Heat exchanger control system

Measured values for primary temperature exit, a heat transfer tube temperature and secondary exit temperature are feed-back respectively and amounts of feed-back are collected together, to calculate a set value for a secondary fluid flow rate. The secondary fluid flow rate is controlled based on the set value. Since the control deviation for the secondary fluid is increased only with the control for the first fluid, the control deviation for the secondary flow rate is also feed-back to make them compatible. In addition, since the temperature change in the heat exchanger is shown by the flow of the fluid as a temperature change at the exit, the heat transfer tube temperature at the central portion thereof is detected and the control deviation is feed-back, to control the temperature change at the inside. Then the deviation of the temperature is scarcely caused, thereby enabling to change the reactor power following the scheduled value. (N.H.)