Materials developed at the University of Helsinki have been used in Fukushima, and the radioactive liquid waste has been treated so effectively that, according to the International Atomic Energy Agency (IAEA), the wastewater is no longer hazardous to the environment.
“Selective ion exchange materials developed by University of Helsinki researchers Jukka Lehto and Risto Harjula more than 20 years ago have been used to separate the most important fission products in Fukushima,” says University Researcher Risto Koivula. The Ion Exchange for Nuclear Waste Treatment and for Recycling research group headed by Koivula carries on the study of separation materials at the University.
Radioactive water so far stored in containers
According to Koivula’s description, the Fukushima area is home to a tank farm where the treated water has been stored in containers.
However, more contaminated water is arriving via ground water that enters the plant, as well as by way of ongoing decontamination and decommissioning work. While a marked decrease has been seen from the initial input of nearly 400 cubic metres per day, the quantity of water accumulated over the course of a decade is enormous. In practice, the space for storing it is running out, which is why releasing wastewater into the sea has been planned for years, and pipelines constructed in the area for the purpose.
“However, the decision has not been easy, and it has brought back the emotions felt 12 years ago at the time of the disaster,” says Doctoral Researcher Miho Otaki, who specialises in radiochemistry and who volunteered in helping civilians in a village neighbouring Fukushima after the earthquake and the tsunami.
The radioactive water now released into the sea has been treated with the Advanced Liquid Processing System (ALPS), where water is pumped through several adsorption materials. Two of these are selective ion exchange materials developed at the University of Helsinki.
(Image: Jani Närhi)
New materials for iodine separation
Even though most of the radioactivity, and its main components caesium and strontium, have been almost completely eliminated, the wastewater in Fukushima still contains tritium and small quantities of radioactive iodine.
“Separating tritium would be extremely difficult, and above all expensive, with current technology. Moreover, its half-life is 12 years and its radiation properties weak. This is why its controlled release into the environment has been considered the best way forward,” Koivula notes.
The accumulation of iodine in the human thyroid and its radiotoxicity are well known and taken into consideration by the IAEA. However, it has been impossible to separate it entirely from the Fukushima wastewater with currently available methods, which is why a small amount of iodine-129, a radioisotope of iodine with a long half-life, is ending up in the sea with the effluent.
In his soon-to-be-published doctoral thesis, Valtteri Suorsa has developed at the University of Helsinki promising materials suited to iodine separation, and has presented the results in the RSC Advances journal RSC .