Editing Boiling water reactor (section)

=== Safety systems ===
{{main|Boiling water reactor safety systems}}
In order to be considered safe, nuclear reactors must at all time comply with the fundamental nuclear safety functions:

# Control of reactivity
# Removal of heat from the fuel
# Confinement of radioactive materials, shielding against radiation, and control of planned radioactive releases, as well as limitation of accidental releases

During normal operation of the reactor, good design, construction and operation practices ensure the compliance with the safety functions. In addition, dedicated [[Boiling water reactor safety systems|safety systems]] must be installed to ensure that compliance with the safety functions is maintained in case of deviations from normal conditions. The safety systems of a modern reactor are designed to according to a [[Defence in depth (non-military)|defence in depth]] philosophy, which is a design philosophy that is integrated throughout construction and [[Building commissioning|commissioning]] of the plant. In order to minimize the risks of inability to fulfil a safety function, a BWR uses redundant safety systems, relying on different action mechanisms and spatially separated.

Following emergency shutdown of the fission reaction, heat continues to be produced inside nuclear reactors due to the [[radioactive decay]] of fission products and materials that have been activated by [[neutron absorption]]. The decay heat of a reactor core is of the order of a few tens of megawatt (depending on the core's operating power and operation duration) which is sufficient to lead to significant damage and even melting. To prevent such cases, safety systems grouped under the umbrellas of [[Emergency Core Cooling System|emergency core cooling systems]] (ECCS) are provided in order to remove heat through the injection of cooling water.