Evolution of the Design of Fuel Handling Control System in 220 MWe Indian PHWRs

Abstract

Following two CANDU type reactors at Rajasthan (RAPS-l and 2), three nuclear power stations, each of two units of 220 MWe has been in operation at Rajasthan (RAPS-1 and 2). Madras (MAPS-1 and 2). Narora (NAPS-1 and 2) and Kakrapar (KAPS-1 and 2). Two more stations, also of 220 MWe capacity, are under construction at Rajasthan (RAPP-3 and 4) and Kaiga (Kaiga-1 and 2). These are natural uranium fuelled pressurized heavy water cooled and heavy water moderated reactors (PHWRs). The two units at Rajasthan viz RAPS-1 and 2, were built with the technical collaboration with Canada and the rest of the units have been designed and built indigenously incorporating a number of modifications, particularly in the on-power refuelling system. The evolution of the design of the Fuel Handling Control systems of these reactors, taking into consideration operational needs, safety aspects and maintainability are highlighted in this paper. A combination of hydraulic and electronic control has been provided to enable the operations in RAPS-1 and 2, hardwired electronic controls were provided, while in MAPS-182, the hardwired system was improved. From NAPS onwards, a computerized control system with hardwired interlock logic has been provided. New devices like coarse-fine potentiometers, special oil filled potentiometer assembly, rectilinear potentiometers etc., were specified from NAPS onwards. Positioning logic is computerized providing flexibility and expandability. Digital panel meters and indicating lamps have been provided for manual mode operations, while CRT monitors help in computer mode operations. Hydraulic controls which comprise D2O hydraulics, H2O hydraulics and oil hydraulics have been improved from NAPS onwards. Hydraulic panels have been relocated in accessible areas to reduce manrem and for better maintainability. All electric drives including X and Y drives were modified as hydraulic drives for better control. New types of valves have been employed. The paper highlights the details of the changes incorporated.