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. In addition to the material testing function, targets of the MYRRHA reactor are to prove the feasibility of the ADS technology as Minor Actinides (MAs) burner and to act as a demonstrative plant for future Gen-IV heavy metal cooled reactors. SCK•CEN entered the pre-licensing phase for the MYRRHA reactor. In order to provide the safety authority all the required data, a complete safety analysis must be performed, studying the transients defined by the list of postulating initiating events. In particular, an accident with potential serious consequences is the Primary Heat Exchanger Tube Rupture (PHXTR), involving the sudden release of single phase or two-phase water from a tube break in a hot liquid metal pool. This accident evolution is strongly characterized by the design of the MYRRHA Primary Heat eXchanger (PHX) and its direct surroundings in the reactor vessel and by the thermal-hydraulical conditions of the MYRRHA primary and secondary cooling system. In the first phase of a PHXTR accident, the water in the Secondary Cooling System (SCS) is released in the Primary System (PS) pool in regime of choked flow due to the pressure difference. Being the water released in an overheated, low-pressure environment, a flashing with potential sudden specific volume increase is expected. The heat transfer phenomena leading to the phase change velocity depend by the actual number of bubbles released in the hot liquid metal pool, function of the actual break size and shape. Its characterization is important for the definition of the overall specific volume increase and for the estimation of the water mass fraction redirected through the Primary Pump in the reactor Lower Plenum, with the risk of void insertion in the core and consequent reactivity excursion. A simplified calculation model to evaluate the history of any given bubble distribution generated by any water flow rate through any break has been set up. The main purpose is to describe the evolution of the main system state variables during the accidental event, by checking the potential insurgency of any reactor safety issue due to pressure peaks or core void insertions.
|Titolo:||Myrrha primary heat exchanger tube rupture: Phenomenology and evolution|
|Data di pubblicazione:||2017|
|Appare nelle tipologie:||04.01 - Contributo in atti di convegno|
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