Question

1. In a typical CANDU reactor, how many different ways can one control the reactor power? Describe the situations when each of these techniques are used?

Answer 1

Power control: The power of a CANDU reactor is normally controlled by varying the concentration of boric acid in the coolant in the primary circuit. Boron is a very efficient neutron absorber, and therefore increasing or decreasing the concentration of boron in the reactor affects the neutron population in the reactor. In addition the reactor uses control rods that are inserted from above (other than the BWR) between the fuel elements and are normally used only for reactor start and stop operations.

The power of a nuclear reactor is directly proportional to the number of fissions and this depends on the neutron flux. If the number of fissile atoms does not change significantly over time t, the power variation in a reactor depends on the variation in neutron flux. When modulating the neutron flux one must consider the kinetics of the reactor, which studies the variation of the neutron population with time and the time evolution of the reactor power. The neutrons are generated and transformed by generations: n-1, n, n + a, .... The neutron population changes temporarily as the number of neutrons varies from one generation to the next.