Chief Engineer Wang took the sketch and left the STAR Stellarator Research Institute. He returned to the China National Nuclear Corporation headquarters in Beijing and contacted an expert in ferrofluid power generation at the Academy of Engineering. They discussed the feasibility of ferrofluid power generation on controllable fusion devices.
However, even though the team leader left, the China National Nuclear Corporation still stayed in Jinling. They continued to discuss technical issues with the researchers at the STAR Stellarator Research Institute.
At the same time, the STAR experiment didn't stop.
After receiving sufficient funding, the research institute conducted an experiment every three days. They used hydrogen and helium as the research objects, and they observed the various complex physical properties of the plasma in the stellarator.
In order to collect valuable data, Lu Zhou even ordered to inject 1 mg of the precious deuterium/tritium mixture into the reaction chamber. They risked damaging the first wall material to conduct a test ignition.
Actually, this experiment did cause some damage to the STAR machine, but fortunately, the damage was still within the repairable range. However, even though this was the case, the entire machine had to be shut down for a month for maintenance.
Of course, even though the price was high, the return was also quite generous.
Not only did they verify the feasibility of the fusion reaction ignition, but they also obtained a lithium sheet that was bombarded by a neutron beam carrying 14 MeV energy.
Especially the latter, its scientific research value couldn't be measured with money.
In China, they were probably the only place that could conduct such an extravagant experiment.
This hard-earned lithium metal sheet was quietly lying on a specially treated oxygen-free slide. A staff member wearing a protective suit placed it under a scanning electron microscope.
Inside the laboratory, Lu Zhou and a group of researchers stood in front of a computer. They looked at the data and images collected from the scanning electron microscope on the screen.
Just like they expected, the originally neat metal surface was now riddled with holes.
Through the detection of the infrared spectrometer, they could even observe traces of helium and tritium in the curved holes.
Fortunately, this meant that the neutron beam carrying 14 MeV energy did react with 63Li. They successfully recovered a portion of the tritium element in the experiment.
What made them feel helpless was …
There were too many problems that they had to deal with in a few words.
Professor Li Changxia looked at the image on the computer screen and sighed.
"I bet this thing will shatter with the slightest touch."
"There's no need to bet. Even if it hasn't been hit by the neutron beam, this thing isn't that sturdy," Lu Zhou said as he stared at the hard-earned data on the computer screen.
Sheng Xianfu shook his head. "It's not just the problem of radiation damage. The proliferation ratio of tritium production is also too low. Moreover, the most important problem was not the recycling itself. The energy carried by the neutron beam is too high, so it often doesn't react with the 63Li on the surface, but instead runs around inside the cladding material. Even if it produces the thorium element we need, it will be left inside the material and can't be released at all. "
The neutron carrying 14Mev of energy was like a cannonball. In front of it, all the metal keys were as fragile as toys.
Also, the neutron that penetrated the first wall didn't just make a hole in the first wall. It would form a cavity inside the first wall material like a balloon, eventually causing the entire first wall material to swell, become brittle, or even fall off, which would cause a serious accident.
This was one of the main reasons why the cladding material of the fission reactor couldn't be directly used in the fusion reactor.
There was a difference of two orders of magnitude between the two materials in terms of radiation damage.
Up until now, their research had entered an unknown field, which meant that there was no previous experience for them to refer to. What to do next and how to solve these problems would depend on them.
After thinking for a moment, Professor Li Changxia suggested, "How about using molybdenum as the structural material?"
"Molybdenum won't do." Lu Zhou instantly rejected this suggestion and shook his head. He said, "Molybdenum has good heat resistance, but it will become radioactive under neutron irradiation."
Another researcher suggested, "What about tungsten? Tungsten has good heat resistance, and the transmutation products are osmium and rhenium. There is no radioactivity problem! "
This time, Lu Zhou didn't even have to say anything. Professor Li Changxia shook his head and said, "This is an old problem. Tungsten has good heat resistance, but its plasticity is too poor. Thermal stress will cause the surface of the material to crack … When I was visiting the DIII-D laboratory, there was a special report that specifically discussed this problem. In short, it's impossible to use tungsten. "
The laboratory went silent again.
Lu Zhou, who had been staring at the data on the screen, suddenly spoke.
"If we can't block the neutron beam inside, why don't we consider releasing it?"
"Release it?" Sheng Xianfu paused for a second and smiled as he shook his head. He said, "If we release it, how are we going to recover the neutrons produced by the reaction?"
Recovering the neutrons produced in the fusion reaction was a key part of the entire nuclear fusion reactor technology. After all, the price of tritium was tens of thousands of times higher than deuterium. Not only was it sold by the gram, but the cost of one gram was as high as 30000 USD (17 years of data).
If they couldn't recover the neutrons produced by the reaction, not only would it cause a large loss of energy, but it would also cause the reactor to "shut down" due to the loss of tritium.
In an ideal fusion reactor, whether it was tritium or neutrons, they should be preserved as intermediate products. The final waste produced was only helium and heat.
Therefore, it was impossible to release the neutrons. They had to keep them here no matter what.
After hearing Sheng Xianfu's question, Lu Zhou smiled faintly and continued.
"Letting them go doesn't mean letting them go. In theory, no matter how we design the structure of the first wall, we can't avoid the destruction of the metal bond by the neutron beam. But the self-repair ability of the metal is too poor, and there is a transmutation problem that is difficult to solve.
"Therefore, why don't we set the first wall to allow neutrons to pass through and have a strong self-repair ability. Then, we can use liquid lithium to recover the neutrons behind the first wall. As for the other side of the lithium, we can use a layer of beryllium metal to reflect the neutrons that penetrate the liquid lithium layer. "
This design was equivalent to sandwiching liquid lithium between the first wall and beryllium.
Sheng Xianfu lowered his head and thought for a bit. He felt like this method was feasible, but he felt like there were problems everywhere.
After thinking for a while, he picked out the two most obvious ones from the list of questions he could think of and raised them.
"But where can we find the material that allows neutrons to pass through and has a strong self-repair ability? Even if we move the lithium material to the first wall, we still can't solve the damage to the structural material by neutron radiation. Also, like you said, if we recover the tritium behind the first wall, how do we transport it back into the reactor? "
When Lu Zhou heard these two questions, he smiled and said, "The second problem is actually not difficult to solve. At the operating temperature of the liquid lithium, both tritium and helium exist in a gaseous state, and the two are incompatible.
"We only need to apply a weak upward force to the entire liquid lithium neutron recovery system, and we can transport the tritium above the entire system.
"After that, all we need to do is to recycle the 'gas' that is discharged above the entire system."
The generated tritium and helium would be injected back into the reaction chamber to be heated and ionized. As for how to discharge the helium from the reactor, that was the job of the divertor.
As for whether to use a water-cooled divertor, a tungsten-copper divertor, or another divertor, that would depend on the specific needs. Even though this part of the technology was critical, it wasn't impossible to solve.
Lu Zhou paused for a second and said, "As for the first problem you mentioned, this material can't be found in alloys. Therefore, we might as well just throw away the entire metal! "
The second Sheng Xianfu heard this, everyone in the laboratory, including Professor Li Changxia, was stunned.
Throw away the metal material?
This …
Isn't this a bit too futuristic?
"We don't use metal as the structural material?" Professor Li Changxia looked at Lu Zhou and asked, "Then what should we use?"
Could it be ceramics?
Even though some research institutes had tried this before and the results were decent, the fatal problem was that the thermal conductivity of ceramics was too poor.
If the heat generated couldn't be removed from the reactor, there would eventually be a problem.
"Use carbon." Lu Zhou paused for a second and said, "Or more accurately, use carbon fiber composite materials!"
This wasn't an idea that Lu Zhou came up with on a whim. He had been thinking about this for a long time. Even when he was chatting with Professor Keriber at the Wendelstein 7-X Research Institute, he had been thinking about this for a long time.
The carbon core was relatively stable and didn't react with neutrons easily. It could also play a role in buffering the neutron beam, so when the neutron beam came into contact with the liquid lithium layer, most of the neutron beams wouldn't directly penetrate it.
The part of the energy reduced by the carbon fiber layer would be released in the form of heat energy. With its good thermal conductivity, the heat generated inside the reactor could be easily extracted.
As for its heat resistance, there was no problem at all.
When it wasn't in contact with air or oxidizers, the carbon fiber material could withstand temperatures of more than 3000 degrees, which was comparable to the melting point of tungsten. It completely met the requirements of the first wall material!
Lu Zhou looked around at the people in the laboratory and said, "Completely remove the low activation metal material from the first wall material and use carbon fiber as the main structural material. The middle layer is filled with liquid lithium, and the outer layer is coated with beryllium to reflect neutrons. The shielding layer is a mixture of paraffin, water, and boron carbide, and is coated with nuclear power cement. This way, we can completely solve the problem of tritium retention! "
As for what kind of carbon fiber composite materials to use and how to solve the self-repair problem of carbon fiber composite materials, this topic would be researched by the Jinling Institute for Advanced Study.
Even though the problem was serious, there was hope that Lu Zhou could solve it!
Professor Li Changxia couldn't help but say, "This is too …"
What he wanted to say was that this was too unbelievable.
However, he was interrupted by Sheng Xianfu halfway through his sentence.
"No, who knows … there might be hope if we do this!"
Sheng Xianfu interrupted Professor Li and rubbed his chin with his index finger. His eyes were getting brighter and brighter.
"I've read the relevant literature. Using carbon fiber to replace part of the austenitic steel and tungsten steel structure is a promising technical route in the international controllable fusion field, just like nano-ceramics!
"However, using carbon fiber composite materials to completely replace the metal material as the main structural material, as well as using the decelerated neutron beam on the outside of the cladding material to react with the liquid lithium. Then, through transportation, the tritium in the liquid lithium can be recovered … This is the first time I've heard of this."
The difficulty of this wasn't small, and it wasn't just the carbon fiber composite material itself. For example, temperature control. The carbon fiber material on the first wall had an operating temperature of around 3000 degrees, while the boiling point of lithium metal was only 1340 degrees.
If the heat couldn't be removed in time, there was a risk of the liquid lithium in the "liquid lithium neutron recovery system" being vaporized. In the best case scenario, it would be sucked into the reactor along with the tritium helium mixture. In the worst case scenario, the entire reactor could be blown up …
There was also the problem of the volume change caused by the solidification of the liquid lithium when the reactor was shut down …
But just like Lu Zhou said, this idea seemed to be feasible.
At least it was worth a try!
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