page_title: Fukushima Daiichi nuclear disaster (Unit 3 Reactor)
section_title: Unit 3 Reactor
hierarchical_section_title: Fukushima Daiichi nuclear disaster (Unit 3 Reactor) / Unit 3 Reactor
caption_attribution_description: English: The Fukushima I Nuclear Power Plant after the 2011 Tōhoku earthquake and tsunami
context_page_description: Unit 3 of the Fukushima Daiichi Nuclear Power Plant was one of the reactors in operation on 11 March 2011, when the plant was struck by the tsunami produced by the Tohoku earthquake. In the aftermath, the reactor experienced hydrogen gas explosions and suffered a partial meltdown, along with the other two reactors in operation at the time the tsunami struck, unit 1 and unit 2. Efforts to remove debris and coolant water contaminated with radiation are ongoing and expected to last several decades.
context_section_description: Unlike the other five reactor units, reactor 3 ran on mixed core, containing both uranium fuel and mixed uranium and plutonium oxide, or MOX fuel (with the core comprising ~6% MOX fuel), during a loss of cooling accident in a subcritical reactor MOX fuel will not behave differently from UOX fuel. The key difference between plutonium-239 and uranium-235 is that plutonium emits fewer delayed neutrons than uranium when it undergoes fission.
  While water-insoluble forms of plutonium such as plutonium dioxide are very harmful to the lungs, this toxicity is not relevant during a Loss Of Coolant Accident (LOCA) because plutonium is very involatile and unlikely to leave the reactor in large amounts. Plutonium dioxide has a very high boiling point. The toxic effect of the plutonium to the public under these conditions is much less than that of iodine-131 and caesium. During a loss of cooling accident, the fuel is not subject to such intense mechanical stresses, so the release of radioactivity is controlled by the boiling point of the different elements present.
caption: Reactor Unit 3 (right) and Unit 4 (left) on 16 March.
   Three of the reactors at Fukushima Daiichi overheated, causing meltdowns which released large amounts of radioactive material into the air.
   Pipes are the direction of the ocean.[36]
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