Abstract: A safety system (10) for shutting down a nuclear reactor under overload conditions is provided using a series of parallel-connected computing modules (14a, 14b, 14c, 14d, 14e) each of which receives data on a particular reactor parameter (P, T, .phi..sub.T, .phi..sub.B, W) and each of which produces a function [f(P), f(T), f(.phi..sub.T), f(.phi..sub.B), f(W)] indicating the percentage of maximum reactor load that the parameter (P, T, .phi..sub.T, .phi..sub.B, W) contributes. The various functions [f(P), f(T), f(.phi..sub.T), f(.phi..sub.B), f(W)] are added together to provide a control signal (S) used to shut down the reactor under overload conditions.

Abstract: A method for controlling the operation of a nuclear reactor to increase the reactor power in a range in which pellet-clad-mechanical-interaction occurs. The method includes the steps of increasing the reactor power from a power level in which pellet-clad-mechanical-interaction begins to take place up to a predetermined power level for the nuclear reactor and controlling the rate of increase of the linear heat generating rate. The rate of increase is controlled with at least one of a rate no less than 0.15 KW/ft/hr., and a rate no greater than a predetermined critical rate so as to shorten the time necessary to raise the reactor power to the predetermined power level without causing pellet-clad-mechanical-interaction damage to the fuel elements.

Abstract: In a process for running a nuclear reactor cooled with light water, by displacing control rods and modifying the physical and/or chemical state of the coolant, the value of the running parameters of the reactor are continuously measured and recorded and the parameters describing the state of the reactor core are calculated for each substantial modification of the running parameters. The parameters describing the state of the core are measured at defined intervals of time and the calculated parameters are replaced by the measure parameters. The modified parameters resulting from predetermined sequences of action taken on the control rods or the coolant, and the action which must be taken on the running parameters in order to comply with a given program, are calculated by way of predictions. Action is taken on the control rods and the coolant in accordance with the results of the calculation.