There’s a joke in physics that asserts that the time until commercial fusion power generation becomes viable is 15 years - and has been since 1940. Maybe that 15 years is a constant of nature, and like a jogger on a treadmill there’s no forward progress despite all the effort in the world.
Maybe, but there’s reason for optimism. Unlike the treadmill, there is forward progress being made. But let’s step back and ask why we should care. The answer is pretty simple: the world needs more and more power because technological devices need electricity. And especially as China and India develop at great speed, the total number of people using lots of electricity increases dramatically. Right now we get most electricity from fossil fuels. These generate enormous amounts of pollution, and add to the level of CO2 in the air. Renewable power is nice and getting better, but they tend to be rather poor at providing base-load power. Wind and solar farms take up valuable space and fill the local environment. Startup costs are very large.
Nuclear power is very promising, but the public tends to be wary of it. Chernobyl is impossible in a modern design and radioactive waste is fairly easily and safely stored, but the stigma is prohibitive. Further, fuel is not incredibly cheap and they require lots of valuable water for cooling. I think nuclear fission is still the best of the currently viable alternatives to fossil fuel, but it’s far from perfect.
That’s where nuclear fusion comes in. Like the sun, it fuses light atoms (hydrogen isotopes, generally) into heavier ones (helium, generally). Radioactivity is produced, but in vastly smaller and easier-to-handle amounts than in nuclear fission plants. But to get fusion to work, the power plant has to produce conditions of extreme heat and adequate pressure to get the hydrogen to fuse in the first place. On one hand this is a perfect safety feature. If a breakdown ever occurred, damage to the reactor instantly destroys the conditions necessary for continued nuclear reactions. And since only a very small amount of fuel is reacting in a given time, a problem instantly and automatically prevents the reactor from causing
melting down. It’s a physical impossibility.
Unfortunately, those extreme conditions of temperature and pressure are very difficult to achieve. Thus far, it takes much more energy to generate those conditions than it the reactor produces. In the early years of nuclear fusion the reactions required millions of times more energy than they produced. Now it’s much less of a hurdle - depending on how optimistic various theoretical considerations are assumed, we might even be within a factor of 2 of true breakeven. Once we reach the level of breakeven, it’s possible we will have found a low-cost, safe, and powerful source of abundant energy fueled by the hydrogen found in all water.
ITER is the next step in this process. It is expected to operate at several times higher than breakeven, but it’s not possible for this design to actually generate electricity. It’s just a proof-of concept. Here’s hoping it works spectacularly well!
4 responses so far ↓
1 nc // May 23, 2008 at 5:57 pm
“That’s where nuclear fusion comes in. Like the sun, it fuses light atoms (hydrogen isotopes, generally) into heavier ones (helium, generally). Radioactivity is produced, but in vastly smaller and easier-to-handle amounts than in nuclear fission plants. But to get fusion to work, the power plant has to produce conditions of extreme heat and adequate pressure to get the hydrogen to fuse in the first place. On one hand this is a perfect safety feature. If a breakdown ever occurred, damage to the reactor instantly destroys the conditions necessary for continued nuclear reactions. And since only a very small amount of fuel is reacting in a given time, a problem instantly and automatically prevents the reactor from causing melting down. It’s a physical impossibility.”
You have a bit of disinformation here for some reason. If you know the physics you choose to write about, you are aware that the easiest fusion process to achieve is tritium+deuterium -> helium + neutron + 17.6 MeV.
Since 80% of the mass is helium and only 20% is the neutron, 80% of the energy, i.e. 14.1 MeV of that is carried by the neutron, so in each fusion event of 17.6 MeV, you get 14.1 MeV of neutron energy which can potentially induce radioactivity into the reactor containment vessel or building.
In fission, an average of about 200 MeV of energy is released in each fission event of which only about 30 MeV is residual radioactivity from fission products.
So in fission, about 15% of the energy is released as radioactivity, while in fusion of tritium and deuterium it can be anything up to 80%.
Neutron induced activity is a less severe problem in fission reactors than in experimental fusion reactors, because the neutrons are thermalized to low energy (about 0.025 eV ) and don’t irradiate the entire reactor structure, whereas the 14.1 MeV fusion neutrons are highly penetrating and do go everywhere, turning structural steel radioactive, etc. This is not ‘easily handled’.
‘On one hand this is a perfect safety feature. If a breakdown ever occurred, damage to the reactor instantly destroys the conditions necessary for continued nuclear reactions. And since only a very small amount of fuel is reacting in a given time, a problem instantly and automatically prevents the reactor from causing melting down. It’s a physical impossibility.’
To make a nuclear fusion reactor work at an energy density that gives the gigawatts of power required for economic or meaningful commercial use, you need a massive amount of fuel with an immense pressure, exerted on the plasma by strong magnetic fields which can squeeze the conductive (ionized) plasma.
If anything goes wrong, you get an explosion. Trying to compress a plasma with magnetic fields is like trying to squeeze and compress an orange with your fingers anyway, which is one reason why fusion has always been a crackpot activity (all hype, no commercially viable success).
It is the nuclear fission reactor which is inherently stable, because it has built-in ‘fail safe’ design. The control rods fall back in and make it sub-critical if power fails. By contrast, if power fails to the electromagnets containing plasma as a thousand atmospheres or more in a fusion reactor, you get a nuclear explosion as a matter of course.
The more you go into the details, the more stupid nuclear fusion becomes. If you want to use the most easy to achieve fusion reaction, you need to use tritium as well as deuterium, and tritium is exceedingly expensive (it’s produced by bombarding lithium with neutrons in a fission reactor).
If you just want to use just deuterium, the amount of pressure and temperature you need to make the reaction exothermal is far higher, because the reaction has a higher threshold for ignition, like a high activation energy in a chemical reaction.
The ‘ITER’ reactor page http://www.iter.org/a/index_faq.htm states:
‘The DT fusion reaction creates helium, which is inert and harmless, and neutrons, which can make surrounding materials radioactive for varying amounts of time.’
This seems to indicate that they are planning to demonstate the concept using DT fusion, using tritium presumably made at great expense in fission reactors. (Which would be extremely expensive, but cheap compared to the cost of trying to extract the tiny amount of natural tritium in seawater.)
The whole fusion spin industry is a complete fraud and pseudoscience. If you want to promote safe nuclear fusion energy, make do with sunlight and its derivatives.
Chernobyl didn’t blow up because it was an old design. It blew up because the Soviet RBMK reactor was a stupid design with a massive positive reactivity when the control rods are withdrawn, and the engineers in charge in April 1986 were cowboys, carrying out an unauthorized experiment (to see if the reactor could power its own energency water cooling pumps in the event of losing external electric power), which was obviously dangerous. They switched off the water cooling system, they switched off all the automatic safety systems (which can’t be switched off in Western reactor designs when the reactor is in use), then they withdrew most of the control rods. The reactor design was stupid because the control rods were driven by only slow electric motors which couldn’t quickly insert them in an emergency. It would take 18 seconds in the RBMK reactor to fully insert the control rods (in Western reactors it takes only 2-3 seconds), and the reactor exploded 40 seconds after the experiment began due to stupidity.
Also, nuclear fission waste is easy to handle and has been proved safe for 1.7 billion years, which is longer than any other kind of industrial waste has been verified to be safe for!
Fission products have been proved to be safely confined with only a few feet migration over a time span of 1.7 billion years, as a result of the intense natural nuclear reactors in concentrated uranium ore seams at Oklo, in Gabon:
“Once the natural reactors burned themselves out, the highly radioactive waste they generated was held in place deep under Oklo by the granite, sandstone, and clays surrounding the reactors’ areas. Plutonium has moved less than 10 feet from where it was formed almost two billion years ago.”
- http://www.ocrwm.doe.gov/factsheets/doeymp0010.shtml
2 JM // May 25, 2008 at 7:36 pm
“[Wind and solar] Startup costs are very large.”
Compared to what? Nuclear?
Give me a break
3 JM // May 26, 2008 at 11:40 am
“the nuclear cost-per-kilowatt is pretty competitive”
Then why isn’t it performing in the market?
Your wikipedia reference (I’ve no problem with wikipedia, if I find what I think is a mistake I’ll contribute) refers to commercially deployed installations.
Many of those have been done without the substantial subsidies and insurance guarantees required for nuclear and at lower entry costs.
You can’t have it both ways. If wind (and solar) have low entry costs and are therefore “insubstantial” in some way, they can’t also have “startup costs are very large”
The market is speaking on this issue, and nuclear is losing.
“The future of electric power will probably not be a magic bullet but instead a combination of technologies.”
Of course, but the market says that nuclear’s role is small.
4 CCPhysicist // May 26, 2008 at 7:42 pm
Fusion, nuclear (fission), wind, and solar share the important detail that a substantial part of the cost is the cost of money. This makes all of them sensitive to interest rates. Nuclear has an additional cost for fuel and dealing with waste, but an actinide burner could fix that and earn a profit.
At the current cost of capital, it is pretty clear that nuclear is cheaper than solar in the absence of subsidies, with the exception of solar hot water. (Even there, the $5000 capital cost is a bit much for most homeowners, who also have to pay property tax on it.) I don’t recall the numbers for wind, but what makes the “entry costs” low is that you don’t have to install solar or wind power in 1 GW chunks. You may not realize it, but interest rates in the 10 to 14% range played a major role in killing nuclear power at the time of TMI.
The analysis of fusion power by “nc” misses on many points, but the most significant is that slow neutron capture to produce actinides is a much bigger problem than capturing fast neutrons in, say, a lithium blanket to breed t. A MUCH bigger problem.
The explosion problem is silly. Boilers at regular power plants have been known to explode. That is an engineering problem.
Where you miss the boat with fusion is in not noticing the differences between the different kinds of breakeven that are involved. Muon catalyzed “cold” fusion meets the scientific breakeven point and maybe even the engineering breakeven point, but cannot be commercially viable. ITER claims it might reach the engineering breakeven point (running on its own power) if all goes perfectly, but if you pay attention to what they write, you will see that this is only while it is actually burning. It will likely be well short of this point as a facility when you include costs between burns.
Building ITER will mainly answer the question of whether a larger facility can be economical. They don’t really know that yet.
Leave a Comment