Fukushima Update: How Safe Can a Nuclear Meltdown Get?

by Will Boisvert

Last summer I posted an essay here arguing that nuclear power is a lot safer than people think—about a hundred times safer than our fossil fuel-dominated power system. At the time I predicted that the impact of the March, 2011 Fukushima Daiichi nuclear plant accident in Japan would be small. A year later, now that we have a better fix on the consequences of the Fukushima meltdowns, I’ll have to revise “small” to “microscopic.” The accumulating data and scientific studies on the Fukushima accident reveal that radiation doses are and will remain low, that health effects will be minor and imperceptible, and that the traumatic evacuation itself from the area around the plant may well have been unwarranted. Far from the apocalypse that opponents of nuclear energy anticipated, the Fukushima spew looks like a fizzle, one that should drastically alter our understanding of the risks of nuclear power.

Anti-nuke commentators like Arnie Gundersen continue to issue forecasts of a million or more long-term casualties from Fukushima radiation. (So far there have been none.) But the emerging scientific consensus is that the long-term health consequences of the radioactivity, particularly cancer fatalities, will be modest to nil. At the high end of specific estimates, for example, Princeton physicist Frank von Hippel, writing in the nuke-dreading Bulletin of the Atomic Scientists, reckons an eventual one thousand fatal cancers arising from the spew.

Now there’s a new peer-reviewed paper by Stanford’s Mark Z. Jacobson and John Ten Hoeve that predicts remarkably few casualties. (Jacobson, you may remember, wrote a noted Scientific American article proposing an all-renewable energy system for the world.) They used a supercomputer to model the spread of radionuclides from the Fukushima reactors around the globe, and then calculated the resulting radiation doses and cancer cases through the year 2061. Their result: a probable 130 fatal cancers, with a range from 15 to 1300, in the whole world over fifty years. (Because radiation exposures will have subsided to insignificant levels by then, these cases comprise virtually all that will ever occur.) They also simulated a hypothetical Fukushima-scale meltdown of the Diablo Canyon nuclear power plant in California, and calculated a likely cancer death toll of 170, with a range from 24 to 1400.

To put these figures in context, pollution from American coal-fired power plants alone kills about 13,000 people every year. The Stanford estimates therefore indicate that the Fukushima spew, the only significant nuclear accident in 25 years, will likely kill fewer people over five decades than America’s coal-fired power plants kill every five days to five weeks. Worldwide, coal plants kill over 200,000 people each year—150 times more deaths than the high-end Fukushima forecasts predict over a half century.

We’ll probably never know whether these projected Fukushima fatalities come to pass or not. The projections are calculated by multiplying radiation doses by standard risk factors derived from high-dose exposures; these risk factors are generally assumed—but not proven—to hold up at the low doses that nuclear spews emit. Radiation is such a weak carcinogen that scientists just can’t tell for certain whether it causes any harm at all below a dose of 100 millisieverts (100 mSv). Even if it does, it’s virtually impossible to discern such tiny changes in cancer rates in epidemiological studies. Anti-nukes give that fact a paranoid spin by warning of “hidden cancer deaths.” But if you ask me, risks that are too small to measure are too small to worry about.

The Stanford study relied on a computer simulation, but empirical studies of radiation doses support the picture of negligible effects from the Fukushima spew.

In a direct measurement of radiation exposure, officials in Fukushima City, about 40 miles from the nuclear plant, made 37,000 schoolchildren wear dosimeters around the clock during September, October and December, 2011, to see how much radiation they soaked up. Over those three months, 99 percent of the participants absorbed less than 1 mSv, with an average external dose of 0.26 mSv. Doubling that to account for internal exposure from ingested radionuclides gives an annual dose of 2.08 mSv. That’s a pretty small dose, about one third the natural radiation dose in Denver, with its high altitude and abundant radon gas, and many times too small to cause any measurable up-tick in cancer rates. At the time, the outdoor air-dose rate in Fukushima was about 1 microsievert per hour (or about 8.8 mSv per year), so the absorbed external dose was only about one eighth of the ambient dose. That’s because the radiation is mainly gamma rays emanating from radioactive cesium in the soil, which are absorbed by air and blocked by walls and roofs. Since people spend most of their time indoors at a distance from soil—often on upper floors of houses and apartment buildings—they are shielded from most of the outdoor radiation.

Efforts to abate these low-level exposures will be massive—and probably redundant. The Japanese government has budgeted $14 billion for cleanup over thirty years and has set an immediate target of reducing radiation levels by 50 percent over two years. But most of that abatement will come from natural processes—radioactive decay and weathering that washes radio-cesium deep into the soil or into underwater sediments, where it stops irradiating people—that  will reduce radiation exposures on their own by 40% over two years. (Contrary to the centuries-of-devastation trope, cesium radioactivity clears from the land fairly quickly.) The extra 10 percent reduction the cleanup may achieve over two years could be accomplished by simply doing nothing for three years. Over 30 years the radioactivity will naturally decline by at least 90 percent, so much of the cleanup will be overkill, more a political gesture than a substantial remediation. Little public-health benefit will flow from all that, because there was little radiation risks to begin with.

How little? Well, an extraordinary wrinkle of the Stanford study is that it calculated the figure of 130 fatal cancers by assuming that there had been no evacuation from the 20-kilometer zone around the nuclear plant. You may remember the widely televised scenes from that evacuation, featuring huddled refugees and young children getting wanded down with radiation detectors by doctors in haz-mat suits. Those images of terror and contagion reinforced the belief that the 20-km zone is a radioactive killing field that will be uninhabitable for eons. The Stanford researchers endorse that notion, writing in their introduction that “the radiation release poisoned local water and food supplies and created a dead-zone of several hundred square kilometers around the site that may not be safe to inhabit for decades to centuries.”

But later in their paper Jacobson and Ten Hoeve actually quantify the deadliness of the “dead-zone”—and it turns out to be a reasonably healthy place. They calculate that the evacuation from the 20-km zone probably prevented all of 28 cancer deaths, with a lower bound of 3 and an upper bound of 245. Let me spell out what that means: if the roughly 100,000 people who lived in the 20-km evacuation zone had not evacuated, and had just kept on living there for 50 years on the most contaminated land in Fukushima prefecture, then probably 28 of them—and at most 245—would have incurred a fatal cancer because of the fallout from the stricken reactors. At the very high end, that’s a fatality risk of 0.245 %, which is pretty small—about half as big as an American’s chances of dying in a car crash. Jacobson and Ten Hoeve compare those numbers to the 600 old and sick people who really did die during the evacuation from the trauma of forced relocation. “Interestingly,” they write, “the upper bound projection of lives saved from the evacuation is lower than the number of deaths already caused by the evacuation itself.”

That observation sure is interesting, and it raises an obvious question: does it make sense to evacuate during a nuclear meltdown?

In my opinion—not theirs—it doesn’t. I don’t take the Stanford study as gospel; its estimate of risks in the EZ strikes me as a bit too low. Taking its numbers into account along with new data on cesium clearance rates and the discrepancy between ambient external radiation and absorbed doses, I think a reasonable guesstimate of ultimate cancer fatalities in the EZ, had it never been evacuated, would be several hundred up to a thousand. (Again, probably too few to observe in epidemiological studies.) The crux of the issue is whether immediate radiation exposures from inhalation outweigh long-term exposures emanating from radioactive soil. Do you get more cancer risk from breathing in the radioactive cloud in the first month of the spew, or from the decades of radio-cesium “groundshine” after the cloud disperses? Jacobson and Ten Hoeve’s model assigns most of the risk to the cloud, while other calculations, including mine, give more weight to groundshine.

But from the standpoint of evacuation policy, the distinction may be moot. If the Stanford model is right, then evacuations are clearly wrong—the radiation risks are trivial and the disruptions of the evacuation too onerous. But if, on the other hand, cancer risks are dominated by cesium groundshine, then precipitate forced evacuations are still wrong, because those exposures only build up slowly. The immediate danger in a spew is thyroid cancer risk to kids exposed to iodine-131, but that can be counteracted with potassium iodide pills or just by barring children from drinking milk from cows feeding on contaminated grass for the three months it takes the radio-iodine to decay away. If that’s taken care of, then people can stay put for a while without accumulating dangerous exposures from radio-cesium.

Data from empirical studies of heavily contaminated areas support the idea that rapid evacuations are unnecessary. The Japanese government used questionnaires correlated with air-dose readings to estimate the radiation doses received in the four months immediately after the March meltdown in the townships of Namie, Iitate and Kawamata, a region just to the northwest of the 20-kilometer exclusion zone. This area was in the path of an intense fallout plume and incurred contamination comparable to levels inside the EZ; it was itself evacuated starting in late May. The people there were the most irradiated in all Japan, yet even so the radiation doses they received over those four months, at the height of the spew, were modest. Out of 9747 people surveyed, 5636 got doses of less than 1 millisievert, 4040 got doses between 1 and 10 mSv and 71 got doses between 10 and 23 mSv. Assuming everyone was at the high end of their dose category and a standard risk factor of 570 cancer fatalities per 100,000 people exposed to 100 mSv, we would expect to see a grand total of three cancer deaths among those 10,000 people over a lifetime from that four-month exposure. (As always, these calculated casualties are purely conjectural—far too few to ever “see” in epidemiological statistics.)

Those numbers indicate that cancer risks in the immediate aftermath of a spew are tiny, even in very heavily contaminated areas. (Provided, always, that kids are kept from drinking iodine-contaminated milk.) Hasty evacuations are therefore needless. There’s time to make a considered decision about whether to relocate—not hours and days, but months and years.

And that choice should be left to residents. It makes no sense to roust retirees from their homes because of radiation levels that will raise their cancer risk by at most a few percent over decades. People can decide for themselves—to flee or not to flee—based on fallout in their vicinity and any other factors they think important. Relocation assistance should be predicated on an understanding that most places, even close to a stricken plant, will remain habitable and fit for most purposes. The vast “costs” of cleanup and compensation that have been attributed to the Fukushima accident are mostly an illusion or the product of overreaction, not the result of any objective harm caused by radioactivity.

Ultimately, the key to rational policy is to understand the kind of risk that nuclear accidents pose. We have a folk-conception of radiation as a kind of slow-acting nerve gas—the merest whiff will definitely kill you, if only after many years. That risk profile justifies panicked flight and endless quarantine after a radioactivity release, but it’s largely a myth. In reality, nuclear meltdowns present a one-in-a-hundred chance of injury. On the spectrum of threat they occupy a fairly innocuous position: somewhere above lightning strikes, in the same ballpark as driving a car or moving to a smoggy city, considerably lower than eating junk food. And that’s only for people residing in the maximally contaminated epicenter of a once-a-generation spew. For everyone else, including almost everyone in Fukushima prefecture itself, the risks are negligible, if they exist at all.

Unfortunately, the Fukushima accident has heightened public misunderstanding of nuclear risks, thanks to long-ingrained cultural associations of fission with nuclear war, the Japanese government’s hysterical evacuation orders and haz-mat mobilizations, and the alarmism of anti-nuke ideologues. The result is anti-nuclear back-lash and the shut-down of Japanese and German nukes, which is by far the most harmful consequence of the spew. These fifty-odd reactors could be brought back on line immediately to displace an equal gigawattage of coal-fired electricity, and would prevent the emission of hundreds of millions of tons of carbon dioxide each year, as well as thousands of deaths from air pollution. But instead of calling for the restart of these nuclear plants, Greens have stoked huge crowds in Japan and elsewhere into marching against them. If this movement prevails, the environmental and health effects will be worse than those of any pipeline, fracking project or tar-sands development yet proposed.

But there may be a silver lining if the growing scientific consensus on the effects of the Fukushima spew triggers a paradigm shift. Nuclear accidents, far from being the world-imperiling crises of popular lore, are in fact low-stakes, low-impact events with consequences that are usually too small to matter or even detect. There’s been much talk over the past year about the need to digest “the lessons of Fukushima.” Here’s the most important and incontrovertible one: even when it melts down and blows up, nuclear power is safe.