2006-08-30 08:57:22 · 7 answers · asked by Anonymous in Science & Mathematics ➔ Earth Sciences & Geology
U metal needs to be at a certain concentration and composition in order for a nuclear reaction to take place. U-235 (isotope) must be at 3.5% for the reation to start (relative to the slower-decaying U-238 and other isotopes). U-235 is usually 0.7% of Uranium in nature, so humans need to enrich it to get it to 3.5%. In rare cases, you can get naturally-enriched U, causing a natural reactor (see link).
2006-08-30 09:03:09 · answer #1 · answered by QFL 24-7 6 · 0⤊ 0⤋
Uranium ore , called pitchblende, is about 99% U238
and 1% U235. The difference between 238 and 235 is
3 neutrons. But U238 is not readily fissionable(i.e.,
the atoms don't easily break apart releasing all that energy). It's not bomb material. On the other hand U235
is highly fissionable. And it only takes about 20 pounds
(critical mass) to go into a chain reaction. That's when the radiation within the U235, which is in the form of high speed neutrons hits and splits U235 atoms, releasing more high speed neutrons, etc., etc. Below critical mass
and enough neutrons escape with no explosion, like in
a nuclear reactor. Now U235 and U238 are chemically
identical. They have the same number of protons so they
cannot be separated chemically. They must be separated
physically. With ore being only 1% U235, this is a
rather painstaking process. One way is with a centrifuge.
It's this extraction of U235 that's called enriching.
2006-08-30 09:23:13 · answer #2 · answered by albert 5 · 1⤊ 0⤋
It is the process of concentrating reaioactive uranium 235 from a mixture of uraniums 235, 237 and 238. Uranium is chemically reacted with fluorine to make uranium hexafluoride. This gas is spun in a centrafuge and the (slightly) heaver isotopes of uranium are forced to the outside, enrighing the lighter uranium remaining. The uranium is then brought to a solid state by liberating fluorine gas.
2006-08-31 08:43:57 · answer #3 · answered by Amphibolite 7 · 1⤊ 0⤋
Enriching uranium is a way of purifying it so it can be used in nuclear fuel or in weapons.
2006-08-31 20:13:32 · answer #4 · answered by hamdi_batriyshah 3 · 0⤊ 0⤋
U-235 is usually 0.7% of Uranium in nature, so humans need to enrich it to get it to 3.5%. The problem with this is the continuous decay of radioisotopes (L/2)...
2006-08-30 09:15:27 · answer #5 · answered by victorb81 1 · 0⤊ 1⤋
Natural Uranium contains two isotopes U238 and U235. The U238 which predominates is stable but the U235 is radioactive. Enrichment is concentrating the amount of U235 which is necessary for bombs and reactors.
2006-08-30 09:07:01 · answer #6 · answered by Robert A 5 · 0⤊ 2⤋
Taking the heaviest particles from the compound.
2006-08-30 09:08:49 · answer #7 · answered by brokolay 3 · 0⤊ 2⤋