Reactor and plant instrumentation and control: general architecture

ike all industrial facilities, nuclear power plants and spent fuel reprocessing plants require resources to monitor and control the physical process and associated equipment. These resources are grouped together under the term "control-command".

Control systems are essentially made up of sensors, which transform physical quantities into electrical signals, PLCs, which process these signals, monitoring and control systems, and actuators, which transform electrical control signals into mechanical actions on the process.

The general design of control systems and associated equipment must meet specifications imposed by specific constraints resulting from the type of physical process, nuclear safety regulations and operating conditions.

As far as the physical process is concerned, the constraints are quite different depending on the nature of the installation. What they have in common, however, is the fact that irradiated nuclear fuel emits energy on a permanent basis, and that service continuity of the control system must therefore be total.

With regard to nuclear safety rules, it is worth noting the very stringent requirements for all equipment forming a barrier to radioactive products, and for equipment installed to protect these barriers in the event of accidents.

Finally, with regard to operating conditions, it's worth noting the constraints associated with the existence of controlled-access zones, both for irradiation and safety reasons.

The control architecture has three levels: level 0, which comprises the sensors and actuators, level 1, which comprises the PLCs, and level 2, which comprises the control room. Today, levels 1 and 2 are made up of computer-based equipment. All equipment is classified into three levels of requirements, with level 1 being the most stringent and generally leading to equipment being developed specifically to meet these requirements.