Weather analysis shows there was no plausible Fukushima scenario in which Tokyo, Yokosuka, or Yokota would have been subject to dangerous levels of airborne radiation

Lawrence Livermore National Laboratory calculated the worst case scenarios from the tsunami damaged Fukushima nuclear reactors.

Weather analysis shows there was no plausible Fukushima scenario in which Tokyo, Yokosuka, or Yokota would have been subject to dangerous levels of airborne radiation. Even if all of the reactors went critical and there was a worst case fire in holding pond 4 (the holding pond did not have that worst case fire and the reactors had less problems than the worst case.) The actual weather was even more favorable with wind mainly blowing out into the ocean. The oceans have 4 billion tons of uranium in their natural condition, so more radioactive material is literally a drop in the ocean.

Hours after a massive earthquake and tsunami struck Japan on March 11, 2011, a team of Livermore scientists mobilized to begin assessing the danger from the crippled Fukushima Dai-ichi nuclear plant. The 40-odd team members include physicists, meteorologists, computer modelers, and health specialists. Their specialty is major airborne hazards—toxic matter from chemical fires, ash from erupting volcanoes, or radioactive emissions.

After days of high-intensity analysis and numerous computer runs, the scientists concluded that radiation in Tokyo would come nowhere close to levels requiring an evacuation, even in the event that Fukushima Dai-ichi underwent the worst plausible meltdown combined with extremely unfavorable wind and weather patterns.

These revelations, together with additional new information, debunk some powerful myths about Fukushima and have weighty implications for the debate about nuclear power that has raged in the accident’s aftermath. (The revelations are unrelated to the plant’s current water-leakage problem, which by some reckonings is less severe and more solvable than recent headlines suggest.)

The US administration was bound by exposure-level standards set by the Environmental Protection Agency. Those standards don’t translate into “danger” in the commonly used sense of the word; exposure at such low levels doesn’t make people sick or render them more likely to get cancer someday. There’s a slightly higher risk of fatal cancer—an additional 0.5 percent—for those who receive a cumulative lifetime dose of 100 millisieverts (a measure of radiation’s effect on the body). The EPA standards set trigger points for protecting the general public well below that level, at a dose low enough that the risk of additional cancers is undetectable.

Lengthy and sometimes fierce technical arguments ensued among experts at the various agencies involved. In addition to multiple reactor meltdowns, should the assumptions include the much-dreaded fire in the Reactor No. 4 spent fuel pool even though it turned out to be in much better shape than initially thought? For the “plausible worst case,” the answer was yes, because unseen cracks might still cause the pool to empty, and a severe aftershock might lead to new structural problems.

The most critical factor, according to Fetter, turned out to be assumptions about weather. “We didn’t want to point the plume directly at Tokyo and leave it going there the whole time; that wasn’t realistic, because the wind always changes,” he said. “So [the Livermore researchers] looked back in their weather data and found some worst cases—periods in which the wind blew toward Tokyo for a long while.” Precise modeling of atmospheric dispersion and “plume wander” showed that radiation far from the plant would be substantially reduced; even a light rain would wash many particles out of the air.

By the last three days of March, the computer modeling produced results that settled the debate: A plume delivering radiation doses exceeding U.S. standards would come no closer to Tokyo than 75 miles, so Americans should stay put. In an April 1, 2011, email to Adm. Michael Mullen, chairman of the Joint Chiefs of Staff, Holdren spelled out details. “Our optimism, such as it is … comes not from any assumption that the situation at Fukushima is under control but rather from modeling that shows the worst-plausible releases from one or more reactors at Fukushima would not cross [the U.S. guidelines] in Tokyo even in the event of adverse weather,” Holdren wrote. “Only with big releases from the spent-fuel pools, combined with even more perverse weather than [the scientists deemed realistic], could the [guidelines] be crossed in Tokyo, and even then, according to the modeling to date, not by much,” so “even in these extreme circumstances, sheltering in place might be all you’d want to do.”

Readers who have closely followed Fukushima developments may find this story about the U.S. government’s worst-case scenario interesting though not necessarily conclusive. After all, didn’t the Japanese government draw up its own worst-case scenario? Indeed it did. Didn’t many news articles report that this scenario would have necessitated an evacuation of Tokyo? Indeed they did—wrongly.

There was no plausible scenario in which Tokyo, Yokosuka, or Yokota could be subject to dangerous levels of airborne radiation.

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