October 15th, 2014
Recently I have been looking everywhere for information on uranium. There isn’t a lot to find but I found some that seemed reliable.
The Japan Health Physics Society gives the following description on their website:
“There is in average 1-10 g of naturally occurring uranium in 1 t of soil in Japan just like anywhere else in the world. 1 g of uranium being the equivalent of nearly 10.000 Bq, it means that there is about 10.000-100.000 Bq of uranium in 1 t of soil.”
If we follow this, there could be anything between 12.4 and 124 Bq of uranium-238 in 1 kg of soil in the world. And it would be perfectly natural. (Since 1g of uranium-238 has 12,444.8 Bq and Uranium-238 is the most common natural uranium isotope making up 99.284% of them.)
So in that case it isn’t surprising at all to find a total of 33 Bq/kg of uranium-238/235 in the soil in Japan, as they did in the joint soil survey of the Department of Energy and National Nuclear Security Administration (USA) carried out after the nuclear accident in Fukushima. Nor would it be a surprise that 60 Bq/kg of uranium-238 was found in the soil of the Canadian Embassy in Akasaka, Tokyo, reported in the Journal of Radioanalytical and Nuclear Chemistry (treated in ENENEWS on 22/3/2013).
The following two sources also say that there was between 2-29 Bq/kg in the soil of Japan anyway. One of the two is Professor Hiroaki Koide of the Kyoto University Research Reactor Institute who wrote in his dissertation published in 2004 that there was 29 Bq/kg of the uranium series in the soil in his institute.
The second is the Environmental Radiation Database of Nuclear Regulatory Agency who provides readings of uranium in the soil of Yokosuka city. They detected 2-13 Bq/kg on 01/09/2010 and 2-15 Bq/kg on 04/03/2011. So the reading of the joint DOE/NNSA survey for Yokosuka of a similar 13.4 Bq/kg shouldn’t be alarming at all?
Was I making a mistake saying that uranium was released by the accident at Fukushima Daiichi Nuclear Power Plant and was scattered over Eastern Japan? Is the US soil survey revealing nothing new?
I went back to their survey and the uranium readings. What’s new is that I calculated the total and ratios. And two very important things emerged out of this.
The first was the presence of uranium-232. Uranium-232 is an extremely rare nuclide. You don’t just find it in soil somewhere on earth. According to the web dictionary ATOMICA it is only produced as the concentrated uranium fuels are burnt in a light-water reactor. In other words it is a fission product. ATOMICA writes: “Uranium-232 is not a nuclide that can be included among naturally occurring ones. It has a short half-life and by producing highly radioactive daughter nuclides (Tl208 and Bi232) it builds up the dose rate of the reprocessed uranium, nearly tripling in 10 years”. How come that such a fission product is so prominent in the US survey?
The other thing that caught my attention was the ratio of uranium-235 over uranium-238. Japan Chemical Analysis Center describes in a report of uranium contents in soils of sea beds that the ratio of naturally occurring uranium is always found in a constant ratio, which is U235 / U238 = 0.0073 and that this ratio is used to tell whether there is more or less uranium in a sample than naturally. Now in the calculation above this ratio (⑦) is constant but at 0.046, more than tenfold of the natural ratio. This is because there was concentrated uranium-235 of nuclear fuels.
As much as the amount of uranium found in soil samples after the accident might seem natural on its own, the presence of uranium-232 and the ratio of U235 / U238 are nothing but the proof that these nuclides came from within a nuclear reactor or from spent fuels. Highly dangerous uranium was released and scattered, at least in the places where the surveys took place.
Finally, let me introduce you to a comment by an academic that was posted on Masataka Ota’s site. Masataka Ota is a councellor of the city of Yokohama.
“Unfortunately, the DOE/NNSA soil survey tells that uranium-232 fell all over the metropolitan area of Tokyo and contaminated the soil at about 70 Bq/kg. Uranium-232 can be found in a tiny amount in spent fuels. So parts of spent fuel rods came flying over as the reactors exploded. 70 Bq/kg… is the equivalent of over 4000 Bq/m2, which should be rated a radiation controlled area (by legal definition a radiation controlled area starts at 40.000 Bq/m2, however because the danger of alpha nuclides is 10 times more than that of beta and gamma ones, in practice an area is treated as a radiation controlled one starting from 4000 Bq/m2). People should move to the western part of Japan. No human can live in a radiation controlled area.”