatment, the research will be transferrable to treatment of wastes within the UK ILW envelope (which could also be co-treated with PCM).

The project investigates the credibility of vitrifying various ILW streams. In particular the project investigates vitrifying Pond Scabbling Wastes, which is contaminated concrete (ILW) originating from scabbling of fuel ponds at various NDA sites. It is known that some ILW themselves possess the key oxides for glass making, chiefly SiO2. Therefore some, or possibly all, of the SiO2 in the vitrified product could originate from the ILW itself. One of the objectives of this project is to evaluate whether masonry waste removed from the decommissioned silo ponds as scabblings contain sufficient amounts of glass forming oxides, mainly SiO2, to aid vitrification of a passive glass wasteform.