Two years have passed since the Tōhoku earthquake and tsunami that lead to the nuclear reactor accident in Fukushima, Japan in March 2011. This past month, Tamotsu Baba, mayor of Namie, a town only a few miles north of the nuclear plant, invited Google to explore the city shaken by the earthquake and abandoned following the spread of radiation from Fukushima. This slideshow contains scenes from our virtual exploration of the town that formerly held over 20,000 residents, and now plays home to garbage, a few cleanup crews, and many ghostly abandoned structures.
All estimates indicate that the accident at Japan's Fukushima Daiichi nuclear power plant will have a very small cost in human lives. Still, its overall impact is enormous. The country saw one of its major sources of electrical power go entirely offline at the same time it was attempting to recover and rebuild following a staggering earthquake and tsunami. A large area remains off-limits, and the country's nuclear experts are now forced to secure the material in the melted-down reactors and fuel storage areas before another earthquake hits. The total cost of Fukushima is likely to be astronomical.
It's easy to dismiss the accident as a freak occurrence—both the earthquake and tsunami were of exceptional magnitude, after all. Events of that size aren't unprecedented in Japan, yet the Fukushima reactors were poorly prepared for them. Now there are many indications that the recovery from the initial shock didn't go according to plan either. Today, the Japanese parliament released the English version of its analysis of Fukushima, performed by an independent investigative committee.
The report hammers both TEPCO, the utility that ran the plant, and the government regulators who were meant to oversee it. Although a number of the problems may be unique to the Japanese situation, the report provides lessons that could be valuable for the nuclear programs in other nations.
The same factor that put the Fukushima power plants at risk—proximity to the ocean—ensured that a sizable fraction of the radioactivity liberated from the plants ended up in the Pacific. That helped ensure that the contamination was diluted back to safe levels rapidly, although radioactive isotopes were detectable in fish caught near the plants. But fish don't sit still, and a new study has also detected low levels of radioactivity from Fukushima in tuna that were caught off the coast of California.
The study takes advantage of the fact that there is an isotope of cesium, 134Cs, that is both short lived and only produced through nuclear processes, making it an excellent tracer of contamination from Fukushima. A second isotope, 137Cs, is present at very low levels due to historic nuclear tests thanks to its longer half-life. These can be contrasted with 40K, a potassium isotope that is naturally present throughout the world's oceans.
The cesium isotopes were detected in sea life near Japan and that gave researchers good reason to look into the tuna population elsewhere. The bluefin tuna of the northern Pacific breed along its western shores, including near Japan. Immature fish stay in that area for a year or two before migrating across the Pacific to mature near California. Thus, younger fish caught near California had a good chance of having been near Fukushima when the reactors melted down.
Although the land near the Fukushima nuclear reactors was heavily contaminated by the aerial release of radioisotopes, the majority of the radioactive releases drifted out over the Pacific. There, they were joined by substantial amounts of water that were discharged from the reactors directly into the ocean. A new study, based on data from a NOAA research vessel, takes a look at radioactivity levels near Japan a few months after the disaster. The data suggests that the highest estimates of radioactive discharges are likely to be accurate, but the rapid dilution of the water has kept the levels from Fukushima's isotopes below those of the naturally occurring radioactivity.
Although the peak of discharge into the ocean occurred in early April, NOAA didn't manage to get a vessel in place until June. For the first half of the month, the Ka'imikai-o-Kanaloa (Hawaiian for "Heavenly Searcher of the Sea") sampled the waters and oceanic life off Japan (between 30km and 600km), all while releasing floats that helped researchers identify the predominate currents in the region. Most of the radioactivity was released in the form of cesium isotopes that have half-lives of over two years, so the time needed to get a vessel in place did not allow for a significant decay of the discharged material.
Yesterday's issue of PNAS contains two papers that are first steps in tracking the radiation released by the meltdowns at the Fukushima nuclear plant. Both contain bits of good news: a substantial amount of the radiation went out over the Pacific, and most of the remainder is concentrated immediately northwest of the crippled reactors. However, they also indicate that some isotopes released by the damaged reactors were spread fairly widely across the country, raising the prospect of localized hot spots.
The two papers take somewhat different approaches to understanding where the radiation went. One of them actually involves environmental sampling of the radiation emitted by five different isotopes that were released from Fukushima. The second builds an atmospheric model of the isotopes' spread, and calibrates the model against real-world data.