FUEL & FUEL CYCLE | REPROCESSING
V “Some countries are already operating a partially closed fuel cycle, and others could follow this path using services such as spent fuel reprocessing provided by those countries,” NEFW division director Christophe Xerri told NEI. “The next stage would be to employ fast reactors more
widely. The mono-recycling of MOX fuel in light water reactors is already used in many countries. MOX has also been used in fast reactors, for example in Superphénix in France and Monju in Japan, which are both now closed. Currently, MOX is being used in Russia’s Beloyarsk 4 BN-800 fast reactor. With multi-recycling of mixed U-Pu fuel and minor actinides in fast reactors, nuclear fuel could be used for a very long time and provide a sustainable solution for low carbon energy production,” said Xerri. He added, “Fission is likely to be a factor for a significant period of time based on what we know today of new technology. Unless there is a major breakthrough, it is difficult to see a world in 2050-2100 without fission and fast reactors.”
Reprocessing technologies Currently, partitioning technology for reprocessing used nuclear fuel is based on aqueous media including nitric acid and organic extractant such as tri-butyl phosphate. Aqueous reprocessing is mature on an industrial scale, but its use is limited because of proliferation concerns because it separates plutonium and uranium from the used fuel. In addition, organic extractants are susceptible to radiolysis- induced breakdown, increasing the cost and secondary wastes. Pyrochemical processes, which have been explored
in several countries during the past 50 years, use high temperature oxidation and reduction reactions, with inorganic molten salts, gases and liquid metals as the process media, either in electrolytic or electrorefining steps. Pyroprocessing reduces the risk of proliferation as it does not involve separation of pure plutonium. It is also viewed as a better partitioning technology for used fuel from future fast reactors and accelerator-driven transmutation systems. In Status and Trends in Pyroprocessing of Spent Nuclear Fuels IAEA lists several advantages of pyroprocessing:
● It can be readily applied to high-burnup used fuel without requiring excessive cooling time. So it can accept short-cooled used fuel with an intense radiation level, which helps to prevent illicit or unauthorised removal of sensitive materials from the process facility. “Therefore, pyroprocessing provides an important technical barrier to proliferation”.
● With metal electrorefining it cannot separate pure plutonium because other actinides are recovered with the plutonium. This offers strong proliferation resistance, as well as a high barrier of physical protection due to the extremely high level of heat and radiation.
● Its process medium does not contain hydrogen and carbon (risk factors in criticality accidents) and can absorb tritium and carbon-14, leading to dilute solutions that cannot be separated later.
● The head-end process of voloxidation can remove over 90% of long-lived radioisotopes, including iodine, technetium and tritium, from oxide used fuel and recover it in the form of a target that can be transmuted in appropriate reactor environments.
● The equipment is designed to handle much greater quantities of used fuel than aqueous technology. As the facility is more compact it makes possible reprocessing on the reactor site, which avoids transporting used fuel.
● The final waste volume can be drastically reduced and many reactor designs dedicated to the transmutation of used fuel SNF, including the integral fast reactor and the molten salt reactor (MSR), have adopted pyroprocessing for on-site recycling.
The main disadvantage of pyroprocessing is that it is not
yet fully industrialised. Other drawbacks include: ● Its inhomogeneous nature, which makes it difficult to evaluate the loss of process material. As a result the material accounting system is not clearly defined.
● To complete a fully industrial installation, it requires remote- and automatic-operation of molten salt and metal transfer equipment.
● It uses batchwise operation and is difficult to scale up to more than several hundreds of tonnes throughput a year. U
Above: France has a closed fuel cycle and currently operates reprocessing plants at La Hague 24 | February 2022 |
www.neimagazine.com
Page 1 |
Page 2 |
Page 3 |
Page 4 |
Page 5 |
Page 6 |
Page 7 |
Page 8 |
Page 9 |
Page 10 |
Page 11 |
Page 12 |
Page 13 |
Page 14 |
Page 15 |
Page 16 |
Page 17 |
Page 18 |
Page 19 |
Page 20 |
Page 21 |
Page 22 |
Page 23 |
Page 24 |
Page 25 |
Page 26 |
Page 27 |
Page 28 |
Page 29 |
Page 30 |
Page 31 |
Page 32 |
Page 33 |
Page 34 |
Page 35 |
Page 36 |
Page 37 |
Page 38 |
Page 39 |
Page 40 |
Page 41 |
Page 42 |
Page 43 |
Page 44 |
Page 45 |
Page 46 |
Page 47 |
Page 48 |
Page 49 |
Page 50 |
Page 51 |
Page 52 |
Page 53 |
Page 54 |
Page 55 |
Page 56 |
Page 57 |
Page 58 |
Page 59 |
Page 60 |
Page 61
