Homework Solution

TQ 14-7

In a conventional reactor, uranium is enriched to 2-3% ²³⁵U. Such low enrichments work with thermalized neutrons who cross section for fission is high.

In a fission weapon, the enrichment must be greater than 90% to allow the use of fast neutrons whose cross section for fission is low.

For a conventional reactor to act as a fission nuclear weapon:

• Somehow the enrichment of the fuel would have to increase to greater than 90%.

• Somehow all other materials in the core of the reactor would have to be expelled (moderator, coolant, cladding, control rods).

• Somehow the ²³⁵U would have to be held together for a short period of time to prevent disassembly by melting.

None of these processes are possible. A conventional nuclear reactor cannot explode like a fission nuclear weapon. Chemical explosions are possible, but not nuclear explosions.