Intermediate Physics for Medicine and Biology: Is Japan's Plan to Release Radioactive Water into the Pacific Ocean Safe?

Friday, September 1, 2023

Is Japan's Plan to Release Radioactive Water into the Pacific Ocean Safe?

When listening to NBC Nightly News on August 24, I heard Lester Holt discuss Japan’s plan to release into the Pacific Ocean treated wastewater from the Fukushima nuclear power plant, the reactor that melted down after the 2011 earthquake and tsunami. Apparently this plan has caused an uproar, with Russia banning the import of seafood from Japan and residents of South Korea staging protests.

Is there a significant risk to dumping this treated water into the ocean? I will base my analysis on the recently published IAEA Comprehensive Report on the Safety Review of the ALPS-Treated Water at the Fukushima Daiichi Nuclear Power Station.

Two years ago, Japan developed a plan for the handling of Advanced Liquid Processing System (ALPS) treated water at the Fukushima Nuclear Power Station, which included a proposal to release the water into the ocean. Japan then asked the International Atomic Energy Agency (IAEA) to review the safety of their plan. The IAEA Director General established a task force to conduct this review, consisting of independent experts from all over the world (including Russia and South Korea). The task force recently published its report, whose purpose is “to present the IAEA’s final conclusions and findings of the technical review to assess whether the planned operation to discharge the ALPS treated water into the Pacific Ocean over the coming decades is consistent with relevant international safety standards.” The task force concluded that “the approach to the discharge of ALPS treated water into the sea… [is] consistent with relevant international safety standards” and that “the discharge of the ALPS treated water… will have a negligible radiological impact on people and the environment.”

In Chapter 16 of Intermediate Physics for Medicine and Biology, Russ Hobbie and I analyze the risk of radiation. We write

One way to express risk is to compare medical doses to the natural background. We are continuously exposed to radiation from natural sources. These include cosmic radiation, which varies with altitude and latitude; rock, sand, brick, and concrete containing varying amounts of radioactive minerals; the naturally occurring radionuclides in our bodies such as ¹⁴C and ⁴⁰K; and radioactive progeny from radon gas.

The effective dose of radiation is measured in sieverts, or more conveniently millisieverts (mSv). The typical effective dose from natural sources is about 3 mSv per year. What is the dose expected from releasing Japan’s radioactive water into the Pacific? According to the IAEA report, it is in the range from 0.000002 to 0.00004 mSv per year. So, we constantly are exposed to about 3 mSv/year of radiation and now we will experience 3.00004 mSv/year. The risk is negligible.

According to Table 16.6 in IPMB, flying in a plane at 40,000 feet—where cosmic ray exposure is increased—is 0.007 mSv per hour. That means the extra dose caused by the release of radioactive water is approximately equal to the extra dose received during 20 seconds of airplane flight.

The value of 0.00004 mSv/year assumes the water is slowly released as planned. What if there is an accident? The IAEA report examined two accident scenarios and concluded that the upper limit of exposure is 0.01 mSv per accident. In other words, if three of the holding tanks accidentally dump all of their treated water into the Pacific at one time, your dose would be less than one percent of your yearly dose from natural sources.

Another way to look at it the risk is to analyze the amount of tritium released. The treatment of the water before release removes most of the radioactive contaminates except tritium, which is the radioactive isotope hydrogen-3. Tritium is usually found as part of a water molecule, so it is extraordinarily difficult to separate it form normal water. Tritium is constantly being created in our atmosphere by cosmic rays colliding with nitrogen. About 100,000 TBq is produced each year. A becquerel (Bq) is one nuclear decay and tera- (T) is the metric prefix for 1,000,000,000,000. How much tritium will be released each year from Japan’s wastewater? 22 TBq. In other words, the amount of tritium released is about 5000 times less than the amount naturally produced. Once the released water is diluted and mixed with ocean water, the increase in tritium concentration will be insignificant.

My conclusion is that releasing the treated water into the ocean is safe, with a large margin of safety. Russia and South Korea can relax. Lester Holt, I love ya, but you really gotta read the IAEA report more carefully.

There are plenty of things we all should worry about (just listen to the rest of the news report in the video below). The release of Japan’s wastewater into the ocean is not one of them.