Fluid-to-fluid modelling for the estimation of critical heat flux (CHF) in high latent heat fluids

As per the licensing philosophy of nuclear reactors, design of any new nuclear reactor fuel bundle configuration has to satisfy adequate thermal margins of safety during all possible operating conditions. For this purpose, estimation of CHF under diverse heat and mass fluxes is required. IIT Bombay participated in establishing the CHF values using fluid-to-fluid model for the Advanced Heavy Water Reactor (AHWR). For this purpose, two experimental facilities were built, one for establishing the fluid-to-fluid scaling principle and the other to establish the CHF values in a 54-rod cluster. The talk would first present a review of the scaling principles and the procedure to arrive at the equivalence. Subsequently, the results obtained using two different simulant fluids viz, Freon-11 and FC 84 will be presented. Then the efforts to get CHF using a full scale 54 rod cluster would be presented. It will demonstrate that the flow instability can play a crucial role and it can pose severe problems while getting CHF data at very low inlet subcooling. (author)