A research team that included Virginie Sanial, Ken Buesseler, and Matthew Charette of Woods Hole Oceanographic Institution and Seiya Nagao of Kanazawa University has discovered an unexpected source for radioactive cesium from the meltdown of the Fukushima reactors in 2011.
In a study that lasted three years, the research team found that high levels of radioactive cesium-137 released in 2011 were transported along the coast by ocean currents. For days and weeks after the accident, waves and tides brought the cesium in the contaminated seawater onto the Japanese Coast.
The cesium became “stuck” to the surfaces of sand grains, according to the research paper published October 2 in the Proceedings of the National Academy of Sciences. The cesium-enriched sand stayed on the beaches and in the brackish, slightly salty mixture of fresh water and salt water beneath the beaches.
Interestingly, the team also discovered that in salt water, the cesium no longer adheres to the sand particles and is released back into the ocean. This means that as more recent waves, tides and storms have brought in more salt water from the ocean, the brackish water underneath the beaches became salty enough to release the cesium.
“No one expected that the highest levels of cesium in ocean water today would be found not in the harbor of the Fukushima Dai-ichi nuclear power plant, but in the groundwater many miles away below the beach sands,” said Sanial.
The significance of the find is important
The research team writes that “although this ongoing source is not at present a public health issue for Japan, the release of Cesium of this type and scale needs to be considered in nuclear power plant monitoring and scenarios involving future accidents.
It should be noted that two types of cesium were found – Cesium-137, which may have come from the Fukushima Daiichi plant or from nuclear weapons tested in the 1950s and1960s. The team also found cesium-134, a radioactive form of cesium that can only come from the 2011 Fukushima accident.
Of the approximately 440 nuclear reactors in the world today, almost one-half of them are located along coastlines. The study authors write, “this previously unknown, ongoing, and persistent source of contamination to coastal oceans needs to be considered in nuclear power plant monitoring and scenarios involving future accidents.”
This research was funded by the Gordon and Betty Moore Foundation, the Deerbrook Charitable Trust, and the European Commission Seventh Framework Project “Coordination and implementation of a Pan-Europe Instrument for Radioecology.” The Woods Hole Oceanographic Institution is a private, non-profit organization on Cape Cod, Mass.