China has "vastly increased" the risk of a nuclear accident by opting for cheap technology that will be 100 years old by the time dozens of its reactors reach the end of their lifespans, according to diplomatic cables from the US embassy in Beijing.

The warning comes weeks after the government in Beijing resumed its ambitious nuclear expansion programme, that was temporarily halted for safety inspections in the wake of the meltdown of three reactors in Fukushima, Japan.

Cables released this week by WikiLeaks highlight the secrecy of the bidding process for power plant contracts, the influence of government lobbying, and potential weaknesses in the management and regulatory oversight of China's fast-expanding nuclear sector.

In August, 2008, the embassy noted that China was in the process of building 50 to 60 new nuclear plants by 2020. This target – which has since increased – was a huge business opportunity. To keep up with the French and Russians, the cable urged continuous high-level advocacy on behalf of the US company Westinghouse to push its AP-1000 reactor.

This is crucial, according to the cable dated 29 August 2008 from the American Embassy in Beijing, because "all reactor purchases to date have been largely the result of internal high level political decisions absent any open process."

For the US embassy, a bigger concern was that China seemed more interested in building its own reactors – the CPR-1000 – based on old Westinghouse technology, at Daya Bay and Ling Ao.

"As the CPR-1000 increases market share, China is assuring that rather than building a fleet of state-of-the-art reactors, they will be burdened with technology that by the end of its lifetime will be 100 years old," reads another cable dated 7 August 2008.

For the past 10 years the CPR-1000 has been the most popular design in China. In 2009, the state news agency Xinhua reported that all but two of the 22 nuclear reactors under construction applied CPR-1000 technology.

The cable suggests this was a dangerous choice: "By bypassing the passive safety technology of the AP1000, which, according to Westinghouse, is 100 times safer than the CPR-1000, China is vastly increasing the aggregate risk of its nuclear power fleet. "

"Passive safety technology" ensures that a reactor will automatically shut down in the event of a disaster without human intervention. Plants without this feature are considered less safe as they rely on human intervention which can be difficult to provide in a crisis situation.

China says it has updated and improved the technology on which the CPR-1000 is based, but the government recognises that it is less safe than newer models. China's national nuclear safety administration and national energy administration are currently drafting new safety plans, which are thought likely to include a stipulation that all future plants have to meet the higher standards of third-generation reactors like the AP-1000 or thorium technology.

But it will still have to manage dozens of second-generation reactors for decades to come. Four CPR-1000s were approved by the state council just days before the Fukushima explosions. That accident – which was ranked on the same level as Chernobyl – has prompted a dramatic rethink of nuclear policy in Japan, Germany and Italy.

There is no sign of a change of heart in China, which plans to build more reactors than the rest of the world put together between now and 2020. The latest to be completed was the CPR-1000 at Ling Ao earlier this month.

The US embassy and Westinghouse may have wanted to play up the risks to improve the strength of their own bids, but safety concerns are also expressed within China. This year, Prof He Zuoxiu, who helped to develop China's first atomic bomb, claimed plans to ramp up production of nuclear energy twentyfold by 2030 could be as disastrous as the "Great Leap Forward" – Mao Zedong's disastrous attempt to jump-start industrial development in the late 1950s.

Writing in the Science Times, He asked: "Are we really ready for this kind of giddy speed [of nuclear power development]? I think not – we're seriously underprepared, especially on the safety front."

The rush to build new plants may also create problems for effective management, operation and regulatory oversight. Westinghouse representative Gavin Liu was quoted in a cable as saying: "The biggest potential bottleneck is human resources – coming up with enough trained personnel to build and operate all of these new plants, as well as regulate the industry."

Such worries increased in July when another of China's new industrial projects – a high-speed railway – led to a collision that killed 39 people. It too was built domestically, based on foreign designs and rolled out faster than its operators appear to have been capable of dealing with.