Energy & Resources

The future of fission

Could molten salt reactors soon be added to China’s nuclear network?


Thorium: China’s nuclear future?

In recent years Sino-US superpower rivalry has centred on sectors like chipmaking. China wants to achieve self-sufficiency in semiconductor manufacturing. The US aims to prevent China getting the advanced technology needed to do so. But now the Americans are waking up to another challenge. China may be moving ahead in nuclear energy and in particular beyond the frontier in nuclear reactors known as generation IV.

Earlier this month the Washington Times led with a headline that put that perspective quite bluntly – “China is eating our lunch when it comes to nuclear technology”. Political news site The Hill ran an opinion piece from two Republican congressmen at a similar time outlining how “the US should recognise China’s nuclear ambitions”.

A key area of focus is molten salt technology, which could provide a safer alternative to the current generation III plants that use pressurised water reactors.

Reactors of the newer design use the widely abundant, silvery metal thorium, rather than uranium and plutonium. China launched a research initiative into the technology back in 2011 and the South China Morning Post reports that a thorium-based molten salt reactor in Gansu province is due to be completed next month and could begin its test run in September.

The facility will produce uranium-233, a type of fissile material that could then be used to seed other nuclear reactors designed to run on a thorium fuel cycle.

China needs to create an initial stockpile of uranium-233 because of a key difference between the two metals thorium and uranium. Thorium has very weak radioactivity, while uranium hosts the only fissile isotope (i.e. one capable of sustaining a nuclear reaction) that is naturally occuring (uranium-235).

However, a synthetic fissile isotope (uranium-233) can be created by irradiating thorium. This isotope might then replace or be deployed alongside uranium-235, the current standard as reactor fuel, and is ideally suited to molten-salt based reactors.

Separately, the Chinese journal Nuclear Techniques has just published an article by several academics at the Shanghai Institute of Applied Physics (SINAP) who designed a small-scale molten salt reactor using uranium-233, which is said to be capable of generating up to 100MW of electricity.

The bathroom-sized reactor would generate enough power to service a population of about 100,000 people and the academics say it has the advantage of “being multipurpose, small in size and highly flexible”. Such technology could be used to bolster China’s energy generation but also be exported abroad, perhaps to partner nations in the Belt and Road Initiative, local media commented.

One of the great advantages of uranium-233 as a fuel source (over uranium-235) is that it’s harder to weaponise (or enrich from the 20%-level deployed in nuclear power plants to the 80%-to-90% composition needed for nuclear missiles). This could make the new generation of plants a little less controversial if they are exported to nations like Iran.

However, the piece in The Hill claims another motivation for the Chinese efforts: that while thorium reactors can generate electricity, “the real impetus for the Chinese project comes from the People’s Liberation Army Navy’s intentions to build a fleet of thorium-powered warships to challenge the US worldwide”.

This, the authors argue, is why the Chinese have invested Rmb22 billion ($3.4 billion) in a project set up by SINAP head, Jiang Mianheng (who is the son of former Chinese leader Jiang Zemin).

As we reported in WiC280, Jiang junior was the leading light in the signing of a cooperation agreement with Oak Ridge National Laboratories in Tennessee, which pioneered molten salt technology many decades ago. SINAP and Oak Ridge began working together in 2012 and signed a formal deal in 2015, which was extended in 2018 through to the end of 2020.

Aside from their warning against the cooperation between Oak Ridge and the Chinese, another frustration for the Republican congressmen writing in The Hill is how the US federal government has been “nonsensically destroying” its existing resource of uranium-233.

While the Chinese have started the process of building up a reserve of the isotope at their Gansu reactor, the Americans have spent more than $600 million downgrading their own stockpiles of the same resource, after designating it as a waste material back in the 1990s.

The debate about thorium dates back to the Second World War, after scientists from Nazi Germany discovered the physics of nuclear fission. By 1942 scientists working on the Manhattan Project at Oak Ridge had worked out how to create uranium-233 from thorium and viewed it as one of the most promising materials to power the world’s first atomic bombs. The discovery added to American concerns when they later heard that a German chemical firm had raided French stockpiles of thorium. But the reality turned out to be less threatening: the company in question hoped to use the thorium for a new type of toothpaste. It had its advertising jingle ready too: “Have sparkling teeth – radioactive brilliance”.

A decade later, the US Atomic Energy Commission concluded that of the three reactor types under consideration for civilian use, the molten design had the highest probability of achieving technical feasibility.

During the 1960s, the Oak Ridge lab achieved just that. Its scientists built a pilot reactor that produced uranium-233. However, it was shut down in the early 1970s on the orders of then President Richard Nixon. With the Cold War at its height, his administration preferred another technology (uranium-235) that could be more easily co-opted for both civilian and military uses.

The technology fell into abeyance and the history of the civil nuclear power industry took a different path. Over the past decade China and India – which both have large thorium reserves – have revived interest in the so-called molten salt technique. Thorium also appeals to China’s nuclear strategists because it means the country won’t need to rely as much on uranium – most of which it has to import.

There are other voices in support too. When uranium-233 decays, it produces an isotope called bismuth-213, which can be used for a new form of cancer treatment called targeted alpha therapy that is said to destroy cancer cells but avoid damage to healthy tissue around them.

Many scientists also believe that thorium-based reactors should be inherently safer than the current fleet of nuclear plants – although not everyone agrees on this point.

Those in favour point out that thorium-based plants don’t suffer from a similar kind of risk that led to the explosions that destroyed Chernobyl in 1986 and Fukushima in 2011. To prevent similar disasters, they incorporate a special ‘freeze plug’ that melts if the reactor starts to overheat. The salts in the plug solidify around the nuclear fuel, which falls into an emergency dump. The materials then drop in temperature, solidifying and trapping radioactive substances in the process.

There are some downsides to the newer approach, however. One is that when thorium is irradiated, it creates the highly radioactive uranium-232 as well as 233 (exposure to the former’s gamma rays can be deadly within a few days). There are also technical challenges in maintaining molten salt reactors due to the corrosive effects had on the construction materials.

But perhaps the focus on molten salt technology – which doesn’t rely on uranium fuel rods in the same way as the current generation of light-water reactors – will get more of a hearing following the latest news from the Taishan nuclear power plant in Guangdong.

After the French designers of the plant warned of a “performance issue” in June, Taishan’s bosses acknowledged that a small number of fuel rods had been damaged in one of the reactors but described the situation as a “common phenomenon”, insisting that the plant was operating within safety standards.

Electricite de France (EDF), the junior partner in the venture that owns the plant, still seems uncomfortable, however. Last week it put out another statement acknowledging that there was no “emergency situation” at Taishan but that the fuel rod leak would have resulted in the shutdown of the reactor in the same scenario in France.

“In Taishan, the corresponding decisions belong to TNPJVC [the majority owner and operator of the facility],” its spokesperson explained.


Keeping track, Jul 31, 2021: Just after the publication of this article on Friday 30 July, a reactor at the southern Chinese nuclear power station of Taishan was shut down after what the Financial Times described as “fuel damage”.

In a statement on Friday, China Nuclear Power Corp (CGN) said the nuclear plant had “decided to shut down Reactor No. 1 for maintenance, in order to find the cause of the damage affecting the fuel and to replace the damaged fuel”. France’s EDF, a 30% shareholder in the Taishan plant, had recommended its closure last week, the FT added.

CGN, the majority owner of the joint venture said the reactor had subsequently been shut down “for maintenance” to investigate a potential fuel-rod problem, though it restated the fuel damage was within the allowable range and the plant could have continued to operate safely. Taishan is the first nuclear plant in the world to operate the Franco-German technology EPR (European Pressurised Reactor).

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