Translator: Henyee Translations Editor: Henyee Translations
Chief Engineer Wang left the STAR Stellarator Research Institute with the technical sketch. He flew back to the China National Nuclear Corporation headquarters in Beijing on the same day and contacted ferrofluid electric energy experts at the Academy of Engineering. They began to discuss the feasibility of applying ferrofluid electric energy technology on the controllable fusion device.
However, even though their leader was gone, the China National Nuclear Corporation task force still stayed in Jinling. They were working with the STAR Stellarator Research Institute researchers on technical issues.
At the same time, the STAR machine was undergoing experiments.
After the institute received sufficient research funding, the institute had been conducting experiments almost every three days. Their research targets were hydrogen and helium, and their job was to observe their various complex physical properties in the stellarator plasma.
In order to collect valuable data, Lu Zhou even demanded to mix the 1mg of precious deuterium into the reaction chamber, which had the risk of damaging the first wall material.
In fact, this experiment did actually cause some damages to the STAR machine. Thankfully, the damage was repairable. But even then, the entire machine had to be shut down for at least a month.
Of course, even though the cost was high, the return was also high.
Not only did they verify the feasibility of a fusion reaction ignition, but they also obtained a slice of lithium that was hit by a neutron beam carrying 14MeV of energy.
The scientific research value of the piece of lithium couldn’t be measured with money.
They were probably the only institute in China that could conduct such extravagant experiments.
This hard-fought lithium metal slice was lying quietly in a specially treated oxygen microscope slide. Which was placed under a scanning electron microscope and observed by a worker in protective clothing.
Outside of the isolated room, Lu Zhou and other researchers were standing in front of a computer in the laboratory. Through the computer screen, they were able to observe the numbers and graphs from the scanning electron microscope.
Just like they had expected, the original smooth metal surface was covered with holes.
Through the infrared spectrometer, they could even see traces of tritium and helium in the metal.
A piece of good news was that this proved the 14meV neutron energy beam did react with lithium-3. This meant they were able to successfully recover part of the tritium used in the experiment.
Unfortunately…
They were facing countless problems.
Professor Li Changxia stared at the graphs on the computer screen and gently sighed.
“I’m willing to bet that this thing will break the instant someone touches it.”
Lu Zhou stared at the hard-fought data on the computer screen and replied casually, “There’s no need to bet. Even if it wasn’t hit by the neutron beam, it wouldn’t be that strong.”
Sheng Xianfu shook his head and said, “It’s not just the radiation damage, the recovered tritium is way too low. And the most important problem isn’t even recovering the tritium. The energy carried out by the neutron beam is too high. Not only did the surface of the lithium-3 react, but so did the interior layers. Even if the tritium was collected in the lithium interiors, we wouldn’t be able to extract it.”
The neutron energy beam carrying 14MeV of energy was like a missile, the metals were no match for this monster.
Also, not only did the neutron beam penetrate a hole in the first wall, but it will form an empty space inside the first wall material, just like a balloon. This could ultimately result in the swelling, embrittlement, and even surface material shedding of the first wall material, which could lead to serious accidents.
This was one of the main reasons why the fission reactor layer material couldn’t be used in the fusion reactor.
The two had different orders of magnitude in terms of their radiation-resistant capabilities.
From now on, their research had entered into an unknown field. This meant that there wasn’t any more literature they could consult. All of the problems from this point onward had to be solved by themselves.
Professor Li Changxia thought for a bit and suggested, “What if we use molybdenum instead?”
“Molybdenum won’t work.” Lu Zhou instantly rejected this idea. He shook his head and said, “Molybdenum has decent heat-resistant properties, but it will produce radioactive elements when it undergoes neutron irradiation.”
Another researcher suggested, “What about tungsten? Tungsten has good heat-resistant properties, and its by-products are osmium and rhenium, so there’s no radiation!”
Lu Zhou didn’t even have to speak himself. Li Changxia shook his head and said, “This is a common misconception. Tungsten has good heat-resistant properties, but it is not malleable enough. The thermal stress will cause cracking on the surface of the material… When I was doing an academic exchange in the DIII-D tokamak experiment, there was a specific research project regarding this problem. In short, tungsten won’t work.”
The laboratory became silent again.
Lu Zhou, who had been staring at the data on the computer screen this entire time, suddenly asked, “If we can’t contain the neutron beam inside the stellarator, why don’t we let it pass through?”
“Pass through?” Sheng Xianfu paused for a second and smiled while shaking his head. He said, “If we let it pass through, how are we supposed to recycle the neutrons produced by the reaction?”
Recycling the deuterium-tritium neutrons produced in the fusion reaction was a key part of the nuclear fusion technology. After all, the price of tritium was tens of thousands that of deuterium’s. It was sold by the grams, costing US$30,000 per gram1.
If they couldn’t retrieve the neutrons generated by the reaction, not only would they lose a large amount of energy, but the reactor would also “shut down” due to the loss of tritium.
In an ideal scenario, both the tritium and neutron should be able to be preserved as an intermediate product. The final waste should only be helium and heat.
Therefore, they shouldn’t let the neutron just pass through, they had to preserve it no matter what.
Lu Zhou heard Sheng Xianfu’s remarks and smiled.
“Letting them pass through doesn’t mean releasing them. In theory, no matter the design for the first wall material, we cannot avoid the damage of the neutron beam to the metallic bonds. Also, the repair properties of metals are poor, not to mention the metamorphosis problem.
“Hence, why not make first wall material to be something that allows neutrons to pass through and has a strong self-healing ability. Then we can use liquid lithium-3 to recover the neutrons behind the first wall material. As for the side beyond the liquid lithium, we can put a layer of beryllium metal to reflect the unreacted neutrons that penetrate the liquid lithium layer.”
His design was equivalent to sandwiching liquid lithium between the first wall and the beryllium.
Sheng Xianfu lowered his head and contemplated it for a bit. He thought that this method seemed feasible, but he also felt like there were problems.
He thought for a while and came up with two of the most obvious problems.
“But where can we find a material that allows neutrons to pass through and has great self-repairing capabilities? Even after using lithium as the first wall material, we still can’t solve the radiation damage problem. Also, like you just said, after we recover the tritium, how do we carry the tritium back into the reactor?”
When Lu Zhou heard these two questions, he smiled and said, “The second problem is easy to solve. Under liquid lithium’s temperature, both the tritium and helium are in their gas forms. They are incompatible with each other.
“We just have to apply a weak upward force to the neutrons inside the liquid lithium and transport the neutrons to the top of the reactor.
“Then we just need to recycle the gas that comes out of the reactor.”
The generated tritium and the exhaust gas helium would then be injected into the reaction chamber for ionization. As for removing the helium from the reactor, that was the job of the divertor.
As for choosing a water-cooled divertor, a tungsten-copper divertor, or any other divertor, that choice would depend on their specific needs. Even though this part was crucial, it wasn’t something that they couldn’t solve.
Lu Zhou paused for a second and said, “As for your first question, that metal can’t be found in alloys. So how about we discard the entire metal layer?”
Everyone in the laboratory, including Li Changxia and Sheng Xianfu, was frozen.
Getting rid of the metal layer?
This…
Is outrageous, right?
“We’re not using a metal?” Professor Li Changxia looked at Lu Zhou with an astonished expression. He said, “Then what are we going to use?”
Ceramics?
Even though other research institutes had tried using ceramics and produced decent results, the killing factor was the poor thermal conductivity of ceramics.
If they couldn’t remove heat from the reactor, they would end up with other problems.
“We’re going to use carbon.” Lu Zhou paused for a second and said in a confident manner, “Or more precisely, carbon fiber composites!”
Lu Zhou didn’t suddenly come up with this creative idea. He had been thinking about this for a long time, even back when he was still working with Professor Keriber at the Wendelstein 7-X research institute.
The carbon core was relatively stable. It didn’t react with neutrons easily. Also, it could act as a buffer for the neutron beam, so when the neutron beam contacted with the liquid helium, it could prevent the neutron beams from instantly breaking down.
The energy reduced by the carbon fiber layer would be released in the form of heat energy. Due to its stellar thermal conductivity properties, the heat energy generated inside the reactor could be easily diverted.
It also had good heat-resistant properties.
When it wasn’t exposed to air and oxidants, carbon fiber could withstand temperatures above 3,000 degrees. This was comparable to the melting point of tungsten, which met the requirements for the first wall material!
Lu Zhou looked at the people in the laboratory and said, “Remove the first wall metal layer completely. Use carbon fiber as the main structural material. Then fill in liquid helium in the middle layer and use beryllium on the outer layer to reflect the neutrons. The shielding layer should be a mix of paraffin and water carbon carbide, covered with nuclear-grade cement. If all of this is successful, we will solve the tritium retention problem!”
As for the choice of carbon fiber composite materials and the self-repairing component, that research project would be conducted by the Jinling Institute for Advanced Study materials research division.
Even though the problem was severe, Lu Zhou had a feeling that he would be able to solve it!
Professor Li Changxia couldn’t help but say, “This is too…”
What he wanted to say was that this was too outrageous.
However, before he could finish, Sheng Xianfu interrupted him.
“No, maybe… this could work!”
Sheng Xianfu rubbed his chin with his finger as his eyes began to light up.
“I’ve read the relevant literature on replacing tungsten and steel structures with carbon fiber. The international academic community is optimistic about this technical route, just like nanoceramics!
“However, using carbon fiber composites to completely replace the metal as the main body of the reactor and to allow the neutron beam to react with the liquid lithium outside the first wall before recovering the tritium in the liquid lithium… This is my first time hearing about something like this.”
The difficulty involved in something like this was high. They had to face carbon fiber composite problems. For example, the problem of temperature. The carbon fiber composite material had an operating temperature of around 3,000 degrees, while the boiling point of lithium metal was only at 1,340 degrees.
If they couldn’t transfer the heat in time, the liquid lithium could risk being vaporized, which could result in it being mixed in with the tritium reaction. This could blow up the whole reactor…
There was also the volume changing problem where the lithium liquid would be solidified after the machine was turned off…
However, just like Lu Zhou had said, this idea might be feasible.
It was at least worth a try!
