A new tsunami simulator in Japan aims to prevent the kind of disaster that led to the Fukushima meltdowns.

Researchers showed the new wave machine to the media at a facility near Tokyo.

The simulator is 20 meters long and can hold up to 650 tons of water.

The scientists designed it to simulate what happens when a tsunami overwhelms a seawall.

They plan to use it to test floodgates and other defenses at Japan’s nuclear plants.