The large-scale industrial accident at the Fukushima-Daiichi Nuclear Power Plant was the culmination of three inter-related factors: external natural hazard assessment and site preparation, the utility’s approach to risk management, and the fundamental reactor design.
The reactor accident was initiated by a magnitude 9 earthquake followed by an even more damaging tsunami. However, it was the inability to remove the decay heat in the reactor core that led to core meltdown and radioactive release.
A review of the timeline of the major Fukushima accident sequences: The plant first experienced a station blackout (i.e. loss of all offsite and onsite power) due to flooding of backup critical emergency cooling equipment. The lack of an ultimate heat sink led to the fuel overheating. Subsequently, the generation of hydrogen through steam oxidation of of the fuel cladding led to chemical explosions causing significant structural damage.
The focus of this talk (presentation slides below) is on the engineering aspects of the reactor accident and the prospects for local environmental recovery. Radionuclide measurements in space and time provide important evidence for the exact evolution of fuel damage leading to partial core melting in multiple units. A review of the spent nuclear fuel pools is given where isotopic water composition and visual inspection images provide important evidence for the condition of the spent nuclear fuel.
While it will be several months to a year before we will be in a position to learn most of the lessons from this tragdy, several conclusions about defensive design, mitigation actions, and emergency response have been drawn by international organizations.
While the public health impact appears to have been low, the economic and nearby environmental consequences are severe, There is no doubt that land restoration will take over a decade and perhaps much longer. A review is given of actions taken by the Japanese government for land recovery in areas such as decontaminating top soil and local farmland as well as highly radioactive water used during ‘feed and bleed’ cooling of the core.