Japan continues to drop cooling water on the number three reactor at the Fukushima nuclear power plant, which sustained a hydrogen explosion.

The Tokyo Fire Department said some 60 tons of water was dropped on the reactor from 12:30 a.m. Saturday, adding that a high-performance fire truck was mobilized for the effort.

The injection of water was focused on the water tank that contains spent nuclear fuel rods. If the water in the tank dries up, the fuel rods would become exposed and could heat up to a point where they begin to melt down and raise radiation levels.

The number three reactor’s roof blew off after a hydrogen explosion on Monday. The explosion occurred after the fuel rods became exposed, causing the temperature and pressure in the reactor to rise sharply.

The fire department said it will begin to inject seawater into reactor three starting at noon Saturday.