Let’s produce a GWye!

(1 GWye = roughly the electricity for one million people, living by western standards, for one year)

Let us suppose it is our mission to produce electricity for a run-of-the-mill city with about 1 million inhabitants living by Western standards. This city will need about thousand megawatts of electricity, year round, in short 1GWye. In the visual, I compare four ways to accomplish this, along with the input and output of each of the options. For those who wonder: yes, I redrew the original scheme of Kirk Sorensen. I copied his info on the Liquid Fluoride Thorium Reactor and conventional nuclear, the Light Water Reactor. I added two options though: coal and the IMSR. Coal is what all nuclear options should be compared to. IMSR is LeBlanc’s Integral Molten Salt Reactor, which I think is Sorensen’s main competition in new nuclear.

Comparison for fuel and waste for production of 1GWeY 20130501

Nuclear estimates for LWR and LFTR from ‘Liquid Fluoride Thorium Reactors An old idea in nuclear power gets reexamined’ by Robert Hargraves and Ralph Moir. Nuclear estimates for IMSR by David LeBlanc Coal – carbon conversion: http://www.eia.gov/coal/production/quarterly/co2_article/co2.html

Let’s start with the lower two, coal and conventional nuclear. These are actually in use. Coal we have used since we started producing electricity. But how much coal will we need to accomplish our mission? That would be about 1,5 km of freight train, all wagons filled to the brim with coal. Oh yeah, that’s just for a single day. So for one year of electricity in our city, we will need 570 km of coal train: 3.3 million tons of coal in total.

Of course, our coal powered plant does not only produce electricity, it also produces 9 million tons of CO2 and 330.000 tons of fly ash. This fly ash, roughly 57 kilometers of freight train full of it, contains all sorts of interesting heavy metals, like arsenic, beryllium, cadmium, mercury and…uranium! 5 (for Australian coal) to 60 (for Chinese coal) tons of it and about three times as much thorium. If we’d have burned German coal, there would be 43 tons of uranium and 130 tons of thorium in the fly ash. Interesting, since Germany has taken half of their nuclear power plants offline, and replaced them by plants using… coal.

How much uranium or we going to need to accomplish our mission if we burn it in a conventional nuclear reactor? In a usual Light Water Reactor (LWR) we will first need to mine uranium ore, enough to make about 250 tons of natural uranium. Out of this we will produce 35 tons of enriched uranium that we can use in our light water reactor. This will leave us with 215 tons of depleted uranium, with which we don’t really know what to do. But the 35 tons of enriched uranium will deliver us our year of electric prosperity. Plus about 35 tons of spent fuel that we may have to store for a long time. Notice however, that the amount of waste is much, much less than that of our coal plant. The amount of waste produced by a large number of conventional nuclear power plants is small enough to be stored in a facility like Yucca mountain. And storing it may well turn out to be a brilliant idea if you consider the next option that we will discuss shortly. But take one more look at the pile of fly ash from our coal plant. Nobody talks about storing the toxic heavy metals that are in that pile. Which is understandable, because these toxins are diluted in the enormous pile of ash. So most of the ash ends up in landfills, heavy metals included.

The third option is the Integral Molten Salt Reactor of David LeBlanc (see IMSR). The distinguishing characteristic of LeBlanc’s reactor is its simplicity. Basically it is a closed vessel containing a mixture of molten salts, including a small proportion of uranium salts. A heat exchanger, also filled with molten salts, transports the heat outside the vessel. Other than in the conventional reactor, that uses only about one per cent of the energy contained in the uranium, the IMSR uses almost all of it. The temperature of this reactor is much higher than in the conventional reactor. This makes it possible to use a different type of generator, with a much higher efficiency. Therefore, to produce the 1000MW for our city, LeBlanc uses only 35 tons of natural uranium, no enrichment needed. LeBlanc expects his reactor to produce about 35 tons of fission products. But no transuranics (or TRU, the nasty stuff that makes geological storage necessary for LWR’s waste), as these will stay in the reactor, where they are burned. After 30 years of operation, LeBlanc expects that he’ll need to remove about one ton of TRU from the fuel and reuse that in the next reactor.

Our fourth option is the Liquid Fluoride Thorium Reactor. This is the option pursued by Kirk Sorensen. It’s a bit more complicated than the IMSR of LeBlanc, but the design is still pretty straightforward. Like the IMSR, it basically consists of a vessel containing a mixture of molten salts at high temperature, about 600 degrees Celcius. A small proportion is uranium salts, enough to sustain a fission reaction. In essence, this vessel reactor was tested in the 1960’s, it worked just fine for more than four years. In Sorensen’s design, the vessel is surrounded by a second one, called a blanket. The blanket is also filled with molten salts. This blanket has not yet been tested, but the principles have been, and besides they are pretty straightforward as well. In the blanket, thorium salt is present. The thorium catches neutrons that come from the core salts, and this, through several steps transform the thorium into uranium (U233). This uranium is purified out of the salt and introduced into the core where it, over time, completely fissions. Through this process, all of the thorium is used and the resulting uranium is completely burned.
As a result, we only need a single ton of thorium to produce our GWeY. Most of the waste produced by this process is not really waste. After a year of storage, the waste is separated. 83% consists of precious stuff like rare earth metals and can be sold at a nice profit. The remaining 17% will need to be stored for about 300-500 years. Or sold to NASA: most of it is the very rare Plutonium 238, the stuff used to generate electricity in space when there’s not enough sun. The stuff is rare and priceless…

Next numbers page: 1 tonne of fissionable metal = 1GWye