More than 10 years ago, a tsunami caused an accident at the Fukushima Daiichi nuclear power plant on Japan’s east coast. After the accident, large amounts of radioactivity contaminated the seas leading to the establishment of marine exclusion zones and serious damage to the reputation of the fishing industry.
A large amount of contaminated water has accumulated at the site since then. Water is needed to cool the damaged reactors and groundwater that has been contaminated as it enters the site must be pumped out and stored. More than 1,000 tanks have been built at the site to store more than a million tons of radioactive water.
But the area lacks storage space and tanks can leak, especially in the event of an earthquake or typhoon. So the authorities of the Japanese government have given a permit at this site to release the stored radioactive water through a pipeline to the Pacific Ocean.
As an environmental scientist, I have worked on the effects of radioactive waste on the environment for more than 30 years. I think that wastewater disposal is the best option.
Contaminated water
Before storage, the wastewater produced at Fukushima is treated to remove almost all radiation. These include cobalt 60, strontium 90 and cesium 137. But tritium – the radioactive form of hydrogen – is left out.
When one of the hydrogen atoms in water is replaced by tritium, it forms radioactive tritiated water. Tritiated water is similar to normal water, which makes separating it from wastewater expensive, energy-intensive and time-consuming. A review of tritium separation technologies in 2020 found them unable to process the required amount of water.
But as far as radiation goes, tritium is benign and its existence as tritiated water reduces its environmental impact. Chemically similar to normal water, tritiated water passes through organisms as water does and does not accumulate strongly in living organisms.
Tritiated water has a bioaccumulation factor of about one. This means that the exposed animals would have had the same amount of tritium in their bodies as the surrounding water.
By comparison, radioactive cesium 137, released in large quantities after Fukushima and from the UK’s Sellafield nuclear power plant in the 1960s and 70s, has a bioaccumulation factor in marine environments of about 100. Animals are 100 times more likely to have radiocaesium than in humans. surrounding areas. water because cesium enhances food.
Low dose of radiation
When tritium decays, it emits beta particles (high-speed electrons that can damage DNA when absorbed). But the beta phase of tritium is not very strong. A person needs to drink a lot to get a high dose of radiation.
The World Health Organization’s drinking water standard for tritium is 10,000 Becquerels (Bq) per liter. This is several times higher than the amount of water released from Fukushima.
The difficulty of separating tritium from wastewater and its low environmental impact is why nuclear facilities around the world have been dumping it into the ocean for decades. The Fukushima Daiichi site plans to release about 1 Petabecquerel (PBq – 1 with 15 zeros after) of tritium at a rate of 0.022 PBq per year.
This sounds like a huge number but globally, 50-70 PBq of tritium is naturally produced in our atmosphere by cosmic rays every year. Even annually, the Cap de la Hague nuclear power plant in northern France releases about 10 PBq of tritium into the English Channel.
The higher release rate at Cap de la Hague than planned for Fukushima showed no evidence of environmental impact and the levels for humans are low.
Safe release
But the release of radioactive water must be done properly.
Japanese research estimates that wastewater will be reduced from hundreds of thousands of Bq per liter of tritium in storage tanks to 1,500 Bq per liter in wastewater. Diluting the wastewater before it is released will reduce the radiation dose to people.
The radiation dose to humans is measured in sieverts, or millions of sieverts (microsieverts), where a dose of 1,000 microsieverts represents a one in 25,000 chance of dying prematurely from cancer. The highest level from Fukushima’s released water will be 3.9 microsieverts per year. This is much lower than the 2,400 microsieverts that people receive from natural radiation on average every year.
Japanese authorities must also ensure that there is no “organically bound tritium” in the released water. This is where the tritium atom replaces the normal hydrogen in the organic molecule. Organic molecules containing tritium can be leached into wetlands and ingested by marine life.
In the mid-1990s, molecules containing tritium were released from the Nycomed-Amersham pharmaceuticals plant in Cardiff Bay, Wales. This release resulted in bioaccumulation of up to 10,000.
Treatment of some highly radioactive materials also tends to leave small amounts of these materials in the wastewater. The wastewater stored at Fukushima has been reprocessed to ensure that the levels of these substances are too low to prevent leakage.
On the scale of the environmental problems we face, the release of wastewater from Fukushima is very small. But it seems that it will destroy the history of Fukushima fishing. This will not be supported by the political and media furore that will surround the new release of radioactive water into the Pacific Ocean.
Jim Smith, Professor of Environmental Science, University of Portsmouth
This article is reprinted from The Conversation under a Creative Commons license. Read the first article.
