The story behind China’s fourth generation nuclear reactors

Oct 30, 2022
The central control room of nuclear power plant. Fragment of nuclear reactor control panel.

The fact that only China has implemented a Small Modular Nuclear Reactors is a testament to the skills and capacities of Chinese nuclear engineers and the policy makers that the West, despite renewed interest in the idea, will find difficult to match.
Small nuclear reactors designed to be “fail safe” (PBMRs) have lately gained western proponents.

Small Modular Nuclear Reactors were originally conceived in a suburb of Pretoria, in South Africa. As in China, nuclear power had been seen in the fifties and sixties as one important if contingent solution to political isolation and energy poverty.

The history of the flow of technology and ‘trade secrets between the East and West, a story as old as civilisation. The Chinese Han dynasty defeated a Greco-Bactrian kingdom in the Ferghana Valley to acquire the Greeks “Heavenly horses”.

Of course, paper, the compass, gun powder, silkworms, tea, the secrets of porcelain (which we still call “China”) are but a few of the technologies that did flow the other way.

That post-Cold War China would copy the strategies of Japan, Korea and Taiwan should surprise no one.

They took the same advantage of industrial policy and a long term focus on nurturing engineering and scientific talent as their smaller Tiger siblings. By supporting science as a matter of public policy.

Indeed, a capacity for innovation has in China been long recognised both internationally and locally. The hero of this tale of confident domestic innovation began with a Chinese whitegoods company who discovered that the key to selling washing machines in rural China was rugged functionality and the ability to wash potatoes and carrots without difficulty.

The case of the Pebble Bed Modular Reactor can serve as a canonical example of a technologies that was abandoned for lack of political and academic support in the West, that, apparently on the basis of its conceptual merit and future possibilities nevertheless found a home in China.

NB – studying the literature isn’t spying, its research. The essential features of this type of reactor were accessible to China because science is of its nature information in the public domain.

It was of note to me only because I was writing about the PBMR in 2006, not as a nuclear engineer, but from a share trader speculating in mining juniors (writing for a US site

My essay was only taken up to support the Bullish case for Uranium prices and therefore healthy upsides in the share prices of exploration juniors.

The cleverness of the physics was in the public domain, it formed the basis of the whole discussion at the time.

The concept of a Pebble Bed Reactor was originally based on the AVR reactor modified to drive a Brayton closed-cycle gas turbine.

Pebble Bed Modular Reactor Pty Ltd grew into one of the largest nuclear reactor design teams in the world. The PBMR head-office was in Centurion near Pretoria.

But no one bought the design and the South African company was wound down in 2010.

I wrote in 2006:

“A Pebble Bed Modular Reactor (PBMR) has thousands of pebbles rather than fuel rods. About the size of billiard balls, each billiard ball sized sphere has a core of enriched uranium, about half a millimetre across, surrounded by three layers, pyrolytic carbon, silicon carbide and graphite. Pebbles are added to the top of the reactor and taken from the bottom, inspected and replaced if necessary before being returned to the top of the reactor. Unlike operating a PWR you do not need to shut the reactor down to refuel.

“Helium is used as coolant, entering the core at 482 C and leaving at 900 C. The high temperature of the helium and the fact that it is directly coupled to the gas turbine make a PBMR efficient (unlike a PWR of 2000MW such as the one that exploded at Fukushima) and a loss of coolant isn’t fatal.

“While a single PBMR can produce only about 110 MW each (to maintain the self limiting design safe from meltdown factor) but the possibility that up to 10 PBMRs might be located together and run from a common control suite was a selling point at the time.

A PBMR has unique features that make it much safer than a Pressurised Water Reactor”.

The use of pebbles gives these reactors a lower power density. The pebbles have a large surface area and are good at dissipating heat.

But the unique feature of this reactor is that the loss of coolant cannot cause a meltdown.

The secret of a PBMR is that if the pebbles get too hot, fission slows.

The physics behind this is a phenomenon called “doppler broadening”; long before the absolute temperature in the reactor rises to the melting point of the pebbles, the uranium nuclei at the centre of the pebble have become so blurred by the heat they sidestep the neutrons that would otherwise sustain a chain reaction.

Even in the event of a catastrophic cooling-system failure the core temperature of a PMBR cannot exceed 1,600 degrees Celsius – comfortably below the balls’ 2,000-plus-degree melting point before the temperature and fission rate fall into a stable new equilibrium.

Any committee tasked with finding answers to energy production in a carbon constrained world would have probably jump on it as worthy of examination.

The state of the Small Modular Reactor business in the West is beyond the scope of this article, the political neutron bombs of weapon state wannabees and climate foot draggers are not the remit of this essay.

But, for a fact, a commercial generation IV nuclear power plant using “Pebble Bed” technology went critical for the first time just over a year ago in Shidao Bay, in China.

The Chinese “High Temperature Reactor – Pebble Bed” the HTR-PM was connected to the state power grid and began producing power in December 2021.

Two 250-MWt High-Temperature Pebble-bed Modular Reactors, called HTR-PM (now designated as the High Temperature Reactor ~ Pebble Modular, in China) are now operating and connected to the grid.

That sixteen years after taking an interest only China has implemented a PBMR can only be a testament to the Chinese nuclear engineers and the policy makers that gave them the scope and resources to continue that development process.

As far as I can tell, it’s all good planning and hard work.

Construction began at the end of 2012. The pressure vessel was installed in December 2017. Reactor two achieved criticality in November 2021. The reactors are rated at 110 megawatts each, as could be expected, that’s a signature of a pebble bed reactor.

A further 18 such HTR-PM units are proposed for the Shidaowan site.

China has proposed a scaled-up version called HTR-PM600, which calls for one large turbine rated at 650 MWe driven by six HTR-PM reactor units.

Feasibility studies on HTR-PM600 deployment are under way for Sanmen, Zhejiang province; Ruijin, Jiangxi province; Xiapu and Wan’an, in Fujian province; and in Bai’an, in Guangdong province.

Nuclear electricity may quickly become uneconomic, even in China.

This article is not about the Australian nuclear debate; It only speaks to the determination to complete well conceived projects and ‘skills and capacities that the West will find difficult to match.

How China ended up making most of the planets PERC Solar Panels, originally developed at the University of N.S.W. is the tale of squandered opportunity we will examine in a future article.

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