Staff Site Universitas Negeri Yogyakarta

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PENGOLAHAN URANIUM

Sulistyani, M.Si.

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Pengolahan uranium alam

• Proses konsentrasi, konsentrat uranium disebut yellow cake.

• Proses pem urnian, hingga m encapai kem urnian 99,9%.

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Mining

• Uranium ore is usually

located aerially;

core

sam ples are then

drilled

and analyzed by

geologists. The

uranium ore is extracted by m eans of drilling and

blasting. Mines can be in either open pits or

underground. Uranium concentrations are a

sm all percentage of the rock that is m ined, so

tons of tailings waste are generated by the

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Milling & Leaching

•The ore is first crushed into sm aller bits, then it is sent through a ball m ill where it is crushed into a fine powder. The fine ore is m ixed with water, thickened, and then put into leaching tanks where 90 % of the uranium ore is leached out with sulfuric acid. Next the uranium ore is separated from the depleted ore in a m ultistage

washing system . The depleted ore is then neutralized with lim e and put into a

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Yellowcake

• Meanwhile, the uranium

solution is filtered, and then

goes through a solvent

extraction process that includes

kerosene and am m onia to

purify the uranium solution.

After purification the uranium

is put into precipitation tanks—

the result is a product

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Transport at ion

• In the final processes the

yellow cake is heated to

8 0 0

˚Celcius which makes a

dark green powder which is

98 % U

3

O

8

.

The dark green

powder is put into 20 0 liter

drum s and loaded into

shipping containers and are

shipped overseas to fuel

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Conversion

• _{gas form of UF6. This is called}To enrich uranium it m ust be in the

conversion. The conversion diagram shown here is from Honeywell. First the yellow cake is converted to uranium dioxide through a heating process (this step was also m entioned in the m ining process). Then anhydrous hydrofluoric acid is used to m ake UF4. Next the UF4 is m ixed with fluorine gas to m ake

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Enrichment

• Uranium enrichm ent increases the am ount of U235 in

com parison to U238 . Dom estic power plants use a m ixture that is 3-5% U235, while “highly enriched uranium ” is generally

used for weapons, som e research facilities, and naval reactors. Dom estic reactors usually require fuel in the form of uranium dioxide and weapons use the enriched m ix in the form of a m etal. The conversion and enrichm ent process is very

dangerous because not only is the uranium hexafluoride radioactive, it is also chem ically toxic. In addition, if the

uranium hexafluoride com es in contact with m oisture it will release another very toxic chem ical called hydrofluoric acid.

There have been num erous accidents during the conversion and enrichm ent process. Depleted uranium is the waste that is

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Fuel Fabricat ion

•After being enriched, the UF6 is taken to a fuel

fabrication facility that

presses the powder into sm all pellets. The pellets are put into long tubes. These tubes are called fuel rods. A fuel assem bly is a cluster of these sealed rods. Fuel assem blies go in the core of the nuclear reactor. It takes

approxim ately 25 tonnes of fuel to power one 10 0 0 MWe reactor per year. The picture