Graphite Core Dismantling for Minimising Graphite Waste Volume

The current baseline strategy for the UK AGR and Magnox reactors includes whole brick retrieval followed by basic treatment and grouting in
the specified package. Whole brick retrieval is possible for Magnox reactors where no cracks have been observed but the engineering tools will have to take into consideration the metallic components that are included in the core structure. AGR cores are expected to have a significant number of multiply cracked bricks and hence development of additional engineering solutions will be required. Even if whole brick retrieval is achievable and it is followed by some crushing for packaging, this option does not result in the optimum packaged waste volume.
The objective of this project is to explore the Nibble and Vacuum technique for retrieving the core graphite. Although it is a widely used technique and has been previously proposed for graphite, the TRL is low, and is limited to basic concept studies; in addition, Nibble and Vac has not been tried on core graphite. The aim will be to identify the optimum parameters, potential issues either related to the engineering implementation or to the safety case. The result of this dismantling method is crushed graphite that can then be readily used for waste minimisation methods, such as bulk oxidation or HIP. Significant work has been completed on the former by UoM so this work will focus on the latter with studies on the Nibble and Vacuum methodology to enable industrial scale up.
The research will include a feasibility study, safety case assessment and optimisation of HIP as a treatment method for irradiated graphite. If successful, HIP and subsequent leaching studies will be performed on irradiated graphite. Characterisation of the graphite and its properties will be undertaken before HIPing in order to understand this effect on the HIP process. The optimum achievable volume minimisation method will be established followed by leaching tests on the HIPed graphite to determine its efficiency as an immobilisation method.