TOKYO (AP) — Japan's nuclear regulator said Wednesday that the operator of a crippled nuclear plant knew it might be hit by a far bigger tsunami than it was designed to withstand.
The Nuclear and Industrial Safety Agency said the operator informed it just four days before Japan's massive March 11 earthquake and tsunami that waves exceeding 10 meters (33 feet) could hit the Fukushima Dai-ichi nuclear plant.
The plant was only designed to withstand a tsunami about half that height.
Agency officials said Wednesday they recommended that Tokyo Electric Power Co. take measures to prepare for a bigger tsunami but did not give specific instructions.
The March tsunami hit the plant with waves higher than 15 meters (49 feet), destroying its cooling systems, triggering explosions and fires and sending large amounts of radiation into the environment. The cores of three of the plant's six reactors melted within a few days.
NISA spokesman Yoshinori Moriyama told a news conference Wednesday that TEPCO officials visited the agency on March 7 with calculations showing that a tsunami higher than 10 meters could hit Fukushima Dai-ichi. Moriyama said TEPCO officials used a piece of paper to explain their findings but did not submit any documents.
He said it was not clear how long TEPCO had known of the possibility before notifying the agency.
TEPCO spokesman Junichi Matsumoto said he could not immediately give any details about the tsunami estimate.
The government and TEPCO have been widely criticized for a lack of openness and delays in disclosing information about the accident and conditions at the plant.
In 2006, the government revised earthquake and tsunami safety standards and had all nuclear plant operators re-examine their resistance levels, but the March tsunami hit before any steps were taken at the Fukushima plant.
In 2009, TEPCO notified NISA of a separate calculation showing that a six-meter (20-foot) tsunami could hit the plant, based on studies of a tsunami that occurred in the year 869.
NISA had planned to review TEPCO's estimates but no concrete action was taken either time, Moriyama said.
"We must say that NISA's handling of the matter as a safety regulator was not adequate. It was extremely problematic," he said.
The International Atomic Energy Agency, which inspected the crippled plant in June, also said in a report that a tsunami hazard existed at Fukushima and several other nuclear facilities.
About 20,000 people died or are missing after the March quake and tsunami devastated large parts of Japan's northern coast. Separately, more than 100,000 people were forced to evacuate from the nuclear plant's vicinity because of radiation threats.