The lie:
Nuclear fuel is so dense and we need to move on to the next level of density in the energy ladder because being dense is great.
Just pick up a yellow rock and you get 80,620,000,000,000J like magic. Come be dense with me. Renewables aren't dense.
Background
-- There are some very high yield mines in Canada where you can find 20% ore. If you burnt the yellow rock in a breeder reactor it would do this.
-- The only active large scale breeder reactor is the BN-800. It is configured to destroy plutonium, not create it.
-- Most ore is not like this. Consider Inkai mine in Kazakhstan and Rossing in Namibia. They have Ore that is 0.04% and 0.03% concentrated.
-- In Rossing, to get 1kg of Uranium (0.7% U235), 3 tonnes of ore is dug up, crushed, washed in several tonnes of water, soaked in about 50kg of sulfuric acid and further processed. In Inkai they just pour 100kg of Sulfuric acid down a hole into the ground (don't worry about heavy metal leaching, guys).
-- Then 86-90% of that Uranium is discarded to bring the concentration of U235 up to 3.5%-5%. Then that is put into a nuclear reactor to get hot until that 3.5% of U235 is mostly gone. Some neutrons will hit some U238 on the way and turn it into Pu239 which produces a little extra energy.
-- Reprocessing doesn't create any new fissile material. It is purely to retrieve the left over traces of Pu and U235 which adds another 15%.
This produces 62GWd/MtU in a state of the art reactor. Don't worry about the weird units, it's about 5.3PJ/t or 5.3TJ/kg(already down to about 7% of the initial figure).
But this has to go through a steam engine so you only get 1.7TJ/kg.
But wait, you threw away 860g, so it's 230GJ/kg.
But wait, you had to dig up 3t of ore. This was your fuel, so it's 77MJ/kg.
A substantial increase in PWR production would require moving on to 0.01% ore which is about 23MJ/kg. Roughly on par with gas.
Come be dense and build a PWR. SMRs are even less efficient so we can do that too!
For reference:
Black coal is about 36MJ/kg or 12MJ/kg of electricity after burning.
A 400W bifacial solar panel weighs about 5 to 25kg, is almost entirely (high grade) sand and produces around 100GJ in its life. Depending on design it has 1-2kg of silicon in it (also sand, slightly higher grade). You can recycle it afterwards if you wish and make a slightly worse solar panel at a very small profit (and then again after that, making basically the same panel).