Any figures produced for B12 need to be carefully sourced because, as stated, there is disagreement and claims being made by qualified individuals that measurements from older date is flawed. Here's a page that contradicts totally the 'accepted wisdom': http://www.vibrancyuk.com/B12.html

I don't know enough about the radiation figures involved to compare fukushima to any other event, I just know that given a choice of eating radioactive things or not - I will choose not!