Or we could sit in top of our coal power plants slurping oil, wait for the magical thorium reactor and/or solar power to become another 10 times more economical.
>> "A once-through one-gigawatt nuclear power station uses 162 tons per year of uranium"
>> "World total (conventional reserves in the ground) 4.7[million tons]"
https://en.wikipedia.org/wiki/World_energy_consumption
>> "The IEA estimates that, in 2013, total world energy consumption was 13,541 Mtoe , or 5.67 × 1020 joules, equal to an average power consumption of 18.0 terawatts.[3]"
One gigawatt nuclear plant uses 162 tons per year.
The world uses 18000 gigawatts per year. (40% oil, 10% coal, 15% natural gas, 35% other).
If all the fossil fuel-based energy were replaced with nuclear power, the nuclear power plants need to provide 18000 gigawatts times 65% = 11700 gigawatts.
11700 gigawatts times 162 tons of uranium is 1.9 million tons of uranium, per year.
The world's conventional reserves of 4.7 million tons will last for three years.
The 22 million tons in Phosphate deposits will last for another 10 years. (if and when methods to mine them economically are discovered)
Perhaps the seawater uranium will come in time, but as yet it is not an economical method of uranium extraction. The cost needs to be reduced by 5 to 10 times.
But we can with nuclear plants, and I'm thinking garden variety fission plants, not the always-30-years-from-now fusion ones. There are various areas where we use fossil fuels only because its more convenient - e.g. ground transportation. We can go electric with most of it. Fertilizers - I'm not sure if petroleum is a necessary chemical component or just energy delivery vector for the production process. Plastics are I think the only area where we can't easily sidestep fossil fuels. But with enough electricity we can still synthesize the compounds we need for those processes.