Keywords: power supply, nuclear instrumentation and control, Bode plot, nuclear power plants, nuclear energy, nuclear safety, boost pre-converter, current mode, duty cycle, fault tolerance, feedback, feedforward, fractional order control, gain and phase margin, hot-plug, load sharing, one-cycle control, online maintenance, phase boosting, pole-zero cancellation, power factor, probabilistic safety assessment, pulse by pulse regulation, ramp addition, resettable integrator, safety significant systems, single-pole systems, stability, step demand, total harmonic distortion, voltage mode
Fault-tolerant power supply for safety significant nuclear instrumentation and control
Nuclear Instrumentation and Control (I&C) must address the issue of power supply differently from other commercial control systems. What is doable for commercial plants, such as a thermal power station, should not be applied for Nuclear Power Plant I&C. The hazards arising from power supply failure in nuclear power stations cannot be compared with other commercial systems. Therefore, the use of commercial off-the-shelf power supplies should be minimised in nuclear I&C. Nuclear I&C is of 'safety-significance' class: the power supply delivering power should and must aid the overall system reliability, maintainability, availability and sustainability. Bad experience of using commercial off-the-shelf power supplies earlier forced the authors to develop this fault-tolerant power supply for nuclear I&C, starting from the basics. This has been in reliable, sustainable operation for a decade in 12 reactors, and so, we advocate this concept of not developing through outsourcing or using a commercial product. Outsourcing and commercialisation and reliability are diametrically opposite. This paper deals with how the power supply for nuclear use was developed and, with certain basic issues, how the same has been made robust to be used for safety-significant nuclear I&C. Most I&C designers think of the power supply just as a black box but instead the power supply should be treated as a complete system with a transparent internal theory with all components given due importance with de-rating factor.