Technical complements: Why is France returning residues to Japan?

The nuclear fuel cycle

The nuclear fuel cycle encompasses all the operations involved before loading nuclear fuel in a reactor: the front-end operations (uranium mining, conversion, enrichment, fuel fabrication), and after unloading the spent nuclear fuel, the back-end operations. These operations consist of reprocessing the spent fuel to recover the valuable materials: uranium and plutonium, conditioning the waste into residues for disposal, and recycling the fissile materials. This is called the closed fuel cycle.

Another possibility is promoted by some countries, consisting of storing the spent fuel for an interim period before conditioning the fuel as a waste for its disposal.

This is called the open or throw-away fuel cycle.

At this time, only the closed fuel cycle has been developed internationally on an industrial and commercial basis.

Reprocessing

Fresh nuclear fuel for light water reactors (LWRs) is made of uranium slightly enriched (3 to 4%) in the fissile isotope U235. After 3 to 4 years of electricity production through nuclear fission in the reactor core, the irradiated or spent fuel is unloaded and replaced with fresh fuel.

The precise composition of the spent fuel depends on its time in the reactor, hence the energy produced (measured by the discharge burn-up). For a typical case, the composition is in the range:

  • 94 to 96% of remaining, unburnt uranium which is recyclable,
  • 1% of plutonium (Pu), created in the reactor core by transmutation of some atoms of uranium, which is also recyclable,
  • 3 to 5% of fission products (FP which are the ashes of the fission process: atoms resulting from the splitting of fissile atoms) and traces of minor, long-lived actinides (eg Americium, Cesium). Fission products are highly radioactive; consequently they decay relatively rapidly to form stable, non-radioactive elements: most of them disappear in the very first years after unloading from the reactor; most of the others have half-lives of less than 30 years.

After a few years of cooling down in the electric power company or utility reactor pools, spent fuel is shipped for reprocessing.

Reprocessing is a series of mechanical and chemical operations, which very selectively sort out the various components of the spent fuel: uranium (RepU) as uranyl nitrate, plutonium as plutonium oxide, and the conditioned final waste.

The fissile materials are then available for reuse or recycling in reactors as new fuels: RepU fuel and MOX fuel. The residues are shipped to an interim storage facility, before final disposal.

Japan's energy policy

The nuclear power option and the promotion of the "nuclear fuel cycle" is extremely important for countries that lack abundant natural resources. The maximisation of the fuel value by recycling the uranium and plutonium helps these countries to face difficult choices on how to meet their energy needs. Japan has scarce energy resources, depending on overseas markets for more than 80% of its energy supply. Nuclear power now accounts for about 35% of Japan's total electricity generation and has become established as a stable energy source and an alternative to oil.

A large number of utilities in many countries (Japan, Germany, Switzerland, Belgium, the Netherlands, France...) reprocess and recycle their used nuclear fuel. Japan promotes nuclear fuel recycling from the viewpoint of effective energy utilisation. The consumption of oil is conserved through the development of nuclear energy and the recycling of nuclear fuel. With the prospect of a tightening of the supply and demand for oil worldwide in the future, it is believed that nuclear power will play a significant role in easing the pressure on energy supply in Japan and other countries.

Reprocessing Services Agreement

As a consequence of contracts called "Reprocessing Service Agreements" signed in 1977 and 1978, COGEMA receives fuel from the electric power companies of 5 countries: Japan, Germany, Belgium, Switzerland and the Netherlands. According to the contracts, a total of 7,000 tonnes of fuel will be reprocessed in the 10 years following the start-up of the UP3 plant in 1990.

The service includes:

  • reception and storage of spent fuel prior to reprocessing,
  • separation and purification of uranium and plutonium. These products must comply with stringent specifications in order to allow recycling (RepU and MOX fuels),
  • conditioning of the various categories of waste into residues. The residues must be conditioned in a form suitable for safe transport, in accordance with national and international regulations, and storage.

The Japanese customers of the "Reprocessing Services Agreements" are the 10 power companies: Hokkaido Electric Power Co., Tohoku Electric Power Co., Tokyo Electric Power Co., Chubu Electric Power Co., Hokuriku Electric Power Co., Kansai Electric Power Co., Chugoku Electric Power Co., Shikoku Electric Power Co., Kyushu Electric Power Co., and the Japan Atomic Power Co.

The nuclear fuel cycle

Release: December 1998