Nuke designs.

[gallo]

The following discussion is from "Nuclear Energy: An Introduction to the Concepts, Systems and Applications of Nuclear Processes" 3rd ed., 1988 by Raymond L. Murray. It is freshman text used in the 1st semester at various universities for nuclear engineering students.

The book discusses the two types of fission-based explosive devises as well as considerations of neutron leakage and mean free path in relation to the surface to volume ratio. Technically, a weapon is constructed with a critical mass and the detonation of the conventional explosive creates a supercritical mass. You see, nuclear reactors have a critical mass in the reactor core. In that case, a proper moderator and coolant creates a sustained reaction. Chernobyl (and other reactors in former Soviet Bloc nations) are graphite moderated and water cooled. U.S reactors are water moderated and water cooled.

At any rate, the book also give a table of critical mass vs. enrichment. Any high school student who has taken a semester of algebra could calculate critical mass for U-235 from the table. Just for information, at 100% enrichment, 15 kg of U-235 are required. However, weapons grade Uranium is more usually only 10 to 20% enriched. Enrichment to 20% requires 50 kg. An equivalent unreflected Plutonium assembly requires only 16 kg.

As was mentioned, the problem is getting the weapons grade fissile materials. Typical uranium ores have about 0.711% U-235. Use in power reactors requires enrichment to about 3% U-235 and weapons grade to about 10% (I think). The book quotes the costs from the 1984 Federal Register as $108.55/kg for the purified uranium, $1133.10 for 3% enrichment, and $4689.71 for 10%. The cost for 90% enrichment is over $50,000/kg.

Of course, weapons grade plutonium is even more difficult to get. First it requires highly enriched uranium and a breeder reactor. Actually, any fission reaction in the presence of U-238 will produce plutonium. The "spent" fuel from the breeder reactor then has to be refined to extract the plutoniu. Just think how difficult and costly that process must be since the spent fuel is highly radioactive, and plutonium itself is toxic.

Anyway, the physics involved isn't secret and is covered in any nuclear engineering course.

[Logjam]

Thought I'd mention that the fusion device is VERY difficult to make work. The ignition wires have to be cut so that they explode the sections of the explosive triggers that surrounds the nuclear "pile" as exactly the same moment. Since the initial signal comes from one source the wires must be cut exactly so that they detonate at the same time. The signal moves over the wires at about the speed of light. If one signal gets to the triggering charge too early it will just blow the device to bits, it won't "go nuclear".

The "shotgun" bomb is much simplier to make work, but it's also not as efficient as is the fusion bomb.

It's probably impossible to make one of these things in your garage.

When they talk about a terrorists setting off a nuclear device they are usually talking about a "dirty" bomb. This is simply a standard charge that blows nuclear material around. It's a low radiation bomb. It's not a true nuke. They'd also do little damage, but the terrorists want to spread panic. We shouldn't panic if a dirty bomb goes off, as the threat to you is mimimal.

[Pooeypants]

That's very true, even though the media would have you think otherwise. Seems like people are more ready to believe in sensationalists fiction than the real hard facts.

[Starboy]

Quote by: gallo Anyway, the physics involved isn't secret and is covered in any nuclear engineering course.

Or any nuclear physics course.

Starboy

[MerlinsByte]

They'd also do little damage, but the terrorists want to spread panic. We shouldn't panic if a dirty bomb goes off, as the threat to you is mimimal.

merlin writes....Of course the damage would be proportional to what the dirty radioactive material was and what the the conventional charge was, where, and what time it was detonated. The casualties could be massive, but nothing compared to a small fission or fusion device.

mb

[gallo]

Quote by: Starboy Or any nuclear physics course.

Right. Exactly the courses that are taken by nuclear engineering students.

My younger son has a B.S. in math. He and my elder son, a nuclear engineer, compared their math courses once. The only difference was a course in linear algebra that my younger son had taken. My elder son took it in graduate school. Credit wise, my elder son had enough math credits for a major. He also had enough credits to opt for a degree in nuclear physics. Nuclear engineering is a 5 year degree, heavy on math and nuclear physics, as well as some standard mech eng courses. My younger son, not to be out done, earned two bachelors degrees in 5 years.

[Logjam]

Quote by: MerlinsByte merlin writes....Of course the damage would be proportional to what the dirty radioactive material was and what the the conventional charge was, where, and what time it was detonated. The casualties could be massive, but nothing compared to a small fission or fusion device. mb

What kinds of spent nuclear material could be loaded into a dirty bomb that would be easy to handle and also be dangerous to the general public when it was expended into the atmosphere?

Would they use spent nuke fuel rods? Aren't they heavy and hard to cut up? If you dropped a spent fuel rod into the street would it do much damage?

[Logjam]

Quote by: Mr.Vicchio If anyone thinks I am ASKING for Uranium to build a bomb, thats just plain stupid. Some people, need to get a life and not take things literally.

How about just a little bitty baby bomb?