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.
Radon is rather like blue and brown asbestos – the effect is much, much worse on smokers. Since I don’t smoke, and since I’ve been desensitising myself by scoffing bananas and brazil nuts, I’m keeping calm and carrying on.
Well 150 billion Bq in 10,000 tonnes of water is 15 million Bq per cubic metre, so if you want it down to 150 Bq per cu.m. then it needs to be diluted 100,000 times. So we need a 1 billion cu.m. body of water for the 10,000 tonnes. So that’s conveniently 1 cubic kilometre, which if the water depth is 100 metres covers 10 sq km. If the water is spreading in a half circle (let’s say the coast is absolutely straight) then if the radius of the half circle is 2.5 km, you have your 10 sq.km.
In other words, once the contaminated water has spread 2.5 km (that’s about a mile and a half) from the point of origin, it’s down to Cornwall basement standard. (But I’m not sure if Bqs in water and in air are directly comparable.)
So your zeroes are a bit out…
You need to dilute the water a mere 75-fold (you are currently at 15kBq/m3).
So you need 750kT of water – or 750,000m3.
How big is that? Well, it is a cube a mere 90m in length. Or 300 Olympic swimming pools. Big, ish, but the proverbial drop in the ocean.
Your 100km*100m*(lets assume 100km at the far end so) 50km wedge contains 500 billion cubic metres.
I think you calculated on the basis of 150 gBq/m3 rather than total?
Ignore my previous – you need 750MT of water. Which is a basically a 900m cube.
Or if you take a wedge section of a sphere and have the depth at the far end 100m, the radius of the sphere would need to be 1120m. If you then assume a triangular dispersion, with about 90 degree angle, you get out to about 2km.
I’m just wondering, is the “Olympic Sized Swimming Pool” the volumetric equivalent of the “Football Field” in the Systeme Internationale De Popular Units?
Notice the “depending on the readings taken” bit? Did they not think to ask EXACTLY what this meant?
Ian,
Only for things that can’t be rationally expressed in multiples of the land area of Wales.
Or, in this case, I suppose, the sea area of whales.
Actually the method of release will be a great determining factor. The contaminated water is likely at a different salinity & temperature from the ocean so if dumped in in one go might retain its integrity for some time, only slowly dispersing at the edges. With release over time & better, intermittently even currents of a couple of miles an hour would mean that the volume being dumped into would be several times the calculated one & dispersal more complete.
Swimming pools? Football pitches? Could you convert that into multiples of the size of a London double decker bus, please….?
Isn’t Belgium also frequently on this distinctly non-SI scale? Whereby 1 Wales = 0.6807 Belgium.
150 GBq is 4 curies. Bearing in mind that the radiation release from Chernobyl was of the order of tens of millions of curies, this is trivial (remember, a curie is roughly the specific activity of a gram of radium.)
@David Gillies – I’ll wait till the keystone kops sorting this out have finally finished ( is the estmate still 6 months or more?) before taking stock of Fukishima. It’s simply I’m just not that trusting of the calls of it’s all ok you’re over reacting especially after that was the line that was tried when it first happened …