TOKYO (AP) -- A rat causing a power outage by short-circuiting a temporary switchboard. Another blackout occurring as workers install anti-rat nets. Holes in the linings of huge underground tanks leaking radioactive water.
Japan's crippled Fukushima Dai-ichi nuclear power plant has run into a string of problems the past few weeks that highlight its precarious state more than two years after its reactors melted down in the wake of a devastating earthquake and tsunami.
A makeshift system of pipes, tanks and power cables meant to carry cooling water into the melted reactors and spent fuel pools inside shattered buildings remains highly vulnerable, Nuclear Regulation Authority chairman Shunichi Tanaka acknowledged Wednesday.
"Fukushima Dai-ichi is still in an extremely unstable condition, there is no mistake about that," Tanaka said at a weekly meeting of the regulatory body's leaders. "We cannot rule out the possibility that similar problems might occur again. Whenever a problem occurs, it halts the plant's operations and delays the primary goal of decommissioning the plant."
The problems have raised doubts about whether the plant can stay intact through a decommissioning process that could take 40 years, prompting officials to compile risk-reduction measures and revise decommissioning plans. The regulatory watchdog said Wednesday that it was increasing the number of inspectors from eight to nine to better oversee the plant.
Just over the past three weeks, there have been at least eight accidents or problems at the plant, the nuclear watchdog said.
The spate of problems started March 18, when a rat sneaked into an outdoor switchboard — which was sitting on a pickup truck — powering the jury-rigged cooling system and several other key parts of the plant, causing a short-circuit and blackout that lasted 30 hours in some areas of the plant. Four storage pools for fuel rods lost cooling during the outage, causing Tokyo Electric Power Co., the plant's operator, to acknowledge that it had added backup power only to the reactors, despite repeated concerns raised over a pool meltdown.
The cause of the outage wasn't clear at the time, but TEPCO later released a photo of the electrocuted rat, which had fallen on the bottom of the switchboard outhouse. The most extensive outage since the crisis started after the March 2011 disasters caused some Fukushima residents to even consider evacuation.
Two weeks later, a new water processing machine designed to remove most radioactive elements temporarily stopped after a worker pushed a wrong button. The next day, one of the fuel storage pools lost power again for several hours when part of a wire short-circuited a switchboard while an operator installed anti-rat nets. TEPCO reported three other minor glitches on the same day, including overheating of equipment related to boron injection to the melted reactors.
Regulatory officials acknowledge that rats and snakes are abundant at the plant, and TEPCO has started to take steps to protect pipes and cables from rat gnawing. Replacement of parts and equipment to those of higher quality and long-term use is in progress.
In the latest development, three of the plant's seven underground tanks are leaking. TEPCO reported the first leak early Saturday, hours after the plant's second power outage. Within days, the damage spread to three tanks, paralyzing the plant's storage plans for contaminated water.
TEPCO says none of the about 120 tons of radioactive water that leaked was believed to have reached the ocean. Experts suspect the radioactive water has been leaking from the plant since early in the crisis, citing high contamination in fish caught in waters just off the plant.
The contaminated water is a headache for the plant, and by far the most serious of the recent problems because of its potential impact on water management and the environment.
The tanks are crucial to the management of contaminated water used to cool melted fuel rods at the plant's wrecked reactors. They have since stabilized significantly, but the melted fuel inside must be kept cool with water, which leaks out of the reactors' holes and ruptures and flows into basement areas.
"The contaminated water situation is on the verge of collapse," Tanaka said. But he said there was no choice but to keep adding water, while trying to seek ways to minimize the leaks and their risks.
To address local outrage over the recent problems and TEPCO's failure to detect problems earlier, company president Naomi Hirose traveled to Fukushima and apologized Wednesday for the problems. He promised to expedite the construction of steel containers and move all the water there from the underground tanks, at the request of Industry Minister Toshimitsu Motegi.
The underground tanks, all built by Maeda Corp., come in different sizes, including one the size of an Olympic-size swimming pool and similar to an industrial waste dump. They are dug into the ground and protected by two layers of polyethylene linings inside the outermost clay-based lining, with a felt padding in between each layer.
Regulators suspect a design problem with the underground tanks, which TEPCO allegedly chose over steel tanks as a cheaper option.
"The nuclear crisis is far from over," the nationwide Mainichi newspaper said in a recent editorial. "There is a limit to what the patchwork operation can do on a jury-rigged system."