The credibility of the government was eroded when it had to revise its first reassuring statements in the weeks following the earthquake and tsunami that hit the northeast of the country on March 11.

Yukio Edano, spokesperson for the government at the time had said repeatedly, "No meltdown has taken place" at the area's Fukushima Daiichi Nuclear Power Station, after it suffered power outages, fires and explosions. But about two months later, the government and the operator Tokyo Electric Power Company (TEPCO) conceded that the cores of three reactors suffered meltdowns within days of the disaster.

Japanese Self Defense Forces wearing anti radiation gear search for evacuees in Otama village, Fukushima, March 2011

The plant has leaked radioactive material into the environment ever since. Some critics argue the government and TEPCO have continued to downplay the extent of Japan's worst atomic accident.

Danger of contamination

Hiroaki Koide, assistant professor at the Kyoto University Research Reactor Institute, said the melted nuclear fuel might have broken through the bottom of the containment vessel and the concrete base of the reactor building and seeped into the ground. The operator "must build an underground dam immediately to prevent highly contaminated water from leaking into the ocean," Koide said.

TEPCO spokesman Hiroki Kawamata said the operator hoped to start the construction of an underground wall in January, to stop the estimated 110,000 tons of radiation-contaminated water in the basements of the facility from flowing to the sea. But Koide said the wall's projected completion date of 2014 "is too late." Furthermore, the operator has not addressed the possibility of melted nuclear fuel escaping the vessel and contaminating further groundwater, the professor said.

The Fukushima Daiichi nuclear power plant is seen in Okuma town, Fukushima

Unreliable information

Mitsuhiko Tanaka, a former nuclear plant designer, has also challenged the reliability of information about the accident. TEPCO changed the data, especially from reactor number 3, so frequently until mid-May that even the latest account was open to question, he said. He also said the accident report presented to the International Atomic Energy Agency (IAEA) was not enough: The government had an obligation to explain what happened to its own citizens. Tanaka said he was more concerned about the official explanation for the failure of the plant's cooling systems, which led to the explosions and damage.

He said he was appalled that the government and TEPCO both blamed the failures entirely on flooding from the tsunami, and not on the magnitude-9 quake that hit 45 minutes earlier.

Masashi Goto, a former worker at Toshiba Corp specializing in containment vessel design, said Tanaka's observation was important. If the problem was only due to the tsunami, only low-lying nuclear plants would need extra protection. But a new-found vulnerability to quakes would have implications for almost every plant in seismically active Japan, which relied on nuclear power for 30 per cent of its electricity prior to the crisis.

Dpa

Editor: Manasi Gopalakrishnan