Tokyo Electric Power Holdings (Tepco) plans to excavate a massive slope near the used fuel pool at the Fukushima Daiichi NPP to avert the danger of a landslide, according to Asahi Shimbun. The Nuclear Regulation Authority (NRA) has requested Tepco to deal with the 24-metre-high slope comprising soft ground would present a risk in the event of an earthquake.
The common pool, where 5,197 used and unused fuel assembly units, removed from the reactor units damaged in the 2011 earthquake and tsunami, are being stored, is expected to hold them for a prolonged period. Some 4,000 fuel assembly units still stored in the buildings that house unit 1 reactor are scheduled to be moved to the common pool by 2031. Tepco eventually plans to transfer fuel assembly units to a different storage facility within the plant premises after they are sufficiently cooled in the pool.
Tepco is expected to remove about 100,000 cubic metres of soil from the slope during an approximately 10-year project, company officials said. A drilling survey by Tepco has identified a weak layer that could easily collapse over a wide area within the plant premises.
According to Akira Ishiwatari, a geologist and NRA commissioner, a landslide could occur on the slope in the event of a minor earthquake or even without any tremor. Tepco said a landslide would not affect the safety functions of the nuclear fuel pool. However, NRA is concerned that if sediment from a landside flowed into the pool, the nuclear fuel would no longer be cooled and, in the worst-case scenario, could eventually melt.
Tepco plans to complete the design work and obtain approval for the excavation project over one to two years from fiscal 2024, dismantle and relocate steel towers and other obstacles in the following five years and remove the soil during about three years, officials said.
Image: The building that houses a common pool cooling nuclear fuel, left foreground, stands against a slope at the Fukushima No. 1 nuclear power plant (courtesy of Asahi Shimbun)
