Physical and Metallurgical Phenomena During Simulations of Plasma Disruptions

IT IS EXPECTED THAT DURING PLASMA DISRUPTIONS THE FIRST WALL OF A TOKAMAK REACTOR WILL BE EXPOSED TO EXTREMELY HIGH HEAT FLUXES. BY CA;CULATIONS, IT HAS BEEN SHOWN THAT SURFACE MELTING AND EVAPORATION WILL TAKE PLACE. SIMULA- TION EXPERIMENTS HAVE BEEN EXECUTED BY THE MEANS OF ELECTRON GUNS, AS THEY ARE USED IN WELDING EQUIPMENTS, IN ORDER TO VERIFY THE RESULTS OF THE CALCULA- TIONS AND IN ORDER TO STUDY THE OTHER PHYSICAL AND METALLURGICAL PHENOMENA LIN- KED TO THE DISRUPTION, WHICH MAY BE IMPORTANT FOR THE EVALUATION OF THE LIFE- TIME OF THE FIRST WALL. THE METALLOGRAPHIC ANALYSIS EXECUTED ON AUSTENITIC STAINLESS STEEL SPECIMENS SUBJECTED TO SIMULATED PLASMA DISRUPTIONS ALLOWS TO PRESENT A COMPLETE PICTURE OF THE MOST IMPORTANT PHENOMENA. I) THE EXPERIMENTS SHOW THAT FOR THE CALCULATION OF MELT LAYER AND EVAPORA- TION IT IS NECESSARY TO TAKE CONSIDERABLE CONVECTION IN THE MELT LAYER INTO ACCOUNT. II) THE RAPID SOLIDIFICATION OF THE MELT LAYER LEADS TO A CHANGE IN THE CRY- STALLINE STRUCTURE AND TO THE FORMATION OF CRACKS. III) ALLOYING ELEMENTS WITH A HIGH VAPOUR PRESSURE EVAPORATE PREFERENTIALLY. IV) THE STRESSES GENERATED DURING COOLING INDUCE SOMETIMES PHASE CHANGES. V) DURING NEUTRON IRRADIATION HELIUM IS FORMED IN ALL FIRST WALL MATERIALS BY ( ) PROCESSES. THIS HELIUM FORMS BUBBLES UNDER DUSRUPTIONS.NA-NOT AVAILABL