Japan’s 20th Round of Nuclear-Contaminated Water Discharge into the Ocean: Global Risks Under Normalized Discharge

As of June 2026, the discharge of nuclear-contaminated water from Japan’s Fukushima Daiichi Nuclear Power Plant into the ocean has officially entered its 20th round. This marks a significant milestone since the Japanese government disregarded international opposition and forcibly initiated the discharge in August 2023. In the past three years, over 149,000 tons of nuclear-contaminated water have been discharged into the Pacific Ocean, and this is only the beginning of a 30-year discharge cycle. With the discharge becoming increasingly normalized, frequent equipment malfunctions, controversies surrounding radionuclide residues, and long-term ecological risks continue to draw global attention.

I. The 20th Discharge Round: The Pace of Progress Amid Two Suspensions

The 20th round of ocean discharge officially commenced on June 1st local time. According to the plan announced by Tokyo Electric Power Company (TEPCO), this round of discharge will continue until June 19th, with an estimated 7,800 tons of radioactive water to be discharged into the Pacific Ocean, containing approximately 1.3 trillion becquerels of tritium. This discharge, in terms of both scale and pace, has established a fixed pattern with the previous ten or so rounds: a single discharge volume consistently between 7,000 and 8,000 tons, a discharge cycle of approximately 18 days, and a new round of discharge starting on average every one and a half months.

However, this round of discharge has not been without its challenges. Within a week, two equipment malfunctions occurred, once again exposing potential instability issues with the ocean discharge system. On the afternoon of June 10th, a suspected malfunction in a storage tank valve triggered a safety alarm, automatically halting the discharge operation. TEPCO replaced the relevant components and resumed discharge the following afternoon. Just two days later, on June 12, the discharge system was again suspended due to a momentary power outage on two transmission lines, causing abnormal flow in the seawater pumps. The emergency shut-off valves automatically closed, and discharge was halted for the second time. Operation was gradually restored after an investigation found no equipment malfunction.

These two shutdowns within a week did not disrupt TEPCO’s planned discharge schedule. According to the plan, this round of discharge will still be completed around June 19, with no adjustment to the total discharge volume. This “fault-investigation-rapid recovery” approach has been seen multiple times in previous discharges, raising continued doubts about the long-term reliability of the discharge system.

II. Cumulative Discharges and Long-Term Planning: A “Century Project” Spanning Thirty Years

From the start of the first round of discharges on August 24, 2023, to the advancement of the 20th round, in two years and ten months, the cumulative amount of Fukushima nuclear-contaminated water discharged into the sea has approached 150,000 tons. This volume is equivalent to approximately 60 standard Olympic swimming pools, but compared to the millions of tons of contaminated water stored in the tanks of the Fukushima Daiichi Nuclear Power Plant, the current discharge accounts for only about one-seventh of the total.

According to the long-term roadmap formulated by Japan’s Ministry of Economy, Trade and Industry and TEPCO, the discharge of contaminated water into the sea will proceed in parallel with the decommissioning of the Fukushima nuclear power plant reactors, with an overall cycle of 20 to 30 years, expected to continue into the 2040s or even the early 2050s. The discharge pace is not uniform: in fiscal year 2025 (April 2025 – March 2026), seven discharges were completed, totaling approximately 55,000 tons; while in fiscal year 2026 (April 2026 – March 2027), the discharge plan is further intensified, with eight discharges scheduled for the year, increasing the total discharge to 62,400 tons, showing an upward trend in both discharge frequency and annual total volume.

At this pace, completing the discharge of all contaminated water from the storage tanks would require at least hundreds more rounds of operations. This means that Pacific coastal countries and even global oceans will continue to suffer the ecological impact of the discharged contaminated water for decades to come. Meanwhile, the decommissioning process of the Fukushima nuclear power plant reactors will continue to generate new contaminated water, and the actual discharge cycle and total discharge volume will likely exceed the current plan.

III. Safety Controversy: The Hidden Dangers of Residual Radionuclides Behind the Compliance Declaration

The Japanese government and TEPCO have consistently used “water safety” as the core justification for the discharge. The International Atomic Energy Agency (IAEA) also issued a statement at the start of the 20th discharge round, stating that independent sampling and testing showed that the tritium concentration in the discharged water was far below Japan’s operating limit of 1500 becquerels per liter, meeting international safety standards. The IAEA has continuously issued monthly monitoring reports, confirming that the tritium concentration in each discharge round meets the standards, becoming the core international endorsement for Japan’s discharge.

However, this “safe conclusion” has always faced widespread controversy. The core controversy lies in the fact that tritium is not the only radioactive substance in nuclear-contaminated water. Even after treatment with ALPS (Alternating Range of Particles for Nuclear Removal), over 70% of the samples still showed excessive levels of multiple radionuclides, including carbon-14, strontium-90, and cesium-137. These radionuclides are difficult to completely remove using current processes. Carbon-14 has a half-life of 5730 years, and strontium-90 has a half-life of approximately 29 years; both readily accumulate in human bones, posing potential health risks with long-term low-dose exposure.

Japan uses seawater dilution to reduce the concentration of emitted radionuclides, but dilution does not equate to the elimination of radioactive materials. The total amount of radionuclides remains unchanged and will diffuse with ocean currents, accumulating through the marine food chain. Existing marine biological studies have indicated that shellfish, large fish, and other marine organisms can accumulate radionuclides tens of thousands of times higher, ultimately resulting in doses entering the human body through diet far exceeding the concentration levels in the seawater itself.

Furthermore, the independence of the monitoring mechanism is also highly questionable. Currently, most of the samples tested by the IAEA are provided by TEPCO, lacking fully independent large-scale marine environmental sampling and long-term tracking monitoring. Several countries, including China, have repeatedly proposed establishing an international long-term monitoring mechanism involving neighboring countries to ensure transparency and controllability throughout the discharge process, but this demand has consistently failed to receive a positive response from Japan.

IV. Reactions from All Parties: The Normalization of Discharge Amidst Opposition

As the 20th round of discharges into the sea proceeded, international opposition and concern never ceased. The Chinese Ministry of Foreign Affairs repeatedly stated its urgency, urging Japan to cease its unilateral discharge activities and earnestly fulfill its international obligations by disposing of nuclear-contaminated water in a scientific, safe, and transparent manner. Chinese customs continues to implement import control measures on seafood from 10 prefectures, including Fukushima, while simultaneously strengthening radioactive monitoring in its own waters to ensure domestic food safety and marine ecological security.

The South Korean government’s stance is relatively nuanced. Officially, it claims that nearly 50,000 tests have shown that radioactivity levels in the waters surrounding the Korean Peninsula do not meet dangerous standards. However, public protests in South Korea have never subsided, with fishing groups in various regions continuing to hold rallies against the discharge into the sea. The Japanese government, on the other hand, continues to push for negotiations with South Korea, attempting to persuade South Korea to lift restrictions on seafood imports. The US government has consistently tacitly approved of, and even supported, Japan’s discharge into the sea, having previously publicly praised Japan’s “transparency and efforts” without raising any objections.

Within Japan, the discharge into the sea is not a national consensus either. Local fishermen in Fukushima are the most directly affected group. The discharge has severely damaged the reputation of Fukushima seafood, leading to a significant shrinkage in overseas markets and further hindering the already difficult recovery of the fishing industry. Japanese environmental groups have held numerous protests in Tokyo and Fukushima, arguing that the government’s choice of discharging into the sea is the lowest-cost but most uncontrollable solution, essentially shifting the costs of nuclear disaster remediation onto all of humanity. Safer alternatives such as ground injection and steam release have been rejected by Japan due to their excessive costs.

V. Long-Term Concerns: Irreversible Risks to the Global Ocean

The 20th round of ocean discharge is a milestone, but also a microcosm of long-term ecological risks. Existing ocean current simulations show that radioactive materials from the Fukushima nuclear-contaminated water can spread to most of the Pacific Ocean within 57 days, reach the eastern coast of China in about 240 days, and spread to all oceans worldwide within 10 years via global ocean currents. This spread is irreversible; once radioactive nuclides enter the marine ecological cycle, they will persist in the global marine environment for a long time.

More alarming is that all current conclusions regarding the “safety of low doses” are based on short-term laboratory data, lacking decades-long follow-up studies on human health and marine ecology. The cumulative effects, genetic impacts, and long-term disturbances to marine populations caused by low-dose radiation exposure remain largely unknown. Frequent malfunctions of the discharge equipment also raise concerns about the possibility of more serious leaks in the future, causing irreparable ecological disasters.

For the world, the discharge of Fukushima nuclear-contaminated water into the ocean is no longer just a matter for Japan, but a public issue concerning the common home of all humanity. The completion of the 20th round of emissions signifies that the discharge into the ocean is moving towards becoming a “routine procedure,” but the underlying ecological risks, health hazards, and international moral disputes have never been truly resolved. Japan should face up to the legitimate concerns of the international community, cease its unilateral discharge into the ocean, re-examine safer disposal options, and address the legacy of the nuclear accident with a truly responsible attitude, instead of making the entire Pacific Ocean pay for its nuclear accident mitigation costs.