Inertial impaction behavior of fuel particles under severe accident scenario in pool type sodium cooled fast reactor

During a highly unlikely event of energetic core disruptive accident in sodium cooled fast reactor (SFR), a high temperature and high pressure volume is formed due to neutronic excursion and expands rapidly (∼ms) into the sodium pool in the form of a fuel vapor bubble. This fuel vapor bubble further rises into the cover gas space, carrying radioactive materials along with it, which will contribute to the radiological source term in reactor containment building. In relation to this, a computer code PTRACK has been developed to describe the motion of an expanding and oscillating bubble and to evaluate trajectories of particles inside the bubble. The code considers adiabatic process for bubble expansion and solves particle momentum equation for evaluating the particle trajectories. PTRACK code has been validated against FAUST-1A benchmark experiments and the code predictions are in fairly good agreement with experimental results. Subsequently, a parametric analysis has been carried out to evaluate particle trajectories in a typical pool type SFR with initial fuel vapor bubble pressure of 1, 2 and 4 MPa and for various particle diameters from 3 to 500 μm. From this study, it has been observed that during fuel vapor bubble expansion, fuel particles are effectively retained by the sodium pool due to the inertial impaction behavior over a wide range of particle diameters and initial pressures. A parameter (inertial impaction parameter) has been defined to explain the above mentioned phenomenon. Results show that the fuel particle removal from the oscillating fuel vapor bubble due to inertial impaction phenomenon becomes significant when the inertial impaction parameter is close to unity.