Japan has resumed operations at the world's largest nuclear power plant to help the country meet huge electricity demands during a global oil crisis, but the reboot highlights a big problem: Japan is running out of space for spent nuclear fuel and has no viable plans for permanent disposal of the radioactive waste.

The restart of the number 6.0 reactor at Kashiwazaki-Kariwa Nuclear Power Station earlier this year was meant to spur a movement to bring more nuclear reactors online. Kashiwazaki-Kariwa is one of three plants whose cooling pools will be full in five years, according to the Federation of Electric Power Companies of Japan.

"Without solid (fuel management) plans, our power generation will stall sooner or later," Kashiwazaki-Kariwa General Manager Takeyuki Inagaki said.