Fukushima’s North Pacific Radioactive Seawater Plume Approaches Alaska
ASR Limited is a small team of environmental scientists, engineers and consultants, working out of New Zealand, Jakarta and Venice, California:
ASR’s core philosophy is to understand, innovate, and sustain. Our first step is to understand the natural processes governing a specific project site. After spending time developing an understanding of a system’s natural design and function, we implement an innovative and sustainable solution for the project. This approach is always the same whether the challenge is coastal management, fluid transport, fisheries, engineering, or environmental impacts. We work with the world’s top governments, corporations, and organizations to develop innovative solutions for complex issues around the globe.
ASR’s thorough understanding of marine systems, science, and technology enables us to consider environmental and human health in everything we do. We are one of the few companies in the world developing innovative solutions that work in concert with the natural world, rather than against it. By developing technology inspired by nature, we strive to implement solutions that will satisfy the needs of all stakeholders, including our planet.
One of their recent projects has been to hypothetically model the expanding plume of radioactive seawater that has resulted from the escape of water used to mitigate the meltdowns at the four Fukushima power plants:
We use a Lagrangian particles dispersal method to track where free floating material (fish larvae, algae, phytoplankton, zooplankton…) present in the sea water near the damaged Fukushima Daiichi nuclear power station plant could have gone since the earthquake on March 11th. THIS IS NOT A REPRESENTATION OF THE RADIOACTIVE PLUME CONCENTRATION.
Since we do not know how much contaminated water and at what concentration was released into the ocean, it is impossible to estimate the extent and dilution of the plume. However, field monitoring by TEPCO and modeling by the Sirrocco group in University of Toulouse, France both show high concentration in the surrounding water (highest rate at 80 Bq/L and 24 Bq/L for respectively I-131 and C-137) . Assuming that a part of the passive biomass could have been contaminated in the area, we are trying to track where the radionuclides are spreading as it will eventually climb up the food chain.
The dispersal model is ASR’s Pol3DD. The model is forced by hydrodynamic data from the HYCOM/NCODA system which provides on a weekly basis, daily oceanic current in the world ocean. The resolution in this part of the Pacific Ocean is around 8km x 8km cells. We are treating only the sea surface currents. Particles in the model are continuously released near the Fukushima Daiichi power plant since March 11th.
The dispersal model keeps a trace of their visits in the model cells. The results here are expressed in number of visit per surface area of material which has been in contact at least once with the highly concentrated radioactive water.
Here is the youtube they have published that visualizes the model, from the entry of radioactive elements into the water in March 2011, up through November 11, 2011:
It isn’t clear from ASR’s published material whether or not this model is influenced by the continuing entry of radioactive water into the ocean. It is fairly certain that Tepco and other monitoring agencies do not have anything that could be described as a clear idea as to how much radioactive water has gotten into circulation in the North Pacific, or how much water is continuing to make its way there:
On 21 April, TEPCO estimated that 520 tons radioactive water leaked into the sea before leaks in a pit in unit 2 were plugged, releasing 4,700 TBq of total water release (calculated by simple sum, which is inconsistent with the IAEA methodology for mixed nuclide releases) (20,000 times facility’s annual limit). TEPCO’s detailed estimates were 2,800 TBq of I-131, 940 TBq of Cs-134, 940 TBq of Cs-137.
Another 300,000 tons of relatively less radioactive water had already been reported to have leaked or purposefully pumped into the sea to free room for storage of highly radioactively contaminated water. TEPCO had attempted to contain contaminated water in the harbor near the plant by installing “curtains” to prevent outflow, but now believes this effort was unsuccessful.
According to a report published in October 2011 by the French Institute for Radiological Protection and Nuclear Safety, between 21 March and mid-July around 2.7 × 1016 Bq of caesium-137 (about 8.4 kg) entered the ocean, about 82 percent having flowed into the sea before 8 April. This emission of radioactivity into the sea represents the most important individual emission of artificial radioactivity into the sea ever observed. However, the Fukushima coast has one of the world’s strongest currents and these transported the contaminated waters far into the Pacific Ocean, thus causing a high dispersion of the radioactive elements. The results of measurements of both the seawater and the coastal sediments lead to suppose that the consequences of the accident, for what concerns radioactivity, will be minor for marine life as of autumn 2011 (weak concentration of radioactivity in the water and limited accumulation in sediments).
On the other hand, significant pollution of sea water along the coast near the nuclear plan might persist, because of the continuing arrival of radioactive material transported towards the sea by surface water running over contaminated soil. Further, some coastal areas might have less favorable dilution or sedimentation characteristics than those observed so far. Finally, the possible presence of other persistent radioactive substances, such as strontium-90 or plutonium, has not been sufficiently studied. Recent measurements show persistent contamination of some marine species (mostly fish) caught along the coast of Fukushima district. Organisms that filter water and fish at the top of the food chain are, over time, the most sensitive to caesium pollution. It is thus justified to maintain surveillance of marine life that is fished in the coastal waters off Fukushima.
The last sentence is quite an understatement.