Four workers working at the demolition site of the damaged Fukushima Daiichi nuclear power plant (northeastern Japan) came into contact with water contaminated with radioactive substances and two of them were hospitalized as a precaution, an official said today.

A total of five workers were cleaning pipes of the ALPS filtration system – used for decontamination of water used when the March 11, 2011 disaster occurred – when a hose came out of its place, splashing the two, explained a representative of TEPCO, the plant’s operator.

Two other workers were infected while cleaning up the damage, the spokesman added.

The level of radioactivity in the two men admitted to hospital was above the limit considered harmless. One was found to be contaminated with 6.6 millisieverts (mSv) of beta radiation, while the safe limit is 5 mSv.

The possibility of the two workers suffering burns due to their exposure to radiation was described by a doctor as very low, according to TEPCO.

“We have been informed that the condition of the two workers who are hospitalized is stable,” the spokesman said, adding that “they will remain in the hospital for approximately two weeks to (undergo) repeat tests.”

The company is studying the circumstances of the accident in order to take measures to prevent such an incident from happening again, he added.

TEPCO in late August began the process of dumping into the Pacific Ocean, after treating and dissolving in seawater, quantities of water that had been used to cool the Fukushima Daiichi reactors, which suffered a core meltdown after the 9.1-magnitude earthquake and the giant tsunami of 2011.

The second phase of disposal, which is being phased in and is expected to last until the early 2050s based on the current schedule, was completed this week.

The process has secured a green light from the International Atomic Energy Agency (IAEA) and Tokyo assures that there is no risk to the environment and public health.

The waters are treated with the ALPS (Advanced Liquid Processing System) to get rid of radioactive substances, with the exception of tritium, an isotope of hydrogen that is not classified as dangerous except in very high concentrations.

For this reason TEPCO is now dissolving the tritiated water in seawater before dumping the used water into the ocean, so that the level of radioactivity does not exceed the target limit of 1,500 Becquerels per liter (Bq/L). This level is 40 times lower than the limit in Japan, and is also seven times lower than that set by the World Health Organization (WHO) for drinking water (10,000 Bq/L).

Japan plans to dump more than 1.3 million cubic meters of water containing tritium from the damaged Fukushima nuclear plant into the Pacific Ocean, an amount that would fill 540 Olympic-sized swimming pools.