An explosion blew the roof off an unstable nuclear reactor north of Tokyo today and a government official confirmed a radiation leak had occurred at the plant, operated by Tokyo Electric Power Co (Tepco), following an earthquake.
A evacuation radius of 20km has been set up around the stricken 40-year-old Daiichi 1 reactor plant in Fukushima prefecture. TV footage showed vapour rising from the plant, 240km north of Tokyo.
Here are some facts about resource-scarce Japan's growing use of nuclear energy:
* Japan needs to import some 80 percent of its energy requirements.
* The country's first commercial nuclear power reactor began operating in mid-1966, and nuclear energy has been a national strategic priority since 1973, when the oil shock prompted a turn to nuclear energy in a bigger way, although the country already had five nuclear reactors. Japan adopted a closed fuel cycle to gain the maximum benefit from imported uranium.
* Japan's 54 reactors provide some 30 percent of the country's electricity today, and this is expected to increase to at least 40 percent by 2017, and 50 percent by 2030. Japan has a full fuel cycle set-up, including enrichment and reprocessing of used-fuel for recycling.
* In 2008, Japan generated 1,085 billion kWh gross power, of which 30 percent was from coal, 25 percent from gas, 24 percent from nuclear, 11 percent from oil, and 7.5 percent from hydropower, though 8 GWe of nuclear capacity was shut down for checks following an earthquake in mid-2007. Per capita consumption is about 7900 kWh/yr.
* Japan's existing 54 reactors have a total of 46,102 MWe (net) on line, with two (2,756 MWe) under construction and 12 (16,532 MWe) planned.
Nuclear power seems set to play an even bigger role in Japan's future. The Japan Atomic Energy Agency has modelled a 54 percent reduction in CO2 emissions from 2000 levels by 2050, leading on to a 90 percent reduction by 2100.
This would lead to nuclear energy contributing about 60 percent of primary energy in 2100 (compared with 10 percent now), 10 percent from renewables (now 5 percent) and 30 percent fossil fuels (now 85 percent).
That implies nuclear power would contribute 51 percent of the emission reduction - 38 percent from power generation and 13 percent from hydrogen production and process heat.