Japan's Nuclear Regulatory Authority announced Wednesday it was halting the relicensing process for two reactors at the Hamaoka nuclear power plant after it was found that the operator had fabricated seismic hazard data. Japan is slowly rebuilding its vast collection of nuclear power plants after they were shut down following the Fukushima Daiichi disaster. The latest scandal is especially shocking given that the Hamaoka nuclear power plant is located on the coast near an active subduction fault, just like Fukushima Daiichi.
The Nuclear Regulatory Authority was reportedly alerted by a whistleblower in February last year, but the issue became public this week when regulators stopped assessment process that could lead to a restart of the Hamaoka reactor. This prompted Chubu Electric Power Co., which operates power plants, to release press release detailing how the company manipulated seismic safety data.
Based on English translationIt appears that seismic risks were assessed, at least in part, by downscaling ground motion using data from small earthquakes. This is an imprecise process, so the standard approach is to create a group of 20 different scaled earthquakes and find the one that best represents the average among the 20.
The company now admits that since 2018, its employees have been creating large collections of scaled-up earthquake scenarios, choosing one and then selecting 19 more so that the average makes it representative of the event. The company doesn't mention how this process affected the risk analysis, but it's probably safe to assume that it was chosen specifically to make any risks seem more acceptable.
