The Solvanam Tamil web magazine site brought out a special issue on Science & Technology recently. I contributed an article on Nuclear Fusion for the issue. The title அணு விவாகம் in Tamil means Atomic Wedding. I used the thread of marriage and break-up throughout the article to discuss pros and cons of fusion and fission respectively. What you see below is the translated English version. I am not sure the metaphors work in English as well as they do in Tamil. But the piece below still conveys the main ideas.
Whether we look at Nuclear Power Plants like the one in Kalpakkam (India) that has been running smoothly generating power for decades or the likes of Chernobyl or Fukushima that ended up causing historically significant disasters, they are all dependent on Nuclear Fission technology that splits the atom to generate power. Similar to a divorce or the breakup of a family, splitting up an existing atom usually results in a lot of undesirable consequences, that need to be handled correctly. Over the last two years, thanks to the Koodankulam nuclear power plant related protests in India, the bad effects of running nuclear power plants have been discussed extensively on the media presenting both facts and fiction.
But instead of breaking an atom, we can also merge two atoms and generate power out of that process. This technique called Nuclear Fusion can in theory be used to generate electricity as well.
Similar to a good marriage that brings two people together to form a well functioning new family, when two atoms are fused, the resulting side effects are predominantly good ones. Experts working in this area know/understand this fact very well. But since conducting this wedding is not easy, no one talks about it much. Countries like India, USA, Russia, France and others have joined forces and run projects/tests to move this technology forward. There are also research efforts ongoing at the individual nation level to get nuclear fusion to work and behave. Until the late 90’s this field was mostly relegated to academic research hoping for long term returns. There wasn’t much hope to get this working in a practical way to get usable energy out. But due to recent developments in the last decade or two, several small private companies have entered the fray promising to get this technology working soon and thus generating a good bit of money for the investors.
There are many differences between physical/chemical reaction involved in splitting an atom Vs. fusing the nuclei of two atoms. In nuclear fission, heavy elements such as Uranium (235U) are enriched first and then bombarded with the subatomic particle called neutron. The Uranium atom that gets hit this way, breaks up angrily into two smaller atoms called Krypton and Barium. In the process, it will also spit out three more neutrons and a bunch of energy. When those three freed neutrons attack three other Uranium atoms that are nearby, a chain reaction ensues. This will continue until all the available Uranium is depleted. Since each Uranium atom that gets split also emits a lot of energy, if we leave this chain reaction to continue unabated, it becomes a nuclear explosion. This is effectively the idea behind the atom bomb that can destroy a city in seconds. Instead of letting all the freed neutrons attack the available Uranium atoms, if we capture most of them and remove them from the nuclear reactor where this chain reaction is taking place, letting only a very small number of neutrons to remain in play, it reaches “critical” stage, which just means the chain reaction is stable and sustained while not growing anymore. Now the energy coming out of this sustained reaction can be harvested to heat up water, produce steam, that can then turn the turbine in the generator to generate electricity.
This type of nuclear fission reaction does not take place in the universe naturally. Human beings have to artificially ignite such a chain reaction by breaking up an existing heavy element atom. In order to start the reaction, we also need to mine elements like Uranium hiding deep beneath the earth. When the fission reaction takes place, it also ends up leaving a lot of radioactive residue that will remain radioactive for thousands of years requiring us to manage that toxic (carcinogenic) leftover from the nuclear power plants.
Nuclear Fusion differs from fission in all these characteristics. In fusion, two usually very small atoms are forced to bang into each other under extremely high temperature and pressure condition. When they bang into each other, the nucleus of the two atoms fuse to form a slightly bigger new atom. If we compare the atomic mass of the new bigger atom with the combined atomic mass of the two atoms that combined together, the newer bigger atom will be slightly lighter. The difference in mass, paying tribute to Einstein’s E=MC2 equation, gets converted into a burst of energy spitting out a lot of heat and pressure. That intense temperature and pressure pushes the next couple of atoms nearby to bang into each other continuing the chain reaction.
Unlike nuclear fission, fusion naturally occurs continuously all over the universe. It is this wedding that provides the main source of heat & light in all the stars including our own sun. The light element atoms that usually take part in nuclear fusion are the isotopes of Hydrogen called Deuterium and Tritium. These are not rare to find elements like Uranium that hide inside the earth and had to be dug up through difficult and expensive mining operations before it can be used in fission reactors. Even when the fusion reaction takes place, there is no radioactive material created that had to be safe-guarded for centuries so as not to cause any harm to human beings. There are very few neutrons that emit from fusion compared to fission. As long as we ensure they don’t go around hitting other elements inadvertently, the only byproduct from D-T Fusion reaction is harmless Helium gas that can be safely used to fill up balloons to be given to children. To top it off, the amount of energy generated from fusion is usually four to five times greater than fission!
If everything is hunky-dory with fusion, then why are we still using nuclear fission instead of fusion to take care of our energy needs? Answer to that question is the extreme levels of temperature and pressure needed to trigger this fusion wedding. In stars like our Sun, their weight being extremely high, their own gravity provides a means to create the needed pressure. When the nuclear fusion occurs, the heat generated provides the extremely high temperature needed to sustain the reaction. So, there is no dearth of either temperature or pressure to keep the reaction going in the stars.
If we want to get nuclear fusion going on the surface of earth, we need to create similar temperature/pressure working conditions that exists in the stars! If you wonder if such a thing is even possible, it has already been done in the middle of last century itself. If you had heard of thermonuclear explosion or hydrogen bomb, that is what it was. In those bombs, a regular nuclear fission reaction is initially triggered and then the temperature & pressure generated from that nuclear explosion is in turn used to create a nuclear fusion of hydrogen atoms releasing an order of magnitude more energy. So, we are capable of creating the conditions if it is for exploding a fusion bomb. But under more peaceful conditions when we are trying to use this reaction to generate electricity, exploding a nuclear bomb to trigger fusion is not a good idea. Even after we create the right conditions to trigger fusion, sustaining the chain reaction at the right level ensuring that it neither turns off nor becomes uncontrollable is a big puzzle that has not been fully solved.
To understand how much heat is needed to trigger nuclear fusion we can examine what goes on in the Sun’s environment. The surface temperature in the Sun itself is around 50000 C. If we drill down to the center of the Sun temperature rises to 27 million degrees Fahrenheit (or 15 million deg Celsius)! Sun is also 330,000 times heavier that results in a lot more gravity to create the needed pressure. What goes on in the Sun is an uncontrolled explosion, with a massive amount of hydrogen fuel in play. Since we will be starting the reaction from scratch with limited fuel supply, initially we need close to 100 million degree centigrade temperature to start the reaction.
When Hydrogen atoms are placed in that high a temperature and pressure, they stop being in solid, liquid or gaseous states and switch to a fourth state called plasma. In that state it will vaporize anything that it comes in contact with! So, how do you handle this material safely is another big question perplexing fusion enthusiasts. Since we know plasma reacts to magnetism, current plans envision using massive electromagnetic forces from the instant plasma is formed to handle it safely while simultaneously using it to increase the pressure as well.
In summary, we need to be able to manage two big issues to be able to put nuclear fusion to good use.
- First issue is the creation of the needed extremely high pressure and temperature to get fusion going, while delivering Hydrogen atoms as fuel to that location.
- Second issue is maintaining the chain reaction well once it is initiated and harvesting the generated energy for use in power generation.
To find out ways to create here on earth, albeit on a miniscule area, more heat & pressure than what prevails on the surface of the sun, there is a consortium of 35 countries including India and US working together. This consortium is setting up a monster called International Thermonuclear Experimental Reactor (ITER) in the south of France at a cost of twenty billion dollars with a twenty year building plan. For comparison, the other well-known international physics project called the Large Hadron Collider has a budget that is less than 25% of this one! Do visit this project’s website located here.
ITER researchers are using the traditional Tokamak based approach to managing fusion. Tokamak is a 1950’s Russian invention that has a huge metal doughnut shaped ring construction that is hollow inside. By wrapping it up with a lot of coiled wires outside and passing electricity through those wires, we can generate very strong electromagnetic fields inside the ring. Plan is to manipulate this electromagnetic field to control the plasma flowing inside and make it dance to our tune.
This is a monstrous international science experiment and so characteristically, it has blown past all the previously set deadlines and budgets and is crawling along slowly. When the construction is completed around 2027, this is expected to be the world’s largest fusion reactor. Even though it is swallowing massive amounts of time and money, when it finally works, there are no plans to generate electricity to light up nearby homes. There is not even a generator attached to this reactor. Idea is only to master nuclear fusion and generate knowledge for the field.
In parallel, the Lawrence Livermore National Laboratory in US near San Francisco is attempting another approach. The National Ignition Facility being built there is using a setup shown in the next picture. It will take up the space of three football fields and be as tall as a ten story building. Inside the facility researchers are using extremely high powered laser beams that can consume power that is thousand times more than what the entire US consumes at any given instant. These laser beams are blasted onto Hydrogen atoms in very short (couple of nanoseconds) bursts. This approach is termed Inertial Confinement Fusion.
People making fun of this field say, “Nuclear fusion enthusiasts have been claiming that in the next two decades they will master this technology and start producing endless amount of electricity. They have been very consistent over the past five decades and we expect them to be consistent and continue saying the same thing even after another fifty years!”.
But unlike the last century, more people with money and knowledge have started believing that this is possible. So several small private firms have jumped into the fray to make this a reality. We can list multiple companies like General Fusion of Canada, Helion Energy in Washington state, Tri-Alpha Energy that has been in stealth mode hiding in California with good funding and so forth. Few billionaires in US who made their fortunes in the tech industry like Amazon’s Jeff Bezos, Microsoft’s Paul Allen, PayPal co-founder Peter Thiel have pumped in a lot of funding into these companies. Even the defense manufacturer Lockheed Martin (that produces F-16 fighters, and the forthcoming F-35, etc.) has jumped in with a tall promise that they will deliver a nuclear fusion based generator that will fit in the back of a truck in five years! They said it last year and so four more years to go!
Experts that work in these private firms openly say that unlike researchers in national labs and academia, they are not going to be wasting time discussing their findings in conferences and publishing papers endlessly but will focus on getting things to work quickly, won’t analyze why when things start to work, focus on delivering the fruits of their labor to the society at large with the goal to monetize their work similar to the tech industry.
The technical approaches taken by these private teams differ from academic/government teams on multiple fronts. For example, none of the private firms think that building monstrous tokamak is practical for power generation projects. Sinking so much money into building them while the technology remains experimental for decades is not considered economically viable and may push out power generation into timelines unacceptable to private industry. Even the National Ignition Facility’s approach of using extremely powerful large lasers is not considered practical. So, these smaller private firms have been building reactors that are just the size of a house. These smaller reactors use two or more canons that will shoot plasma towards each other that will collide and result in fusion. Tri-Alpha claims that they are able to trigger and sustain the reaction for up to five milliseconds already. Though this is just 200th of a second, in nuclear fusion this is like a decade!
Most of the nuclear fusion attempts tend to use Hydrogen isotopes Deuterium and Tritium. Though D-T Fusion are much safer compared to fission reaction, they also emit few free neutrons that need to be captured to make sure they don’t end up hitting other atoms nearby inadvertently leading to any radioactive material. So the Tri-Alpha team is avoiding these isotopes altogether and are instead trying to fuse protons into commonly available element Boron. Though the reaction requires even higher temperature, they don’t seem to think it is a difficult to solve problem based on their experience in the field. Since Boron is an abundantly available element, they joke that when they start selling their reactors, they will come with a lifetime free supply of fuel. No fission reactor manufacturer can make that promise!
Though these firms have started to trigger and sustain the reaction for few milliseconds already, till now the energy spent in triggering/managing the reaction is more than the energy that comes out of it. When the energy spent is equal to the energy released, we will reach energy break-even point.
For this technology to become economically viable for power production, the energy RoI (Return on Investment) need to be fifteen to twenty times more and we should be able to harvest the energy properly! Even when the ITER reactor comes online in 2027, the target is to generate 10 times more energy compared to what goes in. Since that won’t be enough for commercial success, the smaller firms are trying to use much smaller reactors that use very little energy to start/run the reaction. They hope to do it for much less money as well so that in the end the generated energy can easily top the 20x goal since what is going in is orders of magnitude smaller. If their math works out, it will end our dependency on fossil fuel for all our energy needs. In that alternate reality, this field will blossom into a great solution providing endless gobs of cheap energy without spoiling the environment. There is not even a spec of doubt or should we say even a subatomic particle size of doubt that such a transformation can change the history of entire human civilization. We will hopefully see that change in our lifetime.
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