Radiation levels in a drainage channel at the devastated Japanese nuclear plant in Fukushima more than doubled overnight, Tokyo Electric Power Co said Thursday.

A record high 140,000 becquerels per litre of beta radiation was detected, compared with 59,000 becquerels on Wednesday, the operator of the Fukushima Daiichi Nuclear Power Station said.

The spike was probably caused after a recent heavy downpour washed radiation-contaminated soil into the ditch, Tokyo Electric said.

A becquerel refers to the amount of nuclear degradation — and emission — per second for a given volume of contaminated material.

As two typhoons are expected to approach Fukushima over the weekend, the Nuclear Regulation Authority has approved the removal of the toxic water to three underground pools, which Tokyo Electric stopped using after similar models leaked in April, broadcaster NHK reported. The operator said it has no choice, NHK added.

The drainage channel is located near a cluster of storage tanks that contain high levels of radioactive water from three nuclear reactors that suffered meltdowns after a tsunami swept through the plant in March 2011.

The operator has been struggling to deal with toxic water as it continues to inject water into the three reactors to keep them cool. In late August, about 300 tons of radiation-contaminated water leaked from a storage tank, some of which may have reached the sea, the operator said.

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