Radiation levels have surged in seawater near a tsunami-stricken nuclear power station in Japan, officials said yesterday, as engineers battled to stabilise the plant in hazardous conditions.
Urgent efforts were under way to drain pools of highly radioactive water near the reactors, after several workers sustained radiation burns while installing cables as part of efforts to restore the critical cooling systems.
The new safety worries further complicated efforts to bring the ageing facility under control, and raised fears that the fuel rod vessels or their valves and pipes are leaking.
“It is becoming very important to get rid of the puddles quickly,” said an official at the nuclear safety agency, Hidehiko Nishiyama.
One of the worst-case scenarios at reactor three would be that the fuel inside the reactor core – a volatile uranium-plutonium mix – has already started to burn its way through its steel pressure vessel.
“Highly radioactive water is flowing inside the buildings and then into the sea, which is worrying for fish and marine vegetation,” said Olivier Isnard, an expert at France’s Institute for Radiological Protection and Nuclear Safety.
“One hypothesis is that the reactor vessel is breached and highly radioactive corium is coming out,” he told AFP.
Fire engines hosed thousands of tons of seawater onto the plant to keep the fuel rods inside reactor cores and pools from being exposed to the air, where they could reach critical stage and go into meltdown.
Several hundred metres offshore in the Pacific Ocean, levels of iodine-131 some 1,250 times the legal limit were detected yesterday, a ten-fold increase from just days earlier, operator Tokyo Electric Power Co. (TEPCO) said.
Drinking a half-litre bottle of fresh water with the same concentration would expose a person to their annual safe dose, Nishiyama said, but he ruled out an immediate threat to aquatic life and seafood safety.
“Generally speaking, radioactive material released into the sea will spread due to tides, so you need much more for seaweed and sea life to absorb it,” he said.
Because iodine-131 decays relatively quickly with a half-life of eight days, “by the time people eat the sea products, its amount is likely to have diminished significantly,” he said.
However, TEPCO also reported levels of caesium-137 – which has a longer half life of about 30 years — almost 80 times the legal maximum. Scientists say both radioactive substances can cause cancer if absorbed by humans.
The government’s assurances did little to lift the gloom that has hung over Japan since a 9.0-magnitude quake struck on March 11 and sent a huge tsunami crashing into the northeast coast in the country’s worst post-war disaster.
The wave easily overwhelmed the world’s biggest sea defences and swallowed entire communities. The confirmed death toll stood at 10,418 yesterday, with little hope seen for most of the 17,072 listed as missing.
The tsunami knocked out the cooling systems for the six reactors of the Fukushima plant, leading to suspected partial meltdowns in three of them. Hydrogen explosions and fires that have also ripped through the facility.
High-voltage electric cables have since been linked up to the reactors again and power has been partially restored in two reactor control rooms.