Japan may restart some nuclear reactors in July following safety checks under rules put in place since the Fukushima disaster two years ago, a government-affiliated institute said on Tuesday.

Japan relied on nuclear power for about a third of its electricity supply before the world's worst nuclear crisis since Chornobyl, but may have as few as four reactors operating by March 2015, the Institute of Energy Economics Japan said, meaning a continued heavy reliance on fossil fuels.

A tsunami crashed into the Fukushima Daiichi power plant north of Tokyo on March 11, 2011, causing fuel-rod meltdowns at three reactors, radioactive contamination of air, sea and food and triggering the evacuation of 160,000 people.

Highly radioactive water still seeping into the ocean is creating an emergency that the operator, Tokyo Electric Power Co is struggling to contain, an official from the Nuclear Regulation Authority (NRA) said on Monday.

2 of 50 reactors operating

Japan has just two of its 50 reactors operating as the nuclear units shut down for checks and upgrades. Both reactors will need to be idled for refuelling and assessments by September.

"Under our low-case scenario, we expect the first reactor to resume from next July," Akira Yanagisawa, the manager of the institute's energy demand, supply and forecast analysis group, said.

The forecast is in line with comments by NRA commissioner Kenzo Oshima in an interview with Reuters on July 9.

Should Japan restart 16 reactors by March 2015, the institute's "middle" scenario, annual fossil fuel imports will be 7 trillion yen ($74 billion Cdn) higher in the year ending March 2015 than in year ended March 2011, the institute forecast.

It also said that Japan, which takes about a third of global liquefied natural gas (LNG) cargoes, was likely to raise LNG imports to fresh record highs for the next two business years.

LNG imports are likely to rise 1.7 per cent to 88.3 million tonnes in the year through March next year from the year before and another 1.5 per cent to 89.7 million tonnes in the year through March 2015, according to Reuters calculations based on the middle scenario.

Japan's total oil sales are projected to fall an annualized 0.1 per cent in the business year ending next March and 4.1 per cent the following year under the middle scenario, the institute said.