The highest radiation levels so far have been found near tanks holding contaminated water used to cool reactors at the wrecked Fukushima nuclear plant in Japan.
Readings of 2,200 millisieverts per hour were found yesterday, in an area where levels were measured last month at 1,800 millisieverts, operator Tepco confirmed.
A spokeswoman for the company said the fluctuation could have been caused by moving around, and that the figure did not necessarily indicate rising radioactivity.
However, the news will not allay fears over the ongoing problems at the plant.
The new readings are equivalent to the amount of radiation that plant workers may be exposed to in a full year under government guidelines.
The reading was at one of four radiation hot-spots near storage tanks reported by Tepco over the weekend, one of which led crews to a leaking pipe that was repaired last week.
Investigators will now deploy more advanced sensors to locate the source of yesterday’s reading, Yoshida said.
Tepco reported a 300-ton leak last month from a tank used to store contaminated water in what the country’s nuclear regulator designated the worst accident since the March 2011 earthquake and tsunami caused reactors to meltdown.
Tepco has subsequently boosted the number of tank- inspection patrols from twice to four times a day and increased its inspection staff to 60 members from 10, it said.