[en] Analysis of primary coolant system of CANDU nuclear power plant was done using software of nuclear power plant type of CANDU. Primary coolant system has unique design. Heat transport pressure and inventory control system is a system to provide a reliable means of controlling inventory and pressure in the heat transport system. The condition of heavy water coolant which covered pressure, inventory and temperature of coolant has implicated to performance of plant operation.Therefore the primary coolant system is important. Heat transport system circulates pressurized heavy water coolant through the fuel channels to remove heat produced by fission of natural uranium fuel. The heat is carried by the reactor coolant tp steam generators where it is transferred to light water to produce steam, which subsequently drives the turbine-generator. The inventory and pressure control system consists of a pressurizer, feed and bleed valves and a storage tank. In this case the malfunction of PHT bleed valve (CV5)PHT feed valve (CV12), PHT LRV (CV20) and PHT steam bleed valve (CV22) are selected. Reactor parameters observed primary coolant pressurize pressure and level, bleed condenser pressure and level, feed flow, bleed flow. From this analysis and simulation the reactor parameter affected by malfunction is known. It is also considered that the trip, controls, safety valve are needed to maintain safety of nuclear power plant. It is also considered that the trip, controls, safety valve are needed to maintain safety of nuclear power plant. It is also observed the phenomenon of LOCA accident requirements and safety standard issued by Atomic Energy Control board of Canada and how the CANDU safety system is applied