Huge blast at Japan nuclear power plant

Huge blast at Japan nuclear power plant


The word “meltdown” goes to the heart of the big nuclear question – is nuclear power safe?

The term is associated in the public mind with the two most notorious accidents in recent memory – Three Mile Island, in the US, in 1979, and Chernobyl, in Ukraine, seven years later.

You can think of the core of a Boiling Water Reactor (BWR), such as the ones at Fukushima Daiichi, as a massive version of the electrical element you may have in your kettle.

It sits there, immersed in water, getting very hot.

The water cools it, and also carries the heat away – usually as steam – so it can be used to turn turbines and generate electricity.

If the water stops flowing, there is a problem. The core overheats and more of the water turns to steam.

The steam generates huge pressures inside the reactor vessel – a big, sealed container – and if the largely metal core gets too hot, it will just melt, with some components perhaps catching fire.

In the worst-case scenario, the core melts through the bottom of the reactor vessel and falls onto the floor of the containment vessel – an outer sealed unit.

This is designed to prevent the molten reactor from penetrating any further. Local damage in this case will be serious, but in principle there should be no leakage of radioactive material into the outside world.

But the term “in principle” is the difficult one.

By: Teni Sow | Senior Editor at and Regular Contributor to

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