Researchers at the University of California, Davis, recently discovered adverse radioactive effects of seawater used to cool nuclear plant damaged during the natural disaster that struck Japan almost a year ago.
On March 11, 2011, a 9.0 magnitude earthquake struck off the eastern coast of Japan. The disaster resulted in over 15,000 confirmed deaths and 3,300 still listed as missing. With an estimated cost of $235 billion, the earthquake and its aftereffects, including the 40-foot tsunami that slammed into the Japanese coast, mark the most expensive natural disaster in human history.
The tsunami caused by the earthquake's tremors resulted in a nuclear crisis at the Fukushima-Daiichi Nuclear Power Plant. Meltdowns due to overheating at three of the plant's six nuclear generators resulted in the release of radioactive material, subsequently causing the Japanese government to declare a 20 km danger zone around the damaged plant.
The tsunami that topped the ineffective seawall at the power plant damaged the backup generators that were being used in the absence of electricity to cool the generators. This resulted in overheating of the nuclear cores of the first three reactors.
The heat given off by the overheated reactors was indicative of spontaneous radioactive decay, since even after the reactor was turned off, there were still enough unstable particles in the surroundings that can release radioactive compounds spontaneously and give off heat energy. To combat this, authorities used seawater to cool the reactors. Even though this method was effective, it also caused the reactors to become damaged beyond repair.
The scientists at the University of California analyzed the effects of using seawater to cool nuclear reactors, such as those damaged at Fukushima. Under controlled conditions, they replicated the events at the power plant, reacting irradiated nuclear fuel and water containing various levels of ions found in seawater. Results showed that the compounds created by the reaction caused corrosion of the nuclear fuel.
The compounds formed by this reaction, called peroxides, form when seawater is stagnant and non-flowing, much like the way seawater was trapped after it was used to cool the reactors during the catastrophe in Japan. The peroxides then corrode radioactive uranium compounds, leading to the release of uranium ions.
The complexity of these compounds is such that it requires a huge amount of energy to break the bonds that hold them together. Therefore, these uranium compounds can exist quite stably for a long time, traveling through the air, dissolving in ground waters and flowing into the ocean via rivers.
In their paper, published in The Proceedings of the National Academy of Sciences this January, the researchers acknowledge that it remains too difficult to determine how much energy is needed to release the radioactive uranium atoms, which may lead to the spontaneous decay and subsequent release of radioactivity into the environment.
Nonetheless, their findings prove conclusively that peroxides are produced where water comes directly into contact with nuclear fuel, especially at the surface of the fuel where the water is relatively stagnant.
This criteria for peroxide formation corresponds directly to the cooling of the reactor cores at Fukushima-Daiichi, thus raising the hypothesis that stable uranium compounds are probably at these locations in high concentrations. Although their stability does not make them an immediate threat, the presence of uranium atoms nevertheless poses a long term concern.
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