The promise of unlimited nuclear energy using fission and fusion has been dealt several setbacks over the years. Accidents at fission reactors like Three Mile Island, Chernobyl and most recently at Fukushima have undermined the industry’s long-term viability. Germany recently announced the phasing out of its nuclear power plants as a direct consequence of the Fukushima event. Germany is the first country to make such a significant statement about nuclear fission for generating electricity and probably will not be the last. Accidents that lead to melt downs may be infrequent but when they happen the consequences are significant.
Even more of a challenge is the safe disposal of spent nuclear fuel. This continues to be an environmental issue for all operating nuclear power plants. The ability to convert spent nuclear fuel from reactors into bomb-making materials creates further fears about the “unintended consequences” of nuclear power.
And finally, the promise of nuclear fusion, an unlimited energy source, has yet to be achieved.
Despite all of the challenges statistics from 2007 show that 14% of the world’s electricity was being generated by fission-based nuclear power stations, a slight decline from the previous year but still a substantial percentage of world production. France led all countries in terms of a percentage of total electricity generated in the country at 78% provided by 16 multi-reactor facilities. The EU countries relied on nuclear for 30% with the United States at 19%. By the amount of energy generated, the U.S. remained the largest consumer of domestically produced nuclear-power. Compared to electricity generated from coal and gas, U.S. consumption of electricity from nuclear remains very small.
Other than issues of safety and disposal of nuclear waste, what are the remaining major inhibitors to nuclear power as an energy source of choice in the 21st century? And why do we continue to look at nuclear power as a solution to global energy requirements?
Probably the most significant inhibitors are cost and time. Conventional nuclear power plants take years of planning and require investments in the multi-billion dollar range. Nuclear power plants are complex requiring multiple safety systems to deal with potential nuclear accidents. But accidents do happen and the environmental consequences represent immeasurable costs.
Finally, the existing nuclear power industry is one that is aging. A large number of existing nuclear power facilities have surpassed 30 years in operation. For example, the United States has 104 operating nuclear reactors located at 65 sites in 31 states. All of them were approved before 1980. Refits for these reactors will cost billions, take a long time, and lead to utilities having to find alternate sources of power during rehabilitation.
What’s on the horizon if nuclear power is to continue to be a fuel source for global society in the 21st century? Next generation nuclear fission power plants are trying to address the challenges the industry has experienced to date. Among the solutions are Generation III+ reactors, micro nukes, and thorium-fueled molten-salt systems. And the promise of fusion continues to be just that, a promise with some progress.
Generation III+ is a Safer Solution Based on Fifty Years of Industry Experience
Two new nuclear reactors are expected to come online in 2016. Westinghouse is the manufacturer. The reactors, called the AP1000, are located in the United States in the state of Georgia. These reactors use U235 as fuel and are classified as light water systems. Water pumps and fans keep the nuclear fuel cool. How they differ from plants like Fukushima is the extra layer of safety that has been designed in the event that power goes out to the pumps and fans as was the case at Fukushima. Generation III+ reactors employ a passive safety system that uses large water tanks situated above the fuel chamber that take advantage of gravity, natural condensation and evaporation to cool the fuel as a backup to power-assisted cooling. Generation III+ plants can operate safely for several days should a disaster like Fukushima occur. In the United States there are 20 Generation III+ plants in planning stages.
Micro Nukes – the Changing Face of Nuclear Power
What is so peculiar about these facilities is how antithetical they are to the early history of nuclear energy technology. The first wide usage of controlled fusion was for the development of a reliable fuel and power source for submarines and other naval craft. More than 150 of these small nuclear power systems have been built to date, all a fraction the size of nuclear power stations. Today the nuclear power industry is looking at returning to what they affectionately call micro nukes, small reactors that generate a few megawatts rather than the thousands of megawatts in conventional nuclear stations.
Micro nukes, however, have little resemblance to their antecedents used in naval craft. Those power plants had limited safeguards. To put a micro nuke in every small town or village will require a much higher degree of safety. Research on micro nukes is largely being done in the United States and Japan. NuScale , Toshiba, Hyperion Power Generation, Sandia National Labs and TerraPower are five competing companies with micro nuke concepts in the works. The beauty of these small nuclear power units is their simplicity. Because they are small they can fit into places where conventional electrical generation by other means may be difficult.
Oregon State University is the creator of NuScale. It is a light water reactor, pressurized and filled with plain water that flows past the Uranium-235 core where radioactive decay produces the heat that is transferred to a boiler that drives a turbine. Looking much like a micro-brewery cylindrical vat, the NuScale design consists of a single self-contained vessel that endlessly recirculates the superheated water inside it. Outside the reactor cylinder, water at lower pressure receives the heat, turns into steam which powers the turbine generating electricity. There is a downside to light water technology for micro nuke plants. The superheated water needs to be placed in a pressurized container so that it retains its heat without boiling away. If a nuclear core were to overheat and cause a reactor breach, the pressurized container can explode leading to a disastrous emission of radioactive steam and water.
Toshiba and Hyperion Power Generation have developed an alternative to a light water system using circulating molten metal to act as a heat conduit. Liquid sodium is used as the coolant. Lead bismuth is used as the heat conductor, not water. These two micro nukes run at higher temperatures, fracturing water molecules to extract hydrogen that is used to power fuel cells. These reactors are not subject to venting in the event of an accident and any leak from the reactor vessel would be easily contained. Toshiba’s 10 megawatt design uses 20 percent Uranium-235 and can run for up to 30 years without refueling. Hyperion’s 25 megawatt technology uses only 5 percent Uranium-235 and can run 8 to 10 years before refueling.
Of course, a proliferation of micro nukes does not solve the nuclear waste problem. All it does is distribute the waste over much larger areas. So the problem of nuclear waste is not solved by fission reactors.
Thorium-fueled Molten Salt Reactors (MSRs)
Often referred to as Generation IV reactors, liquid thorium systems have the potential to replace uranium-fuelled nuclear power plants in the future. The advantage of thorium molten salt is simple – meltdowns will become a thing of the past. What is surprising, like micro nukes, is that this technology has been around since the earliest years of nuclear power. An MSR contains liquid fuel, not solid. The fuel is kept at lower pressures than experienced in solid-fuel reactors. In the event of a power outage, the fuel in an MSR solidifies ending the chain reaction. Thorium is less radioactive than uranium. Thorium is far more abundant and easier to mine. Fuel usage is almost absolute. Uranium-based reactors burn only a small percentage of the fuel within the fuel bundle leaving a lot of nuclear waste. Thorium is almost totally consumed yielding 300 times the power of an equivalent amount of uranium fuel. Thorium waste from spent fuel has a much shorter half-life than uranium and it cannot be converted into a nuclear weapon.
MSRs do not require a large footprint. Like micro nukes they can be small-scale plants operating closer to the communities or facilities they serve and minimizing power loss through transmission lines (transmission lines today lose as much as 30% of the power generated by the industry).
The Current State of Nuclear Fusion in the 21st Century
Building a commercial fusion-based power plant remains elusive. What makes fusion so attractive is the lack of radioactive waste and the potential for meltdown. Fusion reactors require the creation of magnetic fields designed to contain a gas plasma heated to 150,000,000 degrees Celsius (270,000,000 degrees Fahrenheit). The fuel consists of two hydrogen isotopes, deuterium and tritium. Tritium, as a fuel source, is rare because it is a product of radioactive decay and does not occur naturally. Deuterium is relatively abundant and can be distilled from water. The byproduct of fusion is helium. Less than 30 grams (1 ounce) of deuterium-tritium fuel can produce energy equivalent to almost 9,000 liters of heating oil.
Sourcing tritium is the first problem to overcome. Naturally occurring tritium is very rare. Current nuclear fission based power plants can be used to create tritium but in future fusion plants will have to create their own supply of tritium fuel converting it from lithium as a source element.
The containment requirements for a sustainable fusion reaction have led to the development of a doughnut-shaped vessel called a tokamak. Current materials used in tokamaks tend to wear down so the search for better materials is another challenge that needs to be met. Within the containment vessel there are other challenges to deal with that require the development of sophisticated machinery capable of doing ongoing maintenance.
Current fusion research is focused on ITER, the largest tokamak experiment to-date. ITER is expected to generate 500 megawatts of power when it goes live by 2019. If successful the consortium of countries behind it plan to develop a 2,000 to 4,000 megawatt power plant by 2040.