The LORELEI (Light-Water One-Rod Equipment for LOCA Experimental Investigation) test device in the Jules Horowitz Reactor (JHR) is dedicated to study fuel thermo-mechanical behavior during Loss of Coolant Accident (LOCA) in power reactors. By using a displacement device, the fuel sample moves in the neutron flux field and generates heat according to its location.
The goal of this study was to develop a numerical model that calculates, for a given geometry, the transient device position that will generate the desired clad temperature profile that represent real LOCA scenario. The LOCA-type transient sequence has three major features:
- An adiabatic heating of the fuel up to the clad ballooning and burst occurrence.
- High temperature plateau which will promote clad oxidation.
- Passive precooling by thermal inertia.
This work will present the thermal analysis of the LORELEI test device, performed using the COMSOL Multiphysics code. Unique features of the COMSOL code were used to solve the inverse problem – the transient position of the LORELEI test device that will generate the desired temperature variation of the cladding. Two PID controllers were modeled, one that controls the position of the system (represents the power generated in the fuel sample) to generate the required clad temperature profile and the other that controls the heater power to generate adiabatic conditions for the fuel during the adiabatic heating phase. Coupling of a partial differential equation (PDE) was used to represent the power generated by the oxidation reaction of the Zirconium cladding during the thermal sequence. The two PID controllers and the partial differential equation were coupled to a heat transfer model with complex 3D boundary conditions that represents the heating of the structure due to gamma radiation in the reactor pool. With this model, the feasibility of the design to simulate some specific thermal conditions as in a real LOCA scenario has been demonstrated.
