Updated Jan. 30, 2015, NHK World:
Watch this video that explains how operators plan to use muon tomography imaging to figure out where the melted fuel at Fukushima Daiichi is, starting with Unit 1.
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Posted Jan. 25, 2015, The Asahi Shimbun: ” Tokyo Electric Power Co. will use cosmic rays at the crippled reactors at its Fukushima plant to identify sites with melted fuel.
TEPCO will install special equipment to observe muon beams, or particles generated when cosmic radial rays collide with the atmosphere. That will enable it to glimpse inside the reactors, which went into triple meltdown after the March 2011 earthquake and tsunami disaster.
The exercise is intended to generate data that will be useful in deciding how to eventually remove the fuel. Fuel extraction work will be the most difficult phase in decommissioning the beleaguered plant.
While the muons pass through concrete, iron and other construction materials, they become absorbed more easily in high-density materials such as uranium, thereby creating a “shadow.” Based on these shadows, TEPCO expects to be able to identify the location and shape of nuclear fuel.
The industry ministry-backed plan will be led by the International Research Institute for Nuclear Decommissioning, an organization comprising TEPCO and atomic facility manufacturers.
They will first study the No. 1 reactor building and compile results by the end of this fiscal year, estimating how much fuel remains in the reactor.
While some experts argue that almost all of the fuel has melted and dropped to the base of the containment vessel at the No. 1 reactor, others say half of it probably remains in the reactor core.
TEPCO and the central government intend to extract the melted fuel after surrounding it with water to block radiation. To do so, the plant operator will need to repair damaged sections of the containers to prevent water leaks.
An industry ministry official said the survey “will provide important data for deciding how much water to inject into the containers.”
However, as there are also limitations to the method, the study represents just the first step in ascertaining what is happening inside the stricken reactors.
For instance, nuclear fuel at the base of the container cannot be seen using the muon technique, because the particles are not coming from below the reactors. As the system’s resolution is 30 centimeters to 50 cm, small compounds of fuel will also be undetectable.
“Many unknown factors remain, such as what sort of obstacles are at play in the reactor buildings,” said Fumihiko Takasaki, professor emeritus at the High Energy Accelerator Research Organization, which was involved in the development of the observation equipment. “We cannot know whether the efforts will eventually prove successful unless we actually try.” ”