Deep Gouging Technique for Fuel Debris Retrieval in Fukushima Daiichi

Abstract Laser cutting, a contactless remote controlled process, was assessed for nuclear decommissioning applications, in full through-thickness-cutting (emerging cutting) and deep gouging (non-emerging) conditions. This work aims at presenting specific tools developed and implemented at CEA Saclay, to evaluate and to optimize new cutting strategies, in terms of robustness and reliability, in order to best adapt the laser cutting process to fuel debris retrieval specificities of Fukushima Daiichi reactors. Several configurations for deep gouging have been tested in DELIA facility to reach more than 40 mm of cut-thickness in one pass with an 8kW laser power. First, the laser cutting process was assessed on fused cast zirconia blocks and then on 316L stainless steel and fuel debris simulant blocks. This paper presents the main results of the tests performed in representative conditions of “in site conditions” such as: edge or bulk start/stop cutting, complex surface (i.e. surface with a varying topology) cutting, stand-off variation, angle of cut, trajectories misalignment, and material heterogeneity. Moreover, the excellent performances achieved on 316L stainless steel and fuel debris simulants indicate that deep gouging applied to nuclear decommissioning is a promising technology.