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i31

Reprocessing

Outline

Reprocessing is the name of a complex sequence of separation processes, aimed at separation of spent nuclear fuel into several fractions:

• plutonium, generated in the reactor from uranium-238 by neutron absorption,

• left-over uranium, only a small fraction of the uranium in fresh nuclear fuel has been fissioned or transmuted into plutonium in the reactor,

• fission products,

• actinides, the heavy radionuclides formed from plutonium by neutron absorption,

• cladding hulls of the nuclear fuel elements.

Dissolving the spent fuel in boiling nitric acid is the first step of the reprocessing sequence. The zirconium cladding hulls of the fuel elements do not dissolve. In subsequent steps the various fractions are chemically separated form the solution. The recovered plutonium and uranium are purified to high standards, suitable for reuse in nuclear reactors.

Discharges into the environment

The gaseous and volatile fission products escape from the solution and are released into the air and/or sea via waste water. A number of fission products that are difficult to incorporate into inert solids. A significant part of these radioanuclides are also discharged into the waste water.

Because of the massive releases of radioactive substances into the environment, reprocessing is an exceedingly polluting process. Europe has two operating reprocessing plants: at Sellafield in the UK and at La Hague in France. Both plants are situated at the sea coast, for obvious reasons.

Practice

Separation processes are governed by the basic laws of nature, among other the Second Law of thermodynamics. One of the consequences of these laws is that separation processes never go to completion. This fact results in the observation that it is impossible to separate a mixture of different chemical species into 100% pure fractions without losses [more i42]. Separation becomes more difficult and goes less completely as:

• more different kinds of species are present in the mixture,

• the concentration of the wanted for species in the mixture are lower,

• constituting species are chemically more alike.

In addition radioactivity seriously hampers chemical separation processes, due to breakdown of the separating chemical by nuclear radiation. Radioactive and non-radioactive isotopes of the same element cannot be separated.

Spent fuel is an extremely complicated mixture of many dozens of chemical species: the whole Periodic System of the elements is represented in spent fuel. This results in substantial losses of uranium and plutonium into the waste streams of the purification processes of these metals. In addition the recovered metals are easily contaminated with other elements with similar chemical properties. Losses and impurities increase with increasing radioactivity of the mixtures.

Costs

Reprocessing is a very costly process, consuming large amounts of energy and materials and requiring massive buildings and storage facilities. The investment costs are extremely high and often (partially) covered by secret contracts with the customers. The operational costs must be very high, but are not known publicly. In the period when the ‘commercial’ reprocessing plants (La Hague, Sellafield) have been built (1970s-1980s) high costs were no issue, for the recovered plutonium and uranium were expected to be fissioned in breeder reactors a hundred times more efficient than in the common reactors. Consequently the fuel cost of breeder fuel could be high compared to common enriched uranium without a significant impact on the electricity price.

At the end of its operational lifetime the reprocessing plant has to be decommissioned and dismantled. Then the facility is heavily contaminated with all kinds of radioactive materials, so decommissioning and dismantling will be a challenging task. For Sellafield in the UK the preliminary cost estimate of this task amounts already to some €100bn, more than the costs of the complete Apollo project of the USA, which succeeded in the landing of six crews on the Moon in the period 1969-1972. The huge amounts of radioactive waste from the dismantling of a reprocessing plant, heavily contaminated with all kinds of radionuclides, might pose serious hazards [more i20, i27].

Historic purpose

Reprocessing technology has been developed during the late 1940s and Cold War to recover plutonium for weapons. In the following decades the technology has been further developed to reprocess spent fuel from civil nuclear reactors. Purpose was the recovery of the plutonium and unused uranium to fuel the envisioned breeder reactor. The large civil reprocessing plants at La Hague (France) and Sellafield (UK) have been built during the 1970s and 1980s in the belief that uranium and plutonium recycling in the breeder cycle (LMFBR: Liquid-Metal-cooled Fast Breeder Reactor) would soon become the base of civil nuclear power [more i33].

When it became evident – though not admittedly – that the breeder cycle would not be feasible within a foreseeable future, the nuclear industry quietly switched to other arguments to justify the exceedingly high cost of reprocessing:

• recycling of plutonium in MOX fuel in modern light-water reactors [more i32],

• volume reduction of the high-level nuclear waste [more i36],

• shortening the radioactive half-lifes of long-lived hazardous radionuclides by partitioning and transmutation [more i34].

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reprocessingv3

Figure 31-1. Outline of reprocessing of spent nuclear fuel.

Reprocessing is a complicated sequence of separation processes, aimed at the recovery of newly formed plutonium and remaning uranium from the dpent nuclear fuel. The other radioactive consituents of spent fuel are distributed over large volumes of six waste streams, two of which are released into the human environment. For that reason reprocessing is an exceedingly polluting process. A part of the radionuclides from the spent fuel is vitrified, meaning that the radionuclides are chemically fixed in a borosilicate glass. The volume of this glass is very small compared to the other waste streams. When the nuclear industry states that nuclear power produces little waste, they refer to only this glass. The other waste streams are not less dangerous and their volumes are much greater, so there is more chance of inadvertent releases of radioactivity into the human environment. The volumes of the decommissioning and dismantling waste of a reprocessing plant may amount to hundreds of thousands cubic meters. This waste stream is never mentioned by the nuclear industry.