engineering

Thermal Oxide Reprocessing Plant

Thermal Oxide Reprocessing Plant is a engineering 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 Thermal Oxide Reprocessing Plant rather than just read about it. In short: The Thermal Oxide Reprocessing Plant, or THORP, is a nuclear fuel reprocessing plant at Sellafield in Cumbria, England. THORP is owned by the Nuclear Decommissioning Authority and operated by Sellafield Ltd, the site licensee.

Key takeaways

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Reference excerpt

The Thermal Oxide Reprocessing Plant, or THORP, is a nuclear fuel reprocessing plant at Sellafield in Cumbria, England. THORP is owned by the Nuclear Decommissioning Authority and operated by Sellafield Ltd, the site licensee. Spent nuclear fuel from nuclear reactors was reprocessed to separate the 96% uranium and the 1% plutonium from the 3% radioactive wastes, which are treated and stored at the plant. The uranium is then made available for customers to be manufactured into new fuel, and the plutonium incorporated into mixed oxide fuel. On 14 November 2018 it was announced that reprocessing operations had ended at THORP after earning £9bn in revenue. The receipt and storage facility (which makes up nearly half of THORP's physical footprint), will operate through to the 2070s to receive and store spent nuclear fuel from the UK's PWR and AGR fleet. The decommissioning is expected to start around 2075.

History

Between 1977 and 1978 an inquiry was held into an application by British Nuclear Fuels plc for outline planning permission to build a new plant to reprocess irradiated oxide nuclear fuel from both UK and foreign reactors. The inquiry was to answer three questions:

Should oxide fuel from United Kingdom reactors be reprocessed in this country at all; whether at Windscale or elsewhere? If yes, should such reprocessing be carried on at Windscale? If yes, should the reprocessing plant be about double the estimated site required to handle United Kingdom oxide fuels and be used as to the spare capacity, for reprocessing foreign fuels? The result of the inquiry was that the new plant, the Thermal Oxide Reprocessing Plant, was given the go-ahead in 1978. Construction of THORP started in 1979, and was completed in 1994. The plant went into operation in August 1997. Build cost was £1.8 billion. THORP's first irradiated fuel rod was sheared in March 1994, which was followed in January 1995 by the chemical separation plant processing the irradiated fuel feed solution that had been produced in the previous year by the Head End plant. By early 1998 over 1400 t of irradiated fuel has been reprocessed in THORP, and the plant was steadily and successfully ramped up to its normal operating throughput throughout this time. At this time, the performance of the THORP Chemical Separation Plant had been excellent, above all, the uranium-plutonium separation stage, which received extensive development to deal with the effects of the fission product technetium, has given an overall separation performance well in excess of the minimum flowsheet requirement. THORP's discharges represented a small fraction of overall discharges from the wider Sellafield site. On 14 November 2018 it was announced that reprocessing operations had ended at THORP after all existing reprocessing contracts had been fulfilled. It had reprocessed 9,331 tonnes of used nuclear fuel from 30 customers in nine countries, earning £9bn in revenue. The receipt and storage facility within THORP continues to operate. Decommissioning will take place after several decades to allow radiation levels to decline, and is expected to occur between 2075 and 2095. The estimated cost of decommissioning is forecast as £4 billion at 2018 prices. In January 2025, the government announced that the 140 tonnes of civil plutonium produced by reprocessing, originally considered a valuable asset, would be immobilised and eventually disposed of in a geological disposal facility, rather than used to produce MOX fuel which was evaluated as an uneconomic option.

Design

The chemical flowsheet for THORP is designed to add less non-volatile matter to the first cycle PUREX raffinate. One way in which this is done is by avoiding the use of ferrous compounds as plutonium reducing agents. In this plant the reduction is done using either hydrazine or HAN (hydroxylamine nitrate). The plant releases gaseous emissions of krypton-85, a radioactive beta-emitter with a half-life of 10.7 years. The Radiological Protection Institute of Ireland (RPII) commenced 24-hour atmospheric monitoring for krypton-85 in 1993, prior to the plant's commissioning. The cooled oxide fuel is chopped up in the Shear Cell and the fuel dissolved in nitric acid. It is chemically conditioned before passing to the chemical separation plant. Pulsed columns (designated HA/HS) are used to initially separate the majority of the uranium and plutonium from the fission products by transferring them into the solvent phase, which comprises tri-butyl phosphate in odourless kerosene (TBP/OK). The transfer is done in the HA column with the HS column providing further removal of fission products. 2 further pulsed columns (designated BS/BX) and a mixer/settler assembly (1BXX) then separate the uranium and plutonium into separate streams. Plutonium is reduced to the +3 oxidation state, which is insoluble in the solvent phase so ends up in the aqueous phase exiting the 1BX column. The 1BXX mixer/settler completes the removal of Pu from the solvent phase. The 1BS column removes any remaining Uranium from the aqueous phase by the use of fresh solvent. Pulsed columns then purify the plutonium, removing the troublesome fission products that remain. A mixer/settler (1C) is used to transfer (washes) the uranium across to the aqueous phase ready for the next stage. Uranium purification is achieved using three mixer settlers (UP1 - UP3) similar to those in use on the existing Magnox reprocessing plant. Evaporation of the two product streams then occurs before further processing is undertaken. Uranium is converted to UO3 powder while the plutonium is converted to PuO2 powder and sent to storage. Pulsed columns were chosen to avoid the risk of a criticality incident occurring within the plant. This can happen if sufficient fissile material comes together to start an uncontrolled chain reaction, producing a large release of neutrons. The risks and mechanisms are well understood and the plant design is arranged to prevent its occurrence, i.e.: intrinsically safe.

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Illustrations

Worked examples

Example 1 — a first encounter with Thermal Oxide Reprocessing Plant

Start with the simplest possible case. Write down what Thermal Oxide Reprocessing Plant claims or describes in one sentence, then invent the smallest concrete situation in which that sentence is true. In engineering, 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 Thermal Oxide Reprocessing Plant 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 Thermal Oxide Reprocessing Plant 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 Thermal Oxide Reprocessing Plant

In research: Thermal Oxide Reprocessing Plant appears in engineering 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 Thermal Oxide Reprocessing Plant 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: Thermal Oxide Reprocessing Plant is common in secondary-school and first-year university syllabi. It links to neighbouring topics Buildings and structures in Cumbria, Nuclear facilities, Nuclear technology in the United Kingdom, so understanding it makes those chapters shorter.
In everyday life: Look for Thermal Oxide Reprocessing Plant 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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Frequently asked questions

What is Thermal Oxide Reprocessing Plant in simple terms?

Why does Thermal Oxide Reprocessing Plant matter?

Because it connects several engineering 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.

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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 Thermal Oxide Reprocessing Plant.