(Picture from here.)
These are the kinds of posts that get me in trouble.
I am quite pro-environmental. We have as much solar as we can possibly afford at the moment. Our power supply is aggressively electric. The only place where we use fossil fuels is in heating—which, in the northeast, is a difficult thing to do without. (We are looking at heat pumps but we’re trying to figure out how to handle the extra electrical load with solar. Besides, we haven’t figured out a good way to use a heat pump in the greenhouse.) We have purchased a good hybrid. (Ditto EV.) We are trying to grow as much of our own food as possible.
We don’t live in an earthship but we can see it from here.
There are enough renewable technologies and storage co-technologies that I suspect most residential and business needs will be met in the next few years—providing our politicians don’t shoot us in the head in their misplaced loyalty to fossil fuel corporations.
That said, there are needs that are unlikely to be met easily by renewable sources: either by the intense power requirement over a short period of time or for the relentless necessity for heavy power over long periods of time. In the former, think the Large Hadron Collider. In the latter, think the Pentagon or backing up the grid in the case of cascade failures. There is also the issue that we are talking about renewables taking over the power supply now. The need for electrical power is going up, not down, and I suspect it will be every modality on deck before this is over.
All that said, many problems can be handled by not wasting energy either at the point of consumption or in transmission and just being more frugal. But that doesn’t solve the future problem. For example, about 10% of US energy is consumed cooling the interior of buildings. (See here.) That is going to go up as the earth warms. There is technology in the labs and in startups that might make a dent but I suspect this will, at best, bring us back to the starting point. I.e., the advances in technology won’t reverse the trend. We’ll just break even.
For other future work, we all want to go to space, right? That takes a huge investment in chemical energy. SpaceX’s propulsion systems are driven by methane/oxygen combustion, which results in CO2 created in the earth’s atmosphere during launch and is only marginally adequate as propulsion in space. It takes on the order of five months to get from here to Mars, cooking astronauts the whole way.
We need a high density energy production system. Well, the highest of high density energy is nuclear. Note the figure at the beginning.
It is my contention we need reliable nuclear energy sources, will need them in the future, and would be foolish to leave them on the table.
That said, these sources have to be safe. They shouldn’t use 2% of the nuclear material and throw away the west. They should be easy to build and comparatively cheap for what they deliver.
Source #1: Nuclear Fission
This is the one that’s been around the longest and scares people the most. It has the most issues with waste and has injured or killed the most people. Note, however, that global warming has killed and injured and will kill and injure many more people than fission power generation has ever done. The problem with nuclear fission is we’re scared of it.
Not that we shouldn’t be. Note energy density above. Anything with that level of energy density should be treated with respect. You don’t juggle sticks of dynamite. It’s unhealthy.
Part of the problem is categorical. We treat problems encountered with nuclear power as examples of the danger of nuclear fission. For example, the Titanic sank because of a combination of bad judgement and bad engineering. But that did not halt the use of ships. The Chernobyl Disaster also happened because of bad judgement and bad engineering but has been used as a cautionary tale for nuclear power.
It is a cautionary tale—for bad engineering and bad judgement.
Which brings me to the traveling wave reactor.
Most nuclear reactors have at their core a “rod” full of enriched Uranium pellets. Uranium comes in multiple isotopes, depending on the number of neutrons in the nucleus. U-235 is the most fissile and the “enriched” part of enriched Uranium.
The fuel rods generate heat from the Uranium decay. This heat will, if uncooled, will generate enough heat to melt themselves. This is the “meltdown” people talk about. The nuclear fission reaction is mediated by free neutrons and these neutrons are mediated by a material that absorbs them. The controlled release of thermal energy is used to heat a transfer material—usually water—that drives a turbine just like any other regular power plant. When the enriched Uranium burns down to the unenriched Uranium and non-fissile byproducts, the fuel rod is “spent” and must be handled. This is the really dangerous nuclear waste people talk about.
TWRs also use heat energy to drive some kind of turbine but the difference is in the nuclear reaction.
In a normal reactor, U-235 splits into other elements and releases free neutrons and some gamma radiation. These neutrons and radiation are absorbed, transforming into thermal energy.
In a TWR the reaction operates differently.
The TWR fuel rod mix is somewhat different. It is far less enriched in general—most of the material is U-238 with a small bit of enriched U-235. As the U-235 decays in this environment, it creates more fissile products that themselves will decay and transform the U-238 ultimately into Plutonium which continues the reaction. The exciting prospect here is that the same material that is “waste” in a traditional nuclear reactor, is fuel for the TWR. Since the TWR keeps creating the fissile materials it needs as it operates, the percentage of useful material is much, much higher. In addition, the remainder when the reactor burns out can be reprocessed into fuel. Not only does it not produce the dangerous waste, that same dangerous waste can be its fuel.
The other issue of fission reactors is the meltdown problem. In all of the meltdown scenarios we’ve seen—Chernobyl, Fukashima, Three Mile Island—the problem the reactor required active cooling. Failure of the cooling system of the reactors resulted in a runaway reaction. Therefore, the principles of good engineering dictate that the system should cool passively. If the system fails, it should cool itself.
TWRs have not been built yet. The most well known company developing it is TerraPower. TerraPower is using a molten salt design instead of water. The idea here is that if there is an emergency, the fuel drains into tanks where it solidifies and cools. It is passively cooled in an emergency.
TerraPower had a good thing going in China that was halted by the Trump administration’s concern on technology transfer. Now, it looks like it will be building a demonstration system at the Idaho National Labs.
Source #2: Nuclear Fusion
I know, I know: We’ve been hearing we’ll have fusion power in twenty years since World War II.
Fission happens naturally—Marie Curie noticed it by the glow of the material that ultimately killed her. Fusion does to, just 93 million miles away. The other joke is solar power is really fusion power when you think about it.
That said, fusion might well be workable but its utilization usually violates my sense of esthetics: we’re using the fundamental forces of nature to turn a steam turbine? Like it was coal? Aren’t we better than that?
Enter Helion Energy.
What I like about Helion is how they have bypassed the spinning turbine altogether. Imagine a dumbbell shaped device. Each of the large ends contain plasma. The two plasmoids are accelerated toward one another at high velocity while being further compressed, driving up the temperature. When they collide, they create a very hot, very compressed single plasmoid where fusion occurs.
The expansion of the plasma from fusion induces current. That current is the generated power. No turbines need apply.
Helion uses a Deuterium and Helium-3 reaction. It only releases a few neutrons as part of the reaction. Helium-3 is rare on earth but Helion has developed a side gig on its reaction that generates Helium-3 from Deuterium-Deuterium reactions.
Helion has been working steadily for years on this project. The most recent protype has been able generate fusion temperatures in the neighborhood of commercial requirements and they have been capturing power from the reaction. More than break-even? No one is saying but I suspect not.
Even so, they’ve gotten much further on less money than their competitors. I have high hopes for them.
Source #3: Nuclear Space Propulsion
#1 and #2 were for on this planet—though the same technology could be used to generate power in space if we could get the materials in place. (Z-Pinch propulsion has been investigated for a while.)
Remember that energy density cartoon. Chemical reactions have orders of magnitude less energy density than nuclear reactions. While it’s probably a bad idea to use nuclear methods to get payloads from earth to space, there is absolutely no reason not to use them in space.
The easiest way is to use a nuclear fission reaction like we use a chemical reaction: generate heat and gas expansion, causing propulsion as the expanded gas is expelled behind the vehicle. This is a nuclear thermal rocket.
NTRs were investigated back in the fifties—something well document in the National Museum of Nuclear Science and History, a museum in Vegas I highly recommend everyone visit. This was the NERVA program, a highly successful propulsion system. Development began in 1958 and was stopped in 1973, as a victim of Nixon’s cost cutting.
All is not lost: NASA started revisiting this in 2021.
But there are more nuclear methods of space propulsion.
This Big Boy of this is the Project Orion, where nuclear explosives were used as a mechanism of moving massive payloads. This approach had the singular feature of a paper evaluating the retina burn of the west coast were such a vehicle launched from the surface of the earth.
Again: bad judgement and bad engineering.
That said, were the vehicle assembled, say, in the asteroid belt between Mars and Jupiter, it wouldn’t have the same issues. An asteroid could be the payload.
But let’s bring our pipe dreams down a notch.
What nuclear brings to the table is a vast amount of energy in a small mass. This can be used in a number of ways—nuclear thermal rockets is one. But there are others.
One of the most efficient means of space propulsion is an ion thruster where a gas is ionized and the resulting charged particles are accelerated by an electric field. There are limitations on these systems, one of which is the amount of power that can be brought to bear on the particle. Faster particles mean more thrust and require more power.
Another is using the output of a fusion reaction, with all of the heat and velocity of the reaction, directly out the back of the rock.
The point here is to use that enormous energy density in space propulsion. Normal propulsion takes a crew to Mars in seven-nine months. Nuclear propulsion might be able to bring that down to as little 45 days with larger payloads.
So: bad judgement and bad engineering are bad things. But they shouldn’t prevent us from using good judgement and good engineering to do good things.
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