This could force some restarted reactors to shut down again.
The Japanese nuclear regulator Nuclear Regulation Authority (NRA) has approved new rules on back-up safety measures that could force some nuclear reactors having restarted operations to temporarily shut down again. In July 2013, the NRA approved new regulations in response to the Fukushima disaster, and required bunkered back-up control centres at nuclear power plants. In November 2015, it mandated reactors' operators to complete these facilities within 5 years after the approval of each plant's engineering and construction work programme. Operators failing to complete back-up centres about a week before the deadline are required to suspend operations at the reactor and to place the unit in cold shutdown.
So far, nine of the 39 operable nuclear reactors have cleared safety standards inspections and have resumed power operations, including Kyushu Electric's Sendai 1 and 2 reactors and Kansai Electric's Takahama 3 and 4 reactors. Under the new regulations, Kyushu Electric has until March 2020 and May 2020 to complete the back-up control centres at Sendai-1 and Sendai-2, respectively, while Kansai Electric has until August 2020 for Takahama-3. Both utilities have already warned the NRA that construction would be delayed by about one year. Other utilities will also experiment up to 2.5 years of delays. They could then be forced to stop operations again.