The Methods and Results of
Treated Water Discharge
and Monitoring
Based on Scientific Evidence

TEPCO is planning to discharge ALPS treated water accumulated on the site of the Fukushima Daiichi Nuclear Power Station, which was damaged by the Great East Japan Earthquake and tsunami in 2011, into the sea in 2023. This website was created to address your questions and concerns regarding the discharge of ALPS treated water into the sea, the planning and preparation behind it, and the scientific evidence of ALPS treated water.

1Background of a large amount of water accumulation

On March 11, 2011, the Great East Japan Earthquake and tsunami occurred, causing severe damage to the Fukushima Daiichi Nuclear Power Station. The damage sustained by the plant has in turn caused tremendous suffering to neighboring communities surrounding the plant, and ever since then procedures have been underway to decommission the plant. The Japanese government and TEPCO have worked tirelessly together with local communities to rebuild their lives and livelihoods, and reconstruct the affected areas. The government and TEPCO have also stabilized the nuclear power station and removed contaminated materials. As a result, people who were evacuated at the accident have been returning home. One of the effects of the ongoing decommissioning of the nuclear power station has been the accumulation of huge amounts of water while cooling the damaged reactors. This water is currently being held in storage tanks on the site.

2How and why the Japanese government decided to release the water into the sea

Since the early stages of the accident, the Japanese government and TEPCO have made safety the highest priority, working closely with experts and international nuclear organizations around the world. In order to protect the environment and human health, the government considered all possible options and concluded that the most appropriate policy for dealing with the accumulated water at TEPCO’s Fukushima Daiichi Nuclear Power Station was to discharge the water into the sea after thoroughly treating and diluting it. Based on this decision, the government and TEPCO have formulated a course of action wherein rigorous safety standards will continue to be applied and release the accumulated water into the sea will be undertaken in a careful, gradual, and transparent manner.

Treatment Method of the Water

3Treatment Method of the Water

TEPCO has therefore installed the Advanced Liquid Processing System (ALPS) to remove 62 types of radioactive materials from the vast amount of water. Although there is residual tritium even after this long purification process, the water is then further diluted, thereby meeting and actually falling below the concentration levels as stipulated by Japan and other countries’ regulatory standards for radioactive materials in the water. (*1) This water is referred to as “ALPS treated water” to distinguish it from contaminated water that has not yet been purified.

The radiation emitted by tritium is extremely weak, and can be blocked with a single sheet of paper. It also does not accumulate in the body tissues of humans. (*2) Water containing tritium has been regularly released from nuclear facilities around the world for many years. It has been consistently determined that the releases pose no danger to the environment or human health.

Expert opinion on handling treated water

Mr. Paul Dickman, senior policy fellow focusing on nuclear energy at the Argonne National Laboratory, comments

“Nuclear reactors produce tritium and releasing tiny amounts into the air or into the water is the optimum way of managing it. Because the plan approved by the Japanese Nuclear Regulation Authority takes a comprehensive, engineered approach to ensuring the treated waters will not contain any harmful levels of radioactive materials. Anything that contains water will also contain tritium, and always has.”

“The approach taken in managing the treated water releases are to limit any discharges to nearly the same as those that already occur in nature and well below any harmful level.”

ALPS removes 62 types of radioactive materials, leaving only tritium.
ALPS removes 62 types of radioactive materials, leaving only tritium.

4Amount and concentration of tritium to be released

TEPCO will gradually release up to 22 trillion becquerels of tritium per year from the Fukushima Daiichi Nuclear Power Station over the next 20 or 30 years. (*3) The release of tritium in this manner is a globally accepted standard practice for nuclear facilities, and the amount being released at Fukushima is far less than the amount released from many nuclear facilities around the world, including those in Europe, North America, and other parts of Asia. (*4)

Due to ALPS treatment and further dilution, the water discharged from TEPCO’s Fukushima Daiichi Nuclear Power Station will not contain more than 1,500 becquerels per liter. In fact, the level of tritium in the water discharged from the Nuclear Power Station is even below the maximum amount of tritium in drinking water recommended by the World Health Organization (10,000 becquerel per liter). (*5) TEPCO’s assessment, reviewed by the International Atomic Energy Agency (IAEA), suggests that exposure from treated water from the nuclear power station is less than 0.00003 millisieverts per year. (*6) The average radiation dose received by a typical individual living in Japan is 2.1 millisieverts per year. (*7)

Expert opinion on tritium emitted from Fukushima Daiichi

5Expert opinion on tritium emitted from Fukushima Daiichi

Professor Jim Smith of the University of Portsmouth, England, who specializes in environmental science, has also stated that the predicted doses to people and the environment are tiny and are of no significant consequence to the marine ecosystem, or to people's health.
Seafood caught from the sea is controlled for radioactivity levels and is safe to eat.

Mr. Jim Smith, a professor of environmental science at the University of Portsmouth in the UK

"The tritium will be released in the form of ‘tritiated water’ which from decades of past experience does not biomagnify in food chains. Tritium is also a very weak radiation emitter making it much less dangerous than other radioactive elements. Because of this, a lot of tritium needs to be ingested to give a person a significant radiation dose."

6IAEA’s View

The plans of the Japanese government and TEPCO were reviewed by the IAEA, which convened independent international experts to verify the safety of the water treated by ALPS before it was discharged into the sea. Members also monitored regulatory activities and processes and conducted independent sampling and analysis to corroborate Japanese data.

Based on the findings, the IAEA reviewed TEPCO’s plans for discharging ALPS treated water to ensure that they are consistent with international practices.

IAEA Director General Rafael Mariano Grossi visited to Japan in July of 2023 to present IAEA’s comprehensive report.

Director General Grossi’s Foreword of the IAEA’s Comprehensive Report (PDF 5.4MB)

The approach to discharge ALPS treated water into the sea, and associated activities by TEPCO, NRA, and the government of Japan, are consistent with relevant international safety standards.

The discharge of the ALPS treated water to the sea, as currently planned by TEPCO, will have a negligible radiological impact on people and the environment.

IAEA is committed to engage with Japan on the release of ALPS treated water before, during, and after release, and that further reviews and monitoring provide additional transparency and reassurance to the international community.

IAEA’s Comprehensive Report

TEPCO, for its part, will make the most of its state-of-the-art technology, with the highest priority given to the safety of the people and the environment, to carefully, step by step, and transparently treat the water accumulated at the Fukushima Daiichi Nuclear Power Station, and to carry out this release under the review of the IAEA and in cooperation with international organizations from around the world.

7Overview of the Four Batches of ALPS Treated Water Discharge and Monitoring Methods

In order to track the dispersion of tritium in seawater and the status of marine organisms, TEPCO has strengthened monitoring of seawater (outside of the harbor), fish, and seaweed since April of 2022. In addition to this, TEPCO has initiated rapid sea area monitoring at 14 locations around the Fukushima Daiichi Nuclear Power Station. 10 points within 3km and 4 points within a 10km square from the power station-since the discharge of ALPS treated water from August 24, 2023. At the monitoring points, workers collect water samples for analysis in a laboratory. The procedure is designed to yield results within a day, a timeframe that would typically require a month. The ALPS treated water is diluted by seawater before discharge, and the tritium level is as low as approximately 200 Bq/liter, significantly below the government’s indication of 1,500 Bq/liter. The monitoring results are published on TEPCO's website along with the monitoring results from the Ministry of the Environment, the Fisheries Agency, and Fukushima Prefecture.
As of today, four batches of ALPS treated water, each around 7,800 m³, have been discharged as planned under the safety measures. The first batch was discharged from August 24 to September 11, the second batch from October 5 to 23, and the third batch from November 2 to 20. The daily discharge rate was approximately 460 m³, and remained stable.


8Result of Monitoring

Diligent testing is at the center of TEPCO’s efforts to reassure both local and international community that the water discharge is safe. The monitoring results so far have been encouraging.
Specifically, the results of monitoring by TEPCO, the Ministry of the Environment, the Fisheries Agency, and Fukushima Prefecture have shown no significant increase in the levels of radioactive materials in the seawater around the Fukushima Daiichi Nuclear Power Station. Concentrations of tritium have remained well below the index of 350 Bq/liter set by TEPCO, and is only a tiny fraction of the World Health Organization's guidelines of 10,000 Bq/liter for drinking water.


9Onsite audit by IAEA

The IAEA’s review has been conducted by the IAEA Task Force, which consists of the IAEA officials and international experts, from October 24 to 27 in 2023. The task force reviewed the facilities and equipment installed at the power station for discharging ALPS treated water. They also engaged in technical discussions with TEPCO operators and on-site staff, reviewing data from the first two discharges.

10Comments from IAEA

In the report issued by IAEA on January 30, 2024, they confirmed that the Task Force found the discharge to be consistent with international safety standards and reaffirmed the conclusions from the Agency’s comprehensive safety report issued on July 4, 2023.

Lydie Evrard, IAEA deputy director general and head of the department of nuclear safety and security, told a Tokyo news conference on October 23

“I would say that the first two batches of releases went well. No issues were observed.”

Gustavo Caruso, Chair of the Task Force

“No issues were identified during our visit to the facilities this week and we will continue our review to assess whether the IAEA’s findings from our comprehensive report remain valid.”

11Ongoing Decommissioning Plan

The discharge of ALPS treated water into the sea, as part of the decommissioning process, is a long-term and sustained effort. Throughout this period, TEPCO is committed to ensuring the safety and quality of facility operations, maintaining a strong resolve to prevent reputational damage. TEPCO will devote its full efforts to activities such as “ensuring transparency through IAEA reviews,” “implementing measures to counter misinformation,” and “providing prompt and accurate information.” Additionally, TEPCO will work diligently on “proper compensation in the event of damage” as part of our comprehensive approach.


Background and Scientific Explanation for the Discharge of Treated Water

ALPS Treated Water Discharge: Applying Scientific Evidence for Monitoring and Results


IAEA’s Press Release
IAEA Finds Japan’s Plans to Release Treated Water into the Sea at Fukushima Consistent with International Safety Standards | IAEA
Japan's Discharge of ALPS Treated Water in Line with International Safety Standards, New IAEA Task Force Report Confirms | IAEA
The IAEA’s Comprehensive Report
IAEA’s Video: IAEA Reports on Fukushima Water Release Video: IAEA Reports on Fukushima Water Release
Video: IAEA Reports on Fukushima Water Release Video: IAEA Reports on Fukushima Water Release

▼ Table of contents

  1. Background of a large amount of water accumulation
  2. How and why the Japanese government decided to release the water into the sea
  3. Treatment Method of the Water
  4. Amount and concentration of tritium to be released
  5. Expert opinion on tritium emitted from Fukushima Daiichi
  6. IAEA’s View
  7. Overview of the Three Batches of ALPS Treated Water Release and Monitoring Methodsnew
  8. Result of Monitoringnew
  9. Onsite audit by IAEAnew
  10. Comments from IAEAnew
  11. Ongoing Decommissioning Plannew
  12. Videonew
  13. Linknew