More than 70 percent of the nuclear fuel in one of the reactors at Tokyo Electric Power Co.'s Fukushima No. 1 nuclear power plant is highly likely to have melted in the wake of the massive 2011 earthquake and tsunami, according to a university research team.

Using special film that can detect muons, which form when cosmic radiation reaches the Earth, penetrates most matter and changes direction after colliding with uranium in nuclear fuel, the team at Nagoya University has confirmed the high possibility of 70 to 100 percent of the fuel having melted in the plant's No. 2 reactor.

The finding comes after the team first reported in March that it confirmed a core meltdown had occurred in the No. 2 reactor.

Tepco said in the same month it found through a similar test method that nearly all fuel in the No. 1 reactor at the plant had melted.

Three reactors suffered core meltdowns in the Fukushima disaster.

The conclusion was reached after observing muons around the reactor's pressure vessel and comparing results with those of the No. 5 reactor, which was unaffected by the 2011 disaster.

Since results on the bottom of the pressure vessel are less accurate, however, the team says it will continue analysis to see how much of the molten fuel remains in the vessel.

Kunihiro Morishima, designated assistant professor at the university's Institute of Advanced Research, said he hopes the finding will help future work to remove the molten fuel from the reactor.

Tepco and the International Research Institute for Nuclear Decommissioning, a Tokyo-based research body that consists of power plant makers, utilities and government organizations, are also trying to look into the inside of the No. 2 reactor at the plant.