Allison Macfarlane, head of the Nuclear Regulatory Commission, said Friday in Tokyo that an underground repository is needed but finding one is a challenge. She urged countries that are only just introducing nuclear energy to have back-end plans at an early stage.
Japan has no final waste repository.
Her comment comes as Japan finalizes its new energy policy that reverses a phase-out plan set by the previous government after the March 2011 Fukushima disaster.
The new policy under Prime Minister Shinzo Abe's pro-nuclear government is also expected to stick to Japan's shaky fuel cycle program despite international concerns about Japan's massive plutonium stockpile.