TOKYO, May 31 (Xinhua) -- Warning that there are possible risks of collapse of the No. 1 reactor of the crippled Fukushima Daiichi nuclear power plant, Japan's Nuclear Regulation Authority (NRA) recently ordered plant operator Tokyo Electric Power Company (TEPCO) to urgently assess the risks and formulate emergency measures as soon as possible to avoid another sizeable radioactive leakage.
The warning from the nuclear watchdog illustrates how TEPCO customarily practiced negligence and downplayed risks in dealing with the decommissioning of nuclear facilities after the 2011 nuclear disaster. At the same time, it reveals the potential future risks of major accidents that the Fukushima nuclear plant may face.
TEPCO's knowledge of the damage inside the No. 1 unit, the worst-hit of the four damaged units at the plant, is unclear because it continues to release deadly high levels of radiation, keeping workers out of reach.
Videos taken during a robotic probe this March showed that the pedestal of the No. 1 unit's containment vessel, the main supporting structure directly under its core, was severely damaged. The underwater robot found the concrete wall was missing in over half of the pedestal, measuring five meters in internal diameter, leaving the reinforcing bar exposed.
Based on TEPCO's survey results, experts have said that severe damage to the base will inevitably affect the load-bearing performance, and as earthquakes continue around the Fukushima plant, if the base tilts and the pressure vessel falls in the event of a major earthquake, the consequences will be catastrophic.
Japan's newspaper Sankei Shimbun reported on Sunday that if the reactor pressure vessel falls, it could also damage various pipes connected to the vessel, resulting in the leakage of radioactive materials from the pipes. In a worst-case scenario, some falling materials could combine with the melted nuclear fuel accumulated at the bottom, leading to "re-criticality."
Based on this possibility of significant risks, the NRA urged TEPCO last week to face up to and assess the risks from the pedestal damage and formulate measures as soon as possible if the pedestal fails to support the reactor in the event of another disaster.
The No. 1 unit suffered a hydrogen explosion in the Fukushima nuclear accident, blowing off the roof and walls of the building housing the reactor. According to Japanese media reports, TEPCO originally planned to cover the entire unit with a "big roof" in 2023 to prevent the leakage of radioactive materials during the construction process, such as removing nuclear fuel from the fuel pool.
However, due to the high radiation level, waste disposal, such as pipelines around the plant, was slow, and the "big roof" could not be completed as scheduled, while the rickety base could be a problem at any time.
TEPCO has said that, even though the concrete exterior is largely missing, the steel reinforcement remains intact, and there is little safety risk. If the pedestal fails, its surrounding structures could prevent the reactor from collapsing.
But experts from the NRA pointed out that TEPCO is too optimistic. If the pressure vessel falls, it will likely tear the pipeline. Therefore, TEPCO needs to consider responses in case of an accident.
It is a matter of the utmost urgency to clean up the waste, such as high-radiation pipelines, that affect the construction of the "big roof." But TEPCO has shifted the blame for the slow construction to its contractor, which exposed the utility's "low crisis awareness," the Tokyo Shimbun newspaper reported.
Japanese media have questioned TEPCO's actions. On the one hand, the company is promoting the safety of discharging nuclear-contaminated water into the sea. However, on the other, new significant risks and hidden dangers are present in the No. 1 unit. What will TEPCO do about it? ■