chemistry

Uranium hexafluoride

Uranium hexafluoride is a chemistry topic covered in the lgStudy science library. This page brings together a partial reference excerpt, illustrations, worked examples, real-world applications and a short study plan, so you can understand Uranium hexafluoride rather than just read about it. In short: Uranium hexafluoride, sometimes called hex, is an inorganic compound with the formula UF6. Uranium hexafluoride is a volatile, white solid that is used in enriching uranium for nuclear reactors and nuclear weapons.

Key takeaways

Uranium hexafluoride belongs to chemistry; place it in that map before memorising details.
Learn the definition first, then one example that makes the definition concrete.
Connect Uranium hexafluoride to a quantity you can measure, compute or draw — that is where exam questions come from.
Reproduce the core statement of Uranium hexafluoride from memory before moving on to harder problems.

Reference excerpt

Uranium hexafluoride, sometimes called hex, is an inorganic compound with the formula UF6. Uranium hexafluoride is a volatile, white solid that is used in enriching uranium for nuclear reactors and nuclear weapons.

Preparation Uranium dioxide is converted with hydrofluoric acid (HF) to uranium tetrafluoride:

UO2 + 4 HF → UF4 + 2 H2O The resulting UF4 is subsequently oxidized with fluorine to give the hexafluoride:

UF4 + F2 → UF6 In samples contaminated with uranium trioxide, uranyl fluoride, an oxyfluoride compound is produced in the HF step:

UO3 + 2 HF → UO2F2 + H2O which can be fluorinated to produce the same product, uranium hexafluoride.

UO2F2 + 2 F2 → UF6 + O2 The fluorination steps in both reactions above are highly exothermic.

Properties

Physical properties At atmospheric pressure, UF6 sublimes at 56.5 °C. The solid-state structure was determined by neutron diffraction at 77 K and 293 K.

Chemical properties UF6 reacts with water, releasing hydrofluoric acid. The compound reacts with aluminium, forming a surface layer of AlF3 that resists any further reaction from the compound. Uranium hexafluoride is a mild oxidant. It is a Lewis acid as evidenced by its binding to form heptafluorouranate(VI), [UF7]−. Polymeric uranium(VI) fluorides containing organic cations have been isolated and characterized by X-ray diffraction.

Application in the fuel cycle

As one of the most volatile compounds of uranium, uranium hexafluoride is relatively convenient to process and is used in both of the main uranium enrichment methods, namely gaseous diffusion and the gas centrifuge process. Since the triple point of UF6, which is 64 °C (147 °F; 337 K) and 152 kPa (22 psi; 1.5 atm), is close to ambient conditions, phase transitions can be achieved with little thermodynamic work. Fluorine has only a single naturally occurring stable isotope, so isotopologues of UF6 differ in their molecular weight based solely on the uranium isotope present. This difference is the basis for the physical separation of isotopes in enrichment. All the other uranium fluorides are nonvolatile solids that are coordination polymers. The conversion factor for the 238U isotopologue of UF6 ("hex") to "U mass" is 0.676. Gaseous diffusion requires about 60 times as much energy as the gas centrifuge process: gaseous diffusion-produced nuclear fuel produces 25 times more energy than is used in the diffusion process, while centrifuge-produced fuel produces 1,500 times more energy than is used in the centrifuge process. In addition to its use in enrichment, uranium hexafluoride has been used in an advanced reprocessing method (fluoride volatility), which was developed in the Czech Republic. In this process, spent nuclear fuel is treated with fluorine gas to transform the oxides or elemental metals into a mixture of fluorides. This mixture is then distilled to separate the different classes of material. Some fission products form nonvolatile fluorides which remain as solids and can then either be prepared for storage as nuclear waste or further processed either by solvation-based methods or electrochemically. Uranium enrichment produces large quantities of depleted uranium hexafluoride (DUF6 or D-UF6) as a waste product. The long-term storage of D-UF6 presents environmental, health, and safety risks because of its chemical instability. When UF6 is exposed to moist air, it reacts with the water in the air to produce UO2F2 (uranyl fluoride) and HF (hydrogen fluoride) both of which are highly corrosive and toxic. In 2005, about 686,000 tonnes of D-UF6 was housed in 57,122 storage cylinders located near Portsmouth, Ohio; Oak Ridge, Tennessee; and Paducah, Kentucky. Storage cylinders must be regularly inspected for signs of corrosion and leaks. The estimated lifetime of the steel cylinders is measured in decades.

Accidents and disposal There have been several accidents involving uranium hexafluoride in the US, including a cylinder-filling accident and material release at the Sequoyah Fuels Corporation in 1986 where an estimated 29,500 pounds of gaseous UF6 escaped. The US government has been converting DUF6 to solid uranium oxides for disposal. Such disposal of the entire DUF6 stockpile could cost anywhere from $15 million to $450 million.

See also Enriched uranium Hexafluorouranate

References

Illustrations

Worked examples

Example 1 — a first encounter with Uranium hexafluoride

Start with the simplest possible case. Write down what Uranium hexafluoride claims or describes in one sentence, then invent the smallest concrete situation in which that sentence is true. In chemistry, the smallest case is usually a single object, a single equation or a single measurement. Check that every symbol or term in your sentence has a meaning in that case.

Example 2 — changing one variable

Take the situation from Example 1 and change exactly one quantity: double it, halve it, or set it to zero. Predict what should happen to Uranium hexafluoride before you calculate. Comparing your prediction with the result is the fastest way to find out whether you understand the idea or only the words.

Example 3 — an exam-style question

Typical questions about Uranium hexafluoride ask you to (a) state it precisely, (b) apply it to given data, and (c) explain a limitation. Practise writing all three answers in under five minutes; the third part is what separates a full-mark answer from an average one.

Applications of Uranium hexafluoride

In research: Uranium hexafluoride appears in chemistry research whenever the underlying quantities have to be modelled precisely. Papers usually cite it as a starting assumption and then explore where it breaks down.
In technology and industry: Engineering practice reuses Uranium hexafluoride in design rules, simulations and safety margins. Knowing the idea lets you read a specification sheet and understand why the numbers look the way they do.
In the classroom: Uranium hexafluoride is common in secondary-school and first-year university syllabi. It links to neighbouring topics Actinide halides, Hexafluorides, Nuclear materials, so understanding it makes those chapters shorter.
In everyday life: Look for Uranium hexafluoride outside the textbook — in sport, cooking, traffic, electronics or the sky above you. An example you found yourself is remembered far longer than one you were given.

Ask Teacher Smith questions about this articleOpens your AI tutor with a question about “Uranium hexafluoride” →

Affiliate

Preply — study more efficiently by working with a personal tutor. 50% off.

How to study Uranium hexafluoride in 20 minutes

Read the reference excerpt below once, without taking notes.
Close the page and write down what Uranium hexafluoride means in your own words.
Compare your version with the excerpt and mark what you missed.
Work through the three examples above with pen and paper.
Explain Uranium hexafluoride out loud to somebody else — or to Teacher Smith in the lgStudy chat.

Frequently asked questions

What is Uranium hexafluoride in simple terms?

Why does Uranium hexafluoride matter?

Because it connects several chemistry ideas at once: it gives you a definition you can apply, a quantity you can calculate, and a way to check whether a result is plausible.

How should I study Uranium hexafluoride?

Read the excerpt, restate it from memory, then work through the examples and applications listed on this page. The five-step study plan above takes about twenty minutes.

What does this page cover?

It gives you a compact reference excerpt plus original lgStudy explanations, examples, applications and study material on Uranium hexafluoride.