# Ease of chain reaction for enriched uranium

• decafdave
In summary, the conversation discusses the concept of critical mass and its relation to nuclear reactions. It is mentioned that a supercritical sphere can be created by dropping two halves of U-235 onto each other and that this would initiate a chain reaction. The efficiency of the explosion is also discussed, with the comparison between a fission bomb and a nuclear reactor. The conversation also delves into the properties of uranium and its use in nuclear weapons.

#### decafdave

Critical mass is over 50kg so let's say I have 2 halves of a sphere of the isotope U-235, each weighing 30 kg. I drop one onto the other so that they form a supercritical sphere. No doubt a chain reaction would begin, but I assume it would produce energy on the level of a nuclear reactor rather than a fission bomb? Is it a matter of force when they collide? Just how soft is uranium?

My question stems from learning about the "gun type" fission bombs developed during WWII.
My guess is that uranium is a soft metal, and not much force is required to meld the two pieces together although I may be wrong.

The experiment you are describing is that of a bomb. A reactor is much more complicated. In a bomb the fission rate grows exponentially. In a reactor, it is necessary to keep it a constant level, using moderators, etc.

So it's likely that is enough force to initiate the chain reaction? Any guess to the explosion's efficiency since there is no tamper? I know Little Boy didn't even achieve 2% but still yielded 14KT.

It's a good thing it's so difficult to isolate U-235!

It's not force that initiated the chain reaction, only having enough U235 together.

decafdave said:
Critical mass is over 50kg so let's say I have 2 halves of a sphere of the isotope U-235, each weighing 30 kg. I drop one onto the other so that they form a supercritical sphere. No doubt a chain reaction would begin, but I assume it would produce energy on the level of a nuclear reactor rather than a fission bomb? Is it a matter of force when they collide? Just how soft is uranium?

My question stems from learning about the "gun type" fission bombs developed during WWII.
My guess is that uranium is a soft metal, and not much force is required to meld the two pieces together although I may be wrong.
Uranium is a hard metal and it undergoes dynamic strain hardening, which is one reason that it is used for armour piercing shells.

A critical mass of U-235 would get hot rather quickly, to the melting point. Gun type systems have a much larger mass than needed for supercriticality in order to increase yield before dispersion. Implosion devices use the compression of an explosion to increase the density of fissile material rapidly with an consequent increase in yield before dispersion.

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## 1. What is enriched uranium?

Enriched uranium is a type of uranium that has a higher percentage of the isotope uranium-235 than natural uranium. This isotope is important because it is the only one that can sustain a nuclear chain reaction, making enriched uranium a valuable material for use in nuclear power plants and weapons.

## 2. How is enriched uranium produced?

Enriched uranium is produced through a process called uranium enrichment, which involves separating the desired isotope (uranium-235) from natural uranium. This can be done through different methods, such as gaseous diffusion, gas centrifugation, or laser enrichment.

## 3. Why is enriched uranium important for nuclear reactions?

Enriched uranium is important for nuclear reactions because it contains a higher concentration of uranium-235, which is the only isotope capable of sustaining a nuclear chain reaction. In order for a chain reaction to occur, the concentration of uranium-235 needs to be at least 3-5% in the fuel material.

## 4. What factors affect the ease of chain reaction for enriched uranium?

There are several factors that can affect the ease of chain reaction for enriched uranium, including the level of enrichment, the size and shape of the fuel material, and the presence of neutron moderators (such as water or graphite) that help slow down the neutrons and increase the likelihood of a chain reaction.

## 5. Is enriched uranium dangerous?

Enriched uranium can be dangerous if not handled properly. It is a radioactive material that can emit harmful radiation, and it also has the potential to be used in nuclear weapons. However, when used in controlled environments such as nuclear power plants, enriched uranium can provide a safe and reliable source of energy.