Ease of chain reaction for enriched uranium

  • Thread starter decafdave
  • Start date
  • #1
2
0
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.
 

Answers and Replies

  • #2
mathman
Science Advisor
7,898
461
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.
 
  • #3
2
0
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!
 
  • #4
mathman
Science Advisor
7,898
461
It's not force that initiated the chain reaction, only having enough U235 together.
 
  • #5
Astronuc
Staff Emeritus
Science Advisor
19,022
2,392
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.
 
Last edited:

Related Threads on Ease of chain reaction for enriched uranium

  • Last Post
Replies
8
Views
3K
  • Last Post
Replies
22
Views
2K
  • Last Post
Replies
11
Views
7K
  • Last Post
Replies
9
Views
7K
  • Last Post
Replies
2
Views
2K
Replies
19
Views
50K
Replies
14
Views
19K
  • Last Post
Replies
2
Views
3K
  • Last Post
Replies
3
Views
1K
Top