[eloff]

This estimate doesn't seem to account for enrichment. For every KG of uranium mined, you get a much lower ratio of enriched fuel.

[rwcarlsen]

It shouldn't account for enrichment because thorium is a fertile material (not fissile) just like uranium 238 (99.3% of all uranium). Unenrichced uranium can be used in breeder type reactors just like unenriched thorium.