The State Council in October last year decided to resume "normal" construction of nuclear power plants, ending a 19-month suspension of new project approvals amid a thorough safety review of all operating projects and those under construction or being planned following the earthquake-nuclear disaster in Japan in March 2011.

Beijing also scaled back expansion of new plants before the end of 2015 and allowed only a small number of "well-proven" projects in coastal regions.

"Safety is the lifeline of the nuclear power industry," the State Council said at the time, adding the industry must build plants "based on the highest safety requirements globally".

In 2006, Westinghouse, a unit of Japanese engineering and electronics giant Toshiba, won a contract to supply two reactors to Sanmen, and another two to Haiyang, Shandong province, based on its AP1000 technology.

Westinghouse's AP1000 and French rival Areva's European pressurised reactors belong to the so-called third-generation technology and are supposed to be safer, more efficient and have longer operating lives than widely commercialised second-generation technologies that Chinese firms generally use.

According to Westinghouse, its "passive core cooling system" provides "unequalled safety" through "passive residual heat removal".

In the event of an accident, the plant's design allows it to shut down without any operator intervention and without the need for power or pumps to run cooling systems since it relies on natural forces such as gravity to prevent overheating.

"This is very advanced technology, but it has not been commercialised in a nuclear reactor anywhere, so it needs to be proven over time after the first AP1000 reactor is commissioned," Li said.

"[Westinghouse] said its technology is mature since it is based on a proven smaller-scale reactor.

"But its expansion from 600 to 1,000 megawatts has not been commercially proven, that's why Chinese experts have had an intense debate over the adoption of AP1000."

Westinghouse said the AP1000 reactor's "primary system canned motor pumps" were "maintenance-free".

"Without operating history, how can you prove that such pumps do not need maintenance over 60 years [the assumed life of the reactor]?" Li asked.

Westinghouse said the pumps' supplier Curtiss Wright EMD had not specified any inspection and maintenance requirements since "its experience with similar canned motor pumps has demonstrated that inspection and maintenance are not required for the long-term safe operation of the pumps".

Li said Beijing was more prudent when it imported second-generation technology.

He said former premier Li Peng followed what he called the "normal practice" in introducing foreign technology over two decades ago to build the nuclear plant in Daya Bay, 50 kilometres northeast of Hong Kong, by insisting on having a precedent reference plant.

This was a less risky approach since the reference plant's actual performance parameters were typically used as the basis for resolving contractual disputes on technical issues, he said.

By rushing to realise the world's first AP1000 commercialisation project, the mainland was taking on higher risks, Li Yulun said.

In a research paper published last month, Li Yulun said the first four AP1000 reactors bought by CNNC were based on the 15th revision of the original design, and that Westinghouse had told CNNC before signing the supply contract that it was working on the 16th revision with major design changes.

But CNNC insisted on sealing the contract based on the 15th revision, citing a need to start construction early, he added.

CNNC would not comment. A spokesman for State Nuclear Power Technology Corp, which is responsible for importing new technology, said the basic design of AP1000 reactors had not changed despite the revisions.

He added that the reactors being built in China had incorporated technical changes from subsequent revisions, except for requirements aimed at protecting a nuclear plant against the deliberate crashing of large commercial aircraft, which is mandatory in the US but not in China.

In what he considered to be another sign that China has been rushing into a new technology, Li Yulun noted that Britain's Office for Nuclear Regulation had rejected Westinghouse's bid to supply reactors in June 2011, citing some "unresolved technical issues".

He quoted Westinghouse's head of its British unit Mike Tynan as having said that a significant amount of work needed to be done on the safety front.

"Westinghouse has yet to receive approval from British authorities on an improved version of AP1000, while Chinese nuclear safety regulators already approved it several years earlier," Li Yulun said.

Westinghouse's spokeswoman said Britain's Office for Nuclear Regulation in late 2011 granted "interim" approvals to AP1000's design.

She said additional work would be required for the design to move to "final" approval status, and Westinghouse "will embark on the remainder of this work once we have been selected as the preferred reactor design by a British utility customer".

Asked about the delays, Westinghouse quoted State Nuclear Power Technology chairman Wang Binghua's comment at the World Nuclear Conference this month that the first units of Sanmen and Haiyang projects were expected to be completed in December next year, a year behind schedule.

State Nuclear Power Technology said: "Globally, it is normal for a new generation of nuclear plants, particularly the first unit, to experience a certain amount of construction delay."

Based on the Daya Bay project, which took three months longer to complete during its construction in the early 1990s, each day of delay incurred an interest cost of US$1 million.

A reactor of more than 1,000MW, like the AP1000, generates over eight billion kilowatt-hours of power a year. If the power is sold to residential users at 50 fen (63 HK cents) per kilowatt-hour - home price is half the industrial cost - the delay could result in annual lost income of more than four billion yuan.

The World Nuclear Association said on its website the construction cost of the two AP1000 reactors at Sanmen was estimated by the China Nuclear Energy Association at 40.1 billion yuan in May - 24 per cent higher than earlier estimates.

A State Nuclear Power Technology spokesman said the AP1000 design used fewer water pumps, valves, pipes and power cables compared with second-generation reactors.

Construction time is also supposed to be shorter, while the reactors have longer lifespans.

"With localisation of design and mass production, AP1000's economics will be fully realised in the future," he said.