A new nuclear fuel cycle providing acceptable and reliable back-end solutions will be essential to sustain dynamic growth in global nuclear energy, Liudmila Zalimskaya, general director of JSC Tenex, told the World Nuclear Association's Symposium in London last week. Proposed approaches centre on reprocessing and recycling of used fuel, allowing uranium and plutonium resources to be used to their fullest extent while reducing the amounts of waste for disposal. Tenex is the nuclear fuel cycle product supplier subsidiary of Russian state nuclear corporation Rosatom.Zalimskaya addresses the Symposium (Image: World Nuclear Association)
The increase in nuclear power capacity called for by the International Energy Agency's 2 Degrees Scenario and the World Nuclear Association's Harmony initiative will need to be supported by a fuel cycle that is capable of ensuring such growth is sustainable, Zalimskaya said. The existing nuclear fuel cycle faces many challenges, especially at the back-end where current models are far from optimal, she added.
Most nuclear operators currently favour the deferred solution of interim storage of used nuclear fuel because of an absence of "better" scenarios. Unresolved issues at the back-end of the fuel cycle have led to a lowering of public acceptance. Solutions that are not effective enough - inefficient nuclear fuel reprocessing and inefficient use of reprocessed uranium and plutonium - have prompted some big players to suspend reprocessing efforts, she said, and promising international projects have faced delays and barriers.
"Industry needs a new nuclear fuel cycle based on innovative solutions and integrated approaches," Zalimskaya said.
The amount of used nuclear fuel will continue to increase, reaching around 1 million tonnes by 2050. The uranium and plutonium that could be extracted from that used fuel would be sufficient to provide fuel for at least 140 light water reactors of 1 GWe capacity for 60 years, she said. "It makes sense to consider how to turn today's burden into a valuable resource."
The new nuclear fuel cycle must considerably decrease the amount and the hazard of waste to be disposed of, and enhance the consumption of fissile materials recovered through reprocessing. It must do this whilst complying with the non-proliferation regime, and be appropriate to the characteristics of the operating reactor fleet. It would entail obligatory reprocessing of used nuclear fuel, as well as partitioning of high-level waste to facilitate separate treatment of the different fractions. Reprocessed uranium and plutonium could be used in reactors; minor actinides could undergo transmutation in fast reactors, which further reduces the volume and toxicity of waste; and other fission products could become valuable sources of radioisotopes, she said.
Rosatom estimates that the current closed fuel cycle - in which reprocessed uranium (RepU) and plutonium are only used once - can at best use about 21% of used light water reactor fuel, with the remaining 79% - mostly uranium-238 - going into storage. The new nuclear fuel cycle could use a further 77%, with only 2% of used fuel then requiring disposal as waste, Zalimskaya said.
Russia is already working to modernise its nuclear fuel cycle and currently has four main processing facilities operating at the back-end. The Mayak reprocessing facility is in the process of upgrading its infrastructure for high-active waste handling, and is reprocessing a broader range of used nuclear fuel starting with VVER-1000 fuel from last year.
The Siberian Chemical Plant, in Seversk, is a production facility operating with RepU. Mining and Chemical Combine, in Zheleznogorsk, is a cluster of used fuel management with centralised interim wet and dry storage facilities, a pilot demonstration centre for reprocessing, to be commissioned in 2019, and a fabrication plant for mixed oxide (MOX) fuel for fast reactors. The National Operator for Radioactive Waste Management, NO RAO, expects to commission in 2022 an underground research laboratory for the deep geological storage of highly active waste.Back-end scenarios
Zalimskaya presented three possible scenarios for the back-end of the fuel cycle which are currently being tested by Rosatom. The first scenario involves recycling of RepU and plutonium in the existing nuclear power fleet, with RepU used to fuel RBMK reactors and plutonium in the BN-800 fast reactor.
The second scenario is a so-called REMIX nuclear fuel cycle. REMIX fuel is produced directly from a non-separated mix of recycled uranium and plutonium from the reprocessing of used fuel, and can be used in light-water reactors. The used REMIX fuel can be reprocessed and recycled repeatedly.
The third scenario is a two-component nuclear power system involving light water reactors and fast reactors. In this scenario, used fuel from light water reactors is reprocessed with the RepU recycled in the same reactors and the plutonium recycled in MOX fuel in fast reactors. Plutonium separated from used fast reactor fuel is suitable for use in MOX fuel that can then be used in the light water reactors.
All three scenarios have evolved from simple, existing practices, Zalimskaya said, and all are now being tested in practice in Russia.
"So it's not a question of the distant future. There are real development scenarios which can be realised in our lifetime," she said.
These scenarios overcome the challenges facing the current nuclear fuel cycle, offering customisable and comprehensive solutions with an emphasis on advanced scientific and engineering achievements, Zalimskaya said. They also offer opportunities for enhanced international cooperation. Russia is ready to supply "a full set of services" from fuel supply to used fuel reprocessing to countries without such technologies, she said.
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by World Nuclear News