Feasibility of variable speed motor drives for CANDU nuclear power plants

CANDU nuclear power plants presently use fixed speed motors to power their processes. Control of the processes involve the “throttling” of liquids by incremental by-passing pumping action. This is achieved by the use of process control valves of which a typical CANDU station has more than a hundred. The elimination of many of these valves, the simplification of the control circuit algorithm, plus the increased speed and precision of process control and elimination of the need for constant full power motor operation creates an opportunity for capital cost saving, energy efficiency and engineering cost saving for CANDU plants. Safety considerations that may require low speed operations or simultaneous starting of the HT (heat transport) motors can be achieved by powering the motors with variable speed drives. The implementation of mature and at the same time, evolutionary technology used in variable speed drives in new and existing CANDU stations can enhance O, M and A effectiveness, reduce the need for complex process control hardware/software and augment the station net output power by reducing station load requirements. Before this is attempted, all variable speed drive inherent design attributes must be rationalised for CANDU use. In addition, variable speed drive characteristics must be compared against CANDU control and safety requirements and philosophies. This study looks at the pros and cons of variable speed drives and also provides guidance on how to proceed with implementation into the CANDU design