[en] The paper describes the analysis of two transients of loss of flow in a VVER-1000 reactor performed with the Plant Analyser ASTRA compared with the data recorded during the same transients performed at Kozloduy NPP (Bulgaria). The first transients is a coast down of one primary loop pump at a power level of about 70% while the other 3 pumps continue to run at normal speed. The second transient essentially consist of the exclusion of one of the two turbine driven feedwater pumps: 38 second after the beginning of the transient, one of the feedwater regulation valves remains stuck open, the level of one steam generator starts to raise until it reaches the maximum allowed value so that the transient was stopped. These two transients have been simulated by ASTRA: the attention has been focused on the primary side behaviour and on the heat transfer models, taking the secondary side parameters as boundary conditions. The experimental and calculated trends of the addressed parameters are in a good agreement, showing the capability of ASTRA to properly simulate the analyzed transients. (author)