Investigation on MELCOR Code Capabilities for the Simulation of Lithium–Lead Chemical Interactions for Fusion Safety Applications

In the WCLL-BB liquid blanket concept, among the postulated accidental scenarios to be investigated regarding the PbLi system, a loss of liquid metal is one of the most crucial for safety purposes. As a consequence of this loss, chemical reactions might occur between lithium, air, and water. These reactions may lead to significant increases in temperature and pressure and to the formation of hydrogen inside the building; the evaluation of the impact of these events is essential to define future safety guidelines. Using MELCOR for fusion (v.1.8.6.), a first approach for investigating an out-vessel loss of PbLi was presented in this work. The temperature and pressure trends were investigated through the default MELCOR package for lithium air chemical reactions; however, this package works only with pure lithium. Therefore, a new model of the reaction was developed in this work using MELCOR Control Functions, which allows the simulation of the chemical reactions using PbLi as working fluid, in order to investigate a more realistic scenario. The results from different approaches were compared, and the limits of the code were outlined. It was found that the final pressure and temperature in the tokamak building might reach critical values at the end of the transient, if the energy released by the chemical reaction was entirely considered; however, it is important to note that, due to the assumptions and simplifications adopted, the results were very conservative in terms of temperature and pressure reached in the system, and further investigations were suggested in this work.