Yes. Due to the decay heat of fission byproducts, a nuclear reactor remains very hot immediately after being shut down. Active cooling is usually necessary fo

Yes. Due to the decay heat of fission byproducts, a nuclear reactor remains very hot immediately after being shut down. Active cooling is usually necessary for quite some time (weeks or even months). In normal operations, when spent fuel is removed from a reactor, it is stored in pools for many years to cool down (both thermally and radioactively).