Brian Wang and I have been having a good time lately talking to environmentalists on their blogs. On a blog from Australia recently, I took the opportunity to go after the old “nuclear emits as much CO2 as coal” canard. This is one that I seem to see all the time on blogs that have an anti-nuclear bent, and it’s so easy to refute. I took advantage of the fact that there’s an anti-nuclear site that has a very convenient calculator for figuring out the CO2 emissions of the conventional nuclear fuel cycle.

Nuclear Fuel Energy Balance Calculator

You just go in there, tell it you want to see the effect of 1000 MW of electricity produced for a year, and bam, it will tell you how much CO2 was emitted. I didn’t mess with any of the defaults (fuel enrichment, burn-up, CO2 emitted to produce the electricity to enrich the uranium) since I figured they were already set on some pretty pessimistic numbers. And they were, especially since the calculator assumes that all the electricity used to enrich uranium comes from dirty coal plants.

Well, the result was that it takes about 300,000 tonnes of CO2 to produce one gigawatt-year (GWyr) of electricity according to their assumptions.

How does that stack up against alternatives? Well, coal took about 8 million tonnes of CO2 and natural gas about 4 million tonnes of CO2 to do the same thing. So there’s little doubt that, even with these assumptions, that conventional nuclear releases less CO2 than these baseload alternatives.

Which got me wondering, what would a steady-state thorium cycle look like in the same examination?

I have to make some extrapolations and projections to do the calculation, but I assumed that amount of thorium ore required to sustain power production is about 1/300th of what is currently needed for the conventional uranium reactors. This is based on a calculation I did recently that many of you have seen.

First of all, I’ll make the simplifying assumption that it takes about the same amount of parent ore, mining, and milling to get thorium as uranium. The main difference being that I only need about 1/300th the amount of thorium to produce the same amount of electricity.

But the big energy savings comes in the enrichment and fuel fabrication steps. That is where the calculator estimates that the bulk of the energy is consumed. Based on the assumptions that I need no enrichment for the thorium, and that it can be used in the reactor in metallic form, I will assume these number are zero.

(Metallic thorium will be added to the reactor’s blanket during the reductive extraction of protactinium, oxidizing to a fluoride even as protactinium reduces to a metal and is removed.)

Based on all these numbers, I would estimate that the CO2 production from 1000 MW-yr of electricity production would be about 100 tonnes of CO2, assuming that all liquid fuel is diesel and all electricity come from coal. That’s about 1/3000th of the value for the uranium fuel cycle that the program estimates, with most of the improvement coming from the lack of enrichment and fuel fabrication.

Of course, you can save even more energy than this by just going and digging up the 3200 metric tonnes of thorium that the government recently buried in the Nevada desert!