The Sodium-cooled Fast Reactor system is a Gen IV fast-neutrons spectrum reactor, using liquid sodium as coolant, that make possible efficient fuel cycle and management of actinides (plutonium, neptunium, americium, curium, californium). Liquid sodium has good properties as coolant, but implies a significant risk if a leak occurs in the cooling system, as sodium is a very reactive metal with oxygen and water. A sodium fire can have a significant effect even the HRR produced by combustion is usually much less compared to conventional hydrocarbon fires, and its burning is accompanied by production of opaque and dense sodium oxides smoke. Besides, metal sodium has a fast exothermic reaction with liquid water or steam to form sodium hydroxide and hydrogen. This paper presents a mathematical model simulating some phenomena of the dynamical development of a sodium pool fire. This model is based on grid theory and finalized to quantify the vapour mass release rate, from the pool to the surrounding air, caused by pool liquid heating. The “grid” model was developed to extend the capability of ECART numerical tool and his development was focused on the implementation inside such code.