Nuclear alchemy

Last of 2 parts

PICKING up from where this discussion paused on Tuesday, fusion energy, at least in the context of mankind’s current or foreseeable technological capabilities, is not possible and most likely never will be. We understand the science of the process of fusion, and we have developed the technical means to create fusion reactions; but unless we develop scientific and engineering knowledge that we not only do not understand yet but cannot even conceptualize at this point, fusion energy will never be economical because it is not actually economical in nature.

First, let’s dispense with the “fusion breakthrough” achieved by the National Ignition Facility at the Lawrence Livermore National Laboratory in the US and widely and enthusiastically reported over the past year. In every news report, beginning with the initial announcements from the US Department of Energy, the NIF created a reaction that produced more energy than was put into it by smashing isotopes of hydrogen together in a tiny fuel pellet (about the size of a poppy seed) with powerful lasers. Specifically, the lasers delivered about 2.15 megajoules (MJ) of energy to the fuel sample, and the resulting fusion reaction, which lasted about a nanosecond (one-billionth of a second), released about 3.05 MJ of energy. This happened for the first time in December 2022 and was repeated in July last year.

What the US DoE and every news outlet that picked up the story failed to acknowledge, however, was that the experiment has nothing at all to do with the possibility of using fusion power to generate electricity but is actually nuclear weapons research. What the NIF was trying to do, and did successfully, was to replicate, on a very tiny scale, the detonation of a hydrogen bomb. Since the US cannot test nuclear weapons the old-fashioned way by actually exploding them, which is a good thing, laboratory work like this is important for research.

The second and more annoying omission in the news reports was that the “breakthrough” reactions did not even come close to producing an energy gain. The lasers delivered 2.15 MJ of energy to the target sample, but in order to do that, they needed nearly 600 MJ of power to charge up. That means the actual energy output of the reaction was not 142 percent of the energy input but closer to 5 percent.

Naturally inefficient

Even though it is generally accepted that the laser-ignition of fusion is not the direction to pursue to try to create fusion-powered electricity generation, the paltry energy output of the NIF experiments is not much different than what could be achieved with the most promising fusion technology, the tokamak reactor, which uses high-energy magnetic fields to create and contain fusion reactions in extremely hot plasma. A big

part of why even this technology will always be uneconomically inefficient is that fusion reactions are naturally inefficient, and the best example of that is the biggest fusion reactor we can observe — our own Sun.

In the core of the Sun, where temperatures reach about 10 million Kelvin, and the pressure is about 26.5 million gigapascals — about 340 billion times the atmospheric pressure at sea level on Earth — 600 million tons of hydrogen is fused into 596 million tons of helium every second, meaning that 4 million tons of matter are converted into energy, which we feel here on Earth as light, heat and radiation. That sounds like a lot, and it is, but that’s because the Sun is enormous; its mass is roughly 333,000 times that of Earth, or about 90 times the mass of everything else in the solar system combined. However, it only represents an energy conversion rate of about 0.6 percent; in terms of its energy output per unit mass, the Sun is rather weak, producing only about 0.1 watts per kilogram of electrical equivalent. For comparison, an average human produces about 1 watt per kilogram.

That rather modest energy output is because even in the extreme conditions at the center of the Sun, fusion reactions are difficult to achieve, and when they are, they do not actually release a great deal of energy. One fusion reaction, driving an atom of deuterium and an atom of tritium together (two isotopes of hydrogen) to produce one helium atom and a free neutron, releases about 15 megaelectron volts (MeV) of energy. One fission reaction, however, splitting a uranium-235 atom with a neutron, releases 200 MeV of energy. The reason a hydrogen bomb is much more powerful than a regular atomic bomb is that a comparable mass of hydrogen (usually tritium) fuel contains about 240 times more atoms than uranium or plutonium.

Energy waste

So, in a hypothetical controlled, sustained fusion reaction in a tokamak reactor (such as the massive ITER facility being built in France), huge energy input is required to mimic conditions at the center of the Sun just to make fusion happen, with the main energy product being heat. A good rule of thumb for the conversion of heat to electrical energy is about 40 percent, i.e., 100 MW of heat produces about 40 MW of electrical energy.

However, that heat and electrical equivalent is only being produced by about 10 percent of the fuel, with the rest escaping. The fusion fuel that requires the least amount of energy, deuterium and tritium, is problematic because while deuterium is cheap and relatively abundant, the tritium does not occur naturally and is one of the most expensive materials on Earth. So, recovering the tritium, or using the energy of the reaction to create more, is necessary to keep the reactor operating.

Engineers have figured out how to do that, but that process scavenges energy from the reactor’s output. In addition, the superconducting magnets compressing and containing the superheated plasma require a huge amount of energy because, in order to work, they have to be maintained at a temperature of about 4 degrees above absolute zero, or about -269 degrees C. In addition, other systems to provide thermal and radiation shielding will require power; for example, shielding to separate magnetic coils at -269 degrees C and plasma at 150 million degrees C.

Thus, the ratio of energy produced to the energy input of the NIF described above, about 5 percent, is about the best that can be achieved with current technology; a hypothetical fusion reactor producing 1,000 MW thermal will, in other words, only have a net energy output — electricity that can be sent down the wires for use by consumers — of about 50 MW. If our hypothetical fusion plant could be built for the estimated $46 billion price tag of the purely experimental ITER facility, that would mean its levelized cost of electricity at the moment the plant went online would be about $920 million per megawatt-hour, or about P51.63 million per kilowatthour here in the Philippines.

For reference, the recent power supply agreements signed by Meralco, which have come under fire from some for being too expensive, have an LCOE price of around P7 per kWh.

In order for “cheap, limitless” electricity from fusion power to ever be a reality, it will require some technology we cannot even imagine yet. Until then, the work being done is no less an exercise in alchemy than trying to make gold from lead.