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In his paper, presented at the seminar titled "Alternative energies through experiences of Japanese researchers", held by Thammasat University on June 12, Uotani also cited the World Nuclear Association's reports as indicating that nuclear-power plants offer the most economical way to generate base-load electricity in most industrialised countries today.

In Japan, the Atomic Energy Commission adopted the framework for nuclear-energy policy in 2005, in which the basic policy is to promote research, development and utilisation of nuclear science and engineering.

Within this framework, Japan is also expected to maintain or increase its current level of nuclear-power generation from the present 30 per cent to 40 per cent of the total electricity generated by 2030.

At present, Japan has 55 nuclear-power plants in service, with a capacity of 49.58 gigawatt. In 2007, the capacity dropped about 60 per cent because of the suspension of Kashiwazaki power plants, which had been affected by a strong earthquake.

Investigation of plant damage and restoration are now in the advanced stage, Uotani said.

Japan first started commercial nuclear-power generation in 1966 with the opening of the Tokai Power Station and the gas-cooled reactor. In addition, two light water reactors (LWRs), boiling water reactor (BWR) and pressurised water reactor (PWR) were built between 1970 and 1971.

Since the introduction of LWRs, Japan started producing some plant components domestically.

By the end of the 1970s, the Japanese nuclear-power industry virtually established its own domestic production technology.

In the meantime, earlier plants, which are still in service, have experienced problems such as stress corrosion and the cracking of stainless steel piping of BWRs and steam generator tube problems of PWRs.

As a result, the electric utilities and manufacturers started an LWR improvement and standardisation programme in 1975 to improve the reliability and capacity factors while shortening the duration of annual inspection.

The results have been evident in new plants. Today, safe and reliable operations of the ageing power plants have become an important feature of the Japanese nuclear-power industry after more than 30 years of service.

On renewable energies, Toshiya Nanahara of Japan's Central Research Institute of Electric Power Industry, said in a paper presented at the same event that wind, photovoltaic and bio-mass have attracted worldwide attention as environmentally friendly sources of energy.

The installed capacity of wind power has increased exponentially in Western countries, such as Germany, Spain, Denmark and the US, as also in India and China.

As for Japan's experience on wind and photovoltaic power generation, he noted that the advantages are clear, given both are non-exhaustive and carbon-free energy sources.

However, the cost of electricity from photovoltaic generation is still significantly higher than that of conventional power sources, so research and development is focusing on cost reduction.

On wind power, there remain issues to be resolved, such as durability against severe natural conditions such as typhoons.

Another important issue is grid interconnection. For example, photovoltaic generation is a distributed generation - small-scale generation connected to a distribution line - it is, therefore, important to ensure power quality and system protection.

As both wind and photovoltaic power are interruptible sources, it is also a challenge to maintain a supply-and-demand balance in the power system.