And as others have pointed out, if you get a "full meltdown" with the control rods fully inserted, the resulting uranium/boron alloy is not critical.<p>In short hand, once the rods are in, its game over, just a question of how hard the final result is to clean up.<p>If you keep it under the melting point of the core you can just pull the fuel and dispose of it in the normal way, if not you have to clean out the non-critical slag core.