One of the most dangerous accidents of a nuclear power plant is the rupture of the primary circuit and release of coolant with radioactive products: Loss-of-Coolant Accident-LOCA. To prevent the release of radioactive products into the environment most nuclear reactors are supplied with containment systems. The general assumption of a mathematical model and sample results of calculations of thermal parameters distribution within the containment of a WWER-440 nuclear reactor during the Loss-of-Coolant Accident are presented in the paper. The influence of the work of ventilation systems on the long term behaviour of thermal parameters within the containment is analyzed. Three basic cases are considered. In the first case all the ventilation systems are not working. In the second case three ventilation systems assigned for operation in LOCA conditions are working. In the third case work of emergency ventilation systems is considered.