Influence of the break location in the loss of coolant accident analyses for the ITER divertor cooling loop

Abstract

In the frame of the Generic Site Safety Report (GSSR) for the ITER experimental plant, several accident analyses have been carried out to analyse in detail the radiological risk linked with the possible releases. An ex-vessel loss of coolant followed by an in-vessel break, caused by the thermal stress on the divertor (DV) vertical target consequent to the plasma disruption, is the evolution of the accident referred in the study. The plasma disruption happens for the intervention of the fast plasma shutdown system occurring when the flow rate in the pump lowers below 80% of the nominal flow. This accident scenario is critical from the point of view of the vault pressurisation, of the activated materials mobilisation from the plasma chamber and of the hydrogen production inside the vacuum vessel (VV). The scope of the analyses presented in this paper is to quantify the influence of the ex-vessel break position on the accident consequences. A parametric study on the ex-vessel break position has been carried out. The pipe break before the heat exchanger is the most critical for the vault pressurisation and for the releases of activated corrosion products (ACP) and tungsten dust, while the break at the pump outlet maximises the hydrogen production inside the VV. The less critical accident is the break at the pump inlet for all the possible consequences.