Japan’s Kyushu Electric Power Co on 17 November restarted Sendai 1, an 890MWe pressurised water reactor (PWR), at its Sendai nuclear plant after completing the required upgrades to ensure protection against terrorist attacks.

The start-up followed regular maintenance and refuelling, a spokesman said. On 18 November the reactor achieved criticality and is scheduled to begin commercial operation in mid-December.

Kyushu said it plans to restart Sendai 2 reactor in late December following upgrades. The company had earlier said it planned to restart Genkai 3 later this month and is due to shut Genkai 4 in December for regular maintenance.

Japan’s nine regional power utilities and a wholesaler, Japan Atomic Power Co, now have 33 reactors available for commercial use, with a combined generating capacity of 33GWe. However, with the restart of Sendai 1, only two are currently operating, with a total capacity of 2070MWe. Others are still going through a relicensing process under the more stringent safety standards imposed after the 2011 Fukushima disaster.

Sendai 1 had been idled since March because Kyushu failed to meet the deadline for upgrading the facility. Operators are now required to outfit the plants under an anti-terrorism regulatory “backfit” provision so they can continue to control the reactors remotely even in the event of aircraft crashing into the plant.

In November 2015, the Nuclear Regulatory Authority (NRA) ruled that back-up centres must be completed within five years of regulatory approval of each plant's engineering and construction programme. This is the second in a three-step process for assessing the safety of a unit before restarting. The third and final stage includes pre-operational checks to ensure that the plant fully complies with other new safety requirements.

 Sendai 1 reactor was the first unit forced to close due to its failure to meet the latest standards under the retrofit provision. The Sendai anti-terrorism facility passed the authority’s pre-operation test on 11 November. A similar anti-terrorism facility is expected to be completed for unit 2 in late December. Unit 2 has been shut down since May because the facility’s completion was also behind schedule.

Units 3 and 4 of Kansai Electric’s Takahama nuclear power plant in Fukui Prefecture were also forced to close in August and October because of delays in completing backup capacity. Other utilities have also said that the construction of backup centres at their reactors will be delayed by up to two and a half years.