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Comment by fsloth | Hacker News Reader

First nuclear reactor was basically a pile of graphite brics with nuclear fule placed at calculates positions.

You get to critical reactor with just assembling materials of correct chemical composition to a correct geometric configuration.

The most difficult part is probably acquiring the nuclear material.

I've never built one, though :)

https://en.m.wikipedia.org/wiki/Chicago_Pile-1

The physics what we are looking at is the fact that neutron capture requires neutrons that go at a very specific speed. So, the nuclear fule creates some initial neutrinos that go fast, the carbon slows it down to a sufficient speed that they are captures by rest of the fuel, which then causes more chain reactions.

This is the reason reactors are a bit delicate - not enough neutrinos or wrong speed - no reaction. Too much - booom.

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> First nuclear reactor was basically a pile of graphite brics with nuclear fule placed at calculates positions.

Well, there's also this. :) https://en.wikipedia.org/wiki/Natural_nuclear_fission_reacto...

Why do people keep repeating this? Reactors don't go 'boom'. They aren't thermonuclear weapons. The worst you'll get is a bunch of heat when the cooling system fails and a possible steam explosion.

It depends on the design of the reactor, doesn't it?

They aren't thermo-nuclear bombs. They are simple nuclear bombs.

The earliest types of nuclear bomb essentially smacked two sub-critical masses of nuclear material together to form a super-critical mass, or compressed a sub-critical mass to a greater density, such that it was super-critical at that higher density. Then the core material produces heat faster than it can be radiated away, and eventually explodes.

If the non-fuel components of the reactor are destroyed, there may be enough nuclear material present to combine into a super-critical mass. At that point, it will go boom unless someone acts quickly enough to stop it.

It just so happens that all reactors designed to actually be built are ultra-paranoid about not turning even a completely failed reactor into a nuclear bomb. In a backyard DIY reactor that is not following a design blessed by physicists and engineers, you might get a boom. You will more likely get a big, deadly, radioactive fire that drops toxic ash on innocent bystanders, but if you melt cylindrical fuel rods in a graphite moderator, and they pool in the bottom of a spherical containment vessel as one big, connected mass...

I will ask again: Why do people keep repeating this?

You keep throwing around ideas like "They are simple nuclear bombs". It's not like during WWII the US asked some physicists to make a weapon and they replied with "just put some of this in a box and drop it on Japan. Call us when you need more"

Here are multiple explanations as to why a reactor is not and can not be a bomb:

http://physics.stackexchange.com/questions/7149/why-does-nuc...

Did you get your education on nuclear power from the "The China Syndrome"?

"Boom" in this context I assume doesn't mean kilotons of TNT equivalent explosion, it means "criticality event resulting in the release of a lethal dose of radiation". At Los Alamos, Harry Daghlian was killed by the "boom" resulting from simply accidentally dropping a brick onto a core of nuclear material.