Patent Number: 062698737
Section: summary

FIELD OF INVENTION The invention pertains to a method for controlling the heat flux through a heat exchanger immersed in a pool with the aid of a thermal valve. Although the process and apparatus described below can be used in numerous fields, they are particularly useful in respect to the control of heat in a nuclear reactor from which it is desired to remove residual power. BACKGROUND OF THE INVENTION It is useful to understand what is meant by the residual power of a nuclear reactor. When a nuclear reactor is shutdown by introducing a source of high counter reactivity into the core, the number of fissions in the core very rapidly is reduced to a negligible number within a few seconds. However, the radioactive fission products produced in the core of the reactor during normal operation continue to produce a significant amount of power which can amount to several percent of the normal power production of the reactor. Regardless of the cause or the manner in which shutdown is effected, it is necessary to remove such residual power by a reliable means in order to prevent excessive heating of the core, which could lead to shutdown. Numerous devices exist in the prior art for removing the residual power of a nuclear reactor. These devices are generally characterized as having one or more auxiliary loops, in parallel or branched from the main loops which extract heat from the reactor during normal operation. The auxiliary loops are used for the removal of the residual power only when the reactor is shutdown. The heat emitted by the reactor core is consequently extracted into a cold source by two types of circuits, one constituted by main loops for normal operation and the other constituted by auxiliary loops for shutdown operation and removal of the residual power. Such circuitry requires a system to permit the routing of the heat flux to the appropriate heat source. Typically, such routing takes place by closing or opening mechanical valves on the circuits. A typical prior art system is shown in FIG. 1 which is described below. SUMMARY OF THE INVENTION The invention pertains to a method for controlling heat exchange in a nuclear reactor. The nuclear reactor contains: (a) at least one thermal valve; PA1 (b) at least one heat exchanger having a coolant flowing therein; the heat exchanger is immersed in a pool containing a fluid; PA1 (c) a container confining the heat exchanger; the container has an upper part with an opening therein and a lower part having means for introducing the fluid through the lower part; and PA1 (d) means for partially or totally opening or closing the opening in the upper part and means for partially or totally opening or closing the opening in the lower part. PA1 1. closing the opening in the upper part to thereby vaporize the fluid, in order to cause a cessation of heat exchange between the coolant and the fluid; and PA1 2. opening the opening in the upper part to thereby cause the fluid to be heated and to rise by convection, thereby permitting heat exchange to occur between the coolant and the fluid. The method for controlling the heat exchange in the above-described nuclear reactor comprises two steps: