In a report being submitted to the United Nations' nuclear watchdog agency, the government also acknowledged reactor design inadequacies and a need for greater independence for the country's nuclear regulators.
Photos: Earthquake in Japan
The 750-page report, compiled by Japan's nuclear emergency task force, factors in a preliminary evaluation by a team from the International Atomic Energy Agency and was to be submitted to the IAEA as requested.
"In light of the lessons learned from the accident, Japan has recognized that a fundamental revision of its nuclear safety preparedness and response is inevitable," the report says. It also recommends a national debate on nuclear power.
The report says the "inadequate" basic reactor design — the Mark-1 model developed by General Electric — included the venting system for the containment vessels and the location of spent fuel cooling pools high in the buildings, which resulted in leaks of radioactive water that hampered repair work.
GE declined to comment on the specific conclusions of the report.
Hundreds of plant workers are scrambling to bring the crippled reactors to a "cold shutdown" by early next year and end the crisis. The accident has forced more than 80,000 residents to evacuate from neighborhoods around the plant.