Quote by Nucengable
Of course I know that physically impossible , let us assume that happen , well we agreed that nonleakage probability will increase , but I'm not sure why the resonance escape probability will go down because mainly it depends on the neutrons' energies inside the core and that won't change even so the change will be small leaving the biggest effect for the nonleakage probability !! but there is an issue that the geometrical buckling will increase of course won't that decrease the nonleakage probability !!? but still its now several times as thick in meanfree paths! so Neutron pop grows exponentially in time. I'm not totally sure about this.

If the fuel is twice as dense, fission neutrons will have more interactions in the fuel before getting out to the moderator. More interactions in the fast region means more resonance absorption.
The greater surfacevolume ratio would increase leakage, however the doubled material density would decrease the mean free path. I'm not sure which effect would dominate or if they would cancel out.