TOKYO -- Japan's Nuclear Regulation Authority will review its methodology for evaluating nuclear power plants' resistance to earthquake damage in connection with safety screening, sources familiar with the matter said on Tuesday.
Specifically, the NRA will alter the assessment of resistance to the strongest possible seismic shaking caused by a slip on an unknown active fault, according to the sources.
The watchdog will set up a panel of experts in January and aim to introduce the new method in the spring of 2019.
No new active fault has been discovered at facilities such as Kyushu Electric Power's Sendai plant in Kagoshima Prefecture. But it is hoped the revised assessment method can help bolster their resistance to earthquake damage.
The NRA introduced stringent new safety standards in the wake of the Fukushima nuclear disaster, which was triggered by the earthquake and tsunami that hit northeastern Japan on March 11, 2011.
Under the new standards, testing assumes the strongest possible earthquake for each plant, primarily based on fault investigations. Electric power companies are required to take whatever measures necessary to cope with such powerful tremors.
If no active fault is found within the premises or vicinity of a plant, the methodology assumes the occurrence of an earthquake nearby. Seismic shaking is currently assessed based on observation data from the magnitude-6.1 quake that hit the Rumoi region of Hokkaido in 2004.
The new method will be created based on observation data from multiple quakes to improve the accuracy of assessment.
The method will also be reviewed to reflect recent seismological research findings and assume multiple quake occurrence patterns.
Active faults have been found at or around most of the 40 reactors at the 16 nuclear plants in Japan that are currently usable.
The new seismic-shaking assessment method is believed to affect a total of five reactors at Kyushu Electric Power's Sendai and Genkai nuclear power plants. The Genkai plant is located in Saga Prefecture.
If the strongest possible seismic shaking at the five reactors is seen to increase significantly, safety measures will also have to be re-evaluated.