Accident Safety Analysis for Loss of Helium Coolant in Primary Helium Cooling System using the Code RELAP5

Abstract

Test Blanket System (TBS) is the prototype of the proposed Indian DEMO fusionreactor to be tested in International Thermonuclear Experimental Reactor (ITER) in France. TBS consists of a tritium breeding blanket module made of Reduced Activation Ferritic Martensitic Steel (RAFMS), the Test Blanket Module (TBM) structure is cooled by high pressure helium gas. TBM consists of Lead Lithium (Pb- Li) liquid metal and Ceramic Breeder (CB) zones alternately arranged inside the box.Pb-Li liquid metal acts as neutron multiplier, tritium breeder and coolant for the CB zones which also produce tritium by nuclear reactions of neutrons with lithium. Low pressure helium gas is purged through the CB pebble beds to collect the tritium produced during reactor operation. TBS consists of a TBM and its ancillary systems viz. First Wall Helium Cooling System (FWHCS), Lead Lithium Liquid metal System (LLCS), Helium Purge System (HPS) which is a part of Tritium Extraction System (TES) and Lead- Lithium Helium Cooling System (LLHCS). Safety licensing requires accident safety analysis of all these systems to be carried out to prove robustness of the design in case of various accident incident scenarios. An accident safety analysis of Helium Cooling System (HCS) is carried out in this project using the Reactor Excursion Leak Analysis Program (RELAP5). When loss of coolant accident (LOCA) happens the loss of helium coolant leads to the break of First wall channels causing the pressurization of vacuum vessel and evolution of temperature in TBM which remains within the design limit of the ITER safety guidelines. Based on these results it was found that the present helium cooling system is designed with sufficient capability for the accident scenarios.