More info on the strontium contamination found more than 30km from Fukushima Daiichi.

Namie Town and Iitate Village have evidence of strontium 90 contamination, they are 30km (18.6 miles) from the reactors.  Strontium 90 was also found in plant samples from Motomiya City, Ono Town and Otama and Nishigo Villages.  They are between 40 to 80 kilometers (24.8 to 49.7 miles) from Fukushima Daiichi.

The strontium was detected between 16 & 19 March.  One nuclear engineer points out that is immediately after Reactor 3 exploded.   Strontium would only come from fuel rods, and it’s a possible indicator that the reactor itself was damaged.