YOKOSUKA, Japan (AP) — An industrial group developing nuclear decommissioning technology has unveiled a swimming robot designed to be used underwater to investigate damage in three reactors at the wrecked Fukushima Dai-Ichi plant in northeastern Japan.

Remote controlled robots are key to the decades-long decommissioning process, but super-high radiation hampered earlier attempts to probe damage to the reactors from meltdowns following a massive earthquake and tsunami in March 2011.

The developers said Thursday they plan to send the probe into the primary containment vessel of Unit 3 at Fukushima this summer to study the extent of damage and locate parts of melted fuel that is thought to have fallen to the bottom of the chamber and been submerged by highly radioactive water.

Japan hopes to start removing the fuel after Tokyo's 2020 Olympics.