JAPAN'S worsening nuclear crisis has prompted China to take a closer look at its own plans to triple the number of the nation's nuclear reactors in the next five years.

The State Council, China's Cabinet, announced on Wednesday that approval for all new reactors will be frozen pending a "thorough safety assessment" utilizing "the most advanced standards."

The decision came as the eyes of the world were focused on the threat of a meltdown in reactors at the Fukushima Dai-ichi nuclear power plant on the northeastern coast of Honshu in Japan, which were crippled by last week's magnitude-9 earthquake.

Vice Minister of Environmental Protection Zhang Lijun said China must learn lessons from the Japanese nuclear disaster, which is now being dubbed the world's worst since Chernobyl in 1986.

However, he said China has no plans to abandon nuclear power as part of the nation's energy mix.

China currently has 13 nuclear power reactors in operation and plans to increase that number to 40 by 2015. At present, more than 25 reactors are already under construction, and the new freeze won't affect their development.

By contrast, the United States now has 104 reactors, Japan has 55 and Britain operates 19.

The 2011-2015 Five-Year Plan calls for China to increase nuclear power capacity to 40 gigawatts from 10.8 gigawatts last year.

By 2020, Chinese government wants to expand nuclear power capacity to 70 gigawatts or more, accounting for about 5 percent of the nation's electricity production.

Nuclear power is part of a wider strategy to cut carbon emissions and switch to cleaner energy. By 2020, the nation is hoping to derive 15 percent of its energy from non-fossil fuel sources, including nuclear, hydro, solar and wind power.

It's not only China that is pausing to reflect on nuclear power safety in the midst of the Japanese disaster. Governments across the globe, those with nuclear reactors and those contemplating them, are re-examining issues of safety and risk.

China has never experienced a serious nuclear accident since its first reactor went into operation in 1991. The country is ranked among the safest operators of nuclear plants by the International Atomic Energy Agency, said Zhang Guobao, former head of China's National Energy Administration.

Among the issues certain to emerge in China's review of its nuclear power plans is site selection for reactors.

China is prone to earthquakes, so locating power plants as far away from fault lines as possible is important, Zheng Mingguang, director of Shanghai Nuclear Engineering Research and Design Institute, told the Oriental Morning Post.

That's not as easy as it sounds. China, with no less than 23 seismic belts, accounts for about half of the earth's recorded quakes every year, according to data published by the Chinese National Geography magazine.

In the 20th century, China recorded 800 earthquakes of magnitude-6 or greater. An estimated 550,000 people died in the temblors during that time, the magazine reported, citing Han Zhujun, a researcher at the Institute of Geology, China Earthquake Administration.

All the proposed new plants in China are built on high land, and are designed to sustain an earthquake magnitude of least 8, according to Geng Qirui, a consultant at the Shanghai institute.

Still, the Japanese people had been assured that their nuclear plants were quake-proof, too. The sheer force of nature unleashed last week in Japan has served as a stark reminder of mankind's vulnerability in a technological era.

A report by the State Council Research Office, an independent body that makes policy recommendations to the State Council, has cautioned local governments to control their almost unbridled enthusiasm for nuclear energy, at least for the moment.

While citing the enormous progress, China has made on the nuclear energy front, the office suggested the government should limit its 2020 nuclear power target to below 70 gigawatts to prevent development running "too fast" for strict quality control.

"The more developed technology we have, the more clear-headed we need to be," said the report, which was published by Xinhua news agency on January 11.

The office also pointed out that China should focus more on "Generation 3" technology rather than the second-generation technology used in the troubled Japanese reactors, which are now more than 40 years old.

Generation 2 reactors built today are expected to operate 50-60 years. That means one built today could be operating into the 2070s, even as technology moves to the fourth generation and, perhaps more importantly, to fusion reactors, the report said.

The country should be "careful concerning the volume of second generation units under construction ... the scale of those should not be too large" or the nation runs the risk of a perception that it is falling behind international safety standards, the report said.

Shanghai Nuclear Engineering Research's Zheng said Generation 2 technology has one weakness: a cooling system that requires power support to work.

The Japanese plant, built in 1967, used a boiling-water reactor design developed by General Electric in the 1960s, which was then touted as the reactor that was cheapest and easiest to build.

The design has a primary containment vessel, made of thick steel and concrete, surrounding the reactor to prevent melting fuel rods from spewing radiation into the environment if cooling efforts completely fail.

But the cooling system requires electricity support, with diesel engines as backups. In the Japanese disaster, backup systems failed because of the tsunami, Zheng said.

Japanese engineers have been trying to cool down the core of several of the reactors by pumping in seawater and even by aerial spraying. Because seawater has been introduced into the chambers, the reactors will never be able to operate again, Zheng said.

Most of the 13 reactors that are now in operation in China use an enhanced Generation 2 pressurized water design called CPR-1000.

The CPR-1000 system is based on a French design of three cooling loops and is also used in two-thirds of the Chinese reactors already under construction.

The CPR-1000, with a design life of 60 years, uses three-water-loop systems rather than the single one used in the Japanese reactors. The second loop, which does not contain any radioactive substances, can reduce inside pressure by leaking out steam, decreasing the possibility of a burst of the containment vessel, the National Energy Administration's Zhang said.

Secondly, the CPR-1000 system has compound equipment that can turn hydrogen into water, which would make hydrogen blasts like those at the Fukushima plant impossible, he added.

In addition, three evaporators set inside the CPR-1000 reactor can also remove some heat, Zhang said.

He concluded that the safety of China's nuclear reactors can be assured.

But there's one additional point to consider. Chen Jianxin, vice director of the Department of Nuclear Science at Fudan University, said the CPR-1000 still requires power supply to make the cooling system work.

This means, if China suffered an unprecedented natural disaster such as the one in Japan, failure in the cooling system can never be ruled out, even if the chances of that are only "one in a million," Chen said.

A bit of pause and reflection on nuclear power safety and risks are now warranted, he said.

Some experts have already warned of those weaknesses and said China must look forward to a new technology called AP1000 as the basis for its reactor program.

The AP1000 system, developed by United States-based Westinghouse, a unit of Japan's Toshiba, uses a passive core cooling system that doesn't require electricity as an essential driver.

The AP1000's electrical system required for initiating the passive systems doesn't rely on external or diesel power, and the valves used on the reactor don't rely on hydraulic or compressed air systems.

The passive system, when activated, is designed to remove heat for 72 hours. After that, its gravity-drained water tank must be topped up again for as long as cooling is required.

But according to a report published by the New York Times on April 22, the AP1000 may still have one problem.

Arnold Gundersen, a nuclear engineer commissioned by several anti-nuclear groups, cautioned that in the AP1000 design, the liner and the concrete are separated, and if the steel rusts through, "there is no backup containment behind it."

If the dome rusts through, the design would expel radioactive contaminants and the plant could deliver a dose of radiation hazardous to the public, according to Gundersen.

Despite that, the AP1000 design is still considered the most advanced technology in the world right now, and China plans to use it in 12 percent of reactors now under construction, the National Business Daily reported.

China will be the world's first country to build reactors using the AP1000 design. As of January 2010, applications had been filed for 14 AP1000 reactors in the US.

China is bent on developing its own nuclear power technology in the coming years. Zheng said nearly all reactor components in the world will be made in China after 2012.

But still, quality and safety issues mean China will have to work harder, he added.