The Kashiwazaki-Kariwa plant — the world's largest in terms of capacity — announced a barrage of leaks and malfunctions in the wake of Monday's magnitude-6.8 temblor, which killed 10 people and injured more than 1,000.
Plant operator Tokyo Electric Power Co., or TEPCO, and nuclear regulators have stressed the amounts of radioactivity leaked were extremely low and posed no threat to the environment or local residents.
But the damage has raised concerns about the plant's safety, prompting the government to order it shuttered indefinitely until its safety can be confirmed.
Nuclear safety and disaster management officials from Niigata prefecture (state), where the plant is located, visited the site on Saturday, prefectural official Tonoichi Okawa said.
TEPCO and the local government have a safety agreement that allows the latter to conduct onsite inspections, the prefecture said in a statement. The team was to check the sites where the leaks occurred and review radiation measurement data, it said.
Monday's earthquake resulted in a raft of malfunctions, damage and mistakes at the plant, including a fire that charred an electrical transformer, planks that toppled into a pool of spent nuclear fuel and the knocking over of some 400 barrels of atomic waste.
The problems — exacerbated by TEPCO's delays in notifying the public — were capped by news that radioactive water had sloshed out of a tank and was flushed out to sea, and that radioactive material was vented into the air in two separate instances.
Officials at the Kashiwazaki plant acknowledged they had not foreseen such a powerful quake hitting the facility. They also repeatedly underreported its impact after it hit.
The government has urged the operators of Japan's 55 nuclear reactors — which supply nearly one-third of Japan's energy — to speed up safety checks for earthquake resistance, a top concern in the temblor-prone nation.
Ten other operators of nuclear reactors in Japan are also unprepared for emergencies, Kyodo News agency said Friday, citing a report from the Trade Ministry. Only one operator has 24-hour firefighters, and seven of the 10 companies are not equipped with chemical fire vehicles, the agency reported.
Meanwhile, Japan has decided to pass on an International Atomic Energy Agency offer to send a team to help assess the impact of the damage at the quake-struck plant, Kyodo said Saturday, citing unidentified government officials.
IAEA chief Mohamed ElBaradei said earlier this week that a thorough review of the plant's problems was key and offered to have his Vienna-based agency pull together global experts.
Tokyo has already conveyed its decision to the IAEA, though the door has been left open to possibly receiving an inspection team in the future, Kyodo quoted the officials as saying.
Phones rang unanswered Saturday at the Ministry of Economy, Trade and Industry.