We just know that there\’s going to some patns wetting over this release of radioactive water from Fukushima.
Plant operator Tokyo Electric Power Co. released a total of 10,393 tons of radioactive water April 4 to 10, according to the report published Friday evening local time by Japan\’s Nuclear and Industrial Safety Agency, made up of 1,323 tons of groundwater and 9,070 tons of seawater.
The agency said the analysis showed that the water was only lightly contaminated. Most of the radiation was believed to have come from a series of hydrogen explosions that hit the plant in the first week, which was then brought down in subsequent rainfall, it said.
The government estimated the total amount of radiation contained in the released water at 150 billion becquerels—exceeding the legal limits by about 100 times—depending on the sample taken, according to Hiroki Ishigaki, an official with the agency. The data showed that iodine-131, which has a short half-life of eight days, was the most commonly found isotope, with the longer-lived cesium-134 and cesium-137 at lower but still elevated levels.
Gosh, that is a lot. But, umm, how much lots is it?
Let\’s leave aside the \”which isotopes is it?\” thing because we don\’t actually know the split. Let\’s just point out that the majority of the radiation is disappearing of its own accord, 50% vanishing every 8 days.
Let\’s instead look at the really important thing: concentration. There\’s always radiation everywhere (yes, even inside a lead lined box, as one of the isotopes of lead itself is mildly radioactive) and the important thing is \”how much?\”.
One way of looking at this is how many becquerels per volume….which is fortunate, for that\’s the numbers they\’ve given us.
150 billion becquerels in fact in 10,000 (ish) tonnes of water.
So, what\’s a level we know we don\’t have to worry about very much? Fotrunately, we\’ve just had that here in the UK:
Radon is measured in Becquerels per cubic metre of air. The average radon level in homes across the UK is 20 Bq per cubic metre.
The HPA recommends that householders should contact their local authority if they experience radon levels with a reading over 200Bq per cubic metre.
Note that that\’s not a \”get out of Dodge, Quick!\” level, that\’s the \”make an appointment for the man from the council to come round\” sort of level. So it\’s a reasonable enough one to use for where we might start to get concerned about the concentration. We\’ll leave aside that the UK one is the concentration in your basement, the Japanese one the ocean.
So, one thing we know about water is that it mixes with water really quite well. We also know that seas and oceans have currents and tides and storms and things, these do mix things all up together quite nicely. So, how much water do we need to get our 10,000 tonnes down to the safe for a basement in the UK level of concentration?
Well, I make it that by the time the radioactive water is 100 km of the coast (assuming a 100metre depth) then the concentration is less than what would get a bloke from the council around to look at your cellar.
So, umm, I\’d say that 150 billion becquerels isn\’t actually lots of lots, it\’s only a little lots.
That\’s if I\’ve managed to get my zeros all in the right place, something not certain.