What the F--- is happening in Fukushima? (3)

Source:  What the F--- is happening in Fukushima? (3)    Tag:  natural sources of gamma rays

This blog is an attempt to provide explanation of radiation sources, levels and health risks associated with Fukushima.


Much of the media has continued with sensational and unhelpful reporting of “facts” without useful interpretation, and opinion that is not supported by facts. For example TV New Zealand News showed a picture of the sea off Fukushima on around the 24th of March as a leading news item with a huge caption emblazoned across the image which read: “Iodine 131 levels 127 times normal”.


TV News and NZ Herald also ran news stories about contamined spinach and milk from farms in the vicinity of Fukushima, and also about contaminated water supplies, again without useful contextual explanation which would give viewers a perspective whether those incidents represented a significant health risk.


I re-iterate, I vigorously oppose nuclear power for a variety of reasons. However, I strongly object to the hysterical tone of much of New Zealand’s reporting of events that are unfolding in Japan because of the earthquake on Fukushima.


So, this blog look at four topics:



  • what are the sources of radiation at Fukushima;

  • how does radiation get into the environment?

  • how does radiation reach people?

  • what are the levels of radiation that present health risks?

(For this blog I have drawn on my previous blogs and knowledge, plus World Nuclear News Regulation & Safety, Washington’s Blog, Badger Lake Observer Blog.)


Sources of radiation at Fukushima


The nuclear fuel in the reactors is uranium oxide (containing Uranium 235). Uranium oxide is a ceramic with a very high melting point of about 3000 °C. The fuel is manufactured in pellets (think little cylinders the size of Lego bricks). Those pieces are then put into a long tube made of Zircaloy with a melting point of 2200 °C, and sealed tight. The assembly is called a fuel rod. These fuel rods are then put together to form larger packages, and a number of these packages are then put into the reactor. All these packages together are referred to as “the core”. (See Fukushima 2 Blog for pictures of fuel rods.)


The Zircaloy casing is the first containment. It separates the radioactive fuel from the rest of the world.


The core is then placed in the “pressure vessel”. This is like a pressure cooker. The pressure vessel is the second containment. This is one sturdy piece of a pot, designed to safely contain the core for temperatures up to several hundred °C. It is where superheated hot water is pumped, gets heated by the nuclear reaction that happens in there, and is forced out through pipes to turn the turbines and make electricity.


The entire “hardware” of the nuclear reactor – the pressure vessel and all pipes, pumps, coolant (water) reserves, are then encased in the third containment. The third containment is a hermetically (air tight) sealed, very thick bubble of the strongest steel. The third containment is designed, built and tested for one single purpose: To contain, indefinitely, a complete core meltdown.


This third containment is then surrounded by the reactor building itself. The reactor building is that square outer shell you see in the news photos that is supposed to keep the weather out. (This is the part that was damaged in the explosions that happened soon after the tsunami).


So, looking at sources of radiation. The first “type” of radioactive material is the Uranium in the fuel rods, plus the intermediate radioactive elements that the Uranium splits into, also inside the fuel rod, during the nuclear reaction. These elements are mainly Caesium and Iodine.


Once formed Iodine 131 very quickly breaks down into natural Iodine. The time it takes to do this is termed “half-life”. For Iodine 131 it is 8 days. That means if you make a gram of Iodine 131, then 8 days later you only have ½ a gram of Iodine 131, and ½ a gram of natural Iodine. And so on. Iodine 131 decays very quickly. What this means is that Iodine is very radioactive (because it decays fast), but it also means it reverts to its natural form very quickly. Caesium 137 has a half life of about 30 years. This means it is much less radioactive, but it stays around for much longer.


This nuclear reaction is the heart of the science of a nuclear reactor. It is called fission. Uranium atoms split into smaller atoms, giving off heat energy, radiation and neutrons. These neutrons hit other Uranium atoms that are nearby, causing them to split, release energy, and so on. A chain reaction occurs. Just like Hiroshima and Nagasaki bombs, but in a nuclear reactor the speed of the reaction is controlled so it doesn’t turn into a nuclear bomb. But it does need to be carefully controlled, and cooled.


There is a second type of radioactive material created, outside the fuel rods. Those radioactive elements are Nitrogen-16, which is a radioactive isotope (or version) of natural Nitrogen. The others are gases such as Xenon. But where do they come from? When the uranium splits inside the fuel rod, it generates a neutron (see above). Most of these neutrons will hit other Uranium atoms and keep the nuclear chain reaction going. But some will leave the fuel rod and hit the water molecules (that are circulating as steam carrying the heat away), or the air that is dissolved in the water. Then, a non-radioactive element can “capture” the neutron. And it becomes radioactive. These radioactive materials have a very short half-life, that means that they decay very fast and split into non-radioactive materials. By fast I mean seconds. So if these radioactive materials are released into the environment, radioactivity is released, but within seconds these materials will be harmless, because they will have split into non radioactive elements.


It appears that Reactor 3 at Fukushima is powered differntly from the others. Instead of Uranium it uses Plutonium. Like Uranium, this is a very heavy metal. I understand from media reports that traces of Plutonium have been detected in soils on the site of the Power plant.


How does radiation get into the environment?


Straight after the earthquake the Fukushima power plant operators needed to manage each reactor core while it was heating up, and ensure that the first containment (the Zircaloy tubes that contains the nuclear fuel), as well as the second containment (our pressure cooker) remained intact and operational for as long as possible, to give the engineers time to fix the cooling systems.


Because cooling the core is such a big deal, the reactor has a number of cooling systems, each in multiple versions (the reactor water cleanup system, the decay heat removal, the reactor core isolating cooling, the standby liquid cooling system, and the emergency core cooling system). Clearly one or all of these failed for a time.


So imagine our pressure cooker on the stove, heat on low, but on. The operators use whatever cooling system capacity they have to get rid of as much heat as possible, but the pressure starts building up. The priority now is to maintain integrity of the first containment (keep temperature of the fuel rods below 2200°C), as well as the second containment, the pressure cooker. In order to maintain integrity of the pressure cooker (the second containment), the pressure has to be released from time to time. Because the ability to do that in an emergency is so important, the reactor has several pressure release valves. The operators now started venting steam from time to time to control the pressure. The temperature at this stage was probably about 550°C.


This is when the reports about “radiation leakage” starting coming in. The explanation above suggests that venting the steam is theoretically the same as releasing radiation into the environment. Because some radioactive substances were expelled with the steam. But radioactive Nitrogen aloms as well as atoms of gases like Xenon that could be expelled with the vented steam very quickly lose their radioactivity and revert to being ‘natural’ atoms.


So the pressure was brought under control, as steam was vented. But, if you keep boiling your pot, the problem is that the water level will keep falling and falling. The core is covered by several meters of water in order to allow for some time to pass (hours, days) before it gets exposed. Once the rods start to be exposed at the top, the exposed parts could reach the critical temperature of 2200 °C - after about 45 minutes it appears. This is when the first containment, the Zircaloy tube, would fail because it would melt.


And this started to happen it seems. The cooling could not be restored before there was some damage to the casing of some of the fuel rods. The nuclear material itself (the fuel pellets) were still intact, but the surrounding Zircaloy shell started melting on some fuel rods.


What seems to have happened then is that some of the byproducts of the uranium decay – radioactive Caesium and Iodine – started to mix with the steam (because some Zircaloy casings had melted). The uranium was still under control, because the Uranium oxide rods were good until 3000 °C. But reports confirm that small amounts of radioactive Caesium and Iodine were measured in the steam that was released into the atmosphere.


So. Some radiation was released when pressure vessels were vented. All radioactive isotopes from the activated steam will have disappeared (decayed) quickly, but would have been measured escaping.


Small amounts of radioactive Caesium must have been released, as well as Iodine. Some of this went into the air carried by steam.


Some of radioactive Caesium and Iodine isotopes were carried out to the sea when sea water was used for cooling. I understand no Uranium will have been released because the Uranium oxide does not “dissolve” in the water.


Because the control rods that slow/speed the nuclear reaction were fully inserted into the cores automatically when the earthquake occurred, the Uranium chain reaction was stopped. That means the “main” nuclear reaction is not happening, thus no new Iodine 131 or Caesium 137 is being produced. However there is a considerable amount of this material in the “spent” fuel rods that have been stored at Fukushima for years. It is unlikely that these would get hot enough to melt the zircaloy containment and release Caesium/Iodine, but if they were washed out of their cooling tanks (by water dumped from helicopters for example), some may have been broken.


It is unclear how Plutonium got into soil, but this power station has been there for 40 years, so it would be unsurprising to find traces of radioactive materials in the soils around the plant. Fuel rods need to be moved around etc...


How does radiation reach people?


It is obvious from the above how Iodine 131 would get into seawater off Fukushima. What is important to note however that Iodine 131 does not occur in nature. So, when TVNZ reported that there was “127 x normal levels in the seawater”, this information, by itself, is not helpful. This is because you would not expect to find ANY Iodine 131 in seawater normally.


One factor in the rise in detections of radioactivity in Tokyo may be recent rainfall, which would have brought airborne radiation by-products to ground and washed them into reservoirs. These would be small amounts of Iodine 131 and Caesium 137. It is unclear yet what amounts have escaped in this way. Iodine 131 is most dangerous near an accident (eg Chernobyl, because people were evacuated after large amounts of Iodine 131 had escaped), but decays quickly over time. Caesium 137 lasts much longer.


There is an exclusion zone around the Fukushima power plant for people, but the land is currently heavily used for agriculture – for growing vegetables and milk produced from dairy farming. A range of vegetables are now controlled in Japan due to the possibility of elevated levels of iodine-131. "At the moment these vegetables are not harmful to people's health," said chief cabinet secretary Yukio Edano. However, the current situation could continue for a time, he said, and that was the reasoning behind a warning not to distribute or consume some goods from Fukushima prefecture. Again, it is important to note that Iodine 131 decays very rapidly.


Prime minister Naoto Kan has asked the governor of Fukushima prefecture to restrict distribution and consumption of any leafy vegetables (e.g. spinach, cabbage) or any flowerhead brassicas (e.g. broccoli, cauliflower) for the time being. In Ibaraki prefecture the governor has been asked to restrict distribution of milk and parsley.


Edano said that if someone were to eat the vegetables for ten days then they would be exposed to about half of one year's background radiation. This was no risk to future health, he said….


Regarding Plutonium - this is highly unlikely to have moved from the oil at the site. This is because Plutonium is extremely dense and relatively inert.


This brings us to…..


What Radiation Levels present health risks?


This is a very contentious subject because it can come down to luck (statistical probability) whether a particular cancer may have been triggered by a very low level of radiation in the wrong part of the body at the wrong time. Some will say there is no safe level of radiation, and that any increase in radiation – however small – brings with it an increased risk of adverse health effects.


The US EPA provides this information about health effects, which you see vary depending on the intensity of the dose a person receives:

Short-term, high-level exposure is referred to as 'acute' exposure. Unlike cancer, health effects from 'acute' exposure to radiation usually appear quickly. Acute health effects include burns and radiation sickness. Radiation sickness is also called 'radiation poisoning.' It can cause premature aging or even death. If the dose is fatal, death usually occurs within two months. The symptoms of radiation sickness include: nausea, weakness, hair loss, skin burns or diminished organ function. (Medical patients receiving radiation treatments often experience acute effects, because they are receiving relatively high "bursts" of radiation during treatment.)

Different health effects are associated with long-term, low-level (chronic) exposure to radiation. Increased levels of exposure make these health effects more likely to occur, but do not influence the type or severity of the effect.... Cancer is considered by most people the primary health effect from radiation exposure. Simply put, cancer is the uncontrolled growth of cells. Ordinarily, natural processes control the rate at which cells grow and replace themselves. They also control the body's processes for repairing or replacing damaged tissue. Damage occurring at the cellular or molecular level, can disrupt the control processes, permitting the uncontrolled growth of cells--cancer. This is why ionizing radiation's ability to break chemical bonds in atoms and molecules makes it such a potent carcinogen.

All people receive “background radiation”. This is from a variety of sources: gamma rays from the sun; radiation from naturally occuring radioactive minerals in the ground; radiation from TV and computer screens; X-rays. The major proportion is from natural sources.


On average this amounts to 3.5 millisieverts / year.


So what the hell is a Sievert? There are different measures of radiation, because there are different types of radiation and different effects from each type. The Sievert measure is used commonly in newspapers and news reports because it is an agreed measure of the human health effects of the mixture of radiation types from a nuclear reactor accident like Fukushima.


According to Wikipaedia, the single dose of radiation that would lead to the death of 50% of people is 5000 millisieverts, or 5 Sieverts. That’s a single dose. Received in a short time. Like a minute. Would lead to the deaths of about 50% of people exposed to such a dose.


So this is why radiation health effects are tricky to compare and to measure and to predict.


It is not just the intensity of the radiation that causes health problems, it is the length of time that you are exposed to the radiation. That is why you read of the workers at Fukushima being exposed – apparently safely - to radiation leaks for 30 minutes. And then another team takes over.



Safe Level for Adult: 50 Millisieverts The current federal occupational limit of exposure per year for an adult (the limit for a worker using radiation) is "as low as reasonably achievable; however, not to exceed 50 millisieverts" above the 3+ millisieverts of natural sources of radiation and any medical radiation. Radiation workers wear badges made of photographic film which indicate the exposure to radiation. Readings typically are taken monthly. A federal advisory committee recommends that the lifetime exposure be limited to a person's age multiplied by 10 millisieverts (example: for a 65-year-old person, 650 millisieverts).


Safe level for Minor: 5 Millisieverts The maximum permissible exposure for a person under 18 working with radiation is one-tenth the adult limit or not to exceed 5 millisieverts per year above the 3+ millisieverts of natural sources, plus medical radiation. This was established in 1957 and reviewed as recently as 1990.


There have been reports about the workers at Fukushima: “The International Atomic Energy Agency said that 17 personnel have now received radiation doses of over 100 millisieverts. This level remains below an international standard of 500 millisieverts for emergencies, as well as a temporary limit of 250 millisieverts allowed by authorities in the current situation….” (Not sure how to reconcile these numbers with what the Feds were saying in their 1990n review above...)


You can see that if those 17 workers had received 100 millisieverts over a two week period – say – then that would be almost 30 times what they would have received in a year due to background radiation. On the other hand a dose of 100 millisieverts over a two week period would be about a millionth of a fatal dose.


Last few days: Tokyo Electric Power Company has been criticised over exposure to workers operating in ankle-deep water … it is thought that contractors ignored alarms from their dosimeters, while ankle-deep in contaminated water for about three hours. They received doses of 170-180 millisieverts and seem to have suffered shallow burns to their skin from beta radiation….


These workers received almost 200 millisieverts in just three hours. That’s about one three-thousandth of a fatal dose. According to the US Federal guidelines above, it is equivalent to 1/3 of a lifetime’s maximum “safe” dose. These guys should be given a permanent rest from any further work where there are elevated radiation levels.


“Parents in Tokyo have been recommended to avoid giving tap water to infants under one year of age, although no health effect would be expected. Restrictions on food have also been expanded….”


An infant could receive a radiation dose of about 10 microsieverts (that’s 1 hundredth of a millisievert) from drinking one litre of the tap water, meaning an infant would have to drink a litre per day for a year to receive a dose of between 1 and 10 millisieverts in that year from water (noting that “background” radiation is 3.5 millsieverts a year). It appears that the main worry in Japan at the moment is the spread of Iodine 131 in various places. The levels are low – and remember that the half-life is just 8 days - and the risk is reduced through ingestion of small amounts of natural Iodine.


However the spread of Caesium 137 is more of a concern because it lasts much longer in the environment, and can contaminate milk and generally enter the food chain and affect people through what they eat.


When radiation is released with gas, as it was at the Japanese reactors, the particles are carried by prevailing winds, and some will settle on the earth. Rain will knock more of the suspended particles to the ground. “There is an extremely complex interaction between the type of radionuclide and the weather and the type of vegetation,” Dr. Whicker said. “There can be hot spots far away from an accident, and places in between that are fine.”


Initially, some plants will collect more radiation than others: those with big leaves like lettuce, spinach and other greens will naturally collect more radiation than apples, oranges or potatoes, he said. Foods like rice and corn whose edible portion is protected by husks or leaves are relatively safe in this early stage.


Almost 15 years after the Chernobyl accident in what is now Ukraine, studies found that cesium 137 was still detectable in wild boar in Croatia and reindeer in Norway, with the levels high enough in some areas to pose a potential danger to people who consume a great deal of the meat.


Plutonium presents an extremely low health risk away from Fukushima because of its density, and low reactivity, meaning it is unlikely to leave the site. It would need to be absorbed by a person to cause health damage.


It is essential that authorities monitor food and water sources across Japan, checking and reporting Caesium 137 levels in particular. It is also essential that further releases into the air of steam from Fukushima (containing Caesium 137) are prevented. What is happening now is not good because radioactive materials that are dangerous to health are escaping into the environment. These has the potential to at the very least increase the level of background radiation across a very wide area - but this should not present a significant health risk. At worst there may be hot spots which - if not monitored and neutralised - could lead to increased cancers in the population affected.

This blog is an attempt to provide explanation of radiation sources, levels and health risks associated with Fukushima.


Much of the media has continued with sensational and unhelpful reporting of “facts” without useful interpretation, and opinion that is not supported by facts. For example TV New Zealand News showed a picture of the sea off Fukushima on around the 24th of March as a leading news item with a huge caption emblazoned across the image which read: “Iodine 131 levels 127 times normal”.


TV News and NZ Herald also ran news stories about contamined spinach and milk from farms in the vicinity of Fukushima, and also about contaminated water supplies, again without useful contextual explanation which would give viewers a perspective whether those incidents represented a significant health risk.


I re-iterate, I vigorously oppose nuclear power for a variety of reasons. However, I strongly object to the hysterical tone of much of New Zealand’s reporting of events that are unfolding in Japan because of the earthquake on Fukushima.


So, this blog look at four topics:



  • what are the sources of radiation at Fukushima;

  • how does radiation get into the environment?

  • how does radiation reach people?

  • what are the levels of radiation that present health risks?

(For this blog I have drawn on my previous blogs and knowledge, plus World Nuclear News Regulation & Safety, Washington’s Blog, Badger Lake Observer Blog.)


Sources of radiation at Fukushima


The nuclear fuel in the reactors is uranium oxide (containing Uranium 235). Uranium oxide is a ceramic with a very high melting point of about 3000 °C. The fuel is manufactured in pellets (think little cylinders the size of Lego bricks). Those pieces are then put into a long tube made of Zircaloy with a melting point of 2200 °C, and sealed tight. The assembly is called a fuel rod. These fuel rods are then put together to form larger packages, and a number of these packages are then put into the reactor. All these packages together are referred to as “the core”. (See Fukushima 2 Blog for pictures of fuel rods.)


The Zircaloy casing is the first containment. It separates the radioactive fuel from the rest of the world.


The core is then placed in the “pressure vessel”. This is like a pressure cooker. The pressure vessel is the second containment. This is one sturdy piece of a pot, designed to safely contain the core for temperatures up to several hundred °C. It is where superheated hot water is pumped, gets heated by the nuclear reaction that happens in there, and is forced out through pipes to turn the turbines and make electricity.


The entire “hardware” of the nuclear reactor – the pressure vessel and all pipes, pumps, coolant (water) reserves, are then encased in the third containment. The third containment is a hermetically (air tight) sealed, very thick bubble of the strongest steel. The third containment is designed, built and tested for one single purpose: To contain, indefinitely, a complete core meltdown.


This third containment is then surrounded by the reactor building itself. The reactor building is that square outer shell you see in the news photos that is supposed to keep the weather out. (This is the part that was damaged in the explosions that happened soon after the tsunami).


So, looking at sources of radiation. The first “type” of radioactive material is the Uranium in the fuel rods, plus the intermediate radioactive elements that the Uranium splits into, also inside the fuel rod, during the nuclear reaction. These elements are mainly Caesium and Iodine.


Once formed Iodine 131 very quickly breaks down into natural Iodine. The time it takes to do this is termed “half-life”. For Iodine 131 it is 8 days. That means if you make a gram of Iodine 131, then 8 days later you only have ½ a gram of Iodine 131, and ½ a gram of natural Iodine. And so on. Iodine 131 decays very quickly. What this means is that Iodine is very radioactive (because it decays fast), but it also means it reverts to its natural form very quickly. Caesium 137 has a half life of about 30 years. This means it is much less radioactive, but it stays around for much longer.


This nuclear reaction is the heart of the science of a nuclear reactor. It is called fission. Uranium atoms split into smaller atoms, giving off heat energy, radiation and neutrons. These neutrons hit other Uranium atoms that are nearby, causing them to split, release energy, and so on. A chain reaction occurs. Just like Hiroshima and Nagasaki bombs, but in a nuclear reactor the speed of the reaction is controlled so it doesn’t turn into a nuclear bomb. But it does need to be carefully controlled, and cooled.


There is a second type of radioactive material created, outside the fuel rods. Those radioactive elements are Nitrogen-16, which is a radioactive isotope (or version) of natural Nitrogen. The others are gases such as Xenon. But where do they come from? When the uranium splits inside the fuel rod, it generates a neutron (see above). Most of these neutrons will hit other Uranium atoms and keep the nuclear chain reaction going. But some will leave the fuel rod and hit the water molecules (that are circulating as steam carrying the heat away), or the air that is dissolved in the water. Then, a non-radioactive element can “capture” the neutron. And it becomes radioactive. These radioactive materials have a very short half-life, that means that they decay very fast and split into non-radioactive materials. By fast I mean seconds. So if these radioactive materials are released into the environment, radioactivity is released, but within seconds these materials will be harmless, because they will have split into non radioactive elements.


It appears that Reactor 3 at Fukushima is powered differntly from the others. Instead of Uranium it uses Plutonium. Like Uranium, this is a very heavy metal. I understand from media reports that traces of Plutonium have been detected in soils on the site of the Power plant.


How does radiation get into the environment?


Straight after the earthquake the Fukushima power plant operators needed to manage each reactor core while it was heating up, and ensure that the first containment (the Zircaloy tubes that contains the nuclear fuel), as well as the second containment (our pressure cooker) remained intact and operational for as long as possible, to give the engineers time to fix the cooling systems.


Because cooling the core is such a big deal, the reactor has a number of cooling systems, each in multiple versions (the reactor water cleanup system, the decay heat removal, the reactor core isolating cooling, the standby liquid cooling system, and the emergency core cooling system). Clearly one or all of these failed for a time.


So imagine our pressure cooker on the stove, heat on low, but on. The operators use whatever cooling system capacity they have to get rid of as much heat as possible, but the pressure starts building up. The priority now is to maintain integrity of the first containment (keep temperature of the fuel rods below 2200°C), as well as the second containment, the pressure cooker. In order to maintain integrity of the pressure cooker (the second containment), the pressure has to be released from time to time. Because the ability to do that in an emergency is so important, the reactor has several pressure release valves. The operators now started venting steam from time to time to control the pressure. The temperature at this stage was probably about 550°C.


This is when the reports about “radiation leakage” starting coming in. The explanation above suggests that venting the steam is theoretically the same as releasing radiation into the environment. Because some radioactive substances were expelled with the steam. But radioactive Nitrogen aloms as well as atoms of gases like Xenon that could be expelled with the vented steam very quickly lose their radioactivity and revert to being ‘natural’ atoms.


So the pressure was brought under control, as steam was vented. But, if you keep boiling your pot, the problem is that the water level will keep falling and falling. The core is covered by several meters of water in order to allow for some time to pass (hours, days) before it gets exposed. Once the rods start to be exposed at the top, the exposed parts could reach the critical temperature of 2200 °C - after about 45 minutes it appears. This is when the first containment, the Zircaloy tube, would fail because it would melt.


And this started to happen it seems. The cooling could not be restored before there was some damage to the casing of some of the fuel rods. The nuclear material itself (the fuel pellets) were still intact, but the surrounding Zircaloy shell started melting on some fuel rods.


What seems to have happened then is that some of the byproducts of the uranium decay – radioactive Caesium and Iodine – started to mix with the steam (because some Zircaloy casings had melted). The uranium was still under control, because the Uranium oxide rods were good until 3000 °C. But reports confirm that small amounts of radioactive Caesium and Iodine were measured in the steam that was released into the atmosphere.


So. Some radiation was released when pressure vessels were vented. All radioactive isotopes from the activated steam will have disappeared (decayed) quickly, but would have been measured escaping.


Small amounts of radioactive Caesium must have been released, as well as Iodine. Some of this went into the air carried by steam.


Some of radioactive Caesium and Iodine isotopes were carried out to the sea when sea water was used for cooling. I understand no Uranium will have been released because the Uranium oxide does not “dissolve” in the water.


Because the control rods that slow/speed the nuclear reaction were fully inserted into the cores automatically when the earthquake occurred, the Uranium chain reaction was stopped. That means the “main” nuclear reaction is not happening, thus no new Iodine 131 or Caesium 137 is being produced. However there is a considerable amount of this material in the “spent” fuel rods that have been stored at Fukushima for years. It is unlikely that these would get hot enough to melt the zircaloy containment and release Caesium/Iodine, but if they were washed out of their cooling tanks (by water dumped from helicopters for example), some may have been broken.


It is unclear how Plutonium got into soil, but this power station has been there for 40 years, so it would be unsurprising to find traces of radioactive materials in the soils around the plant. Fuel rods need to be moved around etc...


How does radiation reach people?


It is obvious from the above how Iodine 131 would get into seawater off Fukushima. What is important to note however that Iodine 131 does not occur in nature. So, when TVNZ reported that there was “127 x normal levels in the seawater”, this information, by itself, is not helpful. This is because you would not expect to find ANY Iodine 131 in seawater normally.


One factor in the rise in detections of radioactivity in Tokyo may be recent rainfall, which would have brought airborne radiation by-products to ground and washed them into reservoirs. These would be small amounts of Iodine 131 and Caesium 137. It is unclear yet what amounts have escaped in this way. Iodine 131 is most dangerous near an accident (eg Chernobyl, because people were evacuated after large amounts of Iodine 131 had escaped), but decays quickly over time. Caesium 137 lasts much longer.


There is an exclusion zone around the Fukushima power plant for people, but the land is currently heavily used for agriculture – for growing vegetables and milk produced from dairy farming. A range of vegetables are now controlled in Japan due to the possibility of elevated levels of iodine-131. "At the moment these vegetables are not harmful to people's health," said chief cabinet secretary Yukio Edano. However, the current situation could continue for a time, he said, and that was the reasoning behind a warning not to distribute or consume some goods from Fukushima prefecture. Again, it is important to note that Iodine 131 decays very rapidly.


Prime minister Naoto Kan has asked the governor of Fukushima prefecture to restrict distribution and consumption of any leafy vegetables (e.g. spinach, cabbage) or any flowerhead brassicas (e.g. broccoli, cauliflower) for the time being. In Ibaraki prefecture the governor has been asked to restrict distribution of milk and parsley.


Edano said that if someone were to eat the vegetables for ten days then they would be exposed to about half of one year's background radiation. This was no risk to future health, he said….


Regarding Plutonium - this is highly unlikely to have moved from the oil at the site. This is because Plutonium is extremely dense and relatively inert.


This brings us to…..


What Radiation Levels present health risks?


This is a very contentious subject because it can come down to luck (statistical probability) whether a particular cancer may have been triggered by a very low level of radiation in the wrong part of the body at the wrong time. Some will say there is no safe level of radiation, and that any increase in radiation – however small – brings with it an increased risk of adverse health effects.


The US EPA provides this information about health effects, which you see vary depending on the intensity of the dose a person receives:

Short-term, high-level exposure is referred to as 'acute' exposure. Unlike cancer, health effects from 'acute' exposure to radiation usually appear quickly. Acute health effects include burns and radiation sickness. Radiation sickness is also called 'radiation poisoning.' It can cause premature aging or even death. If the dose is fatal, death usually occurs within two months. The symptoms of radiation sickness include: nausea, weakness, hair loss, skin burns or diminished organ function. (Medical patients receiving radiation treatments often experience acute effects, because they are receiving relatively high "bursts" of radiation during treatment.)

Different health effects are associated with long-term, low-level (chronic) exposure to radiation. Increased levels of exposure make these health effects more likely to occur, but do not influence the type or severity of the effect.... Cancer is considered by most people the primary health effect from radiation exposure. Simply put, cancer is the uncontrolled growth of cells. Ordinarily, natural processes control the rate at which cells grow and replace themselves. They also control the body's processes for repairing or replacing damaged tissue. Damage occurring at the cellular or molecular level, can disrupt the control processes, permitting the uncontrolled growth of cells--cancer. This is why ionizing radiation's ability to break chemical bonds in atoms and molecules makes it such a potent carcinogen.

All people receive “background radiation”. This is from a variety of sources: gamma rays from the sun; radiation from naturally occuring radioactive minerals in the ground; radiation from TV and computer screens; X-rays. The major proportion is from natural sources.


On average this amounts to 3.5 millisieverts / year.


So what the hell is a Sievert? There are different measures of radiation, because there are different types of radiation and different effects from each type. The Sievert measure is used commonly in newspapers and news reports because it is an agreed measure of the human health effects of the mixture of radiation types from a nuclear reactor accident like Fukushima.


According to Wikipaedia, the single dose of radiation that would lead to the death of 50% of people is 5000 millisieverts, or 5 Sieverts. That’s a single dose. Received in a short time. Like a minute. Would lead to the deaths of about 50% of people exposed to such a dose.


So this is why radiation health effects are tricky to compare and to measure and to predict.


It is not just the intensity of the radiation that causes health problems, it is the length of time that you are exposed to the radiation. That is why you read of the workers at Fukushima being exposed – apparently safely - to radiation leaks for 30 minutes. And then another team takes over.



Safe Level for Adult: 50 Millisieverts The current federal occupational limit of exposure per year for an adult (the limit for a worker using radiation) is "as low as reasonably achievable; however, not to exceed 50 millisieverts" above the 3+ millisieverts of natural sources of radiation and any medical radiation. Radiation workers wear badges made of photographic film which indicate the exposure to radiation. Readings typically are taken monthly. A federal advisory committee recommends that the lifetime exposure be limited to a person's age multiplied by 10 millisieverts (example: for a 65-year-old person, 650 millisieverts).


Safe level for Minor: 5 Millisieverts The maximum permissible exposure for a person under 18 working with radiation is one-tenth the adult limit or not to exceed 5 millisieverts per year above the 3+ millisieverts of natural sources, plus medical radiation. This was established in 1957 and reviewed as recently as 1990.


There have been reports about the workers at Fukushima: “The International Atomic Energy Agency said that 17 personnel have now received radiation doses of over 100 millisieverts. This level remains below an international standard of 500 millisieverts for emergencies, as well as a temporary limit of 250 millisieverts allowed by authorities in the current situation….” (Not sure how to reconcile these numbers with what the Feds were saying in their 1990n review above...)


You can see that if those 17 workers had received 100 millisieverts over a two week period – say – then that would be almost 30 times what they would have received in a year due to background radiation. On the other hand a dose of 100 millisieverts over a two week period would be about a millionth of a fatal dose.


Last few days: Tokyo Electric Power Company has been criticised over exposure to workers operating in ankle-deep water … it is thought that contractors ignored alarms from their dosimeters, while ankle-deep in contaminated water for about three hours. They received doses of 170-180 millisieverts and seem to have suffered shallow burns to their skin from beta radiation….


These workers received almost 200 millisieverts in just three hours. That’s about one three-thousandth of a fatal dose. According to the US Federal guidelines above, it is equivalent to 1/3 of a lifetime’s maximum “safe” dose. These guys should be given a permanent rest from any further work where there are elevated radiation levels.


“Parents in Tokyo have been recommended to avoid giving tap water to infants under one year of age, although no health effect would be expected. Restrictions on food have also been expanded….”


An infant could receive a radiation dose of about 10 microsieverts (that’s 1 hundredth of a millisievert) from drinking one litre of the tap water, meaning an infant would have to drink a litre per day for a year to receive a dose of between 1 and 10 millisieverts in that year from water (noting that “background” radiation is 3.5 millsieverts a year). It appears that the main worry in Japan at the moment is the spread of Iodine 131 in various places. The levels are low – and remember that the half-life is just 8 days - and the risk is reduced through ingestion of small amounts of natural Iodine.


However the spread of Caesium 137 is more of a concern because it lasts much longer in the environment, and can contaminate milk and generally enter the food chain and affect people through what they eat.


When radiation is released with gas, as it was at the Japanese reactors, the particles are carried by prevailing winds, and some will settle on the earth. Rain will knock more of the suspended particles to the ground. “There is an extremely complex interaction between the type of radionuclide and the weather and the type of vegetation,” Dr. Whicker said. “There can be hot spots far away from an accident, and places in between that are fine.”


Initially, some plants will collect more radiation than others: those with big leaves like lettuce, spinach and other greens will naturally collect more radiation than apples, oranges or potatoes, he said. Foods like rice and corn whose edible portion is protected by husks or leaves are relatively safe in this early stage.


Almost 15 years after the Chernobyl accident in what is now Ukraine, studies found that cesium 137 was still detectable in wild boar in Croatia and reindeer in Norway, with the levels high enough in some areas to pose a potential danger to people who consume a great deal of the meat.


Plutonium presents an extremely low health risk away from Fukushima because of its density, and low reactivity, meaning it is unlikely to leave the site. It would need to be absorbed by a person to cause health damage.


It is essential that authorities monitor food and water sources across Japan, checking and reporting Caesium 137 levels in particular. It is also essential that further releases into the air of steam from Fukushima (containing Caesium 137) are prevented. What is happening now is not good because radioactive materials that are dangerous to health are escaping into the environment. These has the potential to at the very least increase the level of background radiation across a very wide area - but this should not present a significant health risk. At worst there may be hot spots which - if not monitored and neutralised - could lead to increased cancers in the population affected.