URANIUM FUEL CHAIN - front end

[Oscar]

Important Stages in the "front end" of the Uranium Fuel Chain
Dr. Gordon Edwards - October 24, 2021

Explanation of the “front end” of the uranium fuel chain, that is, what happens to uranium before it goes into a nuclear reactor (or a nuclear weapon).

Uranium Mine -
input = a mineralized deposit at the mine site, output = uranium ore
destination = a nearby uranium mill
waste byproduct = waste rock and “steriles"

Uranium is a metal. It is mined in much the same way that gold is mined. The “ore” refers to any rock that has a sufficient amount of uranium in it, depending on the price, to make it profitable to extract the uranium. The uranium in the ore is always in the form of a molecular compound, whereby uranium atoms are chemically bound to other kinds of atoms. If the price of uranium increases by a lot, some of the waste rock may be re-classified as “ore”.

U = uranium (metallic); O = oxygen. Any molecular combination of U and O atoms is called a uranium oxide. Three different kinds of uranium oxides are mentioned below.

Uranium Mill -
input = uranium ore, output = yellowcake
destination = Blind River
waste byproduct = uranium tailings

The ore is sent to a “mill” where it is ground into a fine sand-like consistency. Sulphuric acid, or some other solvent, is used to “leach” the uranium out of the ore. After the uranium has been extracted from the ore all the other unwanted material, in the form of a "slurry” of crushed rock (sand), gets dumped into a tailings pond, after spending time in a “settling” pond to allow some of the dangerous heavy metals like radium to precipitate out at the bottom of the settling pond. The tailings are voluminous and contain more than three quarters of all the radioactivity that was in the original ore. This radioactive inventory does not decrease by one-half until 76,000 years have passed.

When the extracted uranium is solidified and dried it is is in the physical form of a fine sand or powder, called yellowcake, that is packed in drums and shipped to the refinery at Blind River. Yellowcake can be yellow or orange or grey or even black depending on the kind of impurities it contains. Chemically, yellowcake is about 80% or more of uranium oxide, mostly U3O8, and the other 20% or less is made up of impurities including radium and thorium (two of the natural radioactive byproducts of uranium, always present in uranium ore).

Uranium Refinery [Blind River since 1983]
input = yellowcake (U3O8 or uranium concentrates), output = uranium trioxide (UO3)
destination = Port Hope
waste byproduct = raffinate

Uranium concentrates - “yellowcake" - are sent from uranium mills in Canada, in Australia, in South Africa - even in the USA and elsewhere - arriving at the refinery in Blind River for treatment. Each molecule of U3O8 is made up of 11 atoms - 3 uranium atoms combined with 8 oxygen atoms. That is quite a large molecule compared with the molecules of "refined” oxide that are produced at Blind River The output from the Blind River refinery is uranium trioxide (UO3) in the form of a kind of gel. Each molecule of uranium trioxide has only one uranium atom, combined with 3 oxygen atoms. That’s a much smaller molecule (about 3 times less massive) than a U3O8 molecule. All of the uranium trioxide produced at Blind River goes directly to Port Hope for further treatment.

The impurities in the drums of yellowcake are removed at the refinery in the form of a radioactive fine-grained sandy waste called “raffinate”, some of which is sold as fertilizer for use in agriculture. Radioactive fertilizer is responsible for most of the radioactivity in tobacco leaves. In particular radioactive lead-210 (a natural radioactive byproduct of radium, with a half-life of 22 years) is harvested along with the tobacco and remains in the cigarettes on the shelves of stores. When the smoker inhales cigarette smoke, he or she is also inhaling minute amounts of polonium-210 (a natural radioactive byproduct of lead-210) and this extremely dangerous material lodges in the lungs of the smoker and is responsible for a great deal of the lung cancers that are attributed to smoking. The polonium-210 is also present in the second-hand smoke, posing an inhalation danger to non-smokers in the same room.

Because the raffinate contains radium, it constantly gives off radon gas (the immediate byproduct of the disintegration of radium atoms). Using raffinate as building material endangers the people living or working or attending school in those buildings, as the radioactive radon gas accumulates inside (it is seven times heavier than air). The radon gas becomes about six times more radioactive as it hovers in stagnant air for an hour or so, as a result of the gradual inbreeding of other polonium isotopes that are even more toxic than the notorious polonium-210.

Uranium Conversion Plant [Port Hope]
Input = trioxide (UO3) from Blind River, output = (1) dioxide UO2 (15%) (2) hexafluoride UF6 (85%)
waste byproduct = fugitive emissions
destination = (1) UO2 for CANDU fuel fabrication; (2) UF6 for enrichment plant [not in Canada]

Since 1983, when the Blind River refinery started operation, Port Hope receives all of the uranium trioxide (UO3) output from Blind River and converts the trioxide into two other chemical compounds: uranium dioxide (UO2) and uranium hexafluoride (U6).

About 15% of the Canadian-origin uranium is converted into uranium dioxide (UO2), a black powder that is packed in drums and shipped to a nuclear fuel fabrication plant where the dioxide is used to make ceramic uranium fuel pellets for Canadian CANDU reactors. There are three such fuel fabrication plants: the Zircatec facility at Port Hope and two BWXT facilities, one on Lansdowne Avenue in Toronto and the other in Peterborough, just across the street from an elementary school. As the name implies, a uranium dioxide molecule has one uranium atom combined with two oxygen atoms.

The other 85% of all Canadian-origin uranium, as well as all of the foreign-origin uranium, is converted from the uranium trioxide form (the output from Blind River) into a highly toxic and volatile compound called uranium hexafluoride (UF6). A molecule of uranium hexafluoride has one uranium atom combined with 6 fluorine atoms. With very few exceptions, all of the uranium that is exported from Canada is in the form of uranium hexafluoride.

Uranium Enrichment Plant [none exists in Canada]
Input: uranium hexafluoride; output: enriched uranium (LEU or HALEU or HEU)
Waste byproduct: depleted uranium (DU)
Destination: (1) LEU for light-water reactors; (2) HALEU for SMNRs; (3) HEU for Bombs or research reactors

It so happens that UF6 is one of the very few chemical compounds of uranium that can be turned into a gas at a relatively low temperature (57.2 degrees C) , and that is the only reason it is useful. Every bit of UF6 is exported from Canada to a uranium enrIchment plant in another country, where it is turned into a gas (by heating) and fed into an expensive, sophisticated, slow, energy-intensive enrichment facility that operates either by “gaseous diffusion” or by “ultracentrifuges” (sometimes called “calutrons”) in order to increase the concentration of the lighter isotopes of uranium (U235 and U234) compared with the heavier and much more abundant isotope (U238). The enriched uranium is then sent on to the ultimate customer, often in a country different from the one where the enrichment is done.

In natural uranium, mined from the Earth, no matter where on Earth it is, the concentration of U-235 in pure metallic uranium is 0.7 percent. In other words, in any sample of pure uranium, without any impurities, seven atoms out of 1000 are uranium-235 atoms. The other 993 atoms are heavier they are uranium-238 atoms.
It is possible that one of those thousand atoms is an atom of uranium-234, but this is usually not the case. Uranium-234 is MUCH less abundant than uranium-235.

All of these uranium atoms are virtually IDENTICAL. They behave in EXACTLY the same way as the others. The only difference between them is that most of them are a bit heavier than the others. A tiny bit heavier (1.2% heavier). To separate the lighter atoms from the heavier atoms, you make them into a gas and pass the gas through an EXTREMELY FINE MESH filter, so fine that the lighter atoms pass through just a bit easier than the heavy atoms. So on the other side of the filter you have a FEW more atoms of uranium-235 compared with uranium-238. This has to be done TENS OF THOUSANDS of times to achieve any substantial increase in the percentage of U-235. It takes a lot of energy to do this. A uranium enrichment plant typically uses as much energy as a pretty large city.

Unat = Natural uranium: 0.7% U-235, 99.3% U-238; slight amount of U-234. [fuel for CANDU reactors]
LEU = Low Enriched Uranium: 3% to 5% U-235; 95% to 97% U-238. [fuel for light water reactors]
HALEU = High Assay Low Enriched Uranium: 6% to 20% U-235; 80% to 94% U-238. [fuel for many SMNRs]
HEU = Highly Enriched Uranium: over 20% U-236; less than 80% U-238. [weapons-usable, strategic material]
WGU = Weapons Grade Uranium: over 90% U-235; less than 10% U-238. [ideal for weapons use - Hiroshima]