Reports Suggest Fukushima Radiation Release, RPV Damage Worse Than Thought

Government reports cited by Japanese media in recent days give an assessment of conditions following the March 11 Fukushima Daiichi station blackout that are significantly worse than initially reported by Tokyo Electric Power Co.

A report released by Japan's Nuclear and Industrial Safety Agency Monday said its analysis of TEPCO data placed the amount of iodine-137 released into the atmosphere from the accident at 770,000 terabecquerels - more than twice the estimate initially given by the utility and higher than previous estimates by Japanese regulators. The Asahi Shimbun reported NISA made the calculation based Unit 4 spent-fuel tank support. Source: TEPCOon estimated damage to unit 2 that assumes leaks as large as to 50 square centimeters in its containment vessel and up to 300 square centimeters in its suppression pool. The NISA report also indicated unit 1's pressure vessel sustained damage from melting fuel 5 hours after the March 11 earthquake, whereas TEPCO reported the damage occurred the following morning. Unit 2 sustained similar damage late on March 14, NISA said, more than a day earlier than TEPCO reported.

Fuel within all three reactors in operation the day of the earthquake has been presumed to have melted after a subsequent power outage to safety systems. The Yomiuri Shimbun quoted a report the government is preparing for the International Atomic Energy Agency that the newspaper obtained Tuesday as saying the molten fuel not only collected in the bottom of reactor pressure vessels, but it may have melted through them.

The report has not been released publicly. Earlier data from TEPCO indicated it had detected small holes where water has leaked from the bottom of pressure vessels. If the final draft of the IAEA report includes the assertions quoted by the newspaper, it would be the first public indication that Japanese regulators believe molten fuel in reactors may have collected at the bottom of containment vessels.

(Photo: Recently installed support pillars beneath the spent-fuel tank at Fukushima Daiichi unit 4, pictured June 7. Source: TEPCO)

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