The CANDU reactor uses natural uranium fuel and heavy water (known as D2o). Heavy water is used as both moderator and coolant (the moderator and coolant are two separate systems). Heavy water is very similar to ordinary water, except that it is slightly heavier due to the existence of an extra neutron in the hydrogen atom that form a part of a water molecule. CANDU reactors use heavy water to moderate the fission process.

In simple terms, fission occurs when a neutron strikes a particular isotope of uranium atom, called Uranium-235 creating the unstable element of Uranium-236. The extra neutron results in the U-236 atom splitting two fragments and releases other neutrons, energy and radiation. After moderation, the released neutrons go on to cause further fission and the cycle is repeated.

There are 380 fuel channels in the CANDU-6 reactor each containing 12 uranium fuel bundles. The uranium fuel bundle weighs about 20kg. Each bundle stays in the reactor between six months to one year. Through each fuel channel heavy water of the primary heat transport system flows to pick up the heat released by the fission in the fuel. This system called the heat transport system, takes this heat energy to the boilers where it is used to heat up and boil ordinary water to generate steam which in turn drive the turbine and generate electricty.

The nuclear reactor is housed in a concrete containment building 42 meters tall with 1.2 metre thick wall. The containment system consists of pre-stressed, post-tensioned concrete structure, an automatically initiated dousing sytem, local building coolers, two airlocks and a filtered aire discharge system.

Reactor Building