"Dude", it's not so easy.
As Japan deals with the after-effects of its strongest earthquake on record and an even more devastating tsunami, the world’s attention is focussed on the Fukushima nuclear power plant
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However, once the chain reaction stops, ordinary nuclear reactions take over and will continue to generate heat albeit at a lower rate. In fact, even once nuclear fuel is used up, it still needs to be kept cool for a number of years until these natural decay processes eventually fizzle out. This is also the case for a working reactor that has been shut down or fuel that has reached the end of its life - cooling is required to take away the heat generated by regular decay processes.
Thus in order to shut down a nuclear power plant safely, the fuel needs to be kept cool for an extended period of time even once the chain reaction is quenched.
This is why the Japanese government has decided to use seawater to cool the fuel. In a worst case scenario, if the temperature is not controlled, leaked fuel can melt and then aggregate, potentially allowing the chain reaction to restart in an uncontrolled way in what is known as a meltdown. Using seawater in this way effectively ends the chance of ever using the plant again but should prevent the prospect of a meltdown.