Nuclear reactor fail-safe unit having the function of control relay and current regulation

In a fail-safe circuit for controlling the current in the coils of electromagnets for maintaining the safety absorbers of a nuclear reactor in a top position outside the reactor core under normal conditions and permitting the safety absorbers to drop under gravity into the reactor core when certain monitored physical quantities deviate to an appreciable extent from predetermined reference values, the improvement comprising:

• a self-supplied "AND.sub.1 " logic circuit of the positive safety type for performing logical multiplication of m input direct-current signals a, b, c, . . . . , i . . . , m, each of said input direct-current signals being capable of assuming one out of two distinct values including a 0 voltage value, said "AND.sub.1 " circuit comprising
• m series-connected dc/ac converter modules which are coupled to each other by means of electrical isolation transformers each of said m dc/c converter modules being supplied with a corresponding one of said direct-current input signals and with the alternating-current output voltage of the preceding module,
• an output isolation transformer having first and second secondary windings, and
• a rectifier and a self-oscillation dc/ac converter, the output of the last dc/ac converter module of the series being coupled on the one hand to the first dc/ac converter module through the first secondary winding of said isolation transformer, said rectifier followed by said self- oscillation dc/ac converter to supply the first dc/ac converter module with an alternating-current voltage and coupled to the other hand through the second secondary winding of said isolation transformer to the output of the "AND.sub.1 " logic circuit, there being obtained at said output a square-wave signal whose amplitude valve corresponds to the result of the logical multiplication of the different input direct-current signals a, b, c, . . . , i, . . . , m,
• a static intensity regulator with negative current feedback, the input of which is coupled to the output of said "AND.sub.1 " logic circuit, said regulator modulating the width of the square-wave signal delivered by the output of said "AND.sub.1 " logic circuit,
• an output isolation transformer, the modulated square-wave signal from said static intensity regulator being coupled to the primary of said output isolation transformer, and
• a rectifier connected to the secondary winding of said output isolation transformer for delivering a constant current to a load constituted by one of the coils of said electromagnets, the output of said rectifier also being connected to said static intensity regulator to produce the negative current feedback.