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This series follows the construction on Hinkley Point C, Britain’s new nuclear power station being built in a remote corner of Somerset. Costing over £22 billion and covering an area the size of 250 football pitches, this site is one of the largest in Europe and the UK’s first new nuclear power station for a generation.
Cameras follow the engineers, technicians and the behind the scenes staff who are under pressure to keep the project on track, including building the mammoth foundations for the two nuclear reactors, excavate 3.5km cooling water tunnels out under the Bristol Channel, and construct the critical airtight inner steel lining designed to contain any radioactive material in the unlikely event of a meltdown.
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How can nuclear energy help, beyond just generating electricity?
The flows of energy in the UK in 2019. Source: UK Government
Nuclear power stations are an important part of low-carbon electricity generation in many countries. In the UK, roughly 20% of all electricity is generated using nuclear energy. The Hinkley Point C power station contributes to the renewal of the UK’s national infrastructure. Together with renewables, and possibly natural gas fired stations linked to carbon capture and storage, the UK electricity system will be decarbonised in the coming years. Electricity, however, currently plays a role in only 1/5th of the energy used in the UK. Noting the benefits arising from the coming decarbonisation of electricity, the role played by electricity will surely grow as the UK and other countries try to achieve Net-Zero emissions by 2050. However, electricity alone won’t be able to do everything. Even with substantial growth in electricity use, and even with large improvements in energy efficiency, there will still be a need for action in other important sectors, some of which are hard to decarbonise. It is here that nuclear technology has the potential to play an exciting role.
US nuclear powered ship NS Savannah, Copyright: Ray Krantz/Getty Images
The list of hard to decarbonise sectors is varied and broad. It includes maritime shipping, aviation, steel making, glass and cement making, domestic heating and many more. The idea of using nuclear energy to address these challenges is not new and, indeed, it long predates concern for global climate change. For example, in the period of early enthusiasm for civil nuclear technology in the 1960s various countries produced nuclear powered ships for non-military purposes. One such example was the American NS Savannah shown below. Fifty years ago, the conventional use of heavy fuel oil was too economically attractive and the nuclear technologies somewhat too cumbersome. Consequently, the idea of nuclear merchant ships faded away. However, our concerns are different now and given that maritime shipping represents about 2.5% of global greenhouse gas emissions, the NS Savannah concept might be a good example of a much needed Back to the Future technology.
Copyright: Figure 6: Process and supply temperature range in Nuclear cogeneration: civil nuclear energy in a low-carbon future policy briefing Issued: October 2020 DES7116 ⓒ The Royal Society
n October 2020, a Royal Society Policy Brief was published following a knowledge gathering process led by Professor Robin Grimes of Imperial College London. The briefing stresses that the electricity system of the future will, given a growing reliance on renewables, face more variation. One way to make up that shortfall would be to develop new nuclear power stations. In the situation that the weather and time of day favours renewable generation the new nuclear energy sources are best not turned off, but rather redirected to other beneficial uses such as supplying low-carbon industrial process heat or district heating. This variable mix of electricity generation and heat supply is termed ‘co-generation’. In the spirit of addressing the deep decarbonisation challenges listed earlier, one can further imagine nuclear reactors not tasked with generating electricity at all.
One particularly attractive path for nuclear energy utilisation would be for it to facilitate low-carbon hydrogen production. This could be achieved using nuclear cogeneration for high-temperature steam electrolysis. For high levels of efficiency, temperatures far above those currently available from today’s nuclear power plants would be needed. One solution would be for a gas-cooled very high temperature reactor not too dissimilar from the UK’s unique Advanced Gas Cooled reactor concept from 40 years ago. Future Very High Temperature Reactors could also drive catalytic thermochemical splitting of water. One more easily achieved route to low-carbon hydrogen production would be for nuclear energy to provide a heat input into the steam reformation of natural gas (methane) coupled with carbon capture and storage. This could be a very attractive option in the medium term. Low-carbon hydrogen production could greatly assist with a range of hard decarbonisation challenges. Hydrogen could cleanly fuel ships, trains, trucks and aeroplanes. Hydrogen can also be used as a reducing agent in iron and steel manufacture (replacing coking coal) and hydrogen can provide a useful storage buffer for volatile electricity systems. Either directly, or via hydrogen, nuclear energy has much to contribute to meeting the difficult challenge of reaching Net Zero emissions by 2050. There is a new golden age of socially beneficial nuclear engineering ahead.
One of the big questions surrounding nuclear power is what to do with the radioactive waste products of the process.
How the components of spent nuclear fuel contribute to its activity over time, Copyright: The Open University
A significant proportion of the radioactive waste that results from operating nuclear power stations is highly hazardous to health and some will remain so for a long time. Whatever our views on the wisdom of nuclear power, the question of what to do with the waste needs to be addressed. This is because after over half a century of nuclear power generation, involving more than 400 nuclear power stations, there is already a volume of over 20 000 cubic metres of high-level waste that needs looking after.
Nuclear waste is classified into three groups, according to their activity and hence their storage needs. Low-level waste includes things like contaminated overalls, lab gloves, paper towels, as well as some of the chemicals, which may be either solid, liquid or gas, that have come from different industrial processes along the way. These don’t need cooling and are considered suitable for storage in surface buildings for up to a few hundred years.
Hand stencils in the El Castillo cave in Spain have been dated to over 37 000 years old., Copyright: Getty Images
Intermediate-level waste is more active, and includes things like fuel cladding material that has become activated. These also require no or little cooling but do need to be more thoroughly contained, and are destined for storage below ground.
It is the high-level waste that concerns most people the most. This is the spent fuel from a reactor core. It has first to spend up to five years at the bottom of a pool of water, where the heat generated from the furious radioactivity can be taken away by the circulating water. The water also acts as a very effective radiation shield, even from the gamma rays the spent fuel is emitting. These pools make great photographs, as the blue glow from the Cherenkov radiation (light emitted by beta particles from the fuel travelling faster than the speed of light in water) is both eerie and (to some) strangely beautiful.
The time spent in the pool is short, relative to the tens of thousands of years it will languish in long-term storage, but the range of timescales involved tells us something about the nature of the spent fuel: it is a complex mixture of many radioactive materials, each having a different half-life, and hence activity. The short dip in the pool gives enough time for the short half-life, very active, reaction products to decay into other, longer lived, less active materials.
Illustration (to scale) of the Olkiluoto long-term nuclear waste depository, Copyright: Posiva https://posiva.fi/
Many sites across the world have been investigated as possible long-term repositories for high-level nuclear waste, but actual completion of a site is still some way off. This is partly because it is hard to persuade any local community to host such a site. There are also some very challenging and interesting questions to answer that come from the 100 000 year timescale in relation to human history. The oldest known cave art in the world is dated to only about 40 000 years ago. Considering the changes in human culture and technology since then, and especially the rapid changes over the last few hundred years, is it possible to imagine what kind of human and human society will be around in the far future - over twice as far away as the time span back to the first faint traces of human culture?
This question is one of many that designers of long-term nuclear storage facilities, such as the one planned at Olkiluoto in Finland, are thinking about now. Should the site be marked and, if so, how? It is almost certain that all the languages we speak now will have transformed so that future people’s efforts to understand whatever warning sign we put up may well be fruitless. Perhaps it is better to eliminate all traces on the surface that anything of interest was ever built there, but what then of the possibility that a future human might unwittingly disturb, or even unearth, the still dangerous waste? But what if, for some reason not foreseen, the waste begins to contaminate our habitat in a dangerous way, for example by leaching into the groundwater? Our descendants may need to recover the waste to make it safe again.
If the site were marked, would our descendants’ natural curiosity not compel them to investigate, as we have done with every archaeological find we have ever made? Is there any way that we could guarantee conveying exactly what was contained below, perhaps by inventing some symbolic system that any civilisation capable of reaching the waste stored in sealed chambers hundreds of metres below would be bound to understand?
Another idea is to defer any decisions for as long as possible, storing everything in such a way as to relatively easily adapt to any new approach or technology that may emerge. This is the default approach that is currently being taken, but for how long is it viable, and how safe from natural or human disruption is the waste in the meantime?
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