Development of a coupling technique between RELAP5 and SIMMER-IV for fusion reactor applications

A critical problem in the Water-Cooled Lead-Lithium Breeding Blanket system (WCLL-BB) is the possible interaction between the water and the Lithium-Lead eutectic alloy - which act respectively as primary coolant and as breeder/neutron multiplier - due to a postulated rupture of the coolant circuit in the Breeding Unit of the BB. This scenario involves a complex multiphase interaction together with an exothermal chemical reaction between the two fluids with the production of hydrogen. The PbLi/water chemical reaction was implemented in SIMMER-IV code by the University of Pisa and, consequently, a coupling methodology was successfully developed between SIMMER-IV and RELAP5/Mod3.3 codes, in order to overcome SIMMER-IV unsuitability in the simulations of complex pipelines. This paper presents an application of the coupling methodology to the simulation of experimental tests, recently performed at ENEA inside the experimental campaign carried out with the LIFUS5/Mod3 facility at the ENEA Brasimone Research Centre. The injection line of the facility is simulated by RELAP5/Mod3.3, whilst the reaction vessel is simulated with SIMMER-IV. Results of different simulations are presented and compared against experimental data, providing both qualitative and quantitative evaluations of the performance of the coupling methodology in the prediction of the chemical and thermal-hydraulic phenomena involved in the experiments, such as the fast pressurisation of the injection line and the pressurisation of the reaction vessel, the energy release due to the chemical reaction and the propagation of pressure waves inside the reaction vessel.