Water is used in nuclear REACTORS both as the heat energy carrier and as a coolant to prevent overheating. Proper cooling is required or the reactor will overheat, causing a meltdown. This is not the same as a nuclear explosion since all that will happen is the extreme heat will melt or destroy the reactor or its containment, but due to the design of reactors it is impossible to have a nuclear explosion similar to nuclear weaponry in a reactor.
A notable reactor meltdown was Chernobyl where the nuclear reaction was allowed to generate too much excess heat and the heat caused melting of reactor components and eventually a steam explosion (water vapour explosion) due to overheating. The main concern for a reactor meltdown is not the immediate destruction of everything in a certain radius but the spraying of highly radioactive materials found only in a reactor over a large radius since this radioactive waste cannot be cleaned effectively and will render the surroundings uninhabitable for decades.
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Water itself does not become radioactive, luckily, but any dissolved material in the water in the reactor primary circuit gets irradiated by the neutron flux and so can become radioactive. Therefore it is very important to control the water purity, it is all treated in a demineralisation plant, but then that is normal practice for power plants anyway, the difference in a nuclear plant is that the removed material can be radioactive. The secondary water/steam system in a PWR will not become radioactive, neither will the station cooling water used to cool the turbine condenser.
Basically, the rate at which the water will cool depends on the difference between the water's temperature, and the temperature of its surroundings. The higher the temperature difference, the faster it cools. There are some other factors, but that's the gist of it...
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It takes longer to cool off, but mostly depending on the temperature.
Water is commonly used to cool the reactor in nuclear power stations. This water absorbs the heat generated by the nuclear reactions and carries it away, preventing the reactor from overheating. The cooled water is then circulated back to the reactor to continue the cooling process.
There is a lot of nuclear waste that is at risk of exploding, so the workers must keep it covered with water to cool it. This prevents explosion. They had a problem with the back up power going out due to the tsunami, and this caused more explosions Tuesday and Wednesday. A huge concern is the massive amounts of radiation coming from the waste.
If you are talking about the Nuclear Reactors in Japan, they were damaged because when they lost power, the water pumps used to cool them stopped, and all of the nuclear material overheated.
So that there is a constant supply of water to cool the reactors with.
to cool the heating rods and generate electricity
the amount of water needed to cool down a a nuclear power station
it depends, where. The sun or the factory. The facories uses nuclear fission. This means they split atoms, usually uranium. Then it heats up quickly. The factory must use water to cool it down. The steam turns turbines to make energy. If they are not enough water, then there will be a melt down. In the sun. It uses nuclear fusion. This means it combines atoms together. this happens in the core. then energy is radiated to the convection zone, then the energy reaches the surface and radiates its energy in to space.
The nuclear power plants are filled with water to keep the atoms from splitting too fast inside the nuclear rod. Because of the earthquake in Japan, the nuclear power plants lost a lot of water in them, which is making the atoms split too fast. Radiation is now leaking from the plants, so crews are going in and dumping seawater into the nuclear plants to cool down the rods.
Coolant Systems on a Nuclear Reactor works by pumping large amounts of Sea Water into the reactors to cool it down and produce steam.
One material that can be used to cool down a nuclear meltdown is water. It is commonly used as a coolant in nuclear reactors to absorb excess heat. Other materials like liquid sodium or helium may also be used in some reactor designs.
The power plant were where they were because the generators needed cool water for the cooling systems at the plant.
In a properly operating nuclear reactor, water used to cool the reactor is not contaminated. This water, called primary coolant, is quite pure. And after shutdown and cooldown, the water has little radiation in it. But if the reactor has some malfunction that overheats the fuel, fuel elements can rupture or melt (a meltdown) and fission products, which are hightly radioactive, can be released into the coolant (the water). The water is then contaminated.