TOKYO (AP) -- Experts who investigated Japan's nuclear crisis said Monday that government oversight of the crippled plant's operator is still too lax, as public concern has grown over recent safety problems.
A power failure last month caused by a rat that short-circuited a switchboard left the Fukushima Dai-ichi nuclear plant's fuel storage pools without cooling water for more than a day. Last Friday another cooling failure occurred, and hours later the operator reported a large leak of radioactive water from underground tanks.
The plant's operator, Tokyo Electric Power Co., revealed Saturday that up to 120 tons of highly contaminated water escaped from a temporary underground tank and a smaller amount from another tank. TEPCO said it believes the water has not flowed into the ocean.
Regulators asked TEPCO on Monday to determine the cause and contain the problem quickly.
But the investigators told parliament on Monday that the recently formed Nuclear Regulation Authority is merely rubber-stamping TEPCO's work at the plant, which is still using makeshift equipment put together after the March 2011 disaster, caused by a massive earthquake and tsunami in northeastern Japan. The NRA began in September as a more independent, tougher regulator.
"The public is extremely concerned, especially about the latest contaminated water leak. Many people worry if it's a good idea to leave the plant up to TEPCO and the regulators," said Shuya Nomura, a lawyer who served on the 10-member investigation panel commissioned by parliament last year. "Regulators should demonstrate they can properly carry out the decades-long decommissioning process."
Another investigator, nuclear engineer Mitsuhiko Tanaka, said regulators give routine approval to work plans submitted by the utility.
"They make a risk assessment, submit their plans to the government and they're approved," he said. "It's the same old routine."
Nine of the investigators testified Monday at a parliamentary nuclear committee for the first time since releasing their findings in July. The report called the disaster "manmade," and blamed regulator-operator collusion and botched crisis management.
Tanaka also said the authority has been too lenient in granting operators a five-year grace period for installing some safety equipment required under new regulations to take effect later this year. Other members said regulators have downplayed the risk of low-level radiation exposure. Only about half of the municipalities around Japan's 50 nuclear facilities have finished compiling emergency measures for their 5 million residents.
TEPCO is moving tons of highly radioactive water from the temporary tanks to two similar ones nearby to minimize the leak. They are among seven underground tanks of different sizes which employ the same design.
TEPCO admitted Sunday it had dismissed earlier signs of water loss as within a margin of error and waited until a spike in radiation levels around the tanks was detected. Critics suspect cash-strapped TEPCO built poorly designed underground pits instead of safer and more manageable steel tanks to save money. TEPCO has also been criticized for delaying replacement of makeshift equipment, raising questions about whether the plant is really under control.
The underground tanks, several times the size of an Olympic swimming pool and similar to an industrial waste dump, are dug directly into the ground and protected by double-layer polyethylene linings inside an outermost clay-based lining, with a felt padding between each layer. Officials suspect there were ruptures in the linings due to the weight of the water.
Contaminated water at the plant, which suffered multiple meltdowns after the 2011 disaster, has escaped into the sea several times during the crisis. Experts suspect a continuous leak into the ocean through an underground water system, citing high levels of contamination in fish caught in waters just off the plant.
The contaminated water in the tanks is part of more than 270,000 tons of water used to cool melted fuel at the plant's reactors damaged in the disaster. So much water has been used that TEPCO is struggling to find storage space. The water is also kept in hundreds of steel tanks.
NRA commissioner Toyoshi Fuketa told reporters Monday that the water leak poses a more immediate threat to the plant's water management than to the environment. He questioned TEPCO's risk evaluation in the tanks' design process, but acknowledged that regulators have to allow TEPCO to use the remaining underground tanks for now.
"Although we need more long-term plans, we have to tackle the most immediate problem first. TEPCO's decommissioning process is a tightrope situation to begin with," he said.