A nuclear reactor and a nuclear weapon are
about as similar as a hamster and an alligator.
They’re both made of cells,
but one is clearly more dangerous than the other.
So, the thing in common
between nuclear weapons and nuclear reactors
is they’re both powered by fissile isotopes,
like uranium 235 or plutonium 239.
Fissile isotopes are special elements
that break apart when neutrons hit them.
When this happens, they release more neutrons,
and little atoms we call fission products,
which carry off a lot of energy.
In nuclear reactors,
this energy’s released over a long period of time,
whereas in weapons, it’s released all at once, instantaneously.
So, fissile isotopes are the key ingredients
in both nuclear reactors and nuclear weapons,
but that’s where the similarity stops.
The difference, one of the many differences,
is that a nuclear weapon is almost pure fissile material,
it’s about 90 percent of the fissile isotopes,
either uranium 235 or plutonium 239,
whereas reactor fuel’s only about five percent.
And, just getting a bunch of uranium and plutonium together
doesn’t make a weapon.
If you lit a block of uranium 235 on fire,
it would burn chemically,
there’d be a fire
just like if you lit any other flammable material on fire,
but it would not be a nuclear explosion.
You actually have to compress it so much
that you get the atoms to slam together
much denser than they’d normally be.
So, a nuclear weapon,
there’s usually some sort of a core
of uranium or plutonium in pieces,
and around that is a bunch of explosive
that smashes them into each other,
and around that is some sort of a shell
that contains the explosion until it gets big enough.
These are exceedingly difficult to make.
If you took millions of sticks of dynamite
and put them around a sphere of uranium
and blew them all up at the exact same time,
the force would not be large enough to
compact the uranium to make a weapon.
If you got the right kind of explosive
and surrounded this sphere of uranium with the explosive,
and got’em all to go off at the same time,
it still wouldn’t make a weapon.
If you took a whole bunch of bricks of uranium
and put them all together,
and then drove a tanker full of gas next to it,
and has a whole bunch of high explosive blowing up all around it,
if you had enough uranium to go super critical,
it would, very very briefly.
You would get a quick pulse of neutrons,
at which point everythingwould heat up and blow apart,
and once all the uranium’s in different pieces too far away,
the reaction stops.
Without the proper physics and design,
which has take countries like ours years to do,
the best you could do is a Michael Bay style explosion,
but you couldn’t actually get a nuclear explosion.
I’ve just described what took the Manhattan Project
about five years to do,
and tens of thousands of absolutely brilliant scientists,
some of whom won the Nobel Prize.
In order to use the MIT reactor fuel to make a weapon,
yeah, that would be difficult,
that’s the definition of easier said than done.
Not only would you have to figure out
how to put the weapon together,
but you’d have to physically get to the reactor’s fuel,
and that’s basically impossible.
The building is about four feet thick
of rebar enforced concrete.
That’s actually been simulated to take a loaded plane crash,
cause that’s one of the safety criteria
for reactors in this country,
you have to be able to fly a plane into it,
and it shouldn’t break apart.
That doesn’t even count the security inside the building,
let alone the SWAT teams that would swarm the place
if anyone even tried to break in,
but lets say the terrorists got passed all of that,
then they still have to get to the fuel itself
which is normally kept behind a lot of shielding to keep it safe,
so we can work with it.
So, if they took away the lead,
the concrete, and the steel shielding,
they’d be faced with the fuel itself,
which is so radioactive that it would kill them on contact.
Even if somebody were to steal
enough material to make a weapon,
you can’t just put it together and have a weapon,
it doesn’t work.
There’s so much other stuff in the fuel.
Most light water reactor fuels in this country
are made of uranium dioxide.
You put oxygen in the way of those uranium atoms,
it doesn’t work anymore.
It works as fuel, but not as a weapon.
Reactor fuel is only about five percent uranium 235,
and there’s other structural materials,
there’s steel holding the thing up,
there’s water surrounding it,
there’s zirconium alloys holding pins and fuel rods in,
there’s all this other stuff that would have to be chemically separated.
Another difference between reactors and weapons
is the way the chain reaction is controlled.
A reactor is a tightly controlled chain reaction with negative feedback,
so if anything goes wrong, the reaction stops.
A nuclear bomb is an uncontrolled chain reaction
designed to get as hot as possible, as fast as possible.
So, when you hear the word chain reaction,
you might automatically think of something that’s out of control,
but it’s actually really hard to keep a reactor going.
So, let’s say,
you had a certain number of uranium 235 atoms.
Every time one of those uranium atoms splits apart,
it gives off two or three neutrons,
which could cause another uranium atom to split apart,
but not every one does.
Some of them leak out of the reactor,
and get absorbed by the shielding,
some of them get absorbed by other materials in the reactor,
and some of them can get even captured by uranium 235
without inducing fission.
As the fission reaction proceeds,
more and more other stuff builds up,
and that other stuff, which we call the fission products,
absorb some of those neutrons away,
and makes them unavailable to keep the chain reaction going.
Also, when a fission reaction heats up,
it causes the atoms to spread out,
making it harder for some of those neutrons to hit other fuel atoms,
and keep the reaction going.
In addition to that, there’s control rods.
There are materials that are really, really good at absorbing neutrons,
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like boron, hafnium, or gadolinium.
And you can simply stick those down into the reactor
to absorb away the neutrons and shut down the chain reaction.
The same sorts of reactions are happening
in a nuclear power plant and a nuclear bomb,
but in a nuclear bomb,
they’re happening quintillions of times faster,
and it’s all over in a split second.
The whole nuclear part of the explosion
takes less than a second,
and in a nuclear power plant,
you’re releasing that same energy over years or decades
in a controlled way that we can harness.