This episode is brought to you by Brilliant Many think fission has gotten a bad rap, but
modern reactor designs and the demand for clean power may redeem
what was once thought to be an energy panacea. So today we’ll be talking about the future
of Nuclear Fission, and looking at everything from new reactor designs to applications in
space and in other areas like medicine and agriculture and even portable devices. As quick side note, today marks the 6th anniversary
of our very first episode, Megastructures in Space, and we’ll commemorate that briefly
at the end of the episode, and it’s appropriate for our topic today as power and energy production
are so vital to our grand dreams for the future, and as we’ll see today, fission is likely
to play an enormous role in taking us into that future, especially for the spacecraft
that will actually take us there. The elephant in the room for nuclear power
is always the concerns about its safety and I tend to think a fair amount of that is simply
from nuclear power and radiation being a bit mysterious. I don’t want to dwell too much on safety
concerns or particle physics today but we will spend some time on them before getting
into various reactor designs and future uses and we’ll start with the basics of fission
and fusion. In nature, atoms tend to fall into two categories,
those that were around from the beginning, mostly hydrogen and helium, and those made
by stars. However, it’s inaccurate to think most elements
are made by giant stars exploding. Things like gold, platinum, and uranium are
made when two neutron stars collide, long after the two supernovae that made each of
those neutron stars. They are not made by the classic process of
fusion where lighter elements merge to form heavier ones and release a net positive energy. Protons and neutrons, called nucleons because
they’re what appear in atomic nuclei, are made up of three quarks but those quarks don’t
actually have much mass themselves. We explained it in greater detail in our episode
on Antimatter, but most of the mass of nucleons are composed of the particles that glue them
together, the mediating particle of the Strong Nuclear Force, aptly named the gluon. When you jam or fuse nucleons together with
some glue, it takes less of it per particle the more particles you jam together, until
you get about 60. As you fuse them together, some of those excess
gluons become available as energy. This is nuclear fusion and we discussed it
in detail in our fusion power episode. This peaks out with iron, and Iron-56, it’s
most common isotope composed of 56 nucleons, 26 protons and 30 neutrons, and is the atom
with the lowest binding energy and thus the end of profitable fusion processes and also
why iron is pretty common in the Universe. Atomic nuclei more massive than iron start
taking more energy per particle to jam the stuff together, which is why a pair of neutron
stars, already very jammed together, can collide and spew out tons of heavier elements. While many elements past iron are called stable,
meaning they have no known half-life, the bigger you get the more glue it takes to cram
things together and many isotopes have an unstable arrangement which will reshuffle
to a more stable state, often through emitting a particle and often going through a number
of semi-stable states along the way, we call this nuclear decay and the period of time
in which half of a given type of atomic isotope will do it, on average, is the half-life. Think of it as akin to a heap of material
where something occasionally shifts or breaks and it settles into a more stable heap, emitting
a loud noise - in this case a particle of radiation. Fission includes both nuclear reactions and
technically passive radioactive decay but usually just means splitting atoms not atomic
decay and we’ve discussed the value of rapidly decaying elements as power sources in our
episode Portable Power, and various isotopes with quick decay times hold the potential
to be awesome mobile power sources and safe ones too. It’s their scarcity rather than their radioactivity
that is the problem with using them in common devices like telephones and laptops. We will discuss how to create those elements
today though. Fission by nuclear reaction, which we will
just call fission for the rest of the episode, usually involves smacking an atomic nucleus
with something to split it up. In the case of Uranium-235, if a slow-moving
neutron, only moving a couple kilometers per second, happens by it will break that Uranium-235
into Barium-141 and Krypton-92, 92+141 is 233, and the Uranium-235 plus that neutron
was 236 nucleons, so you also get 3 extra neutrons, each wandering off on its own way. Only the neutrons are moving quite fast in
this case, typically a few percent of light speed. If we slow them down a lot, from about 20,000
kilometers per second to just 2 kilometers per second, then they’d be moving slow enough
that if they ran into another Uranium-235 nucleus they’d cause it to break and spit
out 3 more neutrons--which can them break other nuclei. This is a fissile chain reaction, and can
actually happen in nature but not so much nowadays because there isn’t much Uranium-235
left. The event that made the uranium here on Earth,
the collision of 2 neutron stars, presumably produced about the same amount of the various
isotopes of any given element. Uranium has 6 isotopes, 232, 233, 234, 235,
236, and 238. 238 has the longest half-life, 4.5 billion
years, so about half of whatever was on Earth when the planet formed is still around, while
the next longest-lived, 235, with a 700 million year half-life is down to only about 0.72%
of what is found in nature, and Uranium-234, half-life a quarter of a million years, is
only 0.005%. Which can be a little misleading too, 0.005%
might not sound like much but it’s way more than you’d have left from 4.5 billion years
of decay with a quarter million year half-life, that’s 18,000 half-lives, and you'd only
have 1 in 2^18,000 of the original particles left. After even just 100 half-lives your odds of
finding a single particle of a substance left undecayed in a handful sized-sample are about
your odds of winning the lottery and there are not enough particles of anything in the
entire Universe that you’d expect to find even one undecayed particle of it 18,000 half-lives
later even if every atom in the Universe were originally made of it. Rather, when Uranium-238 decays, which is
pretty rare with a half-life as old as our planet, it decays into Thorium-234, emitting
what’s called an alpha particle, two protons and two neutrons, which is basically a helium
ion without an electron shell. Thorium-234 has a very short half-life, just
24.1 days, and it beta-decays, beta radiation being when a nucleus emits an electron or
its antimatter twin, the positron. The Thorium-234 then turns into Protactinium-234,
same thing but one more proton and one less neutron, and it spits out an electron. This is even more unstable and will beta decay
again, spitting out another electron as it gains a proton and loses a neutron, and becomes
Uranium-234. For every Uranium-238 atom on Earth now, there’s
about an equal number of them that decayed down this chain into Uranium-234, but since
Uranium-234 is only about an 18,000th as long-lived as Uranium-238, only about an 18,000th of
natural Uranium is 234. 234 decays into Thorium-230 incidentally,
and all Isotopes of Uranium, no matter how long lived, decay via alpha particle emission
to a thorium isotope with 4 fewer nucleons, and an atomic mass that is lower by approximately
4. It’s just in Uranium-238’s case it does
it twice, dropping to Thorium-234 then eventually down to Thorium-230 after a rest atop as Uranium-234. This episode, again, is not about passive
decay, but finding short lived isotopes in quantities on Earth after hundreds or thousands
of half-lives indicates there’s a natural process making them not requiring neutron
stars to collide, which can be a big clue for making them in the lab and fairly efficiently. We often do this with a breeder reactor, and
it’s how we make plutonium, by letting Uranium-238 absorb a neutron and emit two electrons and
thus turn into Plutonium-239. It’s easier for Uranium-238 to absorb fast
neutrons than for Uranium-235 to absorb them, and there’s a lot more Uranium-238 in a
natural sample. So to create a good sustaining fission reaction,
where at least one of the three neutrons spat out by Uranium-235 during fission gets absorbed
by another U-235 atom to sustain the process, we need to either cut down on the Uranium-238
in our sample or slow those neutrons down more, so they interact more easily with the
U-235, or in practice both. Uranium enrichment, separating natural Uranium
into its isotopes, typically produces enriched uranium and depleted uranium, the latter having
half or more of its U-235 removed and leaving it at a higher concentration of U-238. Enriched Uranium has more U-235 in it, low-enriched
would be anything under 20% U-235, which is still up a lot from .72% found in nature,
while weapons grade is usually 85% or higher. Most reactor designs today use low enriched
uranium or even unenriched uranium in the case of the CANDU reactor, but many advanced
designs are based around a middle ground called “High Assay Low Enriched Uranium,” which
is about 20% U-235. Slowing neutrons is the job of what we call
the moderator, and the two most popular kinds are water and graphite, though many things
can slow a neutron. You don’t want it to absorb the neutrons
though, just slow them down, and water will often absorb them whereas heavy-water, water
where the hydrogen in the H2O is actually deuterium, a proton and a neutron instead
of just a proton, is better about not absorbing neutrons. So your basic nuclear reactor, using uranium,
has enriched uranium clumps, be it rods or pebbles, separated by some moderator, and
as some neutrons come out from a fission event they meander through that moderator, slowing
down, till they reach another clump of uranium and cause a fission event. If you set your moderator just right you’ll
get a 1:1 ratio, a stable fission event that just keeps going until you run out of fuel. Or rather get lower on it so less fission
events are happening. This is not a naturally stable process, going
exactly 1:1 like that, and you can tweak the reaction rate by playing with the moderator’s
density – regular water with no deuterium, called light water in this context, acts as
a slightly worse moderator when it’s temperature raises so helps keep the reaction stable. We also have control rods, which are materials
that just absorb neutrons well and can be lowered down between the chunks of uranium
to suppress the reaction. When all goes well you can keep the reaction
at 1:1, and throttle the actual rate up or down to produce more or less power. Power production itself is pretty mundane,
all those fission fragments and neutrons have a ton of kinetic energy – again they’re
moving at a few percent of light speed when they leave the original atom that underwent
fission and that kinetic energy smacking around the core produces a lot of heat. For water as a moderator we usually just use
it as a coolant too, though some reactors will use gases or liquid metal or molten salt
for cooling. Regardless of whether the coolant and moderator
are the same thing or not, the coolant is what drives power production. We generally like to run the reactor as hot
as is safe without melting stuff, because you get better power production efficiency
when dropping from a higher temperature to a lower one. This all runs through the cooling towers of
the plant, though the massive steam and clouds coming off the cooling towers is not stuff
that was running through the core but rather on the other side of a closed loop, cooling
off the coolant as it were. That’s the standard nuclear reactor most
of us know, and most of them are light-water reactors, again that’s regular water, though
heavy water isn’t super-rare. Pebble Bed reactors use graphite as a moderator
– as did the first reactors, the old atomic piles which was also what we called reactors
back in the day, and instead of rods of uranium in a moderator of water it’s pebbles of
the fuel inside graphite and we dump a bunch of them into the bed which we use gas to cool. These can run hotter and don’t meltdown,
which is basically when the control rods get stuck and can’t lower to quench the reaction,
though they have their own limitations and modern reactor designs have many newer features
than classic reactors to help against meltdowns. One example is having the controls rods constantly
being shoved down by a spring and pushed up by an electric motor so that if anything happens
to the motor, or the power supply in it, or you hit the off switch, it just drops the
control rods. I don’t want to pound the safety angle too
much, nuclear power is dangerous - though it has the fewest deaths and injuries per
unit of power generation of any of our power generation methods and we get better at the
safety angle everyday. Indeed much of the danger is from us using
older reactors still rather than building the new ones. Still, it’s got the best safety record of
any form of power generation we’ve got, but all technology is dangerous and power
generation of any type can be weaponized. The Kzinti Lesson, that a spaceship’s drive
can be used as a weapon, popularized by writer Larry Niven and sometimes called John’s
Law from John W. Campbell’s earlier version, reminds of us of this, or as we say on this
show, there is no such thing as an unarmed spaceship. So too, there is no such thing as un-weaponizable
power generation. Power is power, you can use it to blow stuff
up, even if just by running a munitions factory, to say nothing of powering an electromagnetic
rail gun. Whether or not nuclear fission will ever be
our main source of power production depends a lot on how the economics work out – which
are heavily controlled by regulations for good or ill – and how others technologies
develop, like solar power and batteries for instance. Nuclear power also is one of our best options
for space travel between planets, and we discuss using it for running spaceships in our episode
“The Nuclear Option”. However, if we do go the fission route we
have an effectively limitless supply of fuel for it. I’ve heard folks say we have this or that
many numbers of centuries of fissile fuel left but that’s a careless figure, Uranium
is disgustingly common, most is in the planet’s core but it’s about 2 parts per million
in our crust and you’ve got bunch in your backyard and eat a couple micrograms every
day. And given that it produces a million times
more energy than chemical sources it is worth centrifuging out if you need it. Those stockpiles have to do with known supplies
and existing high-concentration ore deposits, and only discuss Uranium-235, not Thorium
or other fertile materials produced by breeder reactors. It's a good deal lower in concentration in
seawater too but easily removed and one handy application of nuclear power is desalinating
drinking water, as you boil off a lot of water during power production that’s basically
free desalination. The nuclear power plant near me is jokingly
called the cloud factory for a reason, I’m over ten miles away and can still see the
plume of water vapor rising off it from my backyard. That’s one obvious application to agriculture
but we’ll mention a few others in a bit when we get to breeder reactors. I mentioned alternate coolants and molten
salt as one of them and we hear a lot about molten salt these days for power storage. One of the upsides of molten salts is they
do a very good job storing heat, but for reactors we contemplate them as a coolant or even the
fuel itself because they don’t have to be under high pressure. In a light water reactor, to keep that water
a liquid, and not steam, we have to keep it at around 100 atmospheres of pressure. The boiling point of most liquids rises when
you put it under pressure and lowers when you decrease it and most steam driven power
production uses high pressure to keep the water a liquid at high temperatures as that
gets you more efficient power production. Molten salt lets you run things even hotter,
but it also lets you go smaller, as you don’t need the massive containment vessel for keeping
water a hundred times more pressurized than it normally is on Earth. A Molten Salt Reactor – or MSR – has the
potential to let you make much smaller reactors which is nice because normally nuclear power
plants are huge affairs for putting out a thousand megawatts of power and running a
million homes. Smaller ones are attractive for more remote
locations and to avoid transmission losses, about 50% of electricity is lost as waste
heat in the power lines, something we discussed hopefully limiting with superconductors if
we ever get room temperature ones, as we looked at recently in the Impact of Superconductors. With those, the big efficient plants become
more attractive as you can stick your power plant far from anyone else, out in the middle
of a desert or tundra, and not lose any power sending it to where the folks live. Without that, smaller reactors are more attractive
and that includes another type, the Small Modular Reactor or SMR. Multiple types of reactors have been suggested
for SMR usage but the critical concept is essentially one small enough to be moved,
either in total or as completed modules bolted together at the power plant, and which are
better at containment and passive safety features. The basic notion is to make a small black
box reactor, potentially small enough to be loaded on a truck or train, that requires
no real maintenance or construction at its site and which can be picked up after their
lifetime and disposed of after processing unspent fuel. These SMR’s are made in a factory with quality
controls and production efficiencies that site-built, one-off plants don’t have. Incidentally this is an example of Generation
IV reactor. Generation 1 being the old atomic piles and
Generation 2 most of the ones you see, with Generation 3 including examples like the ABWR
or Advanced Boiling Water Reactor. I don’t want to get in the weeds on that
as the differences in many reactor types are basically how you cool the thing and how you
generate power off that coolant. Some Generation IV reactors go for a different
concept, called a fast neutron reactor or FNR’s. We’ve mostly discussed thermal-neutron reactors
thus far, where we slow the neutrons down to the average speed of other particles in
the reactor, the thermal velocity of those particles. Fast neutron reactions don’t use a moderator,
and as you might guess don’t rely on having as much Uranium-235 as a thermal reactor. They can instead, for instance, rely on Uranium-238,
the type of Uranium that’s way more common and much better at absorbing fast neutrons. The product of that, of U-238 absorbing a
neutron, is a Plutonium atom. And this is where we get to breeder reactors,
which FNRs can do too, not just power generation. A breeder reactor is one that’s using the
fission chain reaction process to make some other material, Plutonium being the big one. Plutonium-239 is much better for making atomic
bombs, and while it’s no more sensitive to fast-neutrons than U-235, you can sustain
a reaction on either if you just have enough of it present and an absence of other things,
essentially if it’s very enriched. This lets you remove the moderator from the
equation and make a smaller and in some ways simpler reactor. If we compress plutonium down really densely,
by an implosion for instance, then the neutrons emitted by fission are likely to get absorbed
by their neighbors, which is how atom bombs work. The other route is just to have a lot of it
there, and not much else, though you can wrap your plutonium in U-238 to capture the neutrons
that do escape and breed more Plutonium for later separation and usage. This is not limited to Plutonium incidentally. One of the more interesting options is Americium,
which we don’t find in nature and most of its isotopes have quite short half-lives with
Americium-243 being the longest lived at 7370 years followed by Americium-241 at 432 years,
and that half-life makes it very interesting as a possible power supply by passive decay. Useful passive decay power generators can
really only come from breeder reactors since they don’t occur in nature in useful quantities,
again due to that short half-life. One type of Americium, 241m[a], also requires
the least amount of fissile material to sustain a chain reaction of any isotope that we know
of. If you want to go really small with a fission
reactor or nuclear battery, this is the way to do it. But probably the most interesting breeder
reactor option, or at least the most discussed in recent years, is Thorium. As I mentioned earlier all isotopes of Uranium
eventually decay into thorium and it’s pretty common itself anyway. But Thorium-232 is what’s known as a fertile
material, which means if we whack it with neutrons it does not undergo fission, but
rather turns into something which does, namely Uranium-233 after a brief stopover as Thorium-233,
with its brief half-life of 22 minutes, followed by a time as Protactinium-233 as it pops out
an electron and swaps a neutron into a proton, this last a little longer, with a 27 day half-life,
before beta-decaying into Uranium-233. Uranium-233 is fissile, so we can generate
power from it or leave it in to help breed more of itself or potentially do both at once. This is the big interest in thorium as a power
source, essentially as a source of uranium-233, and thorium is more plentiful than uranium
too. Now the potential for thorium does tend to
get a little over-hyped. It is a great alternative to Uranium but usually
folks are comparing it against old generation II reactors not the newer Uranium reactor
designs, which is a bit unfair. It’s often cited as being better for avoiding
nuclear proliferation but that’s a debatable point. Regardless, I generally warn folks off this
notion, same as ideas like strictly defensive weaponry, there is no such thing as a power
source you can’t weaponize or a defensive weapon you can’t use for offense. You can tinker with a reactor – and Uranium-233
can be made into atomic bombs and indeed, unlike plutonium, it can be used in the gun-type
nuke, the easiest one to build. Also, even ignoring the way you can make electricity
into a weapon, e.g. railguns and lasers, the simple possession of energy abundance is weaponizable,
running your weapons factories and all the bits of your society that build the components
for those, not to mention raising your GDP from cheap energy, allowing you to build more
guns. This isn’t to say you shouldn’t be worried
about folks having potential access to weapons grade material but Thorium’s big benefit
isn’t that it’s super-safe from folks getting nukes or magically super-efficient
& safe reactors. Nuclear is dangerous, all technology is, heck
the rare earth minerals, so prized for solar and wind and so many of our electronics, contain
uranium and thorium. We process it out and the mine tailings are
very rich in them as a result. This is a huge part of why we don’t get
much rare earth production in most countries, as rare earths aren’t even vaguely rare,
but they produce a lot of thorium and a lot of mines shut down because of the thorium
discharges in the tailings and clean up or prevention of that isn’t cheap, unless of
course you don’t care. On the other hand if you’ve got a profitable
use for thorium that isn’t such an issue anymore, when your waste becomes a fuel. I don’t want to minimize the value of thorium
as a reactor fuel either, it has a lot of potential especially for expanding fissile
stockpiles, but it’s not an across the board better alternative to uranium. As time goes on we’re seeing other improvements
too, heat pipes for instance. The ability to move heat efficiently is very
important for any heat engine, but is great for nuclear reactors which need lots of cooling
and where the primary coolant usually has to be kept in a closed loop and heat piped
into another medium resulting in various issues and efficiency losses. Heat Pipe reactors take this a bit further
using heat pipes to move power from the core directly to the power conversion system. Nuclear power isn’t just useful for electricity
generation though. A huge number of other fields use products
from nuclear power, including a few that you might not think of. Perhaps the best known is in medicine. Pretty much every chemotherapy drug used in
cancer treatment was produced in a nuclear reactor, where the neutrons are absorbed by
a precursor material which is kept in a special container in the core until it transmutes
into the correct isotope to use. High contrast MRIs and CAT scans also use
radioactive material produced in nuclear reactors. Radiation imaging, including x-rays and neutron
tomography, use either radioisotopes or sometimes even a dedicated facility next to a nuclear
reactor to produce EM waves or particle beams to provide incredibly detailed images of not
just internal injuries, but the functioning of various organs and processes within the
body. New types of surgery, such as gamma knife
surgery, offer faster-healing surgical options which are much more precise - and sometimes
an external incision isn’t even needed, making healing even faster! Agriculture is another area that has benefitted
from nuclear power as well. From the first experiments in the 1950s and
1960s using radiation to force mutations in crops, which were then selected for the desired
traits like bigger fruit or more drought resistance, to tracking nutrient flows in fields and water
cycles using mildly radioactive isotopes dissolved in water or fertilizer, to pest control using
radiologically sterilized pest insects as decoys to prevent infestations from growing
out of control, a lot of modern agriculture is intrinsically tied to the nuclear industry. Other options include using a nuclear reactor,
not for its electricity generation but for the heat that comes off the core. Many big cities like New York City have district
heating, which is a utility kind of like gas or electricity. With a nuclear reactor, you can not only provide
district heating, but also heat the roads and sidewalks in the winter months to prevent
ice and snow from sticking - a huge safety bonus that would also save cities a lot of
money. In reactors that operate at even higher temperatures
(like gas cooled reactors) you can even get the temperatures high enough to use in industrial
processes, like chemical manufacturing, metallurgy and foundry production, and other energy-intensive
processes. An SMR in a large factory could cover all
its power and heat requirements for very low cost. Finally, perhaps one of the biggest potential
uses for nuclear reactors is in water desalination and carbon capture. Both of these are notoriously power-hungry
processes, which means that they’re expensive and not done unless there’s no other choice,
but both could be done at the same time with a nuclear reactor. The sea water would be drawn into a separate
loop from the cooling loop, run through a chemical process to extract the CO2 and turn
it into hydrocarbons (which is far easier to store and even use), and then be boiled
to purify the water. Of course, you can’t just dump the salt
back into the sea without causing an ecological nightmare, but there’s ways to dispose of
it safely. Lastly, we should discuss radioactive waste
and its disposal and recycling. There are a few different types of nuclear
waste: low level waste, intermediate level waste, and high level waste. Low level waste is often very weakly radioactive
- sometimes it’s even just someone’s shoes if they forgot to switch to those little paper
booties at the plant, but is stored out of an abundance of caution. This is the most common type of nuclear waste,
and usually puts off less radiation than you would get standing in the sun for a few minutes. This comprises 90% of the volume of all radioactive
waste, but only puts out 1% of the radiation of all types of waste combined. Intermediate level waste is a huge range of
waste types, radioactive but not enough to generate a lot of heat. This includes chemicals used in radioisotope
refining, some parts of decommissioned nuclear reactors, and even the protective metal clad
used on the fuel elements in reactors. It makes up about 7% of the volume of nuclear
waste, and accounts for only about 4% of the radiation. Finally, we come to the high level radioactive
wastes. This is stuff like used nuclear fuel and byproducts
from reprocessing, as well as some chemicals and equipment used in weapons production and
some portions of decommissioned reactors. This stuff is so radioactive that not only
does it need to be shielded, but it’s putting out over 2 kW/m^3 of heat, something that
facilities have to be designed around. Much of this radioactivity comes from transuranic
elements produced in reactors, but there are designs for fast neutron reactors that can
burn this fuel and reduce the time it’s dangerously radioactive. Other types, such as Strontium-90, are useful
as either RTG fuel or as a radiation source for various sensors and equipment, so depending
on how much you’re willing to put into your reprocessing facility you can get far more
than just fuel out of high level waste. Reprocessing, or recycling of spent nuclear
fuel, is a complicated process, and one that most countries don’t do in civilian power
production, simply because it’s too expensive. New uranium fuel is cheap, in fact it’s
the cheapest thing about operating a nuclear power plant, so reprocessing is not really
necessary today. The classic way, called the PUREX process
is to grind up your fuel and soak it in nitric acid to dissolve the uranium and plutonium. This process produces a fair bit of low-to-intermediate
level waste in the form of radioactive acidic slurry, but is well-understood and is done
in France (who also reprocesses fuel for most of Europe), Russia, and Japan. The UK also used to have a facility, Sellafield,
but it was closed after repeated accidents. The next option, called pyroprocessing which
replaces the nitric acid with a molten salt mixture, which is then passed through various
chemical synthesis steps to remove the fuel and high level actinides. This salt can be reused far more than the
nitric acid, and promises to be more efficient than the PUREX process, but has only ever
been done on small scales. The last major option for reprocessing is
called “SILEX,” and uses powerful laser beams to deflect a stream of individual ions
of mixed isotopes into different collectors. This was developed in Australia about a decade
ago, and shortly after it was released it was also classified, so details are scarce. It’s hard to tell if this would be more
economical, but using giant lasers to separate nuclear fuel is a cool concept. All nuclear waste needs to be stored for five
half-lives or so, at which point it’s no more radioactive than the environment. How long that is depends on the isotopes involved,
and if their decay results in something chemically toxic. Europe and Russia reprocess their spent fuel,
and the resulting high-level waste is chemically bound in an inert material - France uses glass
for this. There isn’t much of it either, all of it
easily fits into one single foot-ball field sized chamber. In the US the entire fuel structure is kept
in a pool until it cools down to the point it can be stored in giant, armored concrete
cylinders known as dry casks, usually placed next to the reactor that used the fuel. Geological storage repositories for spent
nuclear fuel in the US have failed for political reasons, although Finland is getting close
to completing one in the next few years. Overall disposal and recycling of waste materials
shouldn’t represent a serious problem to increasing nuclear power, especially using
the improved techniques mentioned. Needless to say though there is a big difference
between what science & engineering say is safe and the population’s comfort level
with it. So the future of fission, if we get it cheaper
and safer and more palatable to the public, is not a guaranteed thing on Earth. If you can produce solar panels and power
storage cheaply enough, then nuclear loses some of its value, but if you can do the former
but not the latter, nuclear becomes a great night time or bad weather power source too
and the newer designs can crank the power up or down in mere minutes making them a good
backup power supply or power supplement. And of course if someone gets fusion working
it might become mostly redundant but would still have some handy applications. On Earth anyway, up in space atomic power,
either by itself or in tandem with solar is very promising, and again we explore that
more in our episode “The Nuclear Option”. Fundamentally though, the big challenge is
changing hearts & minds on nuclear, and if we can do so, we have an excellent power source
that can give us cheap, ecological, safe, and long-lasting energy. So as I mentioned at the start of the episode,
today is the 6th Anniversary of our very first episode, Megastructures in space, and what
I usually call Episode 0 as it was the only episode we did in 2014, and indeed our weekly
shows didn’t start till February of 2016, a year and half later, appropriately with
our episode Megastructures: Shellworlds. And I thought we would take some time to look
back over the last 6 years, but before we get to that, I wanted to thank our long time
sponsor Brilliant, whose been helping support the show for years now and whose online interactive
courses make a great compliment to the material we discuss on the show. What I aim to do here is to educate and entertain,
but to truly master the concepts you’ve got to work with with them and Brilliant is
an excellent place to do that. They make a great addition to educational
videos like these, as they let you get hands-on learning and practice with the concepts to
help you truly master them, and learn more about how our world and our Universe work. From courses and quizzes to a community forum
to get help, to daily challenges and an offline app that let you sharpen your analytical abilities
anywhere you are and have a few minutes to spend, Brilliant let’s you learn math, science,
and computer science and have fun while you’re doing it. If you want to learn more, and help support
our show, you can try Brilliant out, for free, by going brilliant.org/IsaacArthur. In the 6 years of doing this show, we’ve
stuck mostly to the same core format, me talking while video and clips played, and will mostly
be keeping to that but I thought I’d show up on camera for a change. Contrary to popular belief though - and the
jokes about the show actually being run by an AI with a synthesized voice, I did actually
have photos of myself up on screen occasionally as far back as that second episode. I just didn’t happen to own a camcorder
or webcam till shortly before we started doing the livestreams two years back, plus I’ve
always liked to keep the focus on the content and not myself. For anyone who takes a trip down memory lane
to watch some of those older episodes after this, you probably remember when I used to
put the Elmer Fudd graphic up for my speech impediment and for the first few years I always
was on the fence as to whether or not to hire a narrator if the show ever got big enough
to afford one. Amusingly when I finally did get talked into
to accepting donations for the show and said that was one of the things we were raising
funds for, so much of the audience was horrified by the notion that I scrubbed the idea in
favor of just getting speech therapy, which has been going on for around 3 years now. Needless to say it's been quite an interesting
6 years for me personally, including get married this year, and I love what I do and plan to
be doing it for at least another 6 years. Over those years we’ve covered so many topics
and have over 300 episodes including all the bonus episodes and livestreams, but amazingly
we still have no end of topics to cover, I guess that’s the neat thing about the future,
there’s just so much of it. However I thought we would also commemorate
the occasion by having another topic poll over on our community tab. Speaking of that community, and of taking
donations, I did want to thank all the folks who have donate to us on Patreon and by other
methods down the years, and if you would like to help support the show, you can do that
on patreon or on our website, IsaacArthur.net. I will shamelessly throw in there that this
weekend is my 40th birthday too. As we head into our seventh, we’ll start
that up next week by a return to the Fermi Paradox, to contemplate how a scarcity of
certain elements, like Phosphorus, might make life and ancient alien civilizations a lot
rarer than we might otherwise believe given the sheer immensity and age of our Universe. Then we’ll close out September with our
monthly livestream Q&A on Sunday, September 30th, at 4 pm Eastern Time, then we’ll head
into October for the third installment of our new series, Becoming an Interplanetary
Species, as we look at heading back to the Moon. For Alerts when those and other episodes come
out, make sure to subscribe to the channel, and if you enjoyed the last 6 years of episodes,
make sure to hit the like button. Until next time, thanks for watching, and
have a great week!
u/IssacArthur mentions the potential of small modular reactors. Looks like we are very close. These folks have just gotten safety approval for one. https://arstechnica.com/science/2020/09/first-modular-nuclear-reactor-design-certified-in-the-us/
"Power is Power"
The Arthurs send their regards
Isaac Arthur what do you think is the steps to making humans intergalactic
It looks like someone finally figured out why thorium is so important to develop... it's almost piling up as a waste product of other mining operations and needs to be dealt with. Fissile material to initialize the breeder reaction is the main hurdle. The other is consuming our current waste stockpile and the small modular reactors can both use the material and power it's processing. Having variety in design is a good thing.
Not only factories can make use of internal reactors. Nearly every major building could have it's own small modular reactor under it's basement, guaranteeing power to the structure and taking as much pressure off of the grid as possible. Critical infrastructure like hospitals need to own their own power generation and have excess to sell to offset some of their cost.
There is another "waste product" piling up that needs a productive use... glycerin. This triple alcohol could actually be used in construction as part of polyurethane. Now we need a tri-isocyanate to pair with it. Toluene triisocyanate is a known compound but not used much commercially at the moment. It can be made in bulk through reducing TNT to TAT (triamino toluene) then reacting with phosgene like other isocyanate componds.
Polyurethane concrete, especially if fortified with vinyl and acrylic fiber for tensile strength, has the potential to become a green (carbon consuming) competitor to traditional concrete. Why dump CO2 underground when you can build cities and even arcologies with it?
There's some cool new fission designs, but the big killer continues to be the upfront cost (at least for fission on Earth). We need cheap, safe reactors that can match solar, wind, and gas on electricity costs. Unfortunately modular reactors don't seem to be doing that - their electricity prices per kWh are quite high from what I've read.
Off-world it's tremendously valuable. We've spotted areas with Thorium on Mars, so you could potentially assemble a reactor there with some U-235 to start it, and then run it off Martian fuel. We'll probably also see the use of a small nuclear reactor at some point for a flagship-class robotic mission to the outer planets (the Jupiter Icy Moon Orbiter concept involved a 200 kWe reactor, which is probably bigger than anything we'd actually send anytime soon).