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Uranium Enrichment Tails Upgrading (Re-enrichment)

(last updated 4 Jun 2007)

Contents:


Introduction

During the enrichment process in uranium enrichment plants, the percentage of the fissile uranium isotope uranium-235 is raised from its natural 0.71% to a reactor grade of 3.2% (for BWRs) or 3.6% (for PWRs). This process not only produces the enriched product, but also a waste stream depleted in uranium-235, typically to 0.3%.
The degree of depletion of uranium-235 in this depleted uranium waste (the "tails assay") is a parameter that can be adjusted to economical needs, depending on the cost of fresh natural uranium and on the enrichment cost (expressed in $ per separative work unit - SWU).
> See graphs: Cost balance of uranium enrichment new window · Optimal tails assay new window (Note: feed cost includes uranium price plus conversion cost)
> See also: Uranium Enrichment Cost Optimizer

In the case of different cost situations at different enrichment plants, it can make an economical sense to further deplete ("strip") in a low-cost plant the depleted uranium produced in a high-cost plant.

An example is the processing of Urenco's enrichment tails in Minatom's external link enrichment plants in Russia. In this case, Minatom, while further depleting Urenco's depleted uranium, produces uranium of natural contents in uranium-235. It thus re-enriches or upgrades the tails to natural uranium grade. This product is then delivered back to Urenco for further enrichment to reactor grade. (see details)


Scenario 1

Mass balance of tails upgrading (per tonne of enriched uranium)

Assumptions:  

Feed
11.9 t UF6
(8.05 t Unat)
0.71% U-235
------> Urenco
enrichment plant
4531 SWU
------> Product
1.48 t eUF6
(1 t eU)
3.6% U-235
|
V
Waste / Refeed
10.42 t dUF6
(7.05 t dU)
0.3% U-235
------> Minatom
enrichment plant
489 SWU
------> Product
1.13 t UF6
(0.77 t U"nat")
0.71% U-235
|
V
Waste
9.29 t dUF6
(6.28 t dU)
0.25% U-235

Observations Scenario 1:


Scenario 2

Mass balance of tails upgrading (per tonne of enriched uranium)

Assumptions:  

Feed
11.9 t UF6
(8.05 t Unat)
0.71% U-235
------> Urenco
enrichment plant
4531 SWU
------> Product
1.48 t eUF6
(1 t eU)
3.6% U-235
|
V
Waste / Refeed
10.42 t dUF6
(7.05 t dU)
0.3% U-235
------> Minatom
enrichment plant
2651 SWU
------> Product
3.18 t UF6
(2.15 t U"nat")
0.71% U-235
|
V
Waste
7.24 t dUF6
(4.90 t dU)
0.12% U-235

Observations Scenario 2:


For other scenarios, use the Uranium Enrichment Tails Upgrading Calculator

The economics of tails upgrading

The economics of tails upgrading depend on a number of parameters: In case of a world market price of 11 US$/lb U3O8, the corresponding price of uranium as UF6 is around 34.2 US$/kg U as UF6.

With a world market enrichment cost of 90 US$/SWU, the break-even point would be reached at a recovery rate of "natural" uranium at Minatom of 2.63 kg U/SWU. The obtained recovery rates for Scenario 1 resp. 2 of 1.57 resp. 0.81 kg U/SWU are by far lower. Urenco would incur a loss of $1700 per t UF6 sent to Minatom.
> See Cost balance of tails upgrading new window

The situation changes, however, if a lower enrichment cost is assumed for Minatom. U.S. DOE's Engineering Analysis Report for the Long-Term Management of Depleted Uranium Hexafluoride of May 1997 estimates operating costs of $20-$30/SWU for centrifuge enrichment plants (there are no such plants in the US though). With US$ 30/SWU, for example, the break-even point would be reached at 0.88 kg U/SWU. For Scenario 1, the obtained recovery rates are 78% higher, and Urenco would make a profit of $1100 per t UF6 sent to Minatom. For Scenario 2, the recovery rates are slightly below the break-even point. The highest absolute cost savings would be obtained at a tails assay of 0.21% at Minatom, in this case.

The situation changes even more dramatically, if Urenco's avoided disposal costs for the depleted uranium are taken into account, since the tails produced at Minatom remain in Russia. In this case, the transfer of Urenco's tails to Russia makes economically sense, independent of Minatom's recovery rates and tails assays.
> See Cost balance of tails upgrading new window


Further Reading

Re-enrichment of depleted uranium tails in Gaseous Diffusion Plants,
by Peter Diehl, June 2007
Abstract
Large amounts of depleted uranium tails are stored in so-called uranium hexafluoride cylinder yards next to the enrichment plants in various countries, waiting for a decision on any future use or final disposal. Now, in the times of steep jumps of the uranium price, the question is raised, whether these tails can be profitably processed to recover some of the residual U-235 contained. So far, such re-enrichment has been performed in very special circumstances only, and in particular only in energy-efficient gas centrifuge plants. Recently, however, several proposals have been made to use also energy-intensive gaseous diffusion plants (GDP) for re-enrichment. This paper analyses the technical and economical viability of these proposals, and their environmental impacts, such as waste balance, consumption of electricity, and associated CO2 emission.

> Download full report (300k PDF - in English)

 

Re-enrichment of West European Depleted Uranium Tails in Russia,
report prepared for Ecodefense Russia by Peter Diehl, Nov. 2004

Abstract
Since 1996, depleted uranium tails from West European enrichers Urenco and Eurodif are being sent to Russia for re-enrichment. In Russia, the imported tails are, instead of natural uranium, fed into surplus enrichment cascades. The product obtained from re-enrichment is mostly natural-equivalent uranium plus some reactor-grade low-enriched uranium. These products are sent back to Urenco and Eurodif, while the secondary tails generated remain in Russia, where they are re-enriched further to obtain more natural-equivalent uranium and/or slightly enriched uranium. The latter is then used as blendstock for the downblending of surplus highly-enriched weapons-grade uranium into reactor-grade low-enriched uranium. The ultimate tails left, still comprising at least two thirds of the amount imported, remain in Russia with unknown fate.
This paper collects the scarce information available on this strange business, sets up a mass balance for it, looks into its odd economics and the policies behind it. Three driving forces are identified: Urenco's and Eurodif's aim to avoid tails disposal cost, Russia's shortage of uranium deposits, and the trade restrictions for Russian enrichment services.

> Download full report (313k PDF - in English)

(Russian edition available from Ecodefense external link)

> See also: Underfeeding at Urenco's Gronau uranium enrichment plant results in reasons for tails exports to Russia becoming obsolete

 

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