Accident Safety Analysis of Helium Purge System using the Code RELAP5

Abstract

Lead Lithium cooled Ceramic Breeder (LLCB) Test Blanket System (TBS) is the Prototype of the proposed Indian DEMO fusion reactor to be tested in the International Thermonuclear Experimental Reactor (ITER) in France. LLCB 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. LLCB 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. The accident safety analysis of Helium

Purge system is carried out in this project using RELAP5. Reactor Excursion Leak Analysis program which is a highly generic thermal hydraulics and safety analysis tool and is widely used publicly to study the fluid behavior at steady state and transient conditions of the system. Loss of coolant accident (LOCA) is performed for 3 cases. To simulate transient thermo-hydraulic behavior of the TBM for the selected scenarios, the helium passage including the TBM and HPS was modeled. LOCA leads to the pressurization of single volume but it was under the design limit of port cell.

Based on the results of RELAP5 programming, it was found that the HPS loop is designed properly for accident scenarios and fulfills the safety requirements of ITER.