What would a Japan without nuclear power be like? Like committing "mass suicide," according to a Japanese ruling-party heavyweight.

Yoshito Sengoku, the deputy policy chief of the Democratic Party of Japan, made the comparison at a speech he was giving in the central city of Nagoya on Monday. It's raising eyebrows here in light of the controversy over whether to restart two reactors at the Oi nuclear plant, which would be the first to come back online since the devastating nuclear accident in Fukushima last year. The Oi units,...