FUEL & FUEL CYCLE | V The design of early nuclear reactors was generally not


tightly integrated with the design of downstream plants for the processing of irradiated fuels and treatment of wastes. The PUREX process for separating spent fuel into uranium, plutonium and HLW achieved wide applicability and commercial maturity because it could be adapted to many different fuel types. Over decades, many processes have been explored and developed for the separation of fissile and non- fissile materials from irradiated fuels, including solvent extraction, fluoride volatility, plasma flame, molten halide electrorefining, fractional crystallisation. While earlier processes such as PUREX were designed


for ‘pure’ uranium and plutonium products, more recent ones have concentrated on separating an actinide stream adequately partitioned for recycle to fast neutron reactors for power production or minor actinide incineration, with a fission product waste stream for near-term waste management. The integration of irradiation, reprocessing, remote


fabrication and recycle to fast reactor is complex, but it has been achieved by both the ANL integral fast reactor and its associated fuel cycle in the USA and by the RIAR BOR60 reactor and its associated fuel cycle in the Russian Federation. These operations have not yet reached the commercial maturity of PUREX reprocessing. Two principal products arise, one suitable for nuclear fuel and another that is a potentially useful source of heat but with no long-term hazard associated with it. The aim of the separation should be to receive, process


and export materials using ‘just in time’ practices to avoid building up large amounts of material in storage. The physical amount of nuclear fuel consumed in a nuclear reactor is very small by industrial standards. The processing of it should be appropriately nimble and small scale. Figure 2 shows how existing spent nuclear fuel and


depleted uranium can potentially be incorporated into the process of recycle. The vast majority of material in SNF has potential value as recycled fuel – only a tiny proportion of the SNF is truly “waste”. The potential locked up in the world’s existing spent fuel


(together with stocks of depleted uranium) represents at least 100 years of mankind’s total energy needs.


Sustainable use of fission product waste If use is to be made of the materials or heat generation from fission product waste, then enough demand must be identified. Russia uses Sr-90 for radioisotope electric generators but it is doubtful that gamma-emitting isotopes can be used in electric generators. Gamma irradiators based on Cs-137 are also established, but not on a large scale. Neither of those applications could fully utilise the supply. (It should be noted that the processing plant would potentially provide access to Np-237, which is a component of SNF. By neutron irradiation in a reactor Np-237 can be converted to Pu-238 — the superior radionuclide for radioisotope generators used in long-distance space exploration. The most flexible use would be district heating in a


remote location. The source would be perhaps up to about 10MW, suitable for a small community of a few hundred people. If fission product canisters were placed in an underground pool with heat exchange to the surface, the resulting output of hot water could supply reliable and


20 | May 2021 | www.neimagazine.com


continuous district heating to homes in those remote communities, akin to supplying geothermal energy but at a location of choice rather than being limited by geographical constraints of availability. For safety the underground pool would need a passive


heat sink path to the surrounding ground in the event of the heat exchange system failing. Constant heat output would be maintained,


compensating for radioactive decay by adding extra fission product canisters to the pool on a periodic basis. At walk- away time, the facility would be allowed to move to passive heat exchange to the ground immediately surrounding the fuel pool. After a hundred years or so the facility would no longer be significantly heat generating and after a few hundred years any radioactive hazard would be effectively gone.


International initiatives The ideas presented here are not new, but focus objectives that have been there almost since the inception of the nuclear industry. In the USA, there has been only intermittent development


of nuclear fuel recycling since the days of President Carter. Whilst there is re-invigoration in the USA as a result of the strength of the National Laboratories, other countries (particularly Russia and China) are further developing partitioning initiatives of this type. The UK has historic capabilities in this field, but these


have become depleted with the shutdown of facilities at Dounreay and Sellafield. France has very significant capability, as has The Siberian Chemical Complex in Tomsk, the RIAR in Dimitrovgrad and various surrounding Russian institutes are active as a centre of development of some of these ideas, and they have the skilled people and facilities to do the relevant work. France’s nuclear research agency, Commissariat à


l’énergie atomique (CEA), indicated in September 2019 that “industrial development of fourth-generation reactors is not planned before the second half of this century.” Significant R&D, development and design work is required to enable full Gen IV reactor and fuel cycle facilities, including those for waste management with adequately short radioactive decay period, to be introduced. This period of development will allow the time for such an industry to be created using fast neutron reactors that can meet the technical requirements and specifications for the whole cycle. Nevertheless, there is nothing to stop this timescale being accelerated if there is an initiative to supply sufficient development resources and industrial sponsorship. Incremental improvements in full-scale Gen III reactors (sometimes referred to as Gen III+ type) are expected in the shorter term and there may be early deployment of small and medium scale reactor types of new concept design such as Moltex, GE-Hitachi, Terrestrial Energy, ARC, Leadcold, NuScale, Holtec, etc. The new concept designs based on fast neutron flux are


normally intended to reduce unit costs and may be leaders in establishing the principles of this Blueprint for Future Nuclear Power. ■


Edit of Blueprint for Future Nuclear Power. Full version at: https://www.tuv-nord.com/fileadmin/user_upload/ Blueprint_for_Future_Nuclear_Power.pdf


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