Not in tpt, energy (heat) release is based on pressure. https://powdertoy.co.uk/Wiki/W/Elements:Radioactive.html#Uranium
Actually, the URAN in tpt is modelled off an isotope of uranium that isn't really fissile; most likely URAN is based off of U-238. In other words, it doesn't undergo nuclear fission when you shoot neutrons at it. I had suggested an element called U235, which would have represented the isotope that comes to mind when most people think of uranium: the one that goes BEWM. Unfortunatley, my suggestion thread got buried under a flood of new topics and was never seen again.