It is the second inspection by the International Atomic Energy Agency (IAEA), which first visited in August and said the Kashiwazaki-Kariwa plant posted no public health risk.

The team of 12 nuclear experts plans on Thursday to look inside the nuclear reactors, which they could not check last year.

The team is looking forward to the inspection and continuing the 'nice collaboration we already had with our Japanese counterparts,' said team leader Philippe Jamet, as quoted by Kyodo News.

Mr Jamet, director of the IAEA's Nuclear Installation Safety Division, said the mission would focus 'on three main subjects'.

'The first is the effect of the earthquake on the plant. The second is to understand the mechanism that created such a big earthquake and the third is a necessary improvement in the domain of fire safety,' he said.

A powerful quake measuring 6.8 on the Richter scale hit central Japan on July 16, causing a fire in the section generating electricity for the plant.

The nuclear reactors automatically shut down.

The epicentre of the earthquake was just 16 kilometres from the Kashiwazaki-Kariwa plant, which supplies power to the Tokyo area to the southeast.

The operator, Tokyo Electric Power Co, said water containing only a small amount of radiation leaked into the Sea of Japan (East Sea) and radioactive particles blew out of an exhaust pipe filter.

But the company came under criticism for initially underreporting the severity of the incident.

Japan is one of the most earthquake-prone nations, experiencing about 20 percent of the world's powerful tremors.

Despite its propensity for earthquakes, Japan relies on nuclear plants for nearly one-third of its power needs as it has virtually no natural energy resources. -- AFP