Palomares and the H-bombs

Dear Reader,

Now some doomsayers may have tried to tell you that once radioactivity appears in soil that you should give up all hope, also on the otherhand some false prophets of insincere reassurance will just tell you to stop worrying and that “everything will be OK”. My advice is not to trust either of these two false friends.

The story of the air crash which involved four H-bombs has popped up again, the BBC report that the local people in Spain are fifty years after the air crash unhappy about what has been done.

The BBC report suggests that the local farmers have a problem getting a good price for their produce at market. I would like to point something out.

The plutonium in the H-bombs would have been in the form of the metal, during the accident this would have been burnt into plutonium dioxide. Now the thing to note about plutonium dioxide is that it is very hard to dissolve in acid, also it is not mobile in soil. Any plutonium which was in a water soluble form is likely to have bonded to the soil minerals thus making it impossible for plants to absorb it via their roots.

M.I. Sheppard and D.H. Thibault, Health Physics, 1990, 59, 471 to 482 gives the binding constants for most metals to the four common soil types. It lists for plutonium the following Kd values.

Sand, 150 L/kg

Loam, 1200 L/kg

Clay, 5100 L/kg

Organic, 1900 L/kg

This means in a bucket containing a mixture of clay type soil and water that the plutonium content of the soil (Bq per kilo) will be 5100 times higher than the plutonium content of the water (Bq per litre).

Hence when 1000 Bq of plutonium is added to a litre of water mixed with a kilo of clay type soil, then the soil will absorb 999.8 Bq of plutonium while 0.2 Bq of plutonium will stay in the water. This calculation is for a static batchwise experiment but it will help experts in the field make predictions about the mobility of plutonium solutions in soil.

Another good bit of news is the fact any plutonium dioxide in the dust will not be well absorbed if it is swallowed (dust on the surface of the food), so orally the plutonium dioxide is not a great threat to life and limb. If you were to swallow a well sintered particle of plutonium dioxide it will pass unchanged through your digestive system.

However plutonium dioxide in the lungs is very dangerous to a persons health, I think that a key thing to do in Spain is to keep the plutonium in the most contaminated soils from entering the air as a dust. I think that the ban on building, farming or walking in the contaminated area is a good idea. But I think that it might be a good idea to pour concrete or asphalt onto the worst hot spots to try to fix the soil to keep it from becoming mobile again.

One of the problems with plutonium is that the colloidal particles of clay can make the plutonium mobile, while the plutonium does not move freely through the soil in aqueous solution the colloidal particles can move through the cracks in the soil. Thus sealing the soil would help to stop the plutonium from reaching the surface again in the form of dust.

Clay again

Dear Reader,

Again we are turning out attention to clay, clay is a wonderful substance on which we play tennis on, make pots from and create art with. Clay is also important when cesium gets into our soil. I recently wrote a little on the subject of the clay minerals in the soils in Japan. Here is a useful set of lecture notes on silicate minerals, most clays seem to be silicates.

I have recently read that the soil from Japan holds tightly onto cesium, when soil which was contaminated by the Fukushima event was soaked in 1 M ammonium chloride solution (at 25 oC) only about 20 % of the cesium radioactivity was liberated from the soil. Then when this soil was treated with 1 M acetic acid only about 10 % more of the cesium was liberated from the soil.

It was also found that treatment with 1 milimole per litre sulphuric acid only was able to liberate less than 1 % of the radioactivity while 1 mole per litre sulphuric acid was able to liberate about half the cesium.

These findings suggest it will be hard to wash the cesium out of the soil, but if the soil is washed with ammonium chloride then the remaining cesium will be hard to transfer to plants. I suspect that as time goes on that the amount of cesium which can be transferred to the plants will become less and less as the cesium becomes more and more fixed to the minerals in the soil.

Update on your new best friend

Dear Reader,

Slightly more than one year ago I wrote about the new best friend of the Japanese people. Rather than a person who will go out and go for a karaoke session with you, drink beer with you or go for a walk in the park with you this new friend is one who can clean up your drinking water and keep your fruit and veg safe. Also this friend can help keep the milk healthy. Now you might ask what sort of super nice person can do all these things, or what sort of imp or kappa is able to do all these things.

The identity of this new friend is a bit more humble sounding, it is the clay in the soil. I have seen a recent paper by Naofumi Kozai, Toshihiko Ohnuki, Makoto Arisaka, Masayuki Watanabe, Fuminori Sakamoto, Shinya Yamasaki and Mingyu Jiang (Journal of Nuclear Science and Technology, 2012, 49(5), pages 473 to 478) in which the cesium behaviour in the soil is reported.

In this paper the soil was examined with X-ray diffraction. This found smectite, mica, hornblende, kaolinite, quartz, orthoclose, cistobalite, feldspar, stishovite, gibbsite, sodalite, olivine and sorosilicate minerals in the soils.

The smectite clay is rather similar to the illite clay which I showed a picture of recently. The two clays are related, I have seen a thesis which explains how the smectite clay transforms into illite clay. For your information the thesis is here. The difference between these two layered clays is in the anionic bread layers between the potassium jam. The smectite and the illite have slightly different layers.

A smectite clay, the oxygens are in orange red, the potassium ions in blue, the aluminium/silicon atoms are in sea green. Note that layers of potassium ions which look like slices of bread.

I think that both the smectite and illite are formed from mica, so I would say that the more mica in the rocks which formed the soil the better when you are considering cesium in soil. The mica is very similar to the two clays, again it is a layered solid.

Many of us know mica, it is a mineral which can be made into thin sheets. We will soon see why it is possible to split mica into thin sheets. It is easy to separate the mica by peeling apart the layers.

Here is a view of a mica (Muscovite) which was studied some time ago. (O.V. Sidorenko, B.B. Zvyagin and S.V. Soboleva, Kristallografiya, 1975, 20, 543-549). Should should see again that the solid is layered, the potassiums (blue) have anionic layers of alumo-magnesium silicate between them. I have shown all the non oxygen atoms in the layers as green.

Mica showing the layers of potassium ions between the anionic layers

The important thing about the mica is that the aluminium atoms are randomly mixed with magnesium and silicon atoms in the two layers. The authors of the paper I am working from expressed the view that one of the types of layers (the middle layer in the trilayer anionic layer) has 20 % magnesium and 80 % aluminium. While the two outer layers of the anionic trilayer have 28.4 % aluminium and 71.6 % silicon. The mica also contains some hydroxyl anions which I have been unable to locate in that solid. I have made a new drawing of the mica which shows the mixed aluminium/silicon and aluminium/magnesium layers in different colours to show you how the solid fits together.

Diagram of mica. The potassium ions are in blue. The mixed aluminium/magnesium sites are in grey. The mixed aluminium/silicon sites are in green. The oxygens are in a rather fetching shade of orange.

It is important to note that the green aluminium/silicon sites have a tetrahedral arrangement of oxygen atoms around the central atoms while the grey mixed magnesium/aluminium sites have a distorted octahedral arrangement of oxygens around the central atoms.

The hornblende clay is a very different mineral, I have looked at the crystal structure and it looks in some ways like a SBA-15 or MCM-41 to me. It has tube like holes which pass in one direction through the clay. These tubes are then filled with sodium and potassium cations. As the clay is so different, I suspect that it may behave differently to the layered clays which I showed you.

The mica based minerals can change the spacing between the anionic layers to suit a new cation which has a larger diameter than the potassium. In this way the larger cesium ions can be held in the solid. But in the case of the hornblende, I do not think it will be so easy to add a larger cation. I think that the holes will get plugged up and blocked by the larger cations.

Here is a view of several unit cells of the hornblende clay, the solid is a little disordered. It has a mixture of sodium (yellow) and potassium (blue) cations in the solid. Also note that it has grey calcium ions in the alumosilicate layers. The aluminiums are purple, the silicons are sea green and the iron atoms in the clay are orange. The oxygen is in a rather fetching orange/red as before.

A view of hornblende clay showing the holes in which the potassium/sodium ions go.

I will try and give you an update soon on the clay and the cesium.

More on the subject of clay and cesium

Dear Reader,

It has come to my attention that only a small fraction of the debris created by the tidal wave in Japan has been disposed of. A report from Japan indicates that only 6 % of the waste has been disposed of, part of the problem it that due to concerns that the debris is radioactive the disposal actions (land filling and incineration) has not been done.

I hold the view that the national government in Japan needs to devise a safe, environmentally acceptable and cheap plan for dealing with the waste. Then it should impose the solution using national law, my worry is that if consent needs to be obtained from each municipality then it is likely that nothing will ever happen. If the Japanese do nothing then after 300 years the waste will be almost totally non radioactive (regardless of the radioactivity in it today) but I do not think that they can wait 300 years for the problem to go away on its own.

I think that the debris should be sorted according to its radioactivity, the debris below 400 Bq per kilo should be treated as non radioactive waste. I hold the view that if the waste is slightly over 400 Bq per kilo but bulk of the additional radioactivity is due to short lived radioisotopes then the waste should be either be allowed to stand for some time before being burnt in a normal incineration plant or it should be land filled.

I think that the contaminated top soil from schools, residential areas and commercial areas (shopping areas) is an important thing to deal with. While in the ideal world it would be best if this decontamination waste was either made to vanish into thin air by a magic genie but in the world we are stuck with someone needs to do something with the soil. While a good quality hazardous waste landfill would be the best place to put contaminated soil, I think that for low level beta active decontamination waste it is better to put it in an ordinary landfill rather than leaving this waste at the site it was dug up from.

If the waste is a lot more than 400 Bq per kilo then it needs to be managed as radioactive waste. One option is to land fill it. The land fill must be equipped with a barrier layer to prevent the radioactivity leaking out of the landfill. If it is cesium then one of the best barrier layers is clay. The cesium will bind to clay, I have found in the literature a crystal structure of a cesium exchanged clay. (D. Gournis, A. Lappas, M. A. Karakassides, D. Többens and A. Moukarika, Phys. Chem. Minerals, 2008, 35, 49-58).

The clay is a layered solid, it has an set of anionic layers of aluminium, oxygen and silicon. These layers are like slices of bread, and the cationic cesium ions go between the slices of “bread” to form layers. I think that the strong binding of clay to cesium will slow the movement of cesium in the barrier layer so that the cesium will decay by the time it escapes from the landfill.

Here is a picture of the clay with the cesium in it. Aluminium is green, oxygen is orange, silicon is purple and the cesium is blue.

 

The clay with cesium cations in it.

 

If the waste is very radioactive then it may be best to put it into drums, add some cement to make the waste into a hard block (less dust and no chance of a liquid spill). The steel drum will then improve the safety of the transport of the waste to the landfill and it will give some decades of additional containment. If the waste is only cesium-137 then assuming that we choose the right drum then it could last for several half lives. A carbon steel is normally passive if it is in contact with cement so we will not get much corrosion on the inside of the drums. If the outside of the drums are painted or better still galvenised then the drums will be very long lasting.

Now whatever the extreme greens say what you need to do is to isolate the waste from humans for a finite time, they hard part is making a choice of how low the threat has to be at the time when you lose the ability to contain the waste. Once the experts work out how much much activity the dump can release per day without breaching the limit then we can work out a design for the land fill.

For example if our release limit is 1 kBq per day and we know that the dump will release 1 % of its contents per year after the barrier has failed. Then if the dump starts with 1 GBq of activity then we can work out how long the dump must contain the waste.

1 kBq per day works out as 365.25 kBq per year.

So if the dump must not start to leak until the total activity is 36525 KBq (or 36.525 MBq).

So the waste must decay by a factor of 27.379 before it starts to leak.

As A = Ao exp -λt

We can work of how long t has to be, if the half life is 1 year, then λ will be 0.693 year^-1

exp -λt must be equal to 0.03652 at the time when leaking can start.

So we start with

exp -λt = 0.03652

-λt = ln (0.03652)

-t = ln (0.03652) / λ

t = ln (0.03652) / -λ = -3.3098 / (-1 x 0.693 year ^-1)

t = -3.3098 / – 0.693 year ^-1 = 4.77 years

So if we can build a waste store which will not leak for five years then we can be sure that not release too much radioactivity per day. I choose a half life of one year to make the maths easy but the same ideas can be used with real waste dumps.

Cesium maps for Japanese farmland

Dear Reader,

The Japanese government have issued maps of cesium contamination on farmland in the areas near to the Fukushima reactor accident. The main map of that area of Japan is here. Based on a google translate examination of the text with the map the soil has been taken from paddy fields at up to 15 cm depth while for upland soils it is the top 30 cm of soil. If any of my readers can read Japanese then I would be very grateful if they could give me a translation of the text from the Japanese Agriculture, Forestry and Fisheries Research Information Technology Center.

The bad news is that the cesium level in some areas is high, but the good news is that there are things which normal farmers can do which will lower the transfer of cesium to the food crops. I think that farms are going to need to learn a few new skills to allow them to farm in a safe and healthy way using their contaminated land.

Peachs, cesium, fruit and fukuashima

Dear Reader,

I have read with interest the blog of a lady called Dr Susan Burton who teaches English at a Japanese University. She is quite reasonable to be concerned about the levels of radioactivity in her diet. In her blog she questioned the wisdom of selling fruit from the Fukuashima area in the supermarket, right now I can not say if they are safe or not to eat. This question is one which can be better answered by the radiation protection authority in Japan.

Susan lamented that the cesium has a half life which is greater than a decade, she was worried that the cesium would spoil her enjoyment of Japan for a very long time. This comment about cesium and peaches prompted me to check the literature on radioactivity and fruit.

Back in 2001 a person in Italy published a review paper on the transfer of radioactivity from soil to fruit (F. Carini, Journal of Environmental Radioactivity, 2001, volume 52, pages 237 to 279). I went through this review and I found some data for peach trees.

One of the most important things to know about farming in a radioactive area is the transfer factor. The transfer factor is a measure of how easy it is for radioactivity to get from the soil into the part of the plant which you eat. It is defined as the ratio of the radioactivity (Bq kg^-1) of the food to the radioactivity level of the soil (Bq kg^-1). It is important to bear in mind that the transfer factor depends on the species of the plant, the soil type and the element.

Element	Soil type	Transfer factor
Cs	Not recorded	0.0131
Cs	Sandy loam	0.009
Sr	Not recorded	0.0218
Sr	Sandy loam	0.07
Pu	Not recorded	0.000163
Am	Not recorded	0.000436
I	Not recorded	0.0109
Ru	Not recorded	0.00109
Ce	Not recorded	0.000436
Cm	Not recorded	0.000436

As the main radioisotopes released by the accident were noble gases, iodines and cesiums it should be clear from the table above that in future years the humble peach tree will have a filtering effect. While most people do not like eating mud, if you were to eat mud then you would get a greater intake of cesium than if you ate the same mass of fruit from a tree grown on the radioactive soil.

I predict that in future years that the radioactivity level in the fruit will be dictated by the absorption of radioactivity by the roots of the tree and the transport of the radioisotopes through the tree into the fruit. But this year due to the direct deposition of radioactivity onto the leaves of the plant we need to consider a different route.

Sadly I could not find any results for peach trees but for bean plants I could find some results. In an experiment a leaf of a bean plant was soaked in a solution of a radioisotope to simulate radioactive rain. Then the plant was grown further before the radioactivity levels in different parts of it was measured. It was found that most of the radioactivity absorbed remained in the leaves.

Only 13 % of the cesium, 0.06 % of the strontium, 0.2 % of the americium and 0.002 % of the plutonium was found in the bean pods.(P. Henner, C. Colle and M. Morello, Journal of Environmental Radioactivity, 2005, volume 83, pages 213 to 229) This suggests that while cesium might be mobile inside plants the other elements are not very mobile inside the plants. While this effect may protect the consumer from plutonium, strontium and americium (which have not been released from Fukuashima in large amounts) due to the fact that the cesium is mobile it is possible that fruit grown this year on trees may be contaminated by cesium which was absorbed directly into leaves and then transferred through the plant into the fruit. So this year great care is needed to check the contamination level of the fruit, in future years it is likely that the cesium contamination level in the fruit could be much lower than this years contamination level.

Now one of the wicked lies which some parts of society like to either spread about deliberately, imply or assume is that humans are powerless in the face of the evil radioactive atoms. This idea is clearly wrong in several ways.

1. Atoms and radiation knows no morality, no matter how good or evil you are atoms / radiation will treat you the same way.
2. Humans can take action to alter their exposure to radiation and radioactivity.

For example by changing farming methods the level of cesium in the crop can be lowered. I saw one paper (W.L. Robison, P.H. Brown, E.L. Stone, T.F. Hamilton, C.L. Conrado and S. Kehl, Journal of Environmental Radioactivity, 2009, volume 100, pages 76 to 83) which explained that by using potassium fertiliser on coconut trees which were growing on Bikini island (Where the Americans used to test H-bombs) that the cesium level in the edible parts of the coconuts can be greatly lowered.

My advice to any Japanese farmers who might be reading this blog is to do the following.

1. Find out what sort of soil your farm has.
1. Clay soil tends to bind cesium more than sandy soil
2. Find out from a cesium map how contaminated your farm is likely to be
3. Ask the farmer’s union, TEPCO and the state radiation protection authority for advice on how to lower the contamination level of your crops. I would suggest that you ask about the following
1. Deep ploughing to prevent the transfer of cesium via grass to livestock
2. Prussian blue to decontaminate livestock
3. Potassium fertilizers to prevent plants taking up cesium
4. Changing to a different crop which is less able to take up contamination. Oilseed rape might be a good plant. The oil pressed from the seeds is normally has very little contamination in it even if the rest of the plant is contaminated. Also onions may be a good crop to plant. Below is some data from 1989 in Finland ( A. Paasikallio, A. Rantavaara and J. Sippola, The Science of the Total Environment, 1994, volume 155, pages 109-124) which shows that some crops are better able to avoid taking up cesium from the soil.

Transfer factors for different crops in three different soil types

Radioactivity and coal part II

OK I am back, I might have shocked some of you today when I explained how coal is not just a global warming threat but also a radioactive threat. I looked in the literature to support the fact which I read as a preteen and now plucked from my memory. The first paper which caught my eye was a Turkish paper on coal fly ash.

Some of the coal ash was very radioactive, by UK rules it would be regarded as nuclear waste if it was made at a nuclear site.

For the uninitiated fly ash from burning coal is a wonderful material which can be used to make a “low carbon cement”, the problem with Portland cement is that while it does not emit carbon dioxide when it sets (if anything it absorbs a little) but it requires a lot of fuel to heat up the furnace in which it is made.

Portland cement is made by heating a mixture of clay and limestone in a big slowly turning steel pipe, the fuel use makes Portland cement a rather ungreen building material. A better cement is the geopolymer type which is made from sodium silicate and gently heated kaolin clay. The reduction in the use of fuel at the cement factory makes the geopolymer a more green cement.

The fly ash after it comes out of the coal fired power station is perfectly ready for mixing with Portland cement, thisPortland/ fly ash mixture is perfect for many applications. As no further fuel is needed to process the fly ash by reheating after it comes out of the bag house of the power station makes the fly ask /Portland mixture more green.

One of the disadvantages with this is if the fly ash is contaminated with either toxic heavy metals or radioactivity. If radioactive fly ash cement is used to make houses then it can lead to people being exposed to harmful levels of gamma radiation and/or radon-222. Both the gamma rays (external threat) and the radon (internal threat) can be bad for your health.

Before you get into a panic over radioactive cement it is important to understand that not all fly ash is radioactive, but it is clear to me that we need to take care with the use of fly ash as a building material. I propose that radioactive cements should be used in places where they can contribute only a little to human radiation exposure.

Such places would include

1. Radioactive waste stores
2. Nuclear power plants and other buildings in the radiological industry
3. As a base layer in road building

Also when high radium cements are used some special precautions should be used to protect both workers and the public, paint films and layers of plastic sheet stop the migration of the dangerous radon gas. If a building uses high radium cement in the basement, then a plastic sheet (radon impervious membrane) should be laid over it before a layer of low radium concrete is poured on top. The Swedes had a problem some years ago with a concrete which was radium rich, this is known as “blue concrete”. The blue concrete has the radium in the aggregate rather than the cement but it is still a threat to public health.

But back to cement, it is important to understand the difference in a power generation system between the carbon dioxide emissions from the stack and all the emissions which have occurred during the building and installation of the generator. Next time anyone suggests to you that a wind farm is environmentally friendly and good for the earth’s climate ask them if they have considered all the cement used to make the bases for the wind turbines and all the fuel used to run the furnaces used to make the metal parts.

I do not want to tell you what to think, but I do view it as my duty to inform you about some of the questions you should ask or consider. I would rather that the public did not accept sound bites about how green a technology is, do yourself and the earth a favour! Ask the industry “experts” and NGO experts from Greenpeace/Friends of the Earth/other organisations why they make their claims and try to ‘take the lid off the box and look inside’ by asking questions like…….

“How much fossil fuel is used to make this green electricity generator ?”

“How long will the green electricity generator last ?”

“How much more electric power will we get over the lifetime of the green machine than if we burnt all the fuel used to make it in a furnace and got heat / electric power the simple way ?”

“How much fuel/pollution is needed to recycle this aluminium can (transport and melting) compared with the amount of fuel/pollution needed to dig aluminium ore from the ground and make aluminium can from this ‘primary’ aluminium?”

N.B. The recycling of aluminium is a very green activity; I have been told by a trustworthy source that it saves a lot of fuel and pollution.

Clay your new best friend ?

I recently wrote about Prussian blue and I also explained how soil absorbs caesium and thus protects wells from caesium contamination, I want now to explain some of the important aspects of soil. The clay in the soil is normally the part of the soil which binds strongly to the caesium, one clay mineral is illite.

Illite is a layered clay which has potassium cations as the jam between slices of aluminium silicate layers (the bread) in a sandwich. Rather than a typical closed sandwich, this clay is more like a stack of open sandwiches. You could think of it like a stack of slices of cheese on toast.

What happens then cesium cations encounter the surface of the clay mineral is that they swap with the potassium cations. The metal cations associate becuase of the attractive electrostatic effect of the negatively charged aluminium silicate layers.

Here is a picture of the solid using the data from A.F. Gualtieri (Journal of Applied Crystallography, 2000, volume 33, pages 267-278). You should be able to see the blue potassium which are the jam which are between the sheets of oxygen (red), aluminium (green) and silicon (purple).

Illite

The ball and stick view is a little misleading, while it allows the viewer to look inside the solid it does not show you how the surface will look to an atom or molecule which is bobbing about in the water which is in contact with the soil. So here is a view using a space filling model. Now the atoms are scaled to be about their real sizes, it is now clear that the only potassium which you can get to is at the edges of the solid.

Space filling view of illite

It so happens with clay that the crystals of the minerals are very small, which increases the surface area which is accessible to water. It is noteworthy that clay can absorb some other cationic substances. Paraquat the weed killer binds very tightly to clay, as a result while it kills the plants which are currently growing it does not leave an active residue in the soil. However it does stay in the soil bonded to the clay for a very long time. If paraquat was to be used again and again on some land then one day it might be possible to saturate the soil with this weed killer. I also suspect that if a person was to use muddy water to mix up their paraquat solution for the weed infested garden path then it might not work as well as some of the herbicide will become inactivated through binding to the clay.