STEAM GENERATOR

PURPOSE: To enable conservation of material used along with a higher heat transfer performance. CONSTITUTION: High temperature sodium comes down in the perimeter of a heat exchanger tube 3 set within a shell of a steam generator from a sodium inlet nozzle 6 provided at an upper part of the steam generator while low temperature water rises through a supply water inlet water chamber 1 and the heat exchanger tube 3 to perform a heat exchange so that water in the heat exchanger tube 3 is heated to turn to steam. The heat exchanger tube 3 varies in thickness corresponding to the temperature of parts of the heat exchanger tube. For example, when the inlet temperature of sodium is 520 deg., the outlet temperature 350 deg. and material of the heat exchanger tube 3 herein used is modified 9Cr-1Mo steel, the intensity is about 1.4 times at a high temperature part than at a low temperature part and hence, a required thickness at the low temperature part is about 75% of that at the high temperature part. In this manner, the less thickness at the low temperature part, about 75% allows upgrading of a heat transferring performance by about 25%. Thus, when a low temperature area is assumed to be one-third of the total area of the heat generator, the heat transfer performance is improved by about 8% at this part alone.