During power operation, heavy water was circulated by primary pumps through the U-tubes containing the fuel assemblies which heated the water. The heated water then flowed through an inverted U-tube steam generator where the heat was transferred to the secondary side light water which turned to steam. The steam flowed to an oil-fired superheater which increased the steam quality before the steam entered the turbine which spun the electrical generator. After passing through the steam generator, the primary loop water was pumped back to the reactor by the primary pumps to repeat the cycle. The primary loop heavy water was pressurized to ensure that the heavy water remained liquid and did not flash to steam at any point in the loop.