►To grasp the effects of the discharge of treated water from the Fukushima Daiichi nuclear power station, it is crucial to understand the terminology of radiation, the Advanced Liquid Processing System (ALPS), and the characteristics of tritium.

►Although Japan’s discharge of ALPS-treated water has been confirmed to have no effect on Korea’s seas through radioactivity monitoring results and the International Atomic Energy Agency (IAEA) report concluded that Japan’s discharge plan met the safety standards, the Korean government should continue to monitor the situation in Fukushima and provide information on the safety of Korea’s seas promptly and transparently to reassure the public.

The upcoming discharge of treated water from Fukushima Daiichi nuclear power station has been a hot issue in the Republic of Korea (ROK) lately. In early July, the International Atomic Energy Agency (IAEA) released ‘IAEA comprehensive report on the safety review of the ALPS-treated water at the Fukushima Daiichi nuclear power station’. However, the controversy surrounding whether the treated water is affecting ROK coastal sea continues. Let’s see if it really a threat to our sea.

Terminology clarification

Radiation is the emission of energy as an electromagnetic wave or a moving subatomic particle. It is released when a structurally unstable nuclide, called radionuclide, transforms. The becquerel (Bq) is the unit of radioactivity that measures the quantity of radioactive material in which one radionuclide is transformed per second. When radiation delivers part or the whole of its energy to a person, such situation is called radiation exposure. The amount of energy delivered to the person is called radiation dose. Even with the same radiation dose, the risk to human health varies depending on the type of radiation and the exposed body part. The radiation dose converted to account for these differences is called the effective dose, and the unit of effective dose is Sievert (Sv) or millisievert (mSv) which corresponds to 1/1000 of 1 Sv.”

Radiation comes from nature as well as man-made facilities such as nuclear power plants (NPPs). Cosmic radiation entering the earth from space reacts with the earth's atmosphere to create various radionuclides. Even on land, uranium and other material undergo radioactive transformation to create radioactive nuclides. Radiation from natural radionuclides is called natural radiation, and radiation emitted from man-made facilities is called artificial radiation. Identical radionuclide has the same radiological properties regardless of its origin, whether it is artificially or naturally produced. According to the 2008 report of UN Scientific Committee on the Effects of Atomic Radiation, the world's average individual radiation dose owing to natural radiation is 2.4 mSv per year. It is an international standard to limit individual radiation dose from artificial radiation to within 1 mSv per year.

ALPS-treated water generation

Groundwater and rainwater near the Fukushima Daiichi NPPs site flowed into the reactor building and contacted the damaged nuclear reactor and fuel, resulting in radioactive contamination of the water. It is known that this contaminated water contains about 62 radionuclides.

In the months soon after the Fukushima NPPs accident, the contaminated water was discharged into the sea at a rate of 300 tons per day without being treated. Since 2013, Tokyo Electric Power Co. has operated the Advanced Liquid Processing System (ALPS), which filters radionuclides from radioactively contaminated water. Contaminated water filtered by ALPS is checked to see if the radionuclide concentration is below the limits for radioactive discharges. If the limits are not satisfied at this time, the nuclide separation and removal process is repeated. After going through this process, radionuclides except tritium are filtered out within the limit.

Among radioactively contaminated water, tritium usually exists in the form of tritiated water (HTO). It has the same characteristics as normal water, so it cannot be completely screened out by ALPS. Tritium is planned to be mixed with seawater in a dilution facility to lower its concentration to less than 1/40 of the Japanese government's limit for discharge (60,000 Bq/L).

Characteristics of tritium

Tritium can also be produced naturally in the atmosphere when cosmic rays collide with air molecules. The most important reaction for the natural production is when high-energy neutrons interact with atmospheric nitrogen. Worldwide, the production of tritium from natural sources is about 280 grams per year. Every year, 0.4g of tritium falls onto ROK with rain and about 4g in the East Sea. The total amount of tritium in the contaminated water stored at the Fukushima NPPs site is 780 trillion Bqs, which is about 2.2 g in terms of mass. The Japanese government plans to release the tritium into the sea every year over the period of 30 years.

Tritium emits beta radiations with a maximum energy of 18.6 keV. The beta radiation is so low in energy that it cannot penetrate human skin. However, it can affect humans when it enters the human body. According to the 2002 report of the International Commission on Radiological Protection, the committed effective dose coefficient of tritiated water for adults, which is a coefficient to calculate the committed effective dose per radioactivity intake, is 1.8×10−8 mSv/Bq. It is about 1/700 of that of Cesium-137, 1.3×10−5 mSv/Bq. As such, tritium has a lower radiological risk to human than other nuclides.

Discharge of the treated water into the sea

Is the Japanese government's decision to discharge the treated water unusual? Not really. It is an international practice to discharge pollutants from various facilities, including NPPs, into the sea or air within the limit for discharges.

Limits for liquid and gaseous radioactive waste discharges generated during nuclear power plant operation are set within the range of not exceeding 1 mSv per year owing to the waste discharge. Korean government also stipulates this in the ‘Nuclear Safety and Security Commission Notification No. 2019-10’, and the limit for discharge for tritiated water is 40,000 Bq/L.

Overview of the recent IAEA report

The IAEA formed a task force with experts from 11 countries to review Japan's Fukushima treated water discharge plan and, in early July, released the report concluding that Japan’s discharge plan met IAEA safety standards and had a minimal impact people and the environment. The radiation dose to residents from the discharge of ALPS-treated water was evaluated at a maximum level of 1/30000 mSv. Even in emergency situations such as pipe damage, the radiation dose to residents was evaluated to be within one hundredth of the annual individual radiation dose limit.

Tokyo Electric Power Co. Ltd. conducted a radioactivity dispersion analysis in a sea area 490 km north-south and 270 km east-west based on the treated water discharge point and showed that the actual effect was limited to the area around the discharge port.

Keeping an eye on the sea near ROK

After the Fukushima nuclear accident, the Korean government has consistently taken measures to protect its citizens. Since September 2013, imports of marine products from eight prefectures of Japan, including the Fukushima Prefecture, have been banned, and Japanese aquatic products have been tested for radioactivity. Radiation surveillance of ROK’s seas has also been strengthened.

According to the '2021 Marine Environmental Radiation Survey Report' published by the Korea Institute of Nuclear Safety in August 2022, the annual average seawater radioactivity concentration in ROK’s seas did not change significantly from 1995 to 2021. It is noteworthy that there has been no significant increase since 2011. Right after the 2011 Fukushima NPPs accident, radioactively contaminated water was discharged without being treated, but there was no effect on our seas.

Although Japan’s discharge of ALPS-treated water has been confirmed to have no effect on our seas through radioactivity monitoring results over a period of over 10 years and the IAEA report, there are still people who are anxious about that. Therefore, the Korean government should continue to monitor the situation in Fukushima and provide information on the safety of our seas promptly and transparently to reassure them