Water Cooled High Current 490 kW 6-Pulse Thyristor Converter for Nuclear Power Plant Safety Analysis

Consideration of severe accidents at a nuclear power plant is an essential component in nuclear safety analysis. The extent and nature of deformation is important to study from plant safety point of view. Under normal operating conditions, heat generated by fission reaction in fuel bundle is removed by pressurized heavy water coolant. During postulated loss of coolant accidents, decay heat is removed by emergency core cooling system. Even in case of complete failure of emergency core cooling system, moderator system prevents gross damage and maintain the integrity of fuel and fuel channels. Under postulated accidents, heat up of pressure tube along with internal pressure may lead to its two modes of deformation i.e. sagging and ballooning which depends on internal pressure in pressure tube. Hence, it is essential to validate safety and safety related systems designed for nuclear power plant to cope up severe accidents. Scale down experimental set-up in power has been designed and installed to simulate sagging and ballooning of pressure tube for 220 MWe Indian Pressurized Heavy Water Reactors. In experimental set-up, heat energy relevant to nuclear fission is simulated by traditional electrical heating. Considering direct heating of metallic pressure tube needing higher power to attain desired temperature of pressure tube to meet the situation of severe accident scenario, high current thyristor controlled converter system of 490 kW capacity has been chosen as a heat source. The converter system comprises forced de-mineralized water cooled rectifier transformer and thyristor controlled six pulse double star hexa-phase configuration with inter phase transformer operating either at constant current or constant power mode. The paper presents design, specifications, forced de-mineralized water cooling system, circuit simulation, hardware implementation along with performance demonstration of water cooled 7 kA at 70 V and 3.5 kA at 140 V, 490 kW thyristor controlled six pulse, hexa-phase converter system.