ON THE CONTROL OF POWER DISTRI13UTION IN THE CANDU NUCLEAR REACTOR

The CANDU is a horizontal pressure tube reactor using natural uranium as fuel and heavy water as both moderator and coolant. CANDU reactors can be refuelled on power. The use of heavy water makes the reactor more susceptible to xenon-induced oscillation of neutron flux in the reactor core. Therefore CANDU reactors are equipped with an automatic spatial control system which regulates die power distribution in the core at short (2 second) intervals. Current operating CANDUs use light water filled compartments at fourteen locations in the core which are filled and drained as necessary to regulate neutron flux and hence reactor power. The new CANDU 3 power plant being currently designed at AECL has 450 Mw net electric output and many innovative features including a mechanical system for spatial flux control. This paper describes the rinciples and the algorithm used for spatial control using the new Mechanical Zone Control system. A comparison with the control methods for other types of reactors will also be made.