UWFDM-1101 Computer Modeling for Lithium Safety in Fusion Systems: LINT and MELCOR

Accidents postulated to occur involving the chemical interaction of lithium with water and air are analyzed for the blanket test module (BTM) in ITER using two different computer models. The first model is a newly developed thermodynamic equilibrium computer model LINT. The second model uses the MELCOR systems code. The same basic logic used in LINT is incorporated into the MELCOR FDI package, though MELCOR allows for non-equilibrium conditions. This addition to MELCORÕs capability allows MELCOR to be used in reactor systems analyses over a wide range of accident conditions; i.e., thermal-hydraulic events with chemical interactions involving molten metals. Pressure and temperature histories are predicted for a control volume in thermal equilibrium (LINT) or non-thermal equilibrium (MELCOR) in any accident scenario involving chemical interaction between lithium and water or air. These computational models are applied to postulated accidents for the ITER blanket test module. In the ITER vacuum vessel, failure is not predicted to occur for lithium leaks from the BTM into water because of low lithium driving pressures resulting in self-limiting leaks. However, failure is predicted in minutes for a high pressure water leak into any amount of pre-existing lithium provided the pressure suppression system fails to work as designed. Assuming a 10 kg/s initial water leak rate, calculated failure times range from a maximum of 15 minutes with no lithium present to a minimum of less than two minutes for an initial lithium pool of 1300 kg. For lithium leaks from the BTM into the ITER reactor vault containing pure air at atmospheric pressure, calculations predict failure if an adiabatic system is assumed, but not if heat loss to the surrounding cold structures is considered. Both pool and droplet configurations are considered for diffusional mass transfer calculations in determining chemical reaction rates, with droplet configurations inducing faster reaction rates and pressurization. Finally, pressure and temperature histories are predicted in the reactor vault for air ingress rates of 1, 10, 50, and 80 vol%/day into an argon atmosphere. Calculations show that this scenario poses no serious threat to the integrity of the reactor vault.