The Tokyo Electric Power Company said Friday that a prove outfitted with a camera, a lamp, heat sensors and a dosimeter has returned images of fuel deposits at the bottom of Unit 2 at the Fukushima Dai-Ichi Nuclear Generating Station, marking the second unit at the damaged plant in which melted fuel has been found.
While an underwater probe returned images of fuel at the bottom of Unit 3 last year, fuel that looked like molten lava, the probe that explored Unit 2 on Friday was lowered into place by a mechanically improved extension pole – improvements made over a previous attempt to use a long pole to explore the debris.
The new pole had several improvements. It was strengthened and it had the ability to extend further once it was positioned inside the reactor. It also contained a method of lowering the camera, much as one might lower fishing tackle into the water at the end of a fishing pole. The monitor also had a protective skirt placed around it, so that the device itself would not get snagged onto debris inside the reactor.
The probe itself was also improved compared to previous devices. This one, created by Toshiba Corp. and the International Research Institute for Decommissioning, a government-funded coalition of nuclear energy companies, is smaller than previous probes and included anti-fogging technology.
Tepco said the exploratory even was quickly successful. “We can see the handle of a fuel assembly in the debris, so we are quite certain that it is surrounded by melted fuel,” said company spokesman Takahiro Kimoto. Close to seven years after the March 2011 earthquake that triggered the tsunnami event that knocked out backup power at the six-unit power plant, “we were able to get very important information, which we will use to determine a way to remove the fuel,” Kimoto said.
High temperatures and intense amounts of radiation prevent the company from sending workers into the units to take a look for themselves. The environment at the plant has forced Tepco to develop new technology to gather information from inside the damaged units. “This next effort at Unit 2 illustrates our commitment to developing technologies that will enable decommissioning at Fukushima Dai-Ichi and also become useful elsewhere,” said Chief Decommissioning Officer Naohiro Masuda.
Prior attempts to capture images inside Unit 2 were thwarted by debris inside the reactor, including a fallen floor grate that obscured the view of the bottom of the pedestal area. The ability of a 2017 probe attempt to penetrate to a useful position was also obstructed by deposits that had formed on the railed that guided the device into the reactor.
“Today's investigation is done, will be considered another day if it is necessary,” Tepco said before the attempt was made. The company said the status inside the pressure containment vessel is stable and there were not changes in radiation levels at the site boundaries of the crippled plant, the company added.
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