Archive for January, 2012

Evacuations from Fukushima and Chernobyl

Sunday, January 15th, 2012

The part of the Fukushima disaster I find so disheartening are the stories of those forcibly evacuated from their homes. There have been a number of articles warning of long evacuation times, such as this in the Washington Post, saying that it might be decades before all of the 78,000 evacuees could return. The exposure to radioactivity appears to be very low among the public. One worker died of a heart attack or stroke, and one worker may die over the next 70 years from cancer—perhaps still safer than a fossil fuel plant. But not being able to go home, because your town/farm is so radioactive?

reactor at Fukushima Daiichi plant
reactor at Fukushima Daiichi plant

Evacuation center
Evacuation center

There have now been two nuclear accidents, Chernobyl and Fukushima, that have led to evacuations. Here is how they compare.

What happened at Chernobyl?

Unless otherwise indicated, the following comes from World Nuclear Association summary of the Chernobyl accident.

April 26, 1986, an accident was caused by an incompetent director of a poorly designed reactor, lacking basic safety devices such as a containment structure, in a country without a regulatory system. When people ask about worst case, this is it. From World Nuclear Association,

It was a direct consequence of Cold War isolation and the resulting lack of any safety culture.

What was the exposure to radioactivity and its effect on health at Chernobyl and Fukushima?

Among the Chernobyl operators and firemen (those putting out the initial fire), 134 suffered acute radiation poisoning (from an exposure of more than 1,000 mSv), and 28 died, all within weeks or months. 2 – 3 died from other causes on the day of the accident, or soon after. No dose at Fukushima was high enough to cause acute radiation poisoning.

IAEA photo of Chernobyl
Chernobyl—Unit 4—See article for interviews with victims of accident

The next most exposed group, the liquidators, numbering 200,000 initially, cleaned up the reactor in 1986 – 7. (Another 400,000 came later, but their exposures were fairly small.) Among this group, the average dose equivalent was 100 millisievert. According to UNSCEAR (see Annex J), “It is, however, notable that no increased risk of leukaemia, an entity known to appear within 2- 3 years after exposure, has been identified more than 10 years after the accident.” The model used by National Academy of Sciences in BEIR VII predicts 168 cases of leukemia, and 135 deaths, in this group. (See appendix for more information on normal exposures.)

This includes 20,000 whose dose equivalents from Chernobyl were about 250 mSv, 500 mSv for a few, with highest doses on the first day.

Worker exposure at Fukushima was considerably lower: 107 workers received a dose equivalent between 100 and 200 mSv, for 8 workers it was 200 – 250 mSv, and for 9 workers, more than 250 mSv.

For the general population, there are a number of pathways that lead to exposure.

Since the thyroid is so small, less than 1 ounce (10 – 15 grams), and iodine was the majority of radioactive ions taken up by the body, thyroid cancer, particularly among the very young, became a serious problem, especially in areas where the soil was iodine deficient. By 2002, according to Chernobyl Forum, 4,000 thyroid cancers had been diagnosed among those who were children at the time of the accident, a large fraction of which are attributable to Chernobyl; 15 of these have died. [Chernobyl Forum recommends continued screening of those who were children and adolescents in 1986, but at some point, the danger from invasive procedures on benign lesions will outweigh the benefits. Some of the lesions counted were benign.]

According to Chernobyl Forum,

Apart from the dramatic increase in thyroid cancer incidence among those exposed at a young age, there is no clearly demonstrated increase in the incidence of solid cancers or leukaemia due to radiation in the most affected populations. There was, however, an increase in psychological problems among the affected population, compounded by insufficient communication about radiation effects and by the social disruption and economic depression that followed the break-up of the Soviet Union….

Any traumatic accident or event can cause the incidence of stress symptoms, depression, anxiety (including post-traumatic stress symptoms), and medically unexplained physical symptoms. Such effects have also been reported in Chernobyl exposed populations. Three studies found that exposed populations had anxiety levels that were twice as high as controls, and they were 3–4 times more likely to report multiple unexplained physical symptoms and subjective poor health than were unaffected control groups.

All 2 million people in Fukushima prefecture are being tested for exposure, and all 360,000 who were 17 or younger in at the time of the accident will have their thyroid tested. United Nations Scientific Committee on the Effects of Atomic Radiation (UNSCEAR) plans a report in late 2012 on total radioactivity released, and exposure to workers and the public.

Who was evacuated from Chernobyl?

International Atomic Energy Agency, in 25 years, 25 stories, tells us about some of them. See especially Strelichevo teacher, the story of a girl evacuated from outside the evacuation zone—other children worried about catching radioactivity from her. Exclusion Zone Life is the story of an older woman who returned to her village to live out her years. Pictures of Pripyat. Abandoned villages, and those not abandoned. Farmers’ stories.

Unit 3
Unit 3 operated until December 2000

While much of the area was evacuated, 6,000 workers continued at the other three reactors at Chernobyl, until the last ceased operations in December 2000; their exposure was within acceptable limits. (Because the graphite at Chernobyl exploded, much of the radioactivity fell far away. The soil near the other reactors was deep-plowed to bury radioactivity. And the control rooms were fairly clean.) 3,800 workers are still there (see Chernobyl Village).

From World Nuclear Association,

The plant operators’ town of Pripyat was evacuated on 27 April (45,000 residents). By 14 May, some 116,000 people that had been living within a 30 kilometre radius had been evacuated and later relocated. About 1000 of these returned unofficially to live within the contaminated zone. Most of those evacuated received radiation doses of less than 50 mSv, although a few received 100 mSv or more.

In the years following the accident, a further 220,000 people were resettled into less contaminated areas, and the initial 30 km radius exclusion zone (2800 km2) [1100 sq miles] was modified and extended to cover 4300 square kilometres [1660 sq miles]. This resettlement was due to application of a criterion of 350 mSv projected lifetime radiation dose, though in fact radiation in most of the affected area (apart from half a square kilometre) fell rapidly so that average doses were less than 50% above normal background of 2.5 mSv/yr.

Assuming the 350 mSv refers to the extra exposure over 70 years due to Chernobyl, an average of 5 mSv/year, the criterion for evacuation was smaller than the 7.5+ mSv/year increase from moving to Denver (population 2.4 million, compared to 340,000 evacuated from Chernobyl). In the beginning, radioactivity was higher, and short evacuation of some towns made sense (especially of those who received 50 – 100 mSv in a fairly short time, definitely hot spots). However, I don’t understand why evacuation was forced on people whose exposure is less than many choose voluntarily in deciding where to live and visit.

What are returnees to the area around Chernobyl facing?

The radioactive iodine decayed pretty rapidly, with a half-life of 8 days. Cesium constitutes the majority of the radioactivity remaining after the iodine is gone. Quoting myself:

Physical half-life of cesium is 2 years for Cs-134 and 30 years for Cs-137. However, even in the absence of remediation, ecological half-life is less. In real ecosystems, cesium disappears more rapidly, at a rate that depends on soil characteristics. A recent report from the United Nations Scientific Committee on the Effects of Atomic Radiation (UNSCEAR) found, “a relatively fast decrease with a half-life of between 0.7 and 1.8 years (this dominated for the first 4–6 years after the [Chernobyl] accident, and led to a reduction of concentrations in plants by about an order of magnitude compared with 1987); and (b) a slower decrease with a half-life of between 7 and 60 years.” In some areas, no decline was found after the first 4–6 years. (pp 76-7) At the end of one year, from 37 – 65% of the cesium remains. After 4 – 6 years, from 3 – 20% of the cesium remains.

Radioactivity does vary across the zone, and some food is more radioactive. According to International Commission on Radiological Protection (ICRP),

Certain areas such as alpine pastures, forests, and upland areas may show longer retention in soils than agricultural areas, and high levels of transfer to particular foods, e.g. berries and mushrooms in forests, may give rise to elevated intakes.

Individual behavior matters: while most average about 0.1 mSv/year exposure above normal from the food they eat, a very small number with “particular dietary habits” may ingest 1+ mSv/year. This is true outside of nuclear accidents; eating shellfish can add 0.5 mSv/year, and 30 – 40 Brazil nuts/week adds 0.2 mSv/year, to a normal intake of 0.27 mSv/year from food.

So the average area in the evacuation zone is a tad more radioactive (<3.75 mSv) than average for the US (3 mSv), <50% as radioactive as Finland, and <40% as radioactive as Denver. Most of us ignore which radon zone we live in, and we ignore the increased radioactivity with altitude. People living in areas near Chernobyl with exposures up to an extra 1 mSv per year, far less than regional variations in the US, even those who will receive as little as 0.1 mSv/year, are seeing protective measures. I also would be neurotic if the government were warning me about such small dangers.

Ukraine’s decision to set a 1 mSv limit wasn’t completely arbitrary. ICRP recommends the “lower part of the 1–20 mSv/year band”. That choice may have been arbitrary, somewhere below where any evidence of health danger has been seen, to meet the ALARA standard, as low as reasonably achievable. Standards for “reasonable” appear to vary, since a good portion of humanity lives willingly in areas that are much more radioactive.

Or work: due to the granite (and marble) at Grand Central Station, workers receive a dose of 1.2 mSv/year.

Yet an evacuation zone remains. Communication about radiation effects doesn’t sound insufficient, but too clear: “You were exposed to dangerous levels and we have to monitor exposures as little as 1 mSv/year or less, because they are dangerous.”

Assuming that the Japanese are aiming for a 20 mSv/year maximum, still safer than air pollution in Tokyo (see here), much of the mandatory evacuation zone is safe now, and almost all of the evacuation zone should be available within 4 – 6 years, assuming the same ecological half life as the area around Chernobyl—the most polluted village, 2 miles from the plant, may be safe as well. Remediation will presumably speed up the process. If the standards are the same as for Chernobyl, where people are not allowed back in unless background radioactivity falls below levels common in the US and elsewhere, the timing of decades makes more sense.

Upcoming post:
• Agriculture after Fukushima

Global warming may cause cold winters

Friday, January 13th, 2012

Earth has warmed, and the Arctic has warmed at twice the rate. Ironically, says ScienceNow,

winters in the Northern Hemisphere have grown colder and more extreme in southern Canada, the eastern United States, and much of northern Eurasia, with England’s record-setting cold spell in December 2010 as a case in point.

Now Judah Cohen, et al, may have explained why in a report in Environmental Research Letters:

Siberian airport trapped in snow
Siberian airport trapped in snow. Picture credit

First, the strong warming in the Arctic in recent decades, among other factors, has triggered widespread melting of sea ice. More open water in the Arctic Ocean has led to more evaporation, which moisturizes the overlying atmosphere, the researchers say. Previous studies have linked warmer-than-average summer months to increased cloudiness over the ocean during the following autumn. That, in turn, triggers increased snow coverage in Siberia as winter approaches. As it turns out, the researchers found, snow cover in October has the largest effect on climate in subsequent months.

That’s because widespread autumn snow cover in Siberia strengthens a semipermanent high-pressure system called, appropriately enough, the Siberian high, which reinforces a climate phenomenon called the Arctic Oscillation and steers frigid air southward to midlatitude regions throughout the winter…

The team’s analyses suggest that climate cycles such as the El Niño-Southern Oscillation, the Pacific Decadal Oscillation, and the Atlantic multidecadal oscillation can’t explain the regional cooling trends seen in the Northern Hemisphere during the past couple of decades as well as trends in Siberian snow cover do.

Aerosols: what they are, and new analysis on how they affect climate

Thursday, January 5th, 2012

Summary: new analysis indicates that the cooling effect of aerosols has been underestimated. Earth will warm as the air clears from lower fossil fuel use, and that warming is likely to be larger than previously estimated.

Aerosols is one of those confusing words that mean one thing in popular parlance (something to do with hair spray) and something different to scientists. To the latter, aerosols are the solid and liquid particles in the air, such as ash, soot, and smoke.

Regulators pay attention to particle size, eg, PM10 (particulate matter <10 microns, one millionth of a meter, in size) and PM2.5 (particulate matter <2.5 microns). Regulators are most concerned about PM2.5 (and China now accepts the obligation to measure PM2.5 after the embarrassment of reporting light pollution on a day when the US embassy recorded PM2.5 levels over 500 microgram per cubic meters, 6 – 10 times the level of the most polluted cities in the world).

As described by NASA,

Climatologists typically use another set of labels that speak to the chemical composition. Key aerosol groups include sulfates, organic carbon, black carbon, nitrates, mineral dust, and sea salt. In practice, many of these terms are imperfect, as aerosols often clump together to form complex mixtures. It’s common, for example, for particles of black carbon from soot or smoke to mix with nitrates and sulfates, or to coat the surfaces of dust, creating hybrid particles.

The bulk of aerosols—about 90 percent by mass—have natural origins. Volcanoes, for example, eject huge columns of ash into the air, as well as sulfur dioxide and other gases, yielding sulfates. Forest fires send partially burned organic carbon aloft. Certain plants produce gases that react with other substances in the air to yield aerosols, such as the “smoke” in the Great Smoky Mountains of the United States. Likewise in the ocean, some types of microalgae produce a sulfurous gas called dimethylsulfide that can be converted into sulfates in the atmosphere.

Sea salt and dust are two of the most abundant aerosols, as sandstorms whip small pieces of mineral dust from deserts into the atmosphere and wind-driven spray from ocean waves flings sea salt aloft. Both tend to be larger particles than their human-made counterparts.

The remaining 10 percent of aerosols are considered anthropogenic, or human-made, and they come from a variety of sources. Though less abundant than natural forms, anthropogenic aerosols can dominate the air downwind of urban and industrial areas.

Fossil fuel combustion produces large amounts of sulfur dioxide, which reacts with water vapor and other gases in the atmosphere to create sulfate aerosols. Biomass burning, a common method of clearing land and consuming farm waste, yields smoke that’s comprised mainly of organic carbon and black carbon.

Air pollution still visible at night
Air pollution still visible at night

No one wants to keep air pollution aerosols at the current level. Even as smoking rates have remained constant in Beijing, lung cancer rates have gone up 60% in the last decade, presumably from increases in air pollution in the last decades of the 20th century.

What effect are aerosols now having on climate change?
Aerosols are an important part of climate feedback, both direct and indirect. An article in the November 11, 2011 Science looks at the complications (subscription needed).

Aerosol feedbacks

Aerosol feedbacks The left edge of each box shows the average estimate of the effects of the changes we’re responsible for; the bar shows the range of estimates. There is a 10% chance that the effect is outside the range shown. All numbers are negative—they provide for a net cooling, although there is some reason to think that the second category might be slightly positive, that is, increasing Earth’s temperature. Since aerosols are in the air only a short time, if we stopped adding aerosols, Beijing would be much cleaner within aerosol residence time of days to weeks, and temperatures would begin to rise simultaneously.

The net warming of Earth caused by people is around 1.6 watts per square meter, as if every square meter on Earth had a 1.6 W bulb running 24 hours a day. The actual estimate is 0.6 to 2.4 watts/m2, with a wide range of assumptions about how much variation is normal. (1.6 W/m2 is almost identical with the warming due to carbon dioxide. Other contributions, positive and negative, currently cancel out.) See more numbers at end.*

The upper bar, aerosol direct effects, is the cumulative change from changing reflection (some aerosols reflect more light, some absorb more and heat up), with a mean estimate of -0.5 W/m2.

The indirect aerosol effect on cloud albedo (reflection) is more complicated, and there is a greater range of estimates of its magnitude. Aerosols change precipitation and cloud patterns, in a variety of ways:
• reducing evaporation
• suppressing cloud formation and redistributing droplets
• increasing precipitation (eg, India monsoons)
• altering atmospheric circulation patterns (which could have led to drying in the Sahel)
• creating more small drops

The average estimate for the cloud albedo effect is around -0.7 W/m2.

The third category includes a number of other indirect effects from aerosols, on a longer time scale than days to weeks. Here is the new, and preliminary, analysis presented in the article.

Non-cloud albedo indirect effects include:
• physical changes to the land or ocean which affect the rate that greenhouse gases are taken up or released
• chemical changes, such as nutrients or toxins, that modify biogeochemical cycles.

Aerosols cool Earth, so more of the atmospheric carbon dioxide is taken up. As long as we keep aerosols in the air, carbon dioxide levels remain 1 – 14 parts per million lower. Aerosols with nitrogen (and gaseous nitrogen) fertilize the soil in some areas, so that an extra 0.24 – 0.7 gigatonnes (billion metric tons) is absorbed each year, a decrease of 0.1 – 0.3 ppm CO2/year. Over 135 years, the net effect is to cool Earth, a change of -0.12 to -0.35 W/m2. Aerosols from burning tropical forests provide a source of phosphorous to phosphorous-limited vegetation—this may explain half the carbon dioxide taken up by the Amazon forest, a change of -0.12 W/m2.

Oceans are not nitrogen or phosphorous limited, but in some areas, iron in desert dust may have led to 4 ppm carbon dioxide taken up by oceans, a change of 0 to -0.14 W/m2.

Aerosols can decrease carbon uptake as well. Acidic aerosols, such as sulfates and nitrates—acid rain—can leach nutrients out of the ecosystem. Acid rain increasing ocean acidification, and toxic aerosols, decrease the rate at which carbon is absorbed by the ocean.

The overall magnitude of the indirect effect of biogeochemical cycles appears to be about the same as the direct effects.

If we stopped putting aerosols in the air tomorrow…
Aerosols currently cool Earth directly, through changing clouds, and by enhancing CO2 uptake by both land and the ocean. As fossil fuel burning become cleaner, and as aerosol production drops from reduced use of fossil fuels, temperatures will rise.

To keep atmospheric temperature increases low, decreases in carbon dioxide and greenhouse gases need to be larger than previously estimated. This means that addressing climate change will be much more expensive than previously estimated.

* More numbers
• Atmospheric carbon dioxide has changed from a pre-industrial value of about 280 parts per million to 390 ppm today.
• 2.13 gigatonnes carbon = 7.8 GT CO2 added to the atmosphere = 1 ppm. The world adds about 30 GT/year from fossil fuel burning and cement manufacture (just under 1/5 of this comes from the US), but about half is currently absorbed by the oceans and land.
• Intergovernmental Panel on Climate Change on contributions from various forcings (changes, natural and anthropogenic, from pre-industrial times that are forcing changes in the climate). If the analysis on indirect effects other than cloud albedo hold up, IPCC’s chart will look different in the Fifth Assessment Report (4 volumes, scheduled to be released between September 2013 and October 2014).

IPCC: radiative forcings

IPCC Frequently Asked Questions: radiative forcings. You can read more at FAQ 2.1