AJ, first off you are correct with your numbers...this level of radiation is basically background. If you painted yourself with a kg of this, and danced around for 6 months, you would equal your normal background exposure.
Hmm. Let's see here. First, let's assume that the mean activity of the whole 1500 tons is 10% of the peak, so we have the most radioactive part at 90kbq/kg, and the mean at 9kbq/kg. That gives us 13.5 GBq of activity (0.3 curies) total. Given that this sludge probably has a density of about 2g/cc (dirt basically), it's 750 cubic meters of sludge, or an activity of (rounding) 18 MBq/m3
Now, to run the numbers. Assuming it's Cs-137, the dose rate at a meter is 0.0087 mrem/hr/MBq.
A sphere, 1m thick, encasing a person, would contain roughly 72 MBq, yielding 0.6mrem per hour. That means, to reach the maximum yearly occupational dose, you would have to live in the sludge-ball for a year. In other words, unless you ate it (it is probably nasty, yet still wouldn't hurt you, radiologically speaking), you might as well just live on it.
BTW, the potassium in a human being has about 5kBq, (75Bq/kg) so this sludge is roughly 120 times as radioactive as a newborn baby on a pound for pound basis.
(I'm going to use 300 Bq as a "baby-equivalent-activity" unit from now on)
Or, if you like it this way, the 50 million residents of Japan contain 250 GBq of potassium, or nearly 19 times as much as this sludge. So, really, if you want to dispose of it, just give a lucky 5% of the population a souvenir "fukushima sludge keepsake" with 300g of the mud, and done.
So if having 3oz of this around is the equivalent of carrying triplets to term (radiologically), and the PEOPLE that live in the area are more radioactive than the sludge...why do we care?
