The core of the reactor uses low enriched uranium fuel rods and light water as moderator and coolant. Nuclear power is controlled by moving neutron absorbers commanded through hydraulic mechanisms. Cooling is provided by a primary circuit that removes heat from the core and transfers it towards the secondary circuit, where steam is generated to produce electricity by means of a turbogenerator.

The primary circuit is under high pressure and temperature in self-pressurized mode, while cooling water circulates naturally through the action of gravity (no pumps incorporated). Heat is removed from the primary circuit through steam generators, located inside the pressure vessel, together with the hydraulic mechanisms, the core and the rest of the primary system (integrated reactor), which notably reduces the quantity and size of the pipelines required with respect to a conventional design.

Safety aspects were specially considered throughout the design, the following criteria being applied:

a. Simple design to minimize the number of components that could experience failure within systems deemed critical for reactor safety, e.g. lack of pumps and pipelines within the primary circuit

b. Limitation through design of the consequences on reactor safety resulting from component and/or system failure, e.g. limitation of the size of pipelines and penetrations related to the primary system

c. Risk-free failure: The failure of a component leads the reactor to a safer situation, e.g. normal failure mode of actuated valves and other active components

d. Safety systems based on physical (passive) phenomena that do not require the use of external energy nor the immediate intervention of operators for their handling and effectiveness, e.g. first and second shutdown system, residual heat removal system, pressure relief, emergency injection and pressure elimination system

Due to these and other aspects, the CAREM reactor is internationally renowned as a reactor of innovative safety features of great impact.