No abnormal radiation readings have been detected from North Korea’s nuclear test on Sunday, the Nuclear Regulation Authority said.

“Generally, radioactive substances are not supposed to be released into the air in case of an underground nuclear test,” an NRA official noted, adding that monitoring would be bolstered.

In addition to its monitoring posts, the NRA will analyze airborne dust and rainwater every day for the time being to check for changes in its regular readings. Such examinations are usually conducted every one to three months.

The NRA is also making use of a diffusion estimate from WSPEEDI, the worldwide version of the System for Prediction of Environmental Emergency Dose Information (SPEEDI) used in Japan.

If radioactive substances were released into the atmosphere by the test, they will show up above the Sea of Japan waters near the continent at around 6 p.m. Monday, according to the computerized forecast. The estimate will be presented to the Air Self-Defense Force and reflected in plans for radiation monitoring using aircraft.

To look for abnormal readings, the NRA compared the average radiation readings measured by Japan’s 308 nationwide monitoring posts starting from 1 p.m., shortly after the nuclear test, until 5 p.m., with the average readings logged over the two years before the test. The survey found no abnormal readings, the NRA said.

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