Heavy Water.

[barrsp]

In a WWII war film the allies had to blow up a German factory that made "Heavy Water".   What is heavy water, what is it used for.

[jake-the-peg]

Heavy water is water where one or more of the hydrogen atom(s) in water are replaced with deuterium. ( which is hydrogen with 1 neutron and 1 proton in the nucleus instead of just a proton)

In order to make an atomic bomb you need either enriched uranium or plutonium. Which generally (although not always) requires a nuclear reactor.

Heavy water is a neutron moderator and is used in some nuclear cores to slow down neutrons so that a chain reaction can be established. Using Heavy water means that you can build a nuclear reactor using raw Uranium without the difficult job of enriching it first. - The Canadian reactors do this I think.

The Nazis were attemting to build nuclear reactors with raw Uranium and Heavy water in order to obtain enough Plutonium to make a bomb.

Therefore blowing up the plant in Norway isolating the heavy water was pretty important.

[fo3nix]

water is H2O, yes?

well heavy water is D2O, where the D is for Deuterium.

Deuterium is known as an "isotope" of Hydrogen, because it is just the same as Hydrogen in every way, except it has one extra neutron within the atom. This makes it slightly heavier, and thus its called heavy water.

Used for example in neutrino observatories, such as the Sudbury one. neutrinos hit what is essentially a huge bowl full of heavy water, and this makes them slow down so the detectors can detect them.

more important for the film (probably), is that its also used as a moderator in nuclear reactors. assuming you know that nuclear reactors work by fuel rods emitting stuff; without a moderator, the stuff will multiply far too fast and would create more of a bomb than a power plant. a moderator is used (again as example above) to slow this stuff down.

[fo3nix]

hehe got there just before I did ;)

[jake-the-peg]

Actually the job of a moderator is to slow down the fast neutrons emmitted in fision to slow (or thermal) speeds at which they can interact with other atoms and cause new fissions.

Control rods are used to absorb neutrons and it is these that regulate the reaction rate

[newtron]

Heavy water also makes a great conservative tracer for studying how water moves through a porous medium.

[barrsp]

Brilliant answers,  Thanx guys.

[Gibboman]

Further to all the previous answers, I also beleive that heavy water is not conductive unlike H2O