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Tritium, or hydrogen-3, is identified by the scientific symbol 3H or T. As an isotype of hydrogen, the lightest of all elements, tritium contains two neutrons, whereas ordinary hydrogen (known as protium, identified by the symbol H) contains none. That makes tritium unstable and, as a result, radioactive.

Tritium exists in the natural world, but only in negligible amounts. It’s typically produced during the fission process inside nuclear reactors. Tritium is part of the coolant that lowers the temperature in the reactor core, which is heated by fission.

Tritium is regarded as a low-risk radioactive substance, causing less harm than other types of radiation. For one thing, the radiation emitted by tritium is so weak that it can’t penetrate the outer layer of the skin. And even when it is absorbed by the body, its biological half-life — the time required for half the substance to leave the body — is only 12 days.

But such safety observations only apply to a single dose of radiation, such as an X-ray, and the actual risk depends on the intensity of exposure. That has led various countries to develop strict safety standards for the substance. The European Committee on Radiation Risk warns that internal radiation exposure can cause mutations that could lead to cancer.

The contaminated water at the Fukushima reactor that the Japanese government seeks to release into the ocean contains tritium at levels that are 10 times higher than levels permitted by the South Korean government. That has terrified people not only in Japan but also in Korea.

The Japanese government says that the contaminated water doesn’t present a problem because it will be decontaminated through Tokyo Electric Power Company’s advanced liquid processing system (ALPS), before release. But the tricky part about releasing the contaminated water is tritium, which can’t be removed by ALPS because of the strong chemical bond it forms with water.

But Fukushima isn’t the only place affected by the risk of tritium. Heavy-water reactors are cooled with heavy water (deuterium oxide, 2H2O) instead of ordinary drinking water, producing a greater amount of tritium. There are four heavy-water reactors at Korea’s Wolsong plant, including Wolsong-1, which has been in the news recently after government auditors questioned a report about its economic viability, the justification given for shutting the reactor down earlier than planned.

Even now, Wolsong-2, Wolsong-3, and Wolsong-4 account for 40% of the tritium released by all of Korea’s nuclear stations. Rates of thyroid cancer among women who live near the Wolsong nuclear plant are 2.5 times higher than in other areas, which some think is linked to tritium contamination. The question of nuclear power safety affects Korea in the same way as it affects Japan. It would be foolish and contradictory to view Japanese nuclear plants through the lens of safety and Korean nuclear plants through the lens of economic viability.

By Kim Eun-hyoung, editorial writer

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