Criticality accident phenomenology: numerical experiments as a learning tool

For decades, the training of French criticality experts has implied performing critical experiments on dedicated devices, which have all been shut down during the last few years. A work for substituting these reactors as a learning tool has then been undertaken. The idea of supplementing the ISIS hands-on with a more criticality-accident-oriented sequence led to the development of a numerical simulator aimed at reproducing the physics of criticality accidents for a range of configurations, while being easy to use. This simulator was written in C++ for the engine and python for the user interface (UI), and was intended to be run on common hardware available in a computer lab, and the simulation running within a reasonable time-span. The developed tool calculates the evolution of a super-critical solution of uranyl nitrate placed in a tank, by solving point kinetics equation and taking into account every meaningful physical phenomenon (radiolysis, thermodynamics, heat exchange, dilatation...) in a simplified way. Reactivity feedbacks are implicitly implemented; they are estimated from neutronic pre-calculations done with APOLLO2 neutron transport code for a given set of physical properties (void fraction, concentration, temperature). Users can configure experiments, tune physics and display physical observable variation with time through a graphical user interface.