ALLEGRO Gas-cooled Fast Reactor (GFR) demonstrator thermal hydraulic benchmark

Highlights: • ALLEGRO Gas-cooled Fast Reactor (GFR). • Thermal hydraulic benchmark. • Loss of coolant (LOCA) transient. • Station blackout (SBO) transient. - Abstract: The European gas cooled fast reactor (GFR) demonstrator, ALLEGRO, is currently being developed by Czech Republic, France, Hungary, Slovakia and Poland. The primary aim of ALLEGRO is to demonstrate the helium-cooled fast reactor technology and to test the new ceramic refractory fuel of the industrial version of the gas-cooled fast reactor, which has an envisaged thermal power of 2400 MW. The development of ALLEGRO highly relies on Thermal Hydraulic (TH) codes which were primarily developed for two-phase flow modelling of pressurized and boiling water reactors, and which are currently being adapted for new generation reactors using gas or liquid metal coolant. In this paper we present CATHARE2, RELAP5-3D and MELCOR code to code benchmark carried out for the 75 MWth ALLEGRO reactor. During our work, first an ALLEGRO database for TH analyses was elaborated based on previous European projects. In the second step a detailed TH benchmark specification was prepared in order to help the TH model development as a third step. Fourthly, each participant calculated their own steady states and subsequently we identified several model distortions. In the final step we carried out transient calculations for 3-inch Loss Of Coolant Accident (LOCA) and total Station Blackout (SBO) initiating events. In general, the results show that there is a good agreement in the simulation results of the different codes, but further experimental code validations are proposed using helium-cooled experimental facilities, namely the S-ALLEGRO being built in Czech Republic and the STU (Slovak University of Technology) loop operated in Slovakia.