On a possibility of power network control by means of nuclear power plants

Problems in ensuring maneuvrability of nuclear power plants with WWER reactors under transient load conditions and their possible solutions are considered. The problems are as follows: elimination of transient xenon poisoning of the core, overcoming of large thermal time lag of the reactor plant and overcoming of thermal inertia of nuclear plant circuits at power rise. A way to maintain the reactor critical and to eliminate the transient poisoning is the removal of the chemical absorber from the reactor cooling circuit, mostly the boric solution. Another way to maintain the reactor critical is the insertion or withdrawal of the control rod cluster. The combined use of these two methods ensures the best characteristics of the reactor manoeuvrability. Additional means promoting the elimination of the reactor poisoning are steam dumping from the steam generator into turbine condensers and reduction in the coolant temperature. To decrease the thermal time lag of the reactor plant, steam dumping into turbine condensers and into atmosphere are used. The main function of the steam dumping system is to prevent the excessive pressure rise in the second circuit. To prevent an accidental steam pressure rise, the capacity of dumping devices is assumed equal to 50-60% of the capacity of the reactor plant. To overcome the thermal inertia of nuclear plant circuits during the power rise, the transition to the regime of power control at the mean coolant temperature kept constant is possible. This allows the change in reactor power level almost without any variation of heat quantity accumulated in the circuit. However, the transition to such a control programme results in making the steam generator heavier and more expensive. Therefore the boric acid control is supposed to be used at present nuclear power plants