Quote:
Originally Posted by TLAM Strike
"Weapons Grade" is a misnomer, Any Uranium can be used to build a bomb, it just requires a lot more U-235 to do it. At 20% enrichment it would need about 400 kg of U-235 to achieve critical mass.
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Not completely accurate.
You are correct, however, in stating that increasing the amount of 235U decreases the critical mass. But the critical mass of Uranium is the minimum density/configuration needed to sustain criticality, not achieve and maintain supercriticality.
Any concentration of 235U can achieve criticality depending on many factors (temperature, shape, reflectors), however, to build a "bomb", the material has to achieve a state of supercriticality.
Criticality is achieved when there is no increase or decrease in power, temperature, or neutron production. The number of neutrons produced is equal to the number of neutrons lost.
Supercriticality is achieved when there is an increase in power, temperature, and neutron production. The number of neutrons produced is greater than the number of neutrons lost.
Under achievable environments, it is incorrect to say that any concentration of Uranium can be made to achieve supercriticality.