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Sodium leaks – LISOF experiments and modeling

pubblicazioni - Poster

Sodium leaks – LISOF experiments and modeling

L’SFR (Reattore veloce raffreddato a sodio) è un reattore nucleare che utilizza i neutroni veloci e, quale fluido refrigerante – termovettore, il sodio liquido che ha buone proprietà come refrigerante, ma il cui utilizzo comporta rischi considerevoli nel caso si verifichi una perdita nel sistema di raffreddamento, in quanto il sodio è un metallo molto reattivo con ossigeno e acqua. Il poster sintetizza l’attività sperimentale e quella modellistica svolte a proposito di spray e pozze di sodio liquido.

The Gen IV SFR (Sodium-cooled Fast Reactor) is a fast-neutrons spectrum nuclear reactor using liquid sodium as coolant, that makes possible efficient fuel cycle and management of actinides (plutonium, neptunium, americium, curium, californium). Liquid sodium has good properties as a coolant, but its use implies a considerable risk if a leak occurs in the cooling system, as sodium is a very reactive metal with oxygen and water. A sodium fire is easy to ignite and it is generating an opaque and dense sodium oxides smoke. Besides, metallic sodium has a fast exothermic reaction with water or steam to form sodium hydroxide and hydrogen. Moreover, hot sodium can react with concrete (mainly because of water and calcareous substances inside). Since the sodium in the liquid phase at high temperature has been shown to have high capacity to bypass / penetrate micro-defects, seals etc., the activity reported here had the objective to investigate the phenomena relative to losses from small cracks in mechanical components constituting the plant. In particular, this work is mainly focused on experimental activity carried out to analyze the leakage of liquid sodium from emission sources of small size. For these reasons a test rig called LISOF (Liquid Sodium Facility) was designed and built and an experimental test program was planned and carried out. That program included experiences about:

•characterization of liquid sodium sprays at high temperature (550° C) generated by micro defects

•combustion ignition of spray / pool of liquid sodium at high temperature (550° C),

• interaction of liquid sodium with samples of cement for high temperature applications and concrete of commercial characteristics.

Several experimental activity contributions were provided by: University of Pisa (Faculty of Engineering – Department of Mechanical, Nuclear and Production Engineering, DIMNP), which made available the Scalbatraio Laboratories; Polytechnic of Milan (Department of Energy) which did the characterization of LISOF sodium sprays. Secondarily, the work involves the modeling of spray and pool fires which may arise as a result of such spills. In particular, in order to complete the experimental work carried out, models dedicated to the simulation of, respectively, liquid sodium pool fire and spray fire have been developed. The implementation of such models within the code ECART is currently underway.

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