physics

Reprocessed uranium

Reprocessed uranium is a physics 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 Reprocessed uranium rather than just read about it. In short: Reprocessed uranium (RepU) is the uranium recovered from nuclear reprocessing, as done commercially in France, the UK and Japan and by nuclear weapons states' military plutonium production programs. This uranium makes up the bulk of the material separated during reprocessing.

Key takeaways

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

Reference excerpt

Reprocessed uranium (RepU) is the uranium recovered from nuclear reprocessing, as done commercially in France, the UK and Japan and by nuclear weapons states' military plutonium production programs. This uranium makes up the bulk of the material separated during reprocessing. Commercial LWR spent nuclear fuel contains on average (excluding cladding) only four percent plutonium, minor actinides and fission products by weight. Despite it often containing more fissile material than natural uranium, reuse of reprocessed uranium has not been common because of low prices in the uranium market of recent decades, and because it contains undesirable isotopes of uranium.

Given sufficiently high uranium prices, it is feasible for reprocessed uranium to be re-enriched and reused. It requires a higher enrichment level than natural uranium to compensate for its higher levels of 236U which is lighter than 238U and therefore concentrates in the enriched product. As enrichment concentrates lighter isotopes on the "enriched" side and heavier isotopes on the "depleted" side, 234U will inevitably be enriched slightly stronger than 235U, which is a negligible effect in a once-through fuel cycle due to the low (55 ppm) share of 234U in natural uranium can become relevant after successive passes through an enrichment-burnup-reprocessing-enrichment cycle, depending on enrichment and burnup characteristics. 234U readily absorbs thermal neutrons and converts to fissile 235U, which needs to be taken into account if it reaches significant proportions of the fuel material. If 235U interacts with a fast neutron there is a chance of a (n,2n) "knockout" reaction. Depending on the characteristics of the reactor and burnup, this can be a larger source of 234U in spent fuel than enrichment. If fast breeder reactors ever come into widespread commercial use, reprocessed uranium, like depleted uranium, will be usable in their breeding blankets. There have been some studies involving the use of reprocessed uranium in CANDU reactors. CANDU is designed to use natural uranium as fuel; the 235U content remaining in spent PWR/BWR fuel is typically greater than that found in natural uranium, which is about 0.72% 235U, allowing the re-enrichment step to be skipped. Fuel cycle tests also have included the DUPIC (Direct Use of spent PWR fuel In CANDU) fuel cycle, where used fuel from a pressurized water reactor (PWR) is packaged into a CANDU fuel bundle with only physical reprocessing (cut into pieces) but no chemical reprocessing. Opening the cladding inevitably releases volatile fission products like xenon, tritium or krypton-85. Some variations of the DUPIC fuel cycle make deliberate use of this by including a voloxidation step whereby the fuel is heated to drive off semi-volatile fission products or subjected to one or more reduction / oxidation cycles to transform nonvolatile oxides into volatile native elements and vice versa. The direct use of recovered uranium to fuel a CANDU reactor was first demonstrated at Qinshan Nuclear Power Plant in China. The first use of re-enriched uranium in a commercial LWR was in 1994 at the Cruas Nuclear Power Plant in France. In 2020, France, one of the countries with the biggest reprocessing capacity, held a stock of 40,020 tonnes (39,390 long tons; 44,110 short tons) of reprocessed uranium, up from 24,100 tonnes (23,700 long tons; 26,600 short tons) in 2010. Every year France processes 1,100 tonnes (1,100 long tons; 1,200 short tons) of spent fuel into 11 tonnes (11 long tons; 12 short tons) reactor grade plutonium (for immediate further processing into MOX fuel) and 1,045 tonnes (1,028 long tons; 1,152 short tons) of reprocessed uranium which is largely stockpiled. There are provisions in place for the storage of this reprocessed uranium for up to 250 years for potential future use. Given France's domestic uranium enrichment capabilities, this stockpile constitutes a strategic reserve for the case of a major disruption of uranium supply as France does not have domestic uranium mining.

References

Further reading Advanced Fuel Cycle Cost Basis - Idaho National Laboratory

Module K2 Aqueously Reprocessed Uranium Conversion and Disposition Module K3 Pyrochemically/Pyrometallurgically Reprocessed Uranium Conversion and Disposition

Worked examples

Example 1 — a first encounter with Reprocessed uranium

Start with the simplest possible case. Write down what Reprocessed uranium claims or describes in one sentence, then invent the smallest concrete situation in which that sentence is true. In physics, 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 Reprocessed uranium 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 Reprocessed uranium 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 Reprocessed uranium

In research: Reprocessed uranium appears in physics 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 Reprocessed uranium 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: Reprocessed uranium is common in secondary-school and first-year university syllabi. It links to neighbouring topics Nuclear materials, Nuclear reprocessing, Uranium, so understanding it makes those chapters shorter.
In everyday life: Look for Reprocessed uranium 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.

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How to study Reprocessed uranium in 20 minutes

Read the reference excerpt below once, without taking notes.
Close the page and write down what Reprocessed uranium 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 Reprocessed uranium out loud to somebody else — or to Teacher Smith in the lgStudy chat.

Frequently asked questions

What is Reprocessed uranium in simple terms?

Why does Reprocessed uranium matter?

Because it connects several physics 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 Reprocessed uranium?

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 Reprocessed uranium.