Training reactor VR-1

Control rods

The control (absorbing) rod UR 70 has an integral style and is intended for use in pool type reactors with fuel elements of the IRT M type. The rod is hanged on a rule of the regulation carrying system and goes with its narrowed down part (absorber pipage) through a six tubes fuel element. The rod motion is procured by a rotating step motor with a position sensor with a tipping pinion that an electromagnet holds in contact with toothed comb carrying an absorber.

During the safety signal activation, the power supply of the electromagnets is lost, the tipping pinion slips and absorber falls down into the active core. The fall is softened by a progressive hydraulic damper. The down position of the absorber is light indicated on the control desk. This signalization, as the most important evidence that the rod is in its down position (reactor scram), is supplied by the 48V DC standby system. The absorber motion speed is changeable in a wide range. The absorber consists of a close steel tube with an aluminum filling with winded cadmium plate inside.

Disassembled control rod UR 70 during operational check

Disassembled control rod UR 70 during operational check

The total number of the control rods is seven. The construction of the rods is identical, the rods differ only in their functions that are determined by the connection to the reactor I&C. Three rods are always connected as the safety rods (labeled B1, B2, B3) and two as control (R1 – the first regulation and R2 – second regulation) rods. According to the active core type and experiments carried out at the reactor, one, two or no experimental rods (E1, E2) can be connected to compensate the influence of experimental equipment on reactivity or to allow finishing of the active core to a demanded shape by fulfilling of ‘Limits and conditions’. During the reactor automatic operation, the automatic power regulator is connected to the control rod R1.

© DNR FNSPE CTU in Prague, 2017