The speed of this neutron affects its probability of causing additional fission, as does the presence of neutron-absorbing material.
Some reactors operate with the coolant in a constant state of boiling, using the generated vapor to turn turbines.
This happened in the RBMK reactor that was destroyed in the Chernobyl disaster due to positive void coefficient and fast power coefficients present at lower reactor power levels, the EPS scram accelerating rather than dampening reactivity resulting in the explosion.
In boiling-water reactors with large negative void coefficients, a sudden pressure rise (caused, for example, by unplanned closure of a streamline valve) will result in a sudden decrease in void content: the increased pressure will cause some of the steam bubbles to condense ("collapse"); and the thermal output will possibly increase until it is terminated by safety systems, by increased void formation due to the higher power, or, possibly, by system or component failures that relieve pressure, causing void content to increase and power to decrease.
Boiling water reactors are all designed (and required) to handle this type of transient.
A loss of coolant in such a reactor decreases the thermal output, but of course heat that is generated is no longer removed, so the temperature could rise (if all other safety systems simultaneously failed).