Little boy used about 64 kilograms of 80% enriched uranium.
The Fukushima site holds approximately 1500 TONS of ~4% enriched uranium.
Well, I’m not going to say you’re wrong, since I don’t know. But here is a webpage that discusses it. Says that each reactor has 144 metric tons of uranium oxide:
http://yeswaterisfuel.com/2011/03/24/amount-of-radioactive-material-at-fukushima/
I am not sure how that converts into U235. I suspect your number is the amount of radioactive water on the site. That’s really a different animal because the lighter radioactive elements like iodine, tritium, strontium, etc. have shorter half-lives (8 days, 12.3 years, and 28 years respectively, I believe).
Irrespective, though, there is a big difference between uranium that is located in a reactor and uranium that is spread over the countryside because an a-bomb went off. Apparently even spreading it over the countryside does not make the land uninhabitable for 10,000 years, as demonstrated by Hiroshima, Nagasaki, as well as all of the nuclear tests that have been done over the years.