The use of nuclear energy is often seen as controversial, something to be at best tolerated but more generally opposed. It is associated with threats originating from large accidents that emit radiation into the environment, terrorist activity and nuclear waste storage. But the use of nuclear power has an important role to play in combating climate change and moving society away from its fossil fuel dependence. With the technology needed for energy generation and waste management well-advanced, nuclear energy promises both high energy density and security for those who embrace it.
Thermodynamics, the study of heat, tells us that energy can neither be created nor destroyed. So when we use the term “energy use” we are ultimately talking about how energy is converted from one form into another to enable us to do work to improve the way we live.
The development and the advancement of mankind in the past has been linked to the use of energy and the efficiency with which it has been converted into forms that made lives easier and more productive. Today is no different: economic development is intrinsically linked to the amount of energy used by society. In very simple terms, progress, arguably, equals energy consumption. The more energy used, the higher the material standard of living, as illustrated above by the Tokyo skyline. But are there limits to the availability of energy which would restrict economic progress for all?
So where does our energy come from?
Chemical energy: The sun is a massive thermo–nuclear engine that converts energy released through nuclear processes into heat that warms the planet and creates the conditions that support life as it is known. The energy of the sun that falls on the Earth is stored in plants (the origin of fossil fuels) and their compound bonds and it is accessed via combustion. In the beginning, fire provided heat and light in hours of darkness . The steam age enabled the energy from combustion processes to be used more efficiently to drive machines, which in turn kickstarted the industrial revolution. The internal combustion engine finally made use of liquid hydrocarbons to provide even more efficient machines. Fossil fuels such as coal, oil and gas can be seen as the earth’s “capital resources” in that they are valuable but finite. In essence, over the past three hundred or so years society has been able to covert this chemical energy with increasing efficiency.
Nuclear energy: The discovery of the neutron and the realization of nuclear fission in the first half of the twentieth century provided a very effective means of converting nature’s energy sources. The sheer size and efficiency of energy conversion from the exploitation of nuclear energy initially prompted the development of nuclear weapons. Once the physics of nuclear energy was understood, engineers were able to make machines (nuclear reactors) to generate electricity. Current nuclear power stations are based upon fission, i.e., splitting of the atom. They use uranium as the source of fuel. These reactors use the fission of the uranium isotope U235 to generate power. However, natural uranium contains only 0.7% of the U235 isotope and hence current nuclear power stations do not make the most out of the world’s uranium reserves.
The next generation of nuclear power stations (so called fast breeder reactors) are designed to convert the other more abundant isotope (99.3%) of uranium, U238, into plutonium. Plutonium is used as a substitute for U235 and thereby increases the utilization of uranium as an energy source by a factor of 60. The use of fast breeder reactors could provide mankind with up to 3000 years of electricity supply.
Research into the harnessing of the fusion process, i.e., the fusing of lighter atoms (in essence the process taking place in the sun) for peaceful purposes has been ongoing for the past 50 years and scientists are getting closer to finding an engineering solution. The latter half of this century could see commercial fusion-based power stations for electricity production. The realization of this technology will provide society with an almost limitless source of energy that would not adversely affect our climate and have fewer radioactive waste issues.
Renewable energy: Energy sources considered as renewable are wind, solar radiation, tidal flows and waves, and rainfall (hydro-power). All these sources of energy have been available to mankind over its entire history but to date, they have not proved sufficient to match the economic development needed for an ever-increasing population.
Economic Development and Energy A Key Partnership
The development of modern society and its economic well being, has been built on the use of fossil fuels. However, as mentioned earlier, fossil fuels are finite and the exploitation of these fuels is a relatively modern activity, effectively starting in the 19th century. The exploitation of fossil fuels coincided not only with increasing prosperity but also with an increasing world population with an ever-increasing demand for energy. If the use of fossil fuels is to be continued at the current rate they will likely be exhausted in a few hundred years.
What are thus the implications for future generations both in developed and developing countries? On the current trajectory, a fossil fuel based world has little, if any, prospect of maintaining our living standards or meeting the aspirations of those in developing countries. Grandchildren, great grandchildren and future generations would have a bleak future compared with the lifestyle society takes for granted today.
There is also the issue of climate change. The combustion of fossil fuels release greenhouse gases. It has been argued that the use of remaining fossil fuel stocks should be limited in order to keep global warming below 2 degrees C. Carbon capture and storage (CC&S) of greenhouse gases emitted from power stations will be technically and economically challenging, and there are potentially significant environmental hazards should the reservoir seals fail. Many specialists suggest that CC&S cannot be relied upon as a solution.
Can society really be content and ignore the finite nature of fossil fuels and carry on using them regardless of the consequences for future generations?
The Importance of Energy Density
One of the key factors to consider when comparing the effectiveness of converting different energy sources is so-called “energy density”. The greater the energy density, the higher is the efficiency of energy conversion. It is interesting to look at the energy density characteristics of renewable energy, fossil fuels and nuclear power. For example, in relation to renewable energy, the density can be measures in terms of electricity produced per unit area. For wind this is typically between 1-2 watts/sqm and for solar energy, this is typically around 6 watts/sqm This is indeed very low when compared with nuclear power. For example a typical nuclear power station generating 1000 million watts (Mw) of electricity would occupy around 0.5 square miles of land. A wind farm generating the same amount of electricity would occupy around 300 square miles. To put this into perspective 300 square miles is roughly half the size of Greater London. 1000 Mw of electricity generated by solar panels would require around 60 square miles.
Another way of considering energy density is in relation to the amount of fuel needed to generate electricity. The energy density in coal is typically around 24 MJ/kg, natural gas has an energy density of around 50 MJ/kg. A 1000 Mw coal fired power station would consume around 9,000 tons of coal per day.
Nuclear power is in a different league. The fission of a single atom of U235 releases 208 MeV of energy which equates to 85,000,000 MJ/kg. A nuclear power station generating 1000 Mw of electricity will consume around 3.5kg of U235 per day. The very high energy density in the atom means that electricity can be generated using considerably less land than any other form of energy. It also means that the nuclear fuels can be manufactured anywhere and economically shipped around the world.
Challenges Associated with Nuclear Energy
Nuclear power offers the best long-term solution to global energy needs, but to be accepted widely it must be safe and secure. In spite of the accident at Fukushima, it has been demonstrated that modern nuclear power stations are safe and nuclear materials are secure.
The other major issue of concern to the public is radioactive waste. However the majority of the radioactive waste formed in the fission process has a half-life of less than 30 years. This means that after about 300 years these isotopes do not present a significant hazard. A small proportion of the radioactive waste have half lives considerably longer than this and these will have to be isolated from mankind for many thousands of years in well engineered deep underground disposal facilities. However, the volume of radioactive waste is often misunderstood. A typical nuclear power station (1000 Mw) will produce electricity for over one million homes and will produce around 1,000 kg of highly radioactive fission products per year. In the UK the total amount of higher activity radioactive waste produced each year is about 0.1% of the non-nuclear hazardous waste, and 0.002% of the total amount of general waste. Properly managed radioactive waste is not the problem that many perceive.
A Nuclear Future
Economic development and well-being is related to the amount of energy used. Society has been built on fossil fuels, but these are finite and their use adversely affects our climate. Renewable sources of energy have a role to play in meeting our energy needs both now and in the future, but because of their low energy densities their use alone will not be sufficient. Nuclear energy can provide a reliable and long-term source of energy that current and, more importantly, future generations will need. It is well understood, its use in nuclear power stations is mature, it is safe and radioactive waste is manageable. Importantly, nuclear power is virtually carbon free, and hence it can play a major role in supporting the COP21 goal of limiting global warming to less than 2 degrees C.