Tokyo Electric Power Co. said almost all the nuclear fuel in the No. 1 reactor at the Fukushima plant likely melted in the aftermath of the 2011 Great East Japan Earthquake and tsunami.
Tokyo Electric Power Co. said almost all the nuclear fuel in the No. 1 reactor at the Fukushima plant likely melted in the aftermath of the 2011 Great East Japan Earthquake and tsunami.
The plant operator said March 19 that internal observations of the reactor building using cosmic rays reinforce earlier suspicions that all the fuel had melted and dropped to the bottom of the containment vessel.
Direct observations have been impossible because high radiation levels are preventing workers from approaching the damage inside the No. 1 reactor building.
TEPCO and the International Research Institute for Nuclear Decommissioning (IRID) have been working since February to study the interior of the reactor building at the Fukushima No. 1 nuclear plant.
The study uses special equipment to examine muons--subatomic particles generated when cosmic radial rays collide with the atmosphere--that have passed through the reactor building to produce images similar to an X-ray.
Although muons can pass through concrete and iron, they are blocked by high-density materials, such as uranium, thereby creating a “shadow” of nuclear fuel.
The muon observation method has been used to study the inside of a volcano and the interior of ancient Egyptian pyramids.
The images of inside the No. 1 reactor did not show any nuclear fuel shadows around the reactor core, indicating that all fuel melted and fell to the bottom of the containment vessel after the earthquake four years ago.
The latest findings corroborate the results of an earlier computer prediction. However, muon observation is unable to detect objects smaller than 1 meter or see through the lower parts of the containment vessel.
TEPCO said it will continue observation efforts to make clear what happened inside the reactor.