Application of plasma cutting in mock-up experiments for decommissioning of internals in heavy water research reactor

The dismantling of internal components within the reactor is one of the primary technical activities in the reactor decommissioning project. Currently, the first nuclear reactor in China, heavy water research reactor (HWRR), is in the phase of decommissioning. By integrating the characteristics of the HWRR with both domestic and international cutting technology experience, plasma cutting has been identified as a suitable and commonly used technique for cutting the reactor internals. Considering that the decommissioning process of nuclear facilities is irreversible, it is essential to conduct mock-up experiments to acquire cutting performance parameters for the cutter prior to decommissioning of the reactor internals, which not only helps optimize the decommissioning plan but also provides data support for decommissioning practices. Based on the characteristics of the outer shell, within the HWRR, parameters such as cutting current, workpiece thickness, cutting speed, working angle, and nozzle standoff were selected for the plasma cutting experiments. Through orthogonal experiments, cutting current, workpiece thickness, and cutting speed were identified as key factors influencing the performance of plasma cutting. Based on the previous research, the maximum cutting speed and workpiece quality loss under various cutting conditions were determined through special experiments. Finally, using the outer shell mock-up of the HWRR as the experimental object and combining it with the decommissioning path provided by simulation, it was demonstrated that the optimal operating parameters obtained from the previous experiments can be successfully applied to practical outer shell cutting.