Nuclear Chemistry, How to Answer???

Question

What is meant by the term enrichment with regard to uranium for fission reactors and why does the fuel in a conventional nuclear reactor have to be "enriched"?

Answer 1

The concentration of the fissionable isotope of uranium in ores is too low to support sustained fission chain reactions. So, enrichment is separating the isotopes at least partially so that you produce uranium with a higher concentration of 238-U.

Answer 2

Uranium is made of a mix of isotopes (atoms with the same atomic number, but different atomic masses).
Some isotopes are more stable than others. Not all isotopes break down through the same process.

Most Uranium is isotope 238. It breaks down by releasing an alpha particle (2 protons, 2 neutrons) and some energy. A "conventional" reactors can be designed (such as the Canadian CANDU) to generate power from that heat. No need to enrich the Uranium.

Uranium 235 is fissile (atoms breaks down by splitting in many parts and releasing neutrons that can trigger more splitting in other atoms). This process releases energy faster (and can be used to create atomic bombs).

However, natural Uranium contains not enough Uranium-235. The Uranium is "enriched" by removing a portion of the Uranium 238, in order to increase the percentage of 235.

Most Uranium reactors (especially in USA and the ex-USSR) were designed to work with enriched Uranium because they can be used to create weapon-grade plutonium:

The neutrons released by the U-235 core will bombard the outer shell made from the discarded U-238 and turn the U-238 to Neptunium and Plutonium. These are called "breeder" reactors (And I guess that in some countries, these are considered the "conventional" reactors).

Also, with sufficient enrichment, you can have a sufficient concentration of U-235 to create a nuclear weapon directly. Therefore, some countries use the fact that they have such a reactor as an excuse to have Uranium-enrichment programs that could lead them to develop atomic weapons based on Uranium, even though they are not allowed to use the Plutonium that is generated -- we control that by taking their "spent" nuclear fuel and recycling them in our controlled areas.

Answer 3

Uranium has many isotopes. Isotopes are atoms with different numbers of neutrons in their nucleus. Only some of these isotopes of uranium will undergo fission releasing more neutrons to created more radioactive fission in other radioactive uranium atoms. Because the element is uranium and behaves chemically as uranium the radioactive isotopes can only be separated out by methods using weight. The extra neutrons make the radioactive isotopes heavier.
This weight based method of getting the radioactive uranium means using expensive centrefuges and in the case of Israel laser based methods.
Uranium metal that is non radioactive is used in Helicopters to make counterwieghts for the blades and as bullets for the military to use against armour. The metal is not dangerous because of radiation but because it is a very toxic heavy metal. Plutonium has the same isotope thing going on. So does Hydrogen. (Hydrogen1 is what we think of as being in water. Hydrogen with 2 neutrons is called dueterium and is in heavy water. It occurs naturally and is not radioactive. Hydrogen with 3 neutrons is tritium and it is born in reactors, is radioactive with a half life od 12 years. Tritium can be put into plastics and anything else Hydrogen can be put into because it is chemically still hydrogenA flourescent plastics block made with hydrogen3(tritium) will glow for years and such lights are used to mark helocopter landing pads in the north.
Tritium is very dangerous because your body uses it just like hydrogen in water, fats and in protiens. making you radioactive inside. Uranium or plutonium are mostly dangerous as toxic heavy metals(like lead and mercury are). When uranium is used as bullets they become airborne dust after they hit armout. That means fine heavy metal dust being inhaled, eaten or absorbed by everybody in the area forever.
So enrichment is the process of concentrating the actual fuel in the uranium to the point where it will support a nuclear reaction.
Note, some reactors like the ?Candu are called breeder reactors because they cause more radioactive material to be made during the reaction. Some reactors can actually generate more fuel than they use.
We burn everything in Candu reactors but still end up with more radioactive material coming out of them than going in. It is almost like a perpetual motion machine.

Answer 4

Uranium has two main isotopes ... U 238 & U 235.

Enrichment is done to extract the U 235 for use in Nuclear reactors for power generation.

(The reactor is used to produce superheated steam for driving the generator turbines).

(I see the 'thumbs down' expert has gone mad again ! Come out, come out wherever you are and let's all hear you're words of wisdom - you are beginning to P**s me off.)

Answer 5

consistent with hazard contain thorium interior the alloys for the engine cylinders. ensure the cost at which lines of thorium develop interior the a number of engine oils for the duration of trial runs of equivalent lengths.

Answer 6

Are you trying to make a bomb or something?