Radiation has spiked to all-time highs at five monitoring points in waters adjacent to the crippled Fukushima No. 1 power station, plant operator Tokyo Electric Power Co. said Friday.
The measurements follow similar highs detected in groundwater at the plant. Officials of Tepco, as the utility is known, said the cause of the seawater spike is unknown.
Three of the monitoring sites are inside the wrecked plant’s adjacent port, which ships once used to supply it.
At one sampling point in the port, between the water intakes for the No. 2 and No. 3 reactors, 1,900 becquerels per liter of tritium was detected Monday, up from a previous high of 1,400 becquerels measured on April 14, Tepco said.
Nearby, also within the port, tritium levels were found to have spiked to 1,400 becquerels, from a previous high of 1,200 becquerels.
And at a point between the water intakes for the No. 1 and No. 2 reactors, seawater sampled Thursday was found to contain 840 becquerels of strontium-90, which causes bone cancer, and other beta ray-emitting isotopes, up from a previous record of 540 becquerels.
At two monitoring sites outside the port, seawater was found Monday to contain 8.7 becquerels and 4.3 becquerels of tritium. The second site was about 3 km away.
Tepco is struggling to reduce contamination at the poorly protected plant, which was damaged by the March 2011 earthquake and tsunami. Measures include plans to build a gigantic underground ice wall around the plant to keep the daily flow of groundwater from entering the cracked reactor buildings and mingling with the highly radioactive cooling water in their basements.
The ice wall project is expected to cost ¥31.9 billion and will put a massive burden on the power grid when completed: It will need about 45.5 million kilowatt-hours of electricity to operate, equal to annual power consumption of 13,000 average households.
The project involves freezing the soil into barricades 30 meters deep and 2 meters thick for a distance of 1,500 meters around the buildings housing reactors 1 through 4.
The soil will be frozen by sinking pipes into the ground and running liquids through them at a temperature of minus 30 degrees.
On Friday, the Ministry of Economy, Trade and Industry and contractor Kajima Corp. demonstrated a miniature ice wall to reporters at the site.
“We can confirm the frozen soil’s effect in blocking water,” a ministry official said afterwards.
The department aims to begin construction next month. But the Nuclear Regulation Authority has not approved the plan, saying its backers have so far provided insufficient reassurances about public safety. International nuclear experts have also expressed concern about the effectiveness of the plan.