Deposition of Iter Vacuum Vessel Dust Inside the Pressure Suppression System During a Loss of Coolant Accident: Experimental and Numerical Analyses

This paper deals with an experimental and numerical analysis of the deposition of ITER dust simulant inside a reduced scale Vacuum Vessel Pressure Suppression System (VVPSS) of the International Thermonuclear Experimental Reactor (ITER). This research, funded by the ITER Organization, aims to analyse the dust deposition in a water container relevant for the ITER VVPSS, the dust removal by means of robotised apparatuses and their decontamination efficiency. The experimental rig, built at the Department of Civil and Industrial Engineering (DICI) of the University of Pisa (Italy), is described and the results of a preliminary experimental test are illustrated, underlining that 2 and 82% of dust mass was strongly and lightly bound to the water container surfaces, respectively, and 16 % were not deposited in the water tank. Furthermore, three numerical analyses were carried out implementing a model of the experimental rig in the Enel Code for Analysis of Radionuclide Transport (ECART) to determine the relevance of different parameters on the deposition, resuspension and removal of dust. The numerical simulations allowed to specify dust mass deposition on the different rig components, revealing a strong dust retention (about 66%) in the first part of the injection piping in case of coarse granulometry. Finest lognormal dust distribution was instead able to reach the water container (about 90%). Moreover, the numerical simulations permitted to define more precisely the test matrix and to analyse the experimental results.