The importance of continuous cooling of nuclear spent fuel

Despite reassurances by the International Atomic Energy Agency (IAEA) that
there is no imminent safety threat posed by the power isolation, it is
important to understand the potential impact going forward.

When nuclear
fuel is removed from the core of a reactor, it is redesignated as
“spent” nuclear fuel and often treated as a waste product for disposal.
But fuel will continue to dissipate heat due to radioactive decay, even
after being removed from the reactor core.

It is therefore of foremost
importance that the spent fuel material contained at the Chernobyl site is
adequately and continuously cooled to prevent a release of radioactivity.
At Chernobyl, as well as other sites, standard procedures to safely handle
such material involves placing the fuel into water-filled ponds, which
shield the near-field environment from radiation.

They also provide a
medium for heat transfer from the fuel to the water via continuous
circulation of fresh, cool water. If circulation is compromised, such as
the recent power shutdowns, the fuel will continue to emit heat. This can
make the surrounding coolant water evaporate – leaving nothing to soak up
the radiation from the fuel. It would therefore leak out to the
surroundings.

 The Conversation 10th March 2022

https://theconversation.com/chernobyl-and-zaporizhzhia-power-cuts-nervous-wait-as-ukraine-nuclear-power-plants-could-start-leaking-radiation-178975