Nuclear reactors

[TheLobo1544]

Hi! I was just wondering, how exactly does a nuclear reactor work?

[Danijel Gorupec]

Intentionally simplified description (not concerned about the chain reaction mechanism)…

 

Nuclear reactor is basically a simple device... It is a large steel pot that contains large enough quantity of nuclear fuel (uranium or plutonium of enough purity) and some neutron-moderator material (water, graphite...). Moderator is used to boost chain reactions by slowing down neutrons.

 

The nuclear fuel has this interesting property - when hoarded in large enough quantities it will engage chain nuclear reaction – that is, it will start producing lot of heat. This heat is then harvested to produce steam for turbines.

 

To control the chain reaction, every reactor is equipped with number of control rods. These can be inserted or extracted to keep chain reaction (heat production) under control. Control rods are just rods made of material that ‘kills’ chain reaction (silver-indium-cadmium, boron…)

 

The nuclear reactor normally is under high pressure (needed for efficient power generation), but if temperature goes overly high, the pressure may increase even further and steel vessel may explode. This would be a major incident (Chernobyl). Therefore, a nuclear reactor is equipped with huge number of complex safety devices, most of them are concerned about cooling.

 

 

[Airbrush]

Are nuclear reactors isolated on rollers to allow the earth to move under the reactor during an earthquake? If not, why not? Major skyscrapers are built on rollers or springs, or whatever means to isolate the building from harmful shaking.

[Danijel Gorupec]

I don't know this detail, sorry. Maybe someone else can teach us.

 

But certainly the nuclear reactor itself is much more robust than a skyscraper.... Other systems around the reactor (cooling eqipment) is probably more harmed by an earthquake. I don't know what protection methods are used.

[lemur]

The nuclear fuel has this interesting property - when hoarded in large enough quantities it will engage chain nuclear reaction – that is, it will start producing lot of heat. This heat is then harvested to produce steam for turbines.

I have a vague intuitive sense that nuclear fuel is like a pile of hot coals that doesn't require any air to heat up and also doesn't burn up quickly.

Just as spreading out hot coals increases their surface area allowing them to cool faster, I would think the same would work with radioactive fuel. Likewise, just as concentrating hot coals and or pushing them against each other (increasing pressure) causes them to heat up more due to each other's heat, I would expect radioactive fuel to do this too.

 

I have the idea that the graphite is comparable to water in a fire, since it absorbs neutrons without reacting to them the way water absorbs heat without combusting.

 

Do you think this is an inaccurate analogy? Obviously there are an enormous number of other factors that are not comparable sense hot coals are a chemical reaction and nuclear fuel is, well . . . nuclear.

Edited March 26, 2011 by lemur

[Danijel Gorupec]

I would agree to 'pile of hot coals' analogy. If you pile uranium up, smaller number of neutrons will skip away and more neutrons will remain for chain reaction (analogly, if you pile coal up, smaller amount of heat will radiate away and more heat will remain for burning).

 

I cannot agree to 'graphite to water' analogy (however, I would agree to 'control-rod to water' analogy). Graphite is used as a moderator and it will assist to chain reaction (it slows down neutrons -> only slow neutrons can break atoms).

[Airbrush]

It takes a disaster, like what we see in Japan, to get the industry to fix safeguards so even with a great earthquake and tsunami, a nuclear reactor should be isolated and insulated enough to not cause any problems. New reactors will be built from these lessons learned. Nuclear power is here to stay, we should learn to live with it safely.

[Sci_Guy]

Here is a great website created by the power workers of Ontario that details how Ontario's rectors differ from the ones in Japan, and how they are on a whole different level of safe. A very interesting article. There are a few actually so feel free to look around.

http://www.abetterenergyplan.ca/#/news/accident-here?