Structural changes of a carbide phase in welded connections from steel 09g2SA-A at various modes of heat treatment are investigated. It is shown that coagulation of a carbide phase in structure of steel allows to receive high values of resistance to fragile destruction of welded connections at a temperature minus 40 °C. On the basis of the received results of experiments and their analysis the mode of postwelding tempering of containers for spent nuclear fuel is optimized. Comparative tests of the samples processed on regular and new technologies showed that the new technology allows to increase by 2-3 times values of impact strength of welded connections from steel 09g2SA-A.