Abstract: In a method of decontaminating a primary loop of a pressurized water reactor, including a steam generator, reactor coolant pump and hot and cold legs in the loop, the primary loop is isolated from a nuclear reactor vessel by closing hot leg and cold leg loop stop valves. Decontamination process water is circulated from one side of the steam generator channel head to the other side of the channel head via a bypass pipe extending between the cold leg and the hot leg without bypassing the water through steam generator tubes extending between the sides of the channel head. The level of the decontamination water in the steam generator is maintained at two to three feet in the tubes.