Nuclear Power and Circular Economy: is there Chemistry?

• The elephant in the room: the nuclear energy

Energy is one of the most important aspects of human existence. All the main activities that affect our lives are linked to the consumption of energy. With the advent of modern technologies, the increase of automation and the constant growth of the human population, energy demand has expanded exponentially. Nowadays, there is a wide range of possibilities to generate energy, also in a sustainable way. One of these energy sources is nuclear energy, which has always represented a debated topic in terms of safety, effectiveness, and sustainability. 

Currently, 10% of the world’s total energy production comes from nuclear energy, with a total amount of 27,044 TWh of energy (International Energy Agency – Nuclear Power in a Clean Energy System).

Global nuclear power generation is not evenly distributed among countries. In order to give a visual representation of this distribution, an image from the World Mapper website is shown below. Here the size of countries is not given by their geography, but by their nuclear energy production, with the US, France, and Japan resulting the largest countries, being responsible for ⅓ of the total nuclear production.

Europe’s reliance on nuclear energy has exponentially grown in the last decades, with 760 thousand GWh generated every year [Sole24Ore: Here who produces energy in Europe the most (2022) ]. The share is equal to 21.8% of the total energy production, which rises to 25% if only the countries of the European Union are considered. Figuratively speaking, one light bulb out of four is turned on with nuclear power. One of the reasons explaining this increase [Mark Hibbs: Why Europe Is Looking to Nuclear Power to Fuel a Green Future, Carneige (2022)] in energy production is certainly due to the classification, occurred on February 2, 2022 by the European Commission, of nuclear energy as a “green investment” within the EU Taxonomy. [EU Taxonomy: Commission presents Complementary Climate Delegated Act to accelerate decarbonisation]. The EU taxonomy aims to target private investment towards climate neutrality by 2050. Thus, gas and nuclear power are considered able to speed up the achievement of the EU’s climate and environmental objectives.

Within this paper, the focus will be on investigating the relationship between nuclear energy and circularity, by exploring the existing literature that attempts at inscribing nuclear energy and its related aspects – power plants and nuclear waste – within the framework of circularity. 

• The basics of nuclear reactions

Nuclear energy can be described as “a form of energy released from the nucleus, the core of atoms, made up of protons and neutrons. This source of energy can be produced in two ways: fission – when nuclei of atoms split into several parts – or fusion – when nuclei fuse together. The nuclear energy harnessed around the world today to produce electricity is through nuclear fission, while technology to generate electricity from fusion is at the R&D phase.”[International Atomic Energy Agency]

Nuclear fission uses uranium. The nuclei of uranium atoms are attacked by a high-energy neutron beam, causing the uranium atom’s nucleus to split into two smaller nuclei. From this division originates energy, in the form of heat, and additional neutrons capable of dividing further atoms. Thanks to a minimal amount of uranium, it is possible to generate a large amount of energy. The so-called “nuclear chain reaction” takes place inside the plant’s nuclear reactor [Atomic Archive: Nuclear Chain Reactions (2020).]. For the sake of simplicity, only the energy generation process resulting from nuclear fission will be discussed in this work, as little is known about the fusion process.

• A green source with grey areas

To determine the relationship between nuclear energy and circularity, it is necessary to understand whether this form of energy is green and sustainable. Although there are energy sources classified as “sustainable”, it is important to bear in mind that all of them produce some kind of pollution, [Inspire- Does Renewable Energy Cause Pollution?, 2021), given the use of certain materials employed to create them – e.g. the cadmium used to create solar panels – or the land that is defaced for the creation of dams, wind, or geothermal installations. However, nuclear energy does not fall within the definition of a renewable source [National Geographic: non-renewable energy]. The uranium used for nuclear fission is limited, with radioactive features that produce toxic waste, especially after its employment.

Despite being non-renewable and potentially dangerous – due to radiation or accidents – why is nuclear energy considered one of the most effective solutions to achieve sustainability?

• So much energy, so little waste

Under the environmental point of view, nuclear power causes less negative externalities than any other existing energy source.

As the graph shows, nuclear power produces a median value of 12g CO2 per kWh, similar to the wind energy, and lower than the solar one [World Nuclear Forum Nuclear Power in the European Union (2022)]. In addition, most CO2 emissions from the nuclear power life cycle stem from cement and steel production, as well as component manufacturing during their construction stage [IPCC].

In terms of land use, nuclear power plants are the ones that consume the least. This factor represents a fundamental characteristic for nuclear energy, as in light of an increase in human population, land appreciation keeps rising for agriculture and housing use. Brook & Bradshaw provides two graphic examples of the abovementioned considerations [Brook & Bradshaw: Key role for nuclear energy in global biodiversity conservation (2015)]. The first one compares the amount of land needed for nuclear energy production with other energy sources. 

As for the second graph, Brook & Bradshaw assume that a human being, on average, consumes 6.4 millions of kW of energy during the whole life. To produce the same amount, they consider 4 different energy sources: 780g or 40.7 cm3 of uranium (a); 20,000-L of compressed natural gas (b); 3,200 t or 4,000 m3 of coal (c); 86,000 t of nickel metal hydride battery (d). In more immediate terms, it is possible to conceive these quantities as: golf ball (a); 56 big tanker trucks (b); 800 elephants (c); 13 13 times the height of Burj Khalifa, for a total of 13.4 km high. 

Because of the high density of uranium, pollution deriving from extraction, transport, consumption and waste production decreases.  [Nuclear Fuel Facts: Uranium: Office of Nuclear Energy.] 

Under the social point of view, nuclear energy triggers a series of positive externalities on the quality of life, specifically in terms of employment and health conditions. When it comes to employment, a single power plant needs roughly 500 to 800 workers, covering multiple generations, being the lifespan of a power plan expected to last from 60 to 80 years – considering construction and operating time. [Joint Report by the Nuclear Energy Agency and the International Atomic Energy Agency: Measuring Employment Generated by the Nuclear Power Sector (2020)]. In the phase of construction, the number of workers can reach the highest peak, which is around 7000 units. Only in Europe, working in the nuclear energy system creates 11 millions of jobs, generating around half trillion EUR, which make up around 3- 3.5 % of the EU GDP [Deloitte: Economic and Social Impact Report: (2019)]. Annually there is an investment of 9.3 billion EUR, which results in the permanent employment of 10.000 workers and 4.3 Bln EUR generated.

The average emissions are estimated to be 29 t of CO2 per GWh of production, which is highly remarkable if compared with the emissions released by renewable sources like solar (85 t per GWh) and wind energy (26 t per GWh). The comparison is even more emphasised when considering fossil fuels like lignite (1,054 t per GWh) or coal (888 t per GWh). This makes nuclear energy one of the safest solutions for human health [IEA Report: Nuclear Power in a Clean Energy System (2019)], being air pollution the first cause for diseases worldwide [Air pollution- World Health Organization]. 

As already mentioned, no source of energy is 100% “green”. Non-renewable materials are always employed to build infrastructures, typically concrete and metals – e.g., aluminium, copper, steel – or are required in specific technological equipment – rare earth metals for gearless wind turbines. Nevertheless, among the existing low-carbon technologies, power plants require the least amount of structural materials [US Department of energy: Annual Report (2015)]. 

Another important aspect concerning uranium and nuclear energy is its affordability. To estimate this value, generation costs must be considered. These represent the ratio between total costs of a generic plant, and the total amount of expected electricity that the plant is supposed to generate over its lifetime. The levelized cost of electricity – LCOE metric –  is employed to report generation costs [IEA: Levelized Costs of New Generation Resources in the Annual Energy Outlook 2021(2021). By covering both capital and operating costs, LCOE represents a relation between the long-term price at which the (nuclear) electricity is produced and the price at which it will be sold to cover all their costs.

According to this measurement, nuclear power is the most advantageous energy source, because in the long run, the cost progressively declines. This statement can be better clarified in the boxplot below (David Dalton: Cost Report / Nuclear Is ‘Most Affordable Dispatchable Source of Low-Carbon Electricity’ (2020). 

• The sun in the palm of our hands: the power plants

Electricity generation takes place inside nuclear power plants. Currently there are 441 active nuclear reactors in the world, concentrated in 29 countries and built by a small group of companies (less than 10) [STATISTA]. Europe holds a leading position, with 148 active reactors in 16 countries. USA, France, and China are at the top of the ladder, with respectively 93, 56 and 51 active reactors. In addition to the already active reactors, 65 are in the construction phase, 8 of which are located in Europe.

Although most of the nuclear reactors are in non-EU countries – US, China, Russia, South Korea, and Canada – those that rely the most on nuclear energy with respect to the total energy consumption are European. Indeed, among the top 15 countries in terms of nuclear reliance, 14 spots are occupied by European member states.

A crucial element to bear in mind when it comes to nuclear energy is that the cost of a nuclear reactor, in absolute terms, remains incredibly high, without considering taxation [Nancy W. Stauffer: Building nuclear power plants- MIT Energy Initiative (2020) ]. The main costs can be resumed as follow: 

• Capital costs: ranging from construction materials, machinery, workers, and site preparation.
• Plant operating costs: which are the maintenance costs of the entire structure.
• External costs: which concern the coverage of any accidents or problems (obviously both assumed to be 0).
• Other costs: taxes.

Obtaining a clear estimate of the total costs of nuclear energy is quite ambitious. Nevertheless, The Energy Information Administration (EIA)  states that “advanced nuclear reactors are estimated to cost $5,366 for every kilowatt of capacity. That means a large 1-gigawatt reactor would cost around $5.4 billion to build, excluding financing costs”.

• Reduce, reuse, recycle: the 3Rs of nuclear reactors

An additional aspect that is worth highlighting is the ageing management. The lifespan of the power plant operating time is supposed to range from 30 to 40 years on average – if kept in good condition and without accidents [SAPL: The True Lifespan of a Nuclear Power Plant]. This raises the issue of the end-of-life power plant dismantling process. In this regard, a large share of the remains is recyclable [Giorgia Marino: HOW TO RECYCLE A NUCLEAR POWER PLANT (2021)]. Once a nuclear power plant reaches its end, the  89-90% of the structure is made out of reusable materials which can then be reused in the construction or industrial sector.

Although this practice turns out to be positive both on an environmental and economic/social level, there are some obstacles. A first problem derives from the first-generation plants which were not designed to be recycled, making the dismantling process more complicated.  A solution is provided by the new generations of nuclear power plants [James A. Lake, Ralph G. Bennett, John F. Kotek: Next Generation Nuclear Power ;New, safer and more economical nuclear reactors could not only satisfy many of our future energy needs but could combat global warming as well (2009)].  Indeed, from the second generation onwards, the element of the duration of the operation has been considered structuring in such a way as   to make recycling and dismantling easier. Another  obstacle has an economic nature.  The  dismantling cost of a nuclear power plant (in the US) is estimated to be around 544-821 million dollars [OECD- Nuclear Agency Survey (2016)].

• Not everything that glitters is radioactive 

One of the most debated topics certainly concerns waste production. The question is quite complex. On one hand, in fact, as has already been anticipated, nuclear energy produces a much lower quantity of waste than other energy sources.The biggest issue in this regard is that principal nuclear fuel – uranium – is highly radioactive. This one occurs in nature and it is extracted by conventional mining techniques [Energy Information Administration: Nuclear explained (2021)] to then be processed so that it can be used as fuel in a nuclear reactor. In its natural state it contains two main isotopes – uranium-238 and uranium-235 [World Nuclear Forum: What is Uranium? How Does it Work? (2021)]. This last is fissile, although it accounts for only 0.79r of natural uranium present on Earth. Nuclear power plants use natural uranium for fuel, but new ones tend to prefer the enriched isotope. Therefore, uranium is enriched before its employment in the nuclear reactor.

• A heavy, heavy fuel 

So, what is exactly “nuclear waste”?

Once fuel is consumed, there are two main paths to travel. The first is direct disposal [Subhan Ali: Nuclear Waste Disposal Methods, Stanford University (2011)]. In this case, is it possible to speak of real “waste” as it is not reused but sealed and stored in such a way as to be able to wait for the radioactivity and heat to decay over thousands of years [Uranium: Its Uses and Hazards: Institute for Energy and Environmental Research (2012)]. Obviously, this solution cannot be considered “circular”. In fact, a series of logistical (where to put the waste) and political problems arise here (how toxic is this waste disposal for the environment?).

Any nuclear power plant produces “radioactive waste”. Part of this is normally dispersed in the environment. For example, the cooling waste is discharged directly into the waters of rivers (from which water is also taken) as they are considered non-dangerous. This is different for all materials which, being in or near the reactor, are subject to a continuous emission of radiation. From simple bolts to larger metal components (walls, containers, etc.).

At the end of the production cycle of the nuclear power plant, these objects become waste “special” to be treated very carefully as they are radioactive and therefore dangerous. They are defined for simplicity as “nuclear waste”. Nuclear waste is distinguished according to the degree of radioactivity (i.e., their danger) [NS Energy: Types of nuclear waste that release radioactivity (2018)]

• High activity (3rd degree waste):
• Medium activity (2nd degree slag)
• Low activity (1st degree slag)

As the picture below clearly explains, the majority of radioactivity (95%) is present in a small quantity of waste (3%).

The second option concerns the recycling of consumed fuel. “Approximately 97% – the vast majority (~94%) being uranium – could be used as fuel in certain types of reactor. Recycling has, to date, mostly been focused on the extraction of plutonium and uranium, as these elements can be reused in conventional reactors. This separated plutonium and uranium can subsequently be mixed with fresh uranium and made into new fuel rods.” [World Nuclear Forum: What is nuclear waste and what we do with it (2022)].

The exploitation of the radioactivity of some atomic elements for useful purposes, is a perfect example of a circular economy both in its energy uses (nuclear power plants) and in health (diagnosis and treatment), industrial and research uses. The useful exploitation of the radioactive properties of some isotopes (not just uranium) provides, in fact, the perfect closure of the cycle of use of the element [Nuclear Power.com :Open fuel Cycle vs Closed Fuel Cycle]: exploitation as a fuel, reuse and recirculation of the residue still usable, treatment to reduce the volumes of the residue , decontamination of the parts that can be safely released, placement of non-releasable and no longer usable residues which appear at this point as “final waste”, which must be safely stored [Ian Hore-Lacy: THE “FRONT END” OF THE NUCLEAR FUEL CYCLE, Nuclear Energy in the 21st Century, (2007)]. In nuclear language, it means guaranteeing the total separation and absence of impact between the residual radioactivity of waste and things, people, and the environment. This method is defined as “closed fuel cycle.”

• A new solution: the breeder fuel cycle

Depending on the type of reactor, it is possible to find an even more circular solution, called “breeder fuel cycle” [Power Magazine: Rapid Advancements for Fast Nuclear Reactors (2019)]. Here fuel can be reprocessed many times, allowing other nuclear power plants to function, and thus reducing the relation between the amount of waste and the use made of it. This operation can be performed a limited number of times, for a maximum of 5, but only for the most advanced recycling systems.

Currently only 20 fast power plants are operating [World Nuclear Forum: Fast Neutron Reactors (2021)], and some are still in a prototype phase, because the technologies needed for this kind of reactor are still not cost-effective.

From the data reported, the nuclear waste problem, even if reused, always returns. Nowadays we still do not have a technology available that allows us to reuse radioactive material repeatedly. In addition, it takes thousands of years for this to decay and reach an acceptable threshold for it to be extracted from the ground again. How then is it possible to consider this energy source “green”?

The answer is derived from the energetic concentration deriving from radioactive materials. In fact, according to the International Atomic Energy Agency data, since the operation of the first nuclear reactor to date, the total nuclear waste produced – globally – is 392,000 t of heavy metals (tHM), 127,000 of which have been reprocessed, nothing compared to the 43 billion t of Co2 produced per year. These numbers take another meaning when translated into units of space. The total amount of nuclear waste is 29,000 m3 of material, which is a cube as wide as a football field and as high as a building of about 6 metres.

• Conclusions 

If it is therefore possible to classify nuclear energy as a sustainable and green energy source, it cannot easily be said that it is also a circular practice. From what can be deduced from this work, it is fair to assume that there are a series of techniques (already available today and cost-effective) that allow us to give a new life not only to nuclear plants, but also to the waste products. Nevertheless, two great limitations remain. On one hand the huge costs for recycling. Even if the practice can be considered circular in environmental terms, it still does not represent an economic advantage in the medium term for companies / countries that should deal with this operation. On the other hand, there is the issue of nuclear material, which is limited in the number of times it can be used. Eventually part of this will necessarily have to become waste. Nowadays, is it possible to reduce the decay times of nuclear materials – from thousands of years to few hundred – and to reuse the same nuclear fuel several times. However, to completely avoid the creation of waste still seems impossible. There are some proposals. One of the most debated concerns waste shipment to space until their radioactive decay. This solution, though, will only increase pollution [North- eastern University: Why we don’t send nuclear waste into space ? (2020)] [Forbes: This Is Why We Don’t Shoot Earth’s Garbage Into The Sun (2019)]. Another, the most promising one, but still far from being achieved, is the creation of nuclear fusion power plants [Jonathan Amos: Major breakthrough on nuclear fusion energy (2022)]. The benefits that could be drawn from this type of technology are countless compared to a current nuclear power plant [Atomic Energy Authority: Fusion in brief]: 

• there would be no carbon emissions. 
• there would be a quantity of material to be used like deuterium which would last for thousands of years thanks to its abundance in the earth’s crust and in salty waters. 
• it would have an energy efficiency millions of times higher than fission power plants. 
• there would be no radioactive waste. 
• the possibility of large-scale accidents would be brought to zero. 
• and there will be a more reliable type of energy.

Unfortunately, there is still a long way from getting this type of technology. Some of the most promising projects in this regard are ITER [Iter.org: What is ITER?] and SPARC [Plasma Science and Fusion Center, MIT: About SPARC], which have set themselves the goal of making the first fusion power plants operational before the end of the decade. What we have now is certainly a technology which, although not completely circular, represents one of the most effective solutions we have, and which could drastically reduce the energy monopolies of certain countries. 

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