Kyushu Electric Power Co. on Thursday started a scheduled three month-long inspection of a reactor at its Sendai Nuclear Power Station in Kagoshima Prefecture.

The checkup requires suspending the reactor's operation and leaves only two reactors active in Japan — reactor 2 at the Sendai plant and reactor 3 at Shikoku Electric Power Co.'s Ikata plant in Ehime Prefecture. The Sendai reactor 2 is also scheduled to be suspended for regular checks from Dec. 16 to Feb. 27.

The Sendai complex's reactor 1 is the first unit to undergo regular checks after passing tougher safety criteria introduced in the wake of the Fukushima reactor meltdowns triggered by a massive earthquake and tsunami in March 2011.

Kyushu Electric said it started gradually moderating reactor 1 Wednesday evening by inserting rods to control nuclear fission. The inspection started early Thursday morning after the reactor ended power generation and was cut off from the transmission unit.

The inspection covers 124 items, including 16 under a new post-3/11 safety regime, such as checking equipment to prevent hydrogen explosions.

Kyushu Electric has already launched special checks at the Sendai plant, after Kagoshima Gov. Satoshi Mitazono demanded the plant be idled following powerful earthquakes in Kyushu in April. The special checks will be conducted along with the regular checks.