Energy density: one ton of Thorium produces one GW for one year

In response to a query from David MacKay (author of “Sustainable Energy — Without the Hot Air”), Charles Barton has assembled authoritative evidence of the energy conversion ratio. The result is the same order of magnitude whether the primary fuel is thorium or uranium. Here is one fragment of the analysis — via email from Argonne Distinguished Fellow Yoon I. Chang:

Dear Charles,

I am not sure if there is an on-line document, but it is a simple, straightforward calculation.

Fissioning of 1 gram produces 1 MWD energy. (This is derived from 1 gm equals Avogadro number 6×10**23 divided by 235 atoms, 1 atom fissioning produces 210 MeV energy. 1 MeV is equivalent to 1.6×10**-13 watt-sec. If you convert in proper units, you reach 1 gm = 1 MWD.)

1,000 MWe plant is equivalent to 2700 MWth if you assume 37% net thermal efficiency.
2700 MWth x 365 days/yr x 1 gm/MWD = 0.9855 tonnes ~ 1T.
Since the reactor does not operate 100%, the net fissioning will be somewhat less than 1 T/GWe-yr.
LWRs have a lower thermal efficiency (~33%), so their consumption will be somewhat grearter.

But as a rounded number, I tend to use 1 T/GWe-yr, regardless of reactor types, actual capacity factors, etc.

In the LWR, the uranium resource utilization is far less than 1%. (About 85-90% discarded in enrichment tails, of the 10-15% loaded in the reactor only 3-5% is fissioned, and therefore >99% is discarded as waste.)

In fast reactors, all uranium, including depleted uranium and used uranium and actinides in spent fuel can be fissioned through continuous recycling. In theory, more than a factor of 100 improvement in uranium resource utilization. In practice, some will be lost as processing wastes and a factor of 60 or 70 is assigned taking this into consideration. The LWR figure is more like 0.6-0.8% (higher number with recycle). Therefore, a factor of 100 is more representative ratio even if very conservative loss factors are assumed.

I hope this helps.


Dr. Chang was General Manager of the IFR for ten years, until the program was killed by Bill Clinton. Historians should award “the most stupid decision of the 20th century” to Bill Clinton for this one.