TAKAHAMA, Japan (AFP) - A vessel under armed guard and loaded with reprocessed nuclear fuel from France arrived at a Japanese port on Thursday, an AFP journalist said, despite nearly all of the country's reactors being shut down.

The cargo of mixed oxide (MOX), a blend of plutonium and uranium, was the first such nuclear fuel to arrive in Japan since the atomic disaster at Fukushima, which was sparked by the earthquake and tsunami of March 2011.

The fuel left the French port of Cherbourg in mid April bound for Japan, French nuclear group Areva has said. The vessel was specially fitted to be able to transport nuclear material and was escorted by an armed sister ship.

Its route was not fully disclosed.

Anti-nuclear activists and residents have said they were planning a protest rally at breakwaters near a port in Takahama town on the eastern coast of central Japan, home to the Takahama nuclear plant, the final destination for the MOX.

Japan has few energy resources of its own and relied on nuclear power for nearly one-third of its domestic electricity needs until the meltdowns at Fukushima.

All but two of the country's 50 nuclear reactors are offline, shuttered for routine safety checks in the aftermath of the disaster and never restarted because of public resistance and new standards.

Uranium reactors produce a mixture of depleted uranium and plutonium as a by-product of fission. These can be re-processed into MOX fuel, which can then be used in other reactors to generate more power.

Japan has built its own nuclear fuel reprocessing plant, in northern Aomori prefecture, but its opening has been delayed by a series of minor accidents and technical problems.

This has left Tokyo dependent on other countries - namely Britain and France - to deal with the plutonium it has produced.

Plutonium can be diverted for producing nuclear weapons, and there are fears that it could fall into the wrong hands and pose a danger from rogue regimes or extremist organisations.

According to a government report to the International Atomic Energy Agency (IAEA), Japan has about 44.3 tonnes of plutonium, of which 35.0 tonnes are held and being processed in France and Britain, and the rest, 9.3 tonnes is stored in Japan.

The fuel was originally due to be shipped back to Japan in the first half of 2011, but the disaster at Fukushima delayed its return and it has been stored in France.

Since coming to power in December last year, pro-business Prime Minister Shinzo Abe has repeatedly spoken of his desire to restart Japan's idle reactors, citing the need to ensure a stable electricity supply for the country's power-hungry industries.

In response to public distrust of the technology, the government has established a new nuclear watchdog, which has announced stricter new standards, including on reinforcing nuclear plants to survive tsunamis and earthquakes.

Power companies wanting to re-start reactors must first get approval from this body, whose rules come into force early next month.

These standards could mean the watchdog will permanently shutter some units because they lie too close to what it will deem as "active" tectonic faults.

Opponents of nuclear power warn of the risk of an accident in Japan, which suffers some 20 percent of the world's most powerful earthquakes, is too high and it should be abandoned in favour of a vast renewables programme.

Protesters also argue that shipping MOX around the world represents an unacceptable risk because of the danger of an accident or attack.

And they say the widening use of MOX increases the dangers of nuclear proliferation, arguing that the plutonium in it is easier to extract for weapons use than the plutonium in conventional spent nuclear fuel.