Beyond the China Syndrome: Thermal reactor breakthrough in Beijing could end nuclear waste problem and remove meltdown threat
Beijing mulling ambitious plan to get first accelerator-driven sub-critical nuclear reactor up and running in Guangdong province by 2025; competing teams are suggesting different models
Chinese scientists have moved a step closer to being able to run a nuclear reactor without generating a chain reaction, a development that could remove the risk of a meltdown while also getting rid of masses of nuclear waste in a faster and safer way.
All reactors today rely on chain reactions, but these can spiral out of control and result in massive explosions, as was the case with the Chernobyl disaster in Ukraine in 1986.
They also generate large amounts of radioactive waste that can take millions of years to safely biodegrade.
The Chinese team experimented with a new approach to resolve both issues by working on proton beams that could potentially be used in a sub-critical reactor.
Nuclear scientists have dreamed of building one of these for decades, but until now they remain a theoretical construct due to various scientific challenges.
The Chinese team used an external high-energy proton beam to generate and sustain the process of nuclear fission. As a result, the nuclear fuel stopped burning as soon as the beam was cut off. This removes the risk of chain reaction, which is used by today’s reactors to sustain nuclear fission, or the splitting of atoms.
Moreover, the proton beam was able to generate neurons fast enough to burn off other fissile material – such as thorium and the waste generated by commercial reactors – after hitting its target. This was hailed an important nuclear “waste-disposal” measure.
“We are really excited,” said Professor Pan Weimin, lead scientist of the Chinese Accelerator Driven System project at the Chinese Academy of Sciences’ Institute of High Energy Physics in Beijing.
“We have solved the problem of getting the [reactor’s] ‘engine’ up and running from a cold start,” he added.
Pan used the automobile analogy of starting up an old car engine on a cold day because of the comparable difficulties in generating a proton beam. Once up and running, it operates smoothly, but getting that initial “blast off” can be problematic.
In order to “get the engine started” smoothly, the Chinese team successfully conducted an experiment in Beijing in October.
In technical terms, they were able to stably accelerate a beam of very slow-moving protons at a current of 10 milliamps to 6.04 milli-electron volts, according to a statement on the website of the Chinese Academy of Sciences.
That meant they were able to achieve the initial “blast off” needed to get a sub-critical reactor going, Pan said. The breakthrough removed a major technological obstacle that has hindered the construction of this as-yet paper-based reactor.
“We built a brand new nuclear ‘engine’,” he said. “It isn’t running at full throttle yet, but it’s up and cruising in a stable manner.”
Meanwhile, China’s central government has been mulling an ambitious plan to try and make a sub-critical reactor a reality in a coastal city in southern Guangdong province.
Pan and other nuclear physicists in China have been involved in this project. Pan said his team has submitted their proposed full-sized accelerator-driven reactor to the authorities and are awaiting – or hoping for - approval.
With the recent pace of technological development, Pan expressed confidence that the new-generation power plant could be built within a decade.
But other Chinese researchers claim his solution may not be the best one, as there are other designs of new reactors and different methodologies.
“The proton accelerator is a very large and sophisticated system, but it is too early to say whether their method is better than ours,” said one physicist, who declined to give his name.
This man’s team has been working on a different way of accelerating protons at the Nuclear Reactor Physics Laboratory in Lanzhou, the capital city of Gansu province in Northwest China.
The idea of a sub-critical reactor was first proposed by American physicist Earnest Lawrence in the 1950s. It attracted international interest thanks to the support of Carlo Rubbia, a co-winner of the Nobel Prize in Physics in 1984.
But they have proven a tough nut to crack. In addition to the problem of generating powerful and stable proton beams, there are numerous other structural and mechanical challenges yet to be solved.
In tackling these, China also faces competition from other countries.
Japan demonstrated a prototype in 2009 and Europe has announced plans to build an industrial-scale reactor called Myrrha by 2023, even though delays are expected.
Moreover, this kind of reactor is just one of several possible options for the future of nuclear power generation. Competing designs include a “fast reactor” and “molten salt reactor”.