The future is very difficult to predict. But I am prepared to put on record my belief that controlled nuclear fusion as a source of power on Earth will never be achieved.
This is not something I want to believe. And the intermittent drip of news stories about ‘progress‘ and ‘breakthroughs‘ might make one think that the technique would eventually yield to humanity’s collective ingenuity.
But in fact that just isn’t going to happen. Let me explain just some of the problems and you can judge for yourself whether you think it will ever work.
One option for controlled fusion is called Inertial Fusion Energy, and the centre of research is the US National Ignition Facility. Here the most powerful laser on Earth can be focussed onto a pellet of deuterium and tritium and the temperature and pressure reached induce fusion. The process releases neutrons and a flash of X-rays and UV light which are captured to produce heat which generates electricity using a conventional steam generator.
- Reality Check#1: Currently one pellet can be hit every few hours. In order to make a one gigawatt power plant this process must be speeded up so that around 10 pellets every second are ignited. This is equivalent to firing a ‘machine gun’ into the centre of the high vacuum reaction chamber, but none of the ‘bullets’ must reach the other side of the chamber: every one must be tracked individually in-flight and blasted by the most powerful laser on Earth. No misses can be tolerated, otherwise a ‘bullet’ will hit the far side of the chamber. This process must continue night and day for months on end. The explosions will release energy at a rate of several gigawatts of thermal power, but this must not affect the vacuum through which the lasers reach their target. Every ‘bullet’ must be identical to within a manufacturing tolerance of 1 micrometre. Getting all this to work is IMHO impossible.
The other option for controlled fusion is called magnetic plasma confinement, and the centre of research is ITER being built near Marseille in the south of France. Here a plasma of deuterium and tritium is heated to around 150 million °C (about 10 times hotter than the centre of the Sun).
- Reality Check#2: About one metre away from the 150 million degree plasma releasing neutrons with several gigawatts of energy are gigantic superconducting magnets at approximately 4 degrees above absolute zero. Superconducting materials are sensitive to radiation and their special property will be lost if they are intensely irradiated. To visualise the temperature, think of about 1 million one kilowatt heaters trapped in a room the size of a small theatre. The plasma must not touch the walls of its container ever. Once initiated, the facility will become intensely radioactive and humans can never enter it again, and the hot plasma must remain confined for months on end exceeding the few seconds that have been achieved to date. Getting all this to work is IMHO impossible.
And even if we suppose these impossible things were somehow made possible by the application of ingenuity, good fortune and cash, there is one more ‘show stopper’: the availability of tritium. In either approach, deuterium (which is found in seawater) is fused with tritium (which is not found naturally at all). Where will all the tritium come from?
- Reality Check#3: The tritium must be generated by capturing every neutron released in the fusion reaction in a blanket of lithium metal (or a salt containing lithium). The neutrons from the miniature star in the reactor induce a reaction in the nucleus of one of the isotopes of lithium (7) which causes it to split in two, releasing helium and tritium. The tritium must be captured and fed back into the fusion reaction. This process must operate close to 100% efficiency otherwise the plant will run out of tritium. Getting all this to work is IMHO impossible.
I am a technological utopian: I think technology can make life better for people. And I would really like to believe that fusion will ‘somehow work’. But when I look at these obstacles, I just can’t see how anyone can overcome them.
As Sherlock Holmes might have said:
When you have eliminated all which is impossible, then whatever remains, however disappointing, must be the truth.