Japan on Tuesday turned on the No. 1 reactor at its Sendai nuclear plant, 1,000km south-west of Tokyo, a move that brought nuclear power back to the country after it was nuclear-free for two years.

The shutdown was triggered by fears from the public after a 2011 earthquake and tsunami cause the meltdown of the Fukushima nuclear plant and the evacuation of tens of thousands.

The nuclear restart came amid still-vociferous protests from the public.

Here are some answers to questions you may have about the restart:

1. How many nuclear reactors are operable in Japan?

Before the 2011 earthquake, Japan's 54 reactors were responsible for 30 per cent of the country's electrical needs.

The quake and resulting tsunami caused all six of the Fukushima No. 1 plant's reactors to shut down.

Five more reactors will also be shut down, as they are too old and costly to retrofit to meet new safety regulations issued in 2013.

This leaves 43 reactors that can be switched on in Japan.

2 . How many more reactors are set to be turned on?

Sendai's No. 2 reactor is set to be restarted later this year.

The other three that have passed checks are reactors No. 3 and No. 4 at the Takahama plant in Fukui prefecture, and the No. 3 reactor at the Ikata power plant in Ehime prefecture. But the three have to pass further hurdles before being turned on.

More than 20 more reactors are being inspected to see whether they meet the new rules.

3. What do the government and businesses want?

The power companies that own the reactors are also keen for them to get back to business as they have had to make up lost generating capacity with pricey fossil fuels.

Last month, Japan's Industry Ministry gave the nod to a target that for nuclear power to generate as much as 22 per cent of electricity by 2030.

4. How do ordinary Japanese feel?

In a poll conducted last week by the Mainichi Shimbun newspaper, 57 per cent were against the Sendai reactor's restarting, and 30 per cent were positive about it.

5. What's going on in Fukushima now?

Source: The Wall Street Journal, Agence France-Presse