> Strictly speaking it is true that nuclear fission does not involve carbon emissions. However, the entire process of mining and processing uranium, manufacturing the materials needed to build a reactor, supporting a reactor all consume large amounts of fossil fuel.

I can google up nuclear industry papers assuring that the volumes are small compared with the energy output from the plant. But they are of course not independent papers. They give figures like 1.35% lifecycle energy input of the electrical output for the Forsmark nuclear plant in Sweden. Other statements are 1,7% up to 2.9% with poor ores. If all that energy is oil and it is 3% we get one unit of oil energy giving 33 units of electricity.

> As yet we have little information about the fossil fuel required to decommission a reactor.

I have a hard time imagining any reasonable way for a decomissioning to need large ammounts of fossil fuels. Most of the volume of materials are not radioactive and can be recycled. The rest needs concrete etc for the burial. It ought to be significantly less then for building the powerplant.

> An analysis has been done showing that in the case of hard rock ores containing low levels of uranium more energy is consumed in processing the ore and enriching the uranium than is produced in the reactor.

This ought to mean that someone is giving energy (oil) for free to the nuclear fuel industry. If the energy input for making the fuel is as large as the energy output from the fuel it would give an enourmous price increase for the  uranium fuel.  

Was it a calculation for the EROI where the rock isent an ore any more?

> Obviously not all reactors are run this way but the point is that it is wrong to assert that nuclear reactors produce zero carbon emissions.

It is wrong for simpler reasons. Much of the mining machines and  all of the transportation infrastructure is run on fossil fuels.  It is worse for some of the nuclear fuel wich for historical reasons use old inefficient gas diffusion plants run by large ammounts of coal generated electricity. I do not know why those plants have not been replaced by gas centrifuges 10 years ago or more.

I'm sorry but your information on the amount of energy required to mine uranium is not correct.  Among other things uranium is found quite often in rather rotten sandstone, which is not that hard to mine relative to most other minerals.  And while it does fall into the definition of hard rock (not being coal) it is actually in most cases almost as weak, or weaker than coal.