Calculation tool for heat exchanger tube rupture in pool-type reactors

In the framework of MYRRHA Project, a pool-type experimental and material testing irradiation facility operated with Lead Bismuth Eutectic (LBE) coolant and able to operate in both sub-critical and critical mode is designed to be built in Mol, Belgium, in SCK•CEN domain. SCK•CEN entered the pre-licensing phase for the MYRRHA reactor. A complete safety analysis must be performed to provide the necessary data to the safety authority. An event with potential serious consequences is the Primary Heat Exchanger Tube Rupture (PHXTR), involving the release of water from a failed tube in a hot liquid metal pool. In the first phase of a PHXTR accident, the water in the Secondary Cooling System is released in the Primary System pool in choked flow regime. Afterwards, the water bubble formation and characterization is important for the definition of the water specific volume increase and for the estimation of the water mass fraction redirected in the reactor Lower Plenum, with the risk of void insertion in the core and consequent reactivity excursion. An analytical calculation model to evaluate the evolution of any bubble distribution has been set up. The main purpose is to describe the evolution of the main system variables during the accidental event, by checking the potential insurgency of any reactor safety issue due to pressure peaks or core void insertion.