The different steps of the fuel cycle are as follows:

1. Mining and milling to extract the ore.

2. Conversion factories to extract the uranium-235 (U235) from the ore and transform it into the well-known yellowcake.

3. Enrichment facilities to transform the yellowcake into UO2 enriched to 3-4% for later production of the fuel for nuclear power plants.

4. Fuel fabrication factories.

5. Irradiation of the fuel in nuclear power plants up to the burn-up desired.

6. Irradiated fuel intermediate storage waiting for a certain decay before being sent to irradiated fuel treatment.

7. Irradiated fuel treatment with a choice between two options: either direct storage of the irradiated fuel in special packages for intermediate

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and later final storage in deep geological storage, or reprocessing for separating the plutonium and used uranium in order to reuse them in mixed oxide fuel (called MOX), and the rest being compacted and vitri­fied into wastes containers for final storage.

8. Final storage in deep geological formations.

These are shown together with their interconnections in Fig. 2.1. The steps up to loading the fuel in a nuclear power plant are called the front end of the fuel cycle, and the steps after unloading the fuel from the reactor are called the back end.

For accomplishing all these steps transportation of radioactive materials and fuel is necessary. The main challenges in the whole fuel cycle are pro­liferation resistance, security and safety as well as ensuring the sustainability of uranium and fuel supply, site remediation after closure of the factories and final siting for disposal of wastes.

The total reported uranium resources in the world in 2009 were 5400/6300 th. tU (reasonably assured resources/inferred resources). These would last for 100 years at recent demand level (source: IAEA). The fuel cost is an advantage for the industry. The price fluctuates depending on the market but recently prices have increased with the expectation of nuclear rebirth. Nuclear power is still economically viable even with increased prices. Since 2003, which was the year of the maximum price, the price has slowly fallen to now some 50 US dollars per pound. The remaining problem is security of supply for all countries engaging in nuclear energy. Some projects are

advancing for creating an international fuel bank under the auspices of IAEA.

Another sensitive area for the front end of the fuel cycle is the enrich­ment process. The key issue is the risk of proliferation: by successive itera­tion, highly enriched uranium, for example, can be diverted to usage in nuclear weapons. The cost of enrichment is around 160 US dollars per SWU (separative work unit). Techniques mostly used for enrichment are gaseous diffusion and centrifuges.

The fuel itself, once in the reactor, has to be highly reliable since it con­stitutes the first physical barrier between the radioactive material and the primary system coolant. It is also needed to reach a high burn-up, which means it can stay in the reactor core for five or six years, thus authorizing longer periods of time between refuelling.

Coming to the back end of the fuel cycle, after the fuel has been unloaded from the reactor core, the main problem is the used fuel management. At this stage the fuel contains 1% Pu and 92.5% U. The total radiotoxicity decreases with time and depends on the material considered.

If the choice has been made of reprocessing the used fuel, the process will separate the nuclear materials reusable from the wastes. 99.9% of the nuclear materials are recovered after reprocessing and the volumes of wastes have been extensively reduced. The high-level wastes are then treated by vitrification into containers for storage.

Nuclear wastes have been categorized in terms of their activity. Table 2.1 the lists terms used together with their siting recommendations. Nuclear wastes are also produced by medical applications, industrial radioactive sources, research and research reactors and accelerators. These too are also stored according to their radioactivity in the same way and with the same precautions as the reactor wastes coming from nuclear power operation or used fuel and wastes from other nuclear activities such as reprocessing and dismantling.

Storage of HLW is considered as an interim solution and final HLW repositories must be found, which means that, from the beginning and throughout the lifetime of the nuclear power plant, solutions should be considered and found for countries coming to develop a nuclear programme. Final repositories are in deep geological disposal sites. The challenges are the social acceptability and the interdisciplinary tasks for safe repository siting and operation.