Kyodo

The number of viable commercial nuclear reactors dropped to 50 from 54 on Friday, after four crippled units at the Fukushima No. 1 plant were officially classified as defunct the day before.

Reactors 1 to 4 at the wrecked power station were scrapped Thursday under the Electricity Business Law, which requires utilities to obtain permission from the trade minister before scrapping part of their power generation operations. Tokyo Electric Power Co. applied for approval in March to abolish the four reactors, three of which suffered meltdowns.

The total number of viable commercial reactors is expected to decline even further, because of aging reactors that will have to be retired and the suspension of plans to build new ones in light of the Fukushima disaster.

Efforts are underway to restart two units at Kansai Electric Power Co.'s Oi power plant in Fukui Prefecture, but as it is considered unlikely that operations will resume by May 5, all of Japan's nuclear reactors are expected be out of commission from that point on.