If this coolant flow is reduced, or lost altogether, the nuclear reactor's emergency shutdown system is designed to stop the fission chain reaction.
[1] If all of the independent cooling trains of the ECCS fail to operate as designed, this heat can increase the fuel temperature to the point of damaging the reactor.
These three factors would provide additional time to the plant operators in order to mitigate the result of the event: The Fukushima Daiichi nuclear disaster in 2011 occurred due to a loss-of-coolant accident.
The circuits that provided electrical power to the coolant pumps failed causing a loss-of-core-cooling that was critical for the removal of residual decay heat which is produced even after active reactors are shut down and nuclear fission has ceased.
The loss of reactor core cooling led to three nuclear meltdowns, three hydrogen explosions and the release of radioactive contamination.
Most reactors use a zirconium alloy as the material for fuel rod claddings due to its corrosion-resistance and low neutron absorption cross-section.
However, one major drawback of zirconium alloys is that, when overheated, they oxidize and produce a runaway exothermic reaction with water (steam) that leads to the production of hydrogen:
The residual decay heat causes rapid increase in temperature and internal pressure of the fuel cladding which leads to plastic deformation and subsequent bursting.
During a loss-of-coolant accident, zirconium-based fuel claddings undergo high temperature oxidation, phase transformation, and creep deformation simultaneously.
Another recent study evaluated Cr and FeCrAl coatings (deposited on Zircaloy-4 using atmospheric plasma spraying technology) under simulated loss-of-coolant conditions.