Assessing the dangers of nuclear power requires coming to some understanding of radiation, how much of it we get exposed to and how dangerous that exposure is. Unfortunately, this is a topic that not only brings out the irrational in some people but also is genuinely difficult to untangle.
The first problem is being clear about what we are measuring. A group of unfamiliar units immediately confronts us. There are at least two different things we might measure and two different systems for measuring them. (Actually, it’s even more complex, but this is enough to sort out for now.)
Radiation is emitted from objects and we can measure how much comes out. But emitted radiation is not the same as what we absorb, and there is a different measure for that. Then, everything can get measured in the units we use in the U.S. (a system which has several names: British units, Imperial Units, or U.S. customary units) or in the metric system (which, in fact, is more properly known as International System of Units (“SI” units for short).
To limit our confusion, we’ll focus on the SI unit for absorbed radiation, which is the sievert (abbreviated Sv, and yes, the spelled out term is lower case and the abbreviation starts with an upper case letter).
A sievert is not just a count of radioactive particles; it is adjusted for the biological impact of different types of radiation on living organisms. It is an attempt to sum up in one number the impact on a person of various types of exposures to radiation.
A sievert is actually a very large amount of radiation and so typically we have to deal with milisievert (mSv or .001 siervert) and the microsievert (uSv or .001 mSv).
How much is too much?
So how much radiation is too much? People vary in size and sensitivity. The amount of radiation that might have no impact on an adult could be damaging to a child. Exposure of a hand would be less worrisome than exposing the entire body. Eating radioactive material would have a different effect than having your skin exposed to it. Getting a dose all at once is worse than the same dose spread out over time.
But simplifying again, it is established that exposure to 4 to 6 Sv in a short period of time will most likely result in death. What about the dangers of lower exposures?
As the amount of radiation goes down, there is less and less agreement on its impacts. It’s not uncommon to hear it asserted that there is no safe level of radiation. It is equally uncommon to read that the health impacts of low dosages are nonexistent or, at the minimum, cannot be detected. An authoritative survey of radiation research by David Bodansky, a physics professor at the University of Washington, “Nuclear Energy: principles, practices and prospects,” (2nd ed. 2004) explains just how difficult detecting small effects is, and that whatever the impact of low dosages might be, they are small enough that they cannot be accurately measured.
But what are we exposed to?
Remember that five sieverts in a short time would likely be fatal. We are routinely exposed to radiation from medical procedures, cosmic rays, radon gas, minerals and our food. The normal figure cited for exposure from all natural causes is .003 Sv, or 3 miliseverts a year. If you live in Denver or another high altitude city, you’d likely absorb 4 mSv a year.
To this natural exposure we add our medical procedures. Figures for a chest X-ray vary from 0.01 mSv to 0.06 mSv. A head CT scan gives us about 2 mSv and other scans of other areas expose us to even more. A person who is in and out of treatment might in a year more than triple their exposure to radiation just from medical procedures.
Workers at nuclear power plants and any who deal with radioactivity are currently limited by federal regulations to 50 mSv a year, with some exceptions permitted for those dealing with life-threatening emergencies. Astronauts who flew into space received considerable more radiation, perhaps up to 250 mSv a flight.
A person who stood at the boundary of a nuclear power plant for a year would be exposed to much less, perhaps .01 mSv. Being near large rocks such as a stone building (or even your granite countertops) also exposes you to some additional radiation, perhaps even more than you get from living near a nuclear power plant.
Despite much research on nuclear workers and people who live in areas with high natural exposure to radiation, there is almost no evidence of increased cancer among them. Or more precisely, any increase of cancers is small enough that its impact can’t be detected.
Risk and worry
We just don’t seem to be very worried about all that natural radiation, our exposure from airplane flights, medical procedures and the like. Perhaps we are slightly at risk from all that, but we don’t seem to notice.
Perhaps in frustration with our inconsistency about radiation risks, a non-standard unit of exposure has entered the folklore: the banana equivalent dose. Bananas contain potassium, and one isotope of potassium is slightly radioactive, thus consuming a banana exposes you to a very small amount of radiation, probably less than a microsievert.
The real issue
The actual concern of course is not our stone buildings or air flights or even bananas and countertops. The concern is that a nuclear power plant will, due to an accident, suddenly release a much larger amount of radiation and expose us to something well beyond our natural levels of risk.
So just how much radiation and how much risk? The two incidents of Three Mile Island and Chernobyl stand at opposite ends of the spectrum. Three Mile Island released a small amount of radiation and no independent research has ever proven health impacts on the surrounding population.
The epitome of uncertainty
Chernobyl, on the other hand, is a very different situation.
How many people died from that disaster? The judgment of one author, writing in the Bulletin of the Atomic Scientists (not an uncritical pro-industry source) was that after ten years “there is no consensus on the number of victims or the overall health impact of Chernobyl.” Indeed, estimates presented by various groups range from a high of 100,000 all the way down to 60 – a difference of over three orders of magnitude.
Chernobyl caused both direct deaths (mostly from acute radiation poising) and long term effects. The short term death toll was given by the Soviets as 31 in 1996 but is likely higher. Sixty immediate deaths is an oft-quoted figure.
A very elaborate study by the International Atomic Energy Agency, the World Health Organization and other U.N. groups that involved an international set of scientists on the 20th anniversary of the disaster is oft-quoted as claiming there were 4,000 deaths. What is generally missed is that this was an estimate of future cancer fatalities, not a calculation of those who had already died.
The IAEA/WHO report typically is dismissed by anti-nuclear critics. The most substantive criticism of it is that it only considered the immediate countries around Chernobyl and did not attempt to project out over all of Europe.
To estimate excess deaths you need to have two groups of people, one that was exposed and one that was not. Then you could measure the difference in fatalities between the groups and come to an estimate of the effects. However, if the group you are estimating for is all of Europe, what group will you use to compare them to? Cancer rates vary widely among different populations, and have changed over time as well. Furthermore, the level of exposure of most of Western Europe was quite low, which brings us back to the problem of estimating health effects of low exposures.
As if this wasn’t enough trouble, there was the blackout imposed by Soviet government in the immediate aftermath of the accident, and later, the chaos due to the collapse of the Soviet Union.
Another approach, used by a report initiated by the European Green Party, is to take the exposure and multiply by a factor that attempts to measure the number of cancers from a given unit of radiation. This report, extrapolating out to all of Europe and 300 years into the future, predicts 30 to 60 thousand excess deaths.
In the end, both the low and high estimates cited claim to have been the result of multiple scientists studying the issue carefully. The Greenpeace report has been harshly criticized for relying on studies that had not been peer reviewed. The Green Party report assumes that low doses do produce effects.
All of these are estimates. Given the uncertainty over the impact of low doses of radiation, small changes in assumptions produce big changes in estimates of deaths.
The worst worst case and the normal worst case
Chernobyl stands as a sort of worst worst-case scenario. A dangerously faulty plant design without a containment structure, a poorly planned and badly executed test, operators being pressured to proceed despite warning signs, cleanup workers heedless of basic safety procedures, inadequate supplies and protection for workers, a government cover-up in the immediate days after the disaster — it would be hard to design a worse situation.
By contrast, the ongoing Fukushima disaster is a more “normal” worst case: extreme conditions at an older plant produce a partial meltdown that does not breach the containment structure. Some modest redesigns would be able to prevent even this extreme a situation from releasing any radiation.
To arrive at useful conclusions about the risks of nuclear power, we have to set them in a framework that compares risks. That’s coming next week.
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