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Shutdown is the state of a nuclear reactor when the fission reaction is slowed significantly or halted completely. Different nuclear reactor designs have different definitions for what "shutdown" means, but it typically means that the reactor is not producing a measurable amount of electricity or heat and is in a stable condition with very low reactivity.
Emergency core cooling systems (ECCS) are designed to safely shut down a nuclear reactor during accident conditions. The ECCS allows the plant to respond to a variety of accident conditions (e.g. LOCAs) and additionally introduce redundancy so that the plant can be shut down even with one or more subsystem failures. In most plants, ECCS is ...
Nuclear reactors generally have automatic and manual systems to scram the reactor in an emergency shut down. These systems insert large amounts of poison (often boron in the form of boric acid ) into the reactor to shut the fission reaction down if unsafe conditions are detected or anticipated.
The Reactor Protection System (RPS) is a system, computerized in later BWR models, that is designed to automatically, rapidly, and completely shut down and make safe the Nuclear Steam Supply System (NSSS – the reactor pressure vessel, pumps, and water/steam piping within the containment) if some event occurs that could result in the reactor entering an unsafe operating condition.
Passive nuclear safety is a design approach for safety features, implemented in a nuclear reactor, that does not require any active intervention on the part of the operator or electrical/electronic feedback in order to bring the reactor to a safe shutdown state, in the event of a particular type of emergency (usually overheating resulting from a loss of coolant or loss of coolant flow).
Nuclear bombs are extremely deadly weapons, but their worst effects are confined to a limited zone. A government safety expert says its entirely possible to survive a nuclear explosion and its ...
A clean-up crew working to remove radioactive contamination after the Three Mile Island accident. Nuclear safety is defined by the International Atomic Energy Agency (IAEA) as "The achievement of proper operating conditions, prevention of accidents or mitigation of accident consequences, resulting in protection of workers, the public and the environment from undue radiation hazards".
The mere fact that an assembly is supercritical does not guarantee that it contains any free neutrons at all. At least one neutron is required to "strike" a chain reaction, and if the spontaneous fission rate is sufficiently low it may take a long time (in 235 U reactors, as long as many minutes) before a chance neutron encounter starts a chain reaction even if the reactor is supercritical.