Humans have long lived with radiation, with numerous radioactive materials existing in nature. The small amount of radiation to which we are exposed is not harmful and indeed sometimes even has positive effects.
In terms of human health, there is an appropriate level for exposure to everything. For instance, a small amount of salt in our diets is essential for our lives. However, an excessive intake of salt can lead to premature death. The recommended daily salt intake for humans is between 0.5 g and 5 g per day, while more than that can cause health problems and 30 g to 60 g can be fatal.
The same applies to radiation. A small amount of radiation may have positive effects on our health. For example, some people visit low-level radium hot spring resorts believing the bathwater will have health benefits. However, exposure to massive amounts of radiation can be fatal. As with daily salt intake, the effects of radiation on humans must be weighed quantitatively.
In Japan, people are exposed to about 2.1 mSv of radiation per year on average, this being the amount emitted from the surface of the earth, outer space, or (the majority) contained in food products. Meanwhile the average medical exposure in Japan per person is 3.9 mSv per year, with dosages varying for CT scans and X-rays, and depends on the frequency of such examinations. The point is, exposure to low levels of background or medical-use radiation does not have immediate health implications for most people, in the same way that an intake of 0.5 g to 5 g of salt per day is not normally harmful.
There are numerous sources of background radiation. Potassium (K-40) is one important source, this being a mineral found in the earth’s crust, the ocean and in the human body. In the sea, natural K-40 background radiation is around 12 Bq/L. Meanwhile the content of K-40 in an adult human is around 4,000 becquerels. K40 decays by emitting beta particles, but in such small amounts they are not harmful to humans, who have evolved to live with low levels of background radiation.
The ocean contains other radioactive materials, such as uranium. The concentration of uranium in seawater is much lower than potassium and other metal ions, at around 0.08 Bq/L. Uranium decays by emitting alpha particles, another form of radiation which has no effect on human health, unless it is ingested or inhaled in large dosages. Overall, then, seawater naturally contains low level background radiation of 12 Bq/L of K-40 and 0.08 Bq/L of uranium. It is worth quantitatively considering other radiation sources against this natural background radiation.
Following the 2011 accident at TEPCO’s Fukushima-Daiichi Nuclear Power Plant (Fukushima-Daiichi-NPP) that resulted from the tsunami triggered by the Tohoku earthquake, many radioactive materials normally contained within the fuel rods were released into the reactor vessel and atmosphere when the fuel melted. Water was continually supplied to the reactor to cool the melted fuel, generating huge volumes of contaminated water, which continues to be held in storage tanks.
The Advanced Liquid Processing System (ALPS) has been used to clean this water, creating so-called ALPS-treated water. The ALPS process is able to remove all radioactive materials from contaminated water except for tritium, since tritium has very similar chemical characteristics to hydrogen (water). With the exception of tritium, however, all radioactive materials are removed from the contaminated water to levels low enough to meet world standards.
Tritium (H-3) is a radioactive isotope of hydrogen which emits beta radiation as it decays. The physical half-life of tritium is around 12 years, meaning that it takes around 12 years for tritium to decay to half its original amount. In around 40 years it will have decayed to about one-tenth its present amount. In the natural environment, quantum particles from the sun generate tritium in the atmosphere. Specifically, quantum particles react with nitrogen or oxygen atoms to become tritium. The tritium in the atmosphere falls to the earth in the form of rain, which explains why the tritium concentration of water on land, such as river water, is around 1 Bq/L, slightly higher than that of seawater.
In the 1960s, atmospheric atomic bomb tests conducted by China put tritium into the atmosphere, and the tritium concentration in rainwater in Japan quickly rose to around 200 Bq/L. Yet even with this greatly increased concentration, Japan suffered no known adverse health effects. Because tritium has a half-life of around 12 years, seawater contains no tritium except near the ocean surface, where the tritium has been supplied by rainfall or rivers. Thus, the ALPS-treated water, which has a tritium concentration of less than 1,500 Bq/L, will diffuse into the sea, resulting in very low concentrations of less than 1 Bq/L that are harmless to people and the environment. Again, for comparison, seawater naturally contains concentrations of 12 Bq/L K-40 and 0.08 Bq/L uranium.
Many countries, including Korea and China, release tritium into seawater. The controlled tritium release from these countries’ nuclear facilities is usually larger than that of the scheduled Fukushima-Daiichi-NPP release. For example, Korea’s Kori-NPP releases tritium amounting to around 50 TBq per year, while Fukushima-Daiichi-NPP releases approximately 22 TBq yearly. No effects from the tritium release have been reported in Korea. The International Atomic Energy Agency also checked the effects of the Fukushima-Daiichi tritium release, and confirmed that it would have no harmful impact on people and the environment. The Japanese government and TEPCO have stated they will increase seawater monitoring frequency to ensure that tritium and other radioactive materials levels are low enough not to have any harmful impact and will open the data gathered to the public.
The ALPS-treated water release will thus have no physical effects. However, it may be accompanied by harmful rumors, which have the potential to cause substantial economic damage to Fukushima and Japan. Harmful rumors are sometimes intentionally started by specific organizations. Any information that is released should be carefully checked and verified to reduce the chance of any hazardous impact. The economic damage caused by information contamination must be avoided.
Fukushima-Daiichi ALPS-treated water will be released this summer under the strict control of the Japanese government and TEPCO. The release will not only be a major step forward in the decommissioning of the Fukushima-Daiichi NPP, it will also mark significant progress for Fukushima and Japan.