Nuclear Power: the How, the Pros and the Cons
We are entering into a nuclear renaissance in the West with new nuclear reactors being constructed here and many other places in Europe and America. As such, the debate on nuclear power is going to become a hot topic and a more scientific understanding is essential. This article will provide a series of arguments in favour of and against nuclear power. However, being scientists, it is also important to understand the technology being debated. This article will first and foremost provide an overview of how nuclear power works and the fuel used.
Nuclear Power and its Fuel
All nuclear power reactors world-wide draw power from a process called fission. This is where a heavy atom (most commonly Uranium – 235) is bombarded with a “slow” moving neutron causing it to break apart with a release of energy. During the break-up, more neutrons are released which go on and cause more fissions in more heavy atoms. To give you an idea of scale: burning a kilo of coal produces between 10 – 30 megajoules of energy (depending on the quality of the coal), the fissioning of a kilo of Uranium fuel produces about 500,000 megajoules depending on the reactor and fuel 1. Power is harnessed by using this energy to heat water (or a gas) and drive a turbine.
All reactors (admittedly there are a few exceptions) have four main components: fuel, a moderator, control systems and coolant. We’ll talk about fuel shortly, but it varies quite a bit depending on the reactor design and they all involve heavy atoms for fissioning. The key ingredient in the process is the neutrons – they kick off the fission process. But neutrons need to travel at the right speed: too fast and they won’t see the heavy atom, too slow and they will eventually stop before reaching it. A material is needed to bring neutrons that are too fast back down to useful speeds, this material is called a moderator (a common one being graphite). A fission break-up gives off between 2-3 neutrons which potentially can go off and fission other atoms giving more neutrons and so on. If this continued in this chain reacting fashion, very quickly we would get a bomb. So the number of neutrons needs to be kept in-check. This is done with control systems, which are fuel poisons and control rods introduced into the system designed to absorb neutrons. Control rods are also used to shut down a reactor if need be. And finally, fission is an energetic process. Thus, a lot of heat is given off – which is good, we use that heat for energy! So we use a coolant to carry the heat off and do something useful with the energy, power a turbine.
The topic of nuclear fuel is where the majority of the controversy is generated. The most common nuclear fuel world-wide is Uranium-Oxide based where we have a mix of Uranium of two different mass numbers: U-235 (active, easily fissionable) and U-238 (mostly inactive, difficult to fission). The ratio of these two depends on the reactor, this known as the enrichment level. It is important to note there are other nuclear fuels, some very interesting – Thorium is a good one to research for the enthusiast. During its time in a reactor, several things happen to the fuel. Firstly, some of the U-235 fissions and leaves behind fission products – two lower mass elements (other smaller mass elements and particles are given off also). These fission products are generally quite intensely radioactive and will be for up to 1,000 years. Radioactive simply refers to a material releasing energy in the form of radiation and most of us are bombarded with this everyday from the earth, the sun, the food we eat etc. However, fission products are intensely radioactive, that is to say the radiation is abundant enough and energetic enough to cause harm to biological systems. Also, the U-238 soaks up a few neutrons and, through several processes, can be bred into being something new such as Plutonium and Minor Actinides. Plutonium is a horribly radiotoxic and radioactive material, and is the most common nuclear weapons material. Less than 1 milligram of plutonium if ingested or inhaled is lethal. Many of the Minor Actinides aren’t much safer. The controversial part is that these materials will be radioactive for millions, billions, trillions of years (depending which atom it is). Overall spent (used) fuel has the following make-up: 95 % Uranium; 1 % Plutonium; 4 % Fission Products; and 0.1 % Minor Actinides.
Pros of Nuclear Power
Now that we know how it works, what are the benefits of this power source? Well one benefit is that there is a security-of-supply. Unlike renewables it is not dependent on weather conditions, and unlike fossil fuel resources it is not dependent on potentially unstable countries for supply. So when a nuclear power station is built, it will deliver a consistent power output everyday for around 50 years, barring any freak accidents. Much like coal, Uranium is a finite resource. However, there is quite a lot of it in “stable” countries – around 150 years of economic Uranium at current consumption. There is around 100 years worth of economic oil at current consumption. However, more oil fields or Uranium mines may be discovered. There also exists the possibility of extracting Uranium from the sea bed and other potential nuclear fuels, such as Thorium.
Following plant construction, it is a zero-carbon technology. To be totally correct, there is a small carbon-footprint associated with the mining and transport of the fuel. However, a nuclear power plant is 100% carbon-free, it actually gives off nothing other than steam (that’s what the massive chimneys are for). This is an obvious argument in favour when climate change and other environmental concerns are becoming ever more prevalent. The effects of mass CO2 pollution and smog are widely known and nuclear power is an effective counter to this.
Another, slightly more esoteric, benefit is that it is a globalised industry and resource. Outstanding technological improvements have already been made through international initiatives. For the enthusiast, the Generation IV initiative have an internationally produced document detailing the reactor designs to be implemented 20 – 30 years from now and they are extremely innovative and interesting. This globalised industry also means that, with clever reactor design, nuclear power can be safely deployed in third world countries without the need for fuel cycle infrastructure (mining, processing, waste management, etc.) in those countries. A cynical counter to this would be that third world countries would be dependent on receiving fuel from developed countries and dependent on them to manage their waste – which would have a price-tag.
In spite of public perceptions, the nuclear industry has a good safety record compared to other energy sources. There are about 2,500 fatalities every year due to the energy industry. Between 1969 and 2000 there has been 2,259 deaths in the coal industry in OECD member countries, and 3,713 in the oil industry. A hydro-power accident in China resulted in the death of 29,924 people. There has only been 31 deaths in the nuclear power industry, which was the result of the Chernobyl accident 2. Now, these numbers can obviously be nuanced when factoring increased cancer risks from radiation releases. It should be noted that the day-to-day operations of coal and oil plants release radioactivity into the environment – not just nuclear accidents! There even exists evidence to suggest nuclear power has saved lives, by occupying some of the energy demand that would otherwise have been occupied by the fossil fuel industry 3.
Cons of Nuclear Power
Unfortunately, nothing is perfect and there are some downfalls associated with the use of this technology, the nuclear waste issue being a serious one. Here in the UK we separate our nuclear waste in the hopes of recycling some of it (a lot of it we can). As such, our volume of radioactive waste is relatively low. Other countries such as America don’t do this because when you separate nuclear waste one of the materials you get is Plutonium. This introduces a proliferation risk. However, separated Plutonium can be used in many reactor designs as fuel. There exists a counter technology to deal with the longer lived Minor Actinide component of the waste called transmutation. This is where once separated, the long lived Minor Actinides can be converted at an energy cost to more inert substances. However, this technology is in its infancy and is not ready for widespread application. Otherwise fuel requires burial in a deep geological repository and it is tough to guarantee, with the certainty the public would demand, that the material would never reach the water table.
We briefly mentioned the topic of proliferation. This is when nuclear fuel, or waste, is misappropriated with the intent of doing harm. This can take two forms. If someone gets their hands on Plutonium of sufficient purity they can make a nuclear bomb – it doesn’t take much (about 10 kg). Or someone can attach nuclear waste to a conventional bomb making something called a dirty bomb. The explosion would propel the radioactive waste over a large area causing many cancers, radiation poisoning and other secondary effects. Admittedly, there has been no major incident of this type as yet in our history. However, it would only take one incident to irreparably harm the industry, necessitating a vigilance that many others need not employ. Additionally, as nuclear fuel and nuclear reactors become more advanced the risk of proliferation becomes more significant – some new reactor designs could be misused to make weapons-grade materials with ease.
A big drawback is that the public perception of the nuclear industry is not good – leading to a trust deficit. This leads to an association with nuclear weapons, reactor accidents and a general fear of radiation. For instance, we all remember the accident at Fukushima two years ago – despite there being no immediate deaths the media coverage and public perception was that of great fear and misunderstanding. Exploring this issue is probably a major study in itself covering topics such as: the nuclear industry’s openness with the public, the media’s influence and bias, the fossil fuel industry’s influence, and so on.
A drawback that is tough to overcome without the public support is that nuclear power is currently more expensive than gas or coal technologies. Though, cost per watt of power generated by Uranium versus coal is similar (because we need to burn a lot of coal for energy). The biggest issue is the high capital costs. It takes 10 – 20 years to licence and construct a nuclear plant (compared with 3 – 5 years for a coal power station). Admittedly, some governments are offering to pay a chunk of this initial cost but it is still not as economic as using fossil fuels. The remedy to this is unclear, is it the public or the legislator’s decision as to whether we should favour the cost of nuclear or the fossil fuel industry? The tragedy is that those are the only two options we presently have. Renewables are becoming more innovative and are worth pursuing. However, they are currently not suited to all countries or conditions, far less reliable and very expensive to the consumer.
I’m not sold!
During this nuclear renaissance the public’s opinion is going to matter more and more as the debate re-enters the media, hopefully this article helped! If you’re more inclined to fence-sit then say you’re waiting for something better as there are other options coming. The renewable industry is improving and is investing heavily in research which could lead to new technologies being able to meet some of the energy demand. More advanced nuclear fuels, and reactors, are on the horizon (look up the Generation IV initiative) where the breeding of Plutonium and Minor Actinides is not an issue. Finally, nuclear fusion is on the way! Unfortunately, it probably will be about a century before it would ever be used as a power source. However, there is a lot of money being invested and there has been some promising initial results to suggest it is not as sci-fi as people think.
Specialist edited by Matthew Bluteau and copy edited by Charlie Stamenova.