Opinion: The Fukishima clean-up continues, 12 years on from the disaster. How safe is the wastewater?

For several years, Japan has been intending to release over 1.25 million tonnes of Fukushima wastewater into the sea as part of its plan to decommission the power station, when its storage capacity reaches its limit in 2023.

Tokyo Electric Power (TEPCO) has built the infrastructure to extract tonnes of newly contaminated water each day, water that is needed to keep the core of each of its three damaged reactors cool. It includes a processing plant called Advanced Liquid Processing System (ALPS), which filters most of the radioactive elements present in the wastewater.

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Of the radioactive elements present in the wastewater, the primary component is tritium, which along with deuterium are isotopes of hydrogen, and they all have an atomic number, Z, of one as they have one proton in the nucleus (and why hydrogen is the first element on the periodic table).

Hydrogen has only the proton and no neutrons; deuterium has the proton and one neutron; and tritum has the one proton and two neutrons. For these isotopes, with the addition of each neutron there is an increase in radioactivity. A radioactive nucleus emits radiation to become more stable and the radioactivity of a given object, or volume of water, is measured in Becquerels (Bq), with one Bq meaning one decay event per second.

Hydrogen has the most stable nucleus of these isotopes. Deuterium and tritium are chemically equivalent to hydrogen, so we can have H2O, D2O, T2O, DOH, TOH, DOT, etc. Naturally, in our biosphere the abundance of these isotopes is that wherever we find hydrogen, including in water, hydrogen occupies 99.9 per cent, deuterium 0.02 per cent and tritium is present in extremely low amounts (~10^-18).

Fukushima wastewater will have a significantly greater concentration of tritium.

Tritium has a half-life, the time it takes to lose half of its radioactivity, of 12.35 years, suggesting that it is rather radioactive. However, the half-life is only part of the story. It tells you how frequently atoms of a particular element and isotope emit radiation to become more stable. The important part for humans and concerns for cancer risk are the type of radiation emitted and most importantly, the energy it carries.

For tritium, beta radiation is emitted, with each emission carrying a maximum energy of 18keV, which is very small for radiation. In air it travels around 10cm before losing its energy, in water it is only a few micrometres, less than the diameter of one strand of hair.

Tritium is therefore of low risk to humans. By releasing into the ocean, the tritium concentration will be extremely diluted (releasing petabecquerels of radioactive material in the wastewater will quickly become trace concentrations of much less than parts per trillion very quickly when deposited into the sea) and over a 30 year period, 81.5 per cent of the tritium radioactivity will be lost.

The main concern for humans is if tritium is ingested through breathing it into our lungs or eating food that contains it in high concentrations. The biological half-life of tritium in humans is estimated to be seven-10 days (the average time for a human to pass half of it out of their body).

Controversy with environmental groups arose because in April and May 2011 over 300,000 tonnes of untreated water was dumped into the ocean to free up water tanks, and these involved over 100 times the legal limit for radioactivity release. While this led to the creation of the ALPS and dramatically improved the elemental profile of the wastewater, this initial dumping started the mistrust.

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In this original unprocessed wastewater, the radioactive isotopes of concern are iodine-131 and caesium-137, which are produced during the decay pathways of the uranium fuel as it is being used. Iodine-131 has a nuclear mass of 131 (it contains a total of 131 nucleons, comprising 53 protons and 78 neutrons), a half-life of eight days, and decays via beta emission with energy 971keV. Caesium 137 decays to barium 137 via emission of a 512keV beta, followed by a 661keV gamma ray.

Both of these isotopes are used in nuclear medicine radiotherapy applications which means that they have sufficient energy to cause cell death and mutation, i.e. are capable of producing cancers. Other radioactive species of note are strontium-90 with a 28 year half-life and a 546keV beta emission, but if ingested, strontium becomes biomineralised like calcium and deposits in teeth and bones; and Cobalt-60 which is most undesirable, with a 5.27 year half-life, and decays via emission of two 1.1732,1.1735 MeV gamma rays and 317keV beta emission being far more harmful than the others.

Cobalt-60 is artificially created in nuclear fission reactors and also forms during the decay pathway of elements that began with uranium fuel. All of these are more hazardous to living species and need to be eliminated from being released into ecosystems, as all food chains will be affected by cumulative effects of these as organisms consume other organisms and end at humans who ingest other species that have accumulated absorbed radioactivity.

So, these radioactive species must be kept out of natural ecosystems as much as possible, especially the ocean.

It is also worthwhile noting that the storage tanks also pose a risk if they release the water in an uncontrolled manner for any reason, including natural disaster.

TEPCO and the Japanese government have sought endorsements from regulatory bodies and have it from the International Atomic Energy Agency (IAEA), which have strict guidelines and international standards on the acceptable practices for radiation protection, and oversee the release of water used in fission reactors around the world.

The IAEA have given their endorsement to the Japanese government and they are planning to go ahead after assessing the risks and dangers of releasing the wastewater from a radiological perspective. In March 2022, an independent panel of global experts on nuclear issues are supporting Pacific Nations in their consultations with Japan over its intentions to discharge treated nuclear wastewater into the Pacific Ocean.

Hopefully, the Japanese government and TEPCO have explored the possibility of seeking a use for the tritiated water through the global nuclear fusion community, as tritium is a key fuel of interest for fusion reactor research. If release of wastewater into the ocean is to proceed, getting the process correct and within regulations is of particular importance to Japan’s aquaculture-based industries.

It is in Japan’s economic interest to ensure that the waterways remain below international acceptable levels for background radiation so that food safety is assured and their capacity for international trade remains unaffected.

Professor Jamie Quinton is the Head of Massey's School of Natural Sciences.