A nuclear reactor design that ensures risk minimisation in the case of an accident by using physical principles such as convection or gravity, without active operator intervention. Modern reactors try to use as many inherent safety features as possible, e.g. negative temperature coefficient (when the temperature rises above the optimum limit, the fission reaction efficiency decreases), negative void coefficient (if the cooling water is converted to steam, its moderation capability is reduced and the intensity of the fission reaction decreases), dropping of shut-off rods into the core due to gravity, or maintaining the circulation of coolant without pumps, only due to convection, i.e. the warm water rises upwards. The inherent safety features do not require external operator intervention, they are always functional and do not depend on, for example, the availability of electrical power.