Most of the nuclear fuel inside the No. 2 reactor at the Fukushima No. 1 nuclear power plant apparently did not melt through the pressure vessel as previously believed, research using muon tomography has revealed.
The assessment was made based on a study that utilized muons, an elementary particle that travels from outer space, to capture the interiors of the crippled reactor building like an X-ray.
Tokyo Electric Power Co., the ill-fated facility’s operator, made the announcement on July 28.
According to the utility, the technique captured a black shadow estimated to account for 180 to 210 tons of substances in the lower part of the reactor’s containment vessel.
There was about 160 tons of nuclear fuel inside the No. 2 reactor, which was operating when it suffered a meltdown in the accident that resulted from the 2011 Great East Japan Earthquake and tsunami.
As the nuclear fuel, control rods and other materials that would have melted down totaled about 210 tons in weight, TEPCO deemed that “a large portion of the nuclear fuel is presumed to be contained within the pressure vessel.”
The latest finding negates past studies that have suggested that most of the nuclear fuel inside the reactor had melted through the vessel.
“We hope to effectively come up with a method to extract the melted fuel,” said Naohiro Masuda, president of TEPCO’s Fukushima Daiichi Decontamination & Decommissioning Engineering Co.
Muons are known to travel through materials such as concrete, but are unable to penetrate highly dense substances such as uranium.
The International Research Institute for Nuclear Decommissioning, an organization made up of the utility and nuclear power plant manufacturers, had been using the particles’ properties to peer inside the No. 2 reactor since March.