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Courtesy of Tokyo Electric Power Company Holdings, Inc. Pipes that TEPCO planned to use for the trial extraction of nuclear fuel debris from the No. 2 reactor at the Fukushima No. 1 nuclear power plant were placed in the wrong order Thursday.
By Yoshimune Numata and Takashi Hayashi / Yomiuri Shimbun Staff Writers
16:50 JST, August 23, 2024
An elementary mistake has stalled the trial extraction of melted nuclear fuel debris from the Fukushima No. 1 nuclear power plant before the process even began.
Tokyo Electric Power Company Holdings, Inc. suspended work to take a sample of the debris from the plant’s No. 2 reactor, which was scheduled to begin Thursday, after discovering an error during preparatory procedures for the delicate operation. The government and TEPCO aim to complete decommissioning of the nuclear plant by 2051, and removing the debris was framed as the beginning of a new phase in that process.
“Debris removal is the most important task in the decommissioning process and must be done in a precise manner,” TEPCO President Tomoaki Kobayakawa told reporters Thursday morning after being notified about the suspension. “Rather than cause a major problem by hurrying, it is important to proceed with the operation safely.”
The trial extraction would have involved using a device resembling a fishing rod that can extend up to 22 meters and has a claw at the tip to collect up to 3 grams of debris. On the first day of the procedure, TEPCO planned to open a valve that keeps radioactive materials from escaping from the reactor containment vessel, and to then insert the device into the vessel. Although the valve was opened, a worker noticed that five pipes that would be connected to push the device into the vessel had been placed in the wrong order, with the first pipe where the fourth pipe should have been. TEPCO then suspended the trial extraction.
Numbers had been written on the pipes in characters about 5 centimeters square to prevent them from being incorrectly connected. The placement of the pipes had been completed by Wednesday, but nobody noticed there had been a mistake in the pipes’ order.
If the extraction had successfully started, the government and TEPCO’s decommissioning process would have entered the third and final phase.
“Operation of the device had been checked at a separate facility, so we were certain the process would succeed,” a government official said despondently. “This development was unexpected.”
Crucial work
Meltdowns occurred at the Nos. 1 to 3 reactors at the Fukushima No. 1 nuclear plant after the Great East Japan Earthquake on March 11, 2011. Nuclear fuel became mixed with concrete and other materials inside the reactors and then solidified into the debris. An estimated total of 880 tons of debris remains inside the three reactors. This debris radiates heat, is extremely radioactive, and would be fatal to humans exposed to it. Extracting this debris is at the heart of the decommissioning process.
Making progress in removing the debris would reduce the volume of water that becomes contaminated with radioactive substances when used to cool the interior of the reactors. It would also reduce plant workers’ exposure to radiation.
The No. 2 reactor was selected for the trial debris extraction because the unit did not suffer a hydrogen explosion in the 2011 disaster and the extent of damage was less severe than at the other reactors.
When removed, the debris will be taken to the Japan Atomic Energy Agency’s Oarai Research and Development Institute in Ibaraki Prefecture to be carefully examined. Learning the hardness of the debris, for example, will be relevant to the choice of equipment and methods for effectively extracting more of it. Also, determining the composition of the debris will advance efforts to determine safe storage methods.
“If even a few grams can be analyzed, it’ll be possible to estimate the temperature inside the reactors at the time of the 2011 accident and other details,” said Yasuaki Miyamoto, director general of the agency’s Fukushima Research and Engineering Institute. “That should help to significantly accelerate decommissioning work.”
However, the spread and melting of the nuclear fuel differ in each reactor, so it remains unclear how useful an analysis of debris from the No. 2 reactor will be for the Nos. 1 and 3 reactors.
Spate of problems
A TEPCO official regretted the situation that resulted in the extraction being suspended Thursday. “It was a basic mistake,” the official said.
Since autumn 2023, a string of problems have occurred at the same nuclear plant, including a power cut and workers being contaminated. In October 2023, two workers cleaning contaminated-water purification equipment were accidently splashed with liquid waste containing radioactive substances. Both workers had to be hospitalized.
In May and June, TEPCO completely examined about 1,000 operations related to the decommissioning, and finished reviewing the procedures for about 680 of them. Despite this, the debris extraction stumbled at the first step.
Nagaoka University of Technology Prof. Hiroshi Yamagata, an expert on system safety engineering, pointed out that improvements could be made.
“Mistakes can be reduced by setting aside plenty of time to do this work, and by ensuring that the workers are properly educated and provided with sufficient information,” Yamagata said. “Decommissioning the reactors will be a long road. TEPCO should do everything it can to make sure such an environment is in place at the nuclear plant.”
