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Sunday, March 20, 2011

Figuring Fukushima - On radiobiology and nuclear power

This post won't be as flippant as my usual outpourings given I'm not quite up to the Gilbert Gottfried singularity on offending people. Just a little discourse on radiation...

Unless you've been living in a bizarre time warp or have encased your head in concrete / attempted a home lobotomy, you can't have failed to notice that Japan is in the middle of a humanitarian crisis after a magnitude 8.9 earthquake and the resultant tsunami. The sheer scale of the damage done is unreal, and the human displacement staggering. Sadly, the death toll continues to rise. In the midst of all this chaos, the spectre of a nuclear accident has almost overshadowed the frankly immense natural disaster. A few people have asked me to explain the biological impact of Fukushima and radiation in general - I'll try to avoid a technical digression onto the design and just stick to the medical physics, given that's my limited sphere of knowledge. So here is the idiot's guide to radiation. I have included a few on my own humble thoughts on nuclear power at the end and links to how you can donate to Japan at the end of the post.

What exactly is radiation ?
Radiation refers to any energetic particle or waves which travel through a medium / space. Generally 'radiation' refers to what is called ionizing radiation - particles or waves with enough energy to knock electrons out of atoms / molecules. Ionizing forms include X-ray, Gamma rays, and Alpha articles. Radiation can also refer to non-ionizing forms of radiation, like radio waves, microwaves and visible light. The concept that visible light is a form of radiation strikes some people as strange given the often times negative associations of the word radiation but it is utterly true to say. Radiation is all around us all the time and has been since the dawn of humanity.


Good God! Radiation EVERYWHERE!!





Why can Ionizing radiation become a problem?
Ionizing radiation can remove electrons from atoms / molecules. So why is this a bad thing ? Aren't there loads of electrons just floating around anyway? Well yes, so I'll explain. And here, to paraphrase L'Oreal adverts of yesteryear, comes to science. When an atom / molecule is stripped of an electron, they become electrically unpaired and free to float around. As a result, they are highly chemically reactive. We call these particles free radicals. Free radicals tend to react everywhere and just love messing about in biological tissue, reacting with whatever organic material happens to be around. The end result can be cancer. So free radicals are not exactly ideal to have running about in biological tissue.


The New Radicals, however, are just fine for biological tissue. You get what you give.




How is radiation dose measured?
Put as simply as possible, the damage from ionizing radiation is directly related to the energy absorbed. Energy is measured in units called Joules (J) and mass is measured in the kilograms (kg). The gray (Gy) is a quick way to express the energy per kilogram (J/kg) deposited into any material but it only tells part of the story when you consider humans; Different biological tissue responds differently to radiation and indeed to different types of radiation. To quantify this, we have to use weighing factors for both the type of tissue AND the type of radiation to calculate the absorbed dose. This new measurement we call the sievert (Sv) and it is the unit most often discussed when we talk about the effects of radiation on human tissue. In practive, the sievert is a big unit, we often times we use the microsievert (1 uSv = 0.000001 Sv) or the millisievert ( 1 mSv = 0.001 Sv). Pretty much everything we do results in some radiation exposure. Even eating a single banana results in a dose of 0.1 uSv. This is sometimes referred to, semi tongue in cheek, as BED: the banana equivalent dose. But don't let this radioactivity put you off delicious bananas - all food has some radioactivity. Over a year, you'll imbue over 0.4 mSv naturally occurring radiation from food. Obviously this isn't so bad, but it raises the question - what is bad ?




This banana's minuscule radioactivity has not damned his enthusiasm for cheer leading



What are the limits ?
So what exactly is the 'safe' radiation level and when does exposure become detrimental ? Well, stolen from the excellent BBC article (they even interview a medical physicist, sometimes my faith in journalism is rewarded!) here are some typical levels.All thanks to BBC for the graphic...


Stealing from the BBC is not only fun, it's informative!


These are exposures over time, but what about acute exposure ? Note these are measured in millisievert (mSv), and 1 Sv = 1000 mSv = 1000000 uSv. This means a one sievert dose is a thousand millisieverts or a million microsieverts. It's important to be clear on the scale, as there's a huge difference between getting one or the other! Single doses above 8 Sv (8000 mSv, 8000000 uS) are almost always fatal. Doses at Fukushima at their maximum were 0.4 Sv / hr. High, but less than half that required to cause radiation sickness. The problems at Fukushima are also thankfully self - contained. But unless you're the kind of person who enjoys rolling around in high level nuclear waste, odds are you'd be more concerned about chronic exposure


What about chronic exposure ?
Given the majority of people don't go swimming in nuclear fuel, the main fear is the effects of Chronic exposure. Ionizing radiation can cause free radicals which can cause cancer. But at what levels do we have to start worrying ? Well, that is a point of major contention. Some schools of thought claim we should always limit our exposure to radiation. Another claims that low levels of radioactive exposure are actually beneficial for us, a theory called radiation hormesis. But as is generally the case, until we know for sure we err on the side of caution and go with the conservative estimate. In this case it's called the Linear no-threshold model (LNT) for exposure. Essentially, it assumes there is no 'safe level' and the effects of exposure are linear - so if a certain amount of exposure produces one new case of cancer per thousand people exposed, the LNT model assumes that 1/1000th of that dose will produce one extra case of cancer in every million people exposed. Opponents point out that we happily tolerate the natural background level while agreeing overexposure is not healthy. It is still an area of active research so I'm afraid I can't give you any thing definite only that we err on the side of caution. The guardian also had a good guide here



The newly introduced Ionizing radiation warning symbol. Subtle.




Conclusion and opinion
And so endeth my very basic introduction to radiobiology. While we fixate on Fukushima I do have to wonder if the engineering woes at the plant are a distraction from the real tragedy of thousands dead and displaced. There has been some rather shrill cries from anti-nuclear power campaigners that this somehow vindicates their position. I would have to disagree - the failure at Fukushima will unlikely cause any long term health issues. The plant itself was 40 years old and scheduled to be decommissioned this year. Comparisons to Chernobyl by some were utterly inaccurate and far from helpful. Chernobyl was a scale 7 disaster in an obsolete plant caused by human error and compounded by a soviet cover-up attempt. At one stage after the explosion at Chernobyl the radiation level on site was 10-30 Sv / hr and unconfined. Fukushima, by contrast, has a modest failure, fail safes and a low potential health threat. 

Nuclear energy can be complicated and has some disadvantages, but it is relatively clean, efficient and doesn't burn fossil fuels. With a constantly rising world population and depleting oil reserves, I am not sure we can afford to dismiss nuclear energy as an option. This does not mean ignoring renewable energy, but recognising that renewable technologies (wind, tide, etc) suffer from the flaw they do not produce constant output and we cannot store electricity for long periods. This is why we still need constant energy producers like nuclear. We also need to maintain perspective - the disaster at Chernobyl was assessed in health terms by the World Health Organisation in 2006. The conclusion ? Chernobyl caused 57 direct deaths and up to 4000 additional cancers predicted as a result. The latest UNSCEAR studies finds these estimates were overstated. In addition, no further birth defects or solid cancers were detected in the population near Chernobyl in the past 20 years. The most common cancer estimated to be related to the disaster is Thyroid from radioactive iodine - a cancer which thankfully can be easily treated and has a 92% 30 year survivability. By contrast when the Vajont hydroelectric dam failed due to a natural disaster failed in 1963, over 2000 (some sources say 2600) people perished. Over ten times worse was the failure in 1975 of Banquio dam, where over 26,000 people died and vast tracks of land destroyed. Another 145,000 died from the resulting famines and epidemics. I do not state this to rubbish hydroelectric power, merely to put things in perspective regarding disasters. To demonise nuclear power seems a little knee jerk, given the hard numbers indicate that accidents involving renewable and fossil fuel plants claim many, many more lives.

In any case, let us not forget the disaster that has just affected Japan. If you can donate, please do.







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