A reactor at the world’s largest nuclear power plant in Japan has resumed operations. The country is pushing to maximize nuclear power generation to cope with growing electricity needs and a global oil crisis. The restart at the Kashiwazaki-Kariwa plant in May captured public attention over safety improvements by the operator behind the 2011 Fukushima meltdowns. But the reboot highlights a dire problem for the country’s nuclear program. Japan is running out of space to store spent nuclear fuel and lacks plans for radioactive waste disposal.