In a foreword to the report, IAEA Director General Yukiya Amano said it “considers human, organizational and technical factors and aims to provide an understanding of what happened, and why, so that the necessary lessons learned can be acted upon by governments, regulators and nuclear power plant operators throughout the world.”
In the report, the IAEA notes that plant vulnerabilities are not merely technical. The report stresses that “an integrated approach that takes account of the complex interactions between people, organizations and technology” is needed.
Along these lines, as well as examining how the reactors were designed and assessed for safety during natural disasters, the report also considers the safety measures and accident management procedures in place at the time, the effectiveness of Japan’s nuclear regulatory programme, the human and organizational factors and the general safety culture.
Among the report’s findings was that the Fukushima No 1 plant’s vulnerability to external hazards “had not been reassessed in a systematic and comprehensive manner during its lifetime”, and that plant operator Tokyo Electric Power Co (Tepco) was “not fully prepared for the multiunit loss of power and the loss of cooling caused by the tsunami.”
The plant’s operators “had therefore not received appropriate training and had not taken part in relevant severe accident exercises,” and “the equipment available to them was not adequate in the degraded plant conditions” after the accident.
The IAEA points to a lack of “co-ordinated arrangements for responding to a nuclear emergency and a natural disaster occurring simultaneously,” arguing that “it was not fully clear which organizations had the responsibility and authority to issue binding instructions on how to respond to safety issues without delay.”
According to the technical volume of the report, pre-construction studies had concluded that the site was “in an area of little seismic activity”. Nevertheless, earthquake protection measures were in place. The report said the March 11 earthquake “met the criterion for the highest level [of severity]” and that the safety measures in place called for, among others, “control room status check, responsibilities for [the] performing structure, system and component checks and general plant area walk-downs.”
Additional safety measures had also been carried out on the plant, the report found. A new automatic depressurization function had “recently” been added to units 2-6 (but not to unit 1 as it already featured two high-pressure core cooling systems). Connecting lines and motor-operated valves were installed to allow for injection of cooling water into the reactor pressure vessel. A new vent line was installed to prevent primary containment vessel failure and release of radioactive material due to overpressurization. Power source cross-tie lines were installed between adjacent units (between units 1 and 2, 3 and 4, and 5 and 6) so they could provide power to each other in case of a total power loss. And, based on lessons learned from Japan’s 2007 Niigata-Chuetsu-Oki earthquake, an independent power facility within a seismically isolated building equipped with a gas turbine generator had been built.
However, many of these emergency systems stopped working after flooding from the tsunami knocked out power at the site, leaving operators with malfunctioning equipment and no functional monitoring technology. “In the absence of procedures addressing the loss of all AC and DC power,” the report said, plant operators “did not have specific instructions on how to deal with a site blackout under these conditions.”
The report, which comes with technical volumes totaling more than 1000 pages, was compiled by 180 nuclear experts from 42 countries. It will be presented to the IAEA’s next annual meeting in mid-September.
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