Refering to the results of our previous works, a procedure for estimating the distribution of heat flux in shell-and-tube heat exchangers is proposed. The stream generator used in a high temperature reactor plant is taken up as the subject of analysis. Particular attention is paid to critical conditions for burnout and the strength of materiel in high temperature conditions. It is found that the distribution of heat transfer coefficient on the shell-side is crucial to the occurrence of burnout in the tubes. The use of a relatively large inlet nozzle (the ratio of its diameter to the shell is roughly half) is recommended. A low level of thermal stress on heat transfer tubes can be realized by the adoption of a relatively thin 2.25 Cr-1 Mo Steel tube wall of 1.24 mm thickness.