Chapter 390 Good News and Bad News

In the Qixiashan Controlled Nuclear Fusion Research Institute, standing in the laboratory, Xu Chuan looked at the images and data on the display screen.

On one side of the laboratory, there is an isolated laboratory room.

In it, scanning electron microscopes, metal in-situ analyzers, mass spectrometers and other equipment are analyzing the materials in the equipment.

The second extreme experiment of the Dawn Fusion Device created not only a two-hour high-density plasma operation record, but also a deuterium-tritium raw material fusion ignition operation experiment.

The data and value brought by the real deuterium-tritium raw material fusion ignition operation experiment are not comparable to the helium-3 and hydrogen simulated high-density plasma flow operation.

Although the latter can also approach the former in terms of temperature, density, etc., it is ultimately impossible to produce fusion.

The former, even if it is only one milligram, can achieve true deuterium-tritium fusion to release energy, release neutrons, increase the temperature of plasma, disrupt plasma operation, etc.

These are all things that helium-3 and hydrogen simulated operation cannot do.

In particular, neutron irradiation damage to the first wall material is the next world problem for the high-temperature plasma turbulence in the controlled nuclear fusion relay control reactor chamber.

The first wall material not only has to deal with the high-temperature deuterium-tritium plasma of hundreds of millions of degrees in the reactor chamber, but also has to deal with the neutron beams produced during the fusion process of deuterium-tritium raw materials.

In addition, the first wall material may even have to bear the function of tritium self-sustaining.

The two raw materials for DT controlled nuclear fusion are deuterium and tritium.

The content of deuterium on the earth is huge. There are about 40 trillion tons of deuterium in seawater alone, and the preparation is relatively simple.

But compared with deuterium, the storage of tritium on the earth is quite scarce.

The stock of tritium in global natural resources is almost negligible, and the stock in nature is only about 3.5 kilograms.

At present, the storage of tritium raw materials in various countries, all countries combined, does not exceed 25 kilograms.

On the one hand, tritium will decay by emitting beta rays autonomously, with a half-life of only 12.5 years.

On the other hand, it can only be prepared through nuclear reactions.

At present, the industrial preparation of tritium mainly uses the neutrons of the reactor, uses lithium-6 compounds as targets, produces tritium, and then uses thermal diffusion to enrich tritium to more than 99% before collecting and storing it.

The neutron beam is uncontrollable, and the amount produced in the nuclear fission reactor is not large, so the output is very low.

Therefore, in the controlled nuclear fusion technology, how to keep tritium self-sustaining is also one of the key issues.

Perhaps some people think that particle accelerators can be used to accelerate neutrons to bombard lithium materials to produce tritium raw materials, but to be honest, those who have this idea are basically those who did not study physics seriously in high school.

Neutrons do not carry electrons, and the magnetic field of the accelerator has no effect on them at all.

If the magnetic field can confine neutrons, the material for the first wall of the controlled nuclear fusion reactor will not be so difficult to find.

Fortunately, a large number of neutrons will be produced during the deuterium-tritium fusion process. If neutrons are used to bombard lithium-6 compound targets, tritium can be maintained self-sustaining in theory.

During the last operation of the Dawn Fusion Reactor, Xu Chuan did such an experiment.

On the first wall, he had people install various material sheets such as lithium-6 compound targets, tungsten alloys, molybdenum alloys, graphite, carbon composite materials, and beryllium alloys.

Among them, the lithium-6 compound target material is used to test whether the neutrons released during the deuterium-tritium fusion process can really bombard lithium materials to produce enough tritium raw materials as in theory.

The other materials are to find the most suitable first wall material.

Neutron irradiation is not a joke.

For now, it can produce a strong transmutation effect on most materials, and most metal materials.

This will not only destroy the structure of the material, but also turn the material into an extremely fragile foam like a foaming agent.

Imagine a piece of steel as thick as a foam box, which is broken into slag by your hand.

Neutron irradiation in a controlled nuclear fusion reactor can do this.

In fact, this is exactly the case. Although the deuterium-tritium raw material used in the last Dawn fusion device was only one milligram, the neutrons produced during the fusion process still caused varying degrees of damage to the various test materials deployed on the first wall.

However, it is gratifying that the lithium-6 compound target did play a corresponding role in the experiment. The neutron beam produced by the deuterium-tritium fusion hit it and produced some tritium elements.

Therefore, theoretically, it is theoretically possible to use lithium-6 compound targets as reactants to solve the problem of tritium self-sustaining.

This is also a major breakthrough.

After all, in the past, no experimental institution or research institution could really use the experimental reactor to test the synthesis of tritium raw materials by neutron + lithium materials for deuterium-tritium fusion reactions.

This should be the first time for them.

However, there is good news, but there is more bad news.

The damage degree of the various neutron irradiation-resistant test materials installed on the first wall material is higher than Xu Chuan calculated.

Looking at the image on the computer screen, Zhao Guanggui, a professor of materials science standing on the other side of Xu Chuan, sighed softly and said: "From the experimental data, there are many more problems than we imagined."

Xu Chuan looked at the image on the computer and said: "No matter how many there are, we have to solve them one by one, right?"

Hearing this, Zhao Guanggui sighed: "That's true, but we have a lot of troubles. And we have now entered a new field. In the area of ​​controllable nuclear fusion, no other research institution or laboratory can Provide us with experience as a reference.”

Hearing this, Xu Chuan smiled and said: "Referring to other people's experiences and ideas can indeed provide us with great convenience, but after all, we are just walking on other people's paths. In order to achieve something in scientific research, , after all, you have to have your own ideas and ideas.”

"The lazy method may be suitable for other fields, but for us who are engaged in academic research, what to do and how to solve problems ultimately require our own independent thinking."

On the side, Xing Xuexing, a professor of materials science who was transferred from Shuimu University, smiled and said: "Being able to go ahead and expand the boundaries is what every researcher and scholar hopes for."

After a pause, he brought the topic back to the experimental data: "But Professor Zhao is right, we are in a lot of trouble this time."

"Whether it is tritium self-sustaining or various damage to neutron irradiation-resistant sample materials, they are far lower than expected before the experiment."

"Using neutrons to bombard lithium targets can indeed generate tritium. But the amount generated and the amount we collect are not as much as theoretically."

"On the one hand, not all of the neutron beam generated by fusion in the chamber acts on the lithium-6 compound target. The energy it carries is too high and will directly penetrate the target, causing the number of reactions to be far lower than expected."

"On the other hand, the energy level carried by these neutrons is too high. At a temperature of 120 million degrees, the energy level of the neutron beam released by deuterium-tritium fusion is comparable to that of a medium-to-large particle collider. This will have a negative impact on the target material and the third It has had a very serious impact on everything.”

Xu Chuan thought for a while and said: "The first problem can be easily solved. At worst, the thickness of the target can be increased. In addition, it can be made into a fully covered type, wrapping the reaction chamber as a whole, so that the neutron beam can be It’s not a waste.”

"As for the second one, it's a bit troublesome."

Controlled nuclear fusion is not nuclear fission, and the temperature of nuclear fission is far lower than that of nuclear fusion.

Even if a large-yield nuclear bomb explodes, the core temperature will be one million degrees Celsius.

When Little Boy was dropped on Hiroshima, the temperature in the core area of ​​the explosion was only over 6,000 degrees. In comparison, this value is simply not worth mentioning in controllable nuclear fusion.

More than six thousand degrees, this data is not even a fraction of the plasma temperature at which the Dawn Fusion Device operates.

The explosion temperature of a nuclear bomb is only this, so the temperature of a nuclear power plant that uses the nuclear fission effect to generate electricity is even lower.

Therefore, most of the anti-irradiation materials that can be used in nuclear fission reactors cannot be used in controllable nuclear fusion reactors.

Not only the lithium target used for tritium self-sustainment was damaged during the experiment, but other experimental materials deployed on the first wall were also damaged.

On the side, Zhao Guanggui said tentatively: "How about lowering the fusion temperature?"

"The temperature of deuterium and tritium fusion can occur at about 12 million degrees, 120 million degrees, which is a full ten times higher."

"Although lowering the temperature will affect the activity of the deuterium-tritium plasma, which will in turn affect the number of fusions and the energy produced. It is not undesirable to sacrifice part of the heat and energy in exchange for the stability of the first wall material."

Xu Chuan thought for a while, shook his head and said: "It's not feasible."

"Although thermal motion can cause neutrons to have inelastic collisions. The higher the thermal motion speed, the greater the impact on matter. However, the energy level of the neutron beam in the fusion reactor is not solely derived from temperature."

"Its main source is the energy generated during the fusion of deuterium and tritium nuclei. Each deuterium and tritium nuclear fusion will produce a 14.1 MeV neutron. This part is destined in high energy physics, and lowering the temperature only reduces part of the external force. "

Zhao Hongzhi nodded and said: "Well, from this aspect, it is basically impossible to lower the temperature to reduce the damage of neutrons to the first wall material."

“From the material analysis data after neutron irradiation, molybdenum, tungsten, and graphene are on the first step and are less affected by neutron irradiation. Austrian steel and ceramics are on the second step and other materials. worse."

On the side, Professor Xing Xuexing from Shuimu University shook his head and said: "Molybdenum is not good. Shuimu has done research before. Molybdenum will transmute into radioactive elements when it is irradiated by neutrons. As for molybdenum alloys, more are needed. tried."

"On the other hand, there may be some hope for tungsten and tungsten alloys. Currently, tungsten alloy is used as the first wall material at ITER and EAST. It has good heat resistance and the transmutation products are osmium and rhenium, so there is no radioactivity problem."

Xu Chuan shook his head and said, "Tungsten probably won't work either."

"There are no problems with tungsten's heat resistance and transmutation products, but problems such as differences in its physical plasticity and thermal expansion coefficient, as well as the accumulation of thermal stress, can cause cracks within the material."

"This would be fatal for a controlled fusion reactor."

Hearing Xu Chuan's rejection of tungsten alloy, the laboratory fell into silence again.

The material problem for the first wall is indeed very troublesome, so troublesome that no one in the world can find a suitable one.

After all, in a controlled fusion reactor, the first wall material is strongly affected by high-energy neutrons, electromagnetic radiation and high-energy particles (deuterium, tritium, helium and other impurities) emitted from the plasma.

In theory, a commercial tokamak reactor generally has a neutron wall load of at least 5MW/m2.

The neutron wall load is a design indicator related to the power density of the fusion reactor, which is numerically equal to the product of the fusion neutron source intensity and the neutron energy on the first wall material per unit area.

The vast majority of heat-resistant materials simply fail to meet these extremely stringent property challenges.

But then again, if this problem had been so easy to solve, it wouldn't have persisted until now.

After all, controllable nuclear fusion is something that everyone in the world can do if they can, and the various technical problems and material issues must have been discussed countless times.

Staring at the data on the computer screen, Xu Chuan pondered for a while and then said: "I think we may have to change our thinking about the material selection for the first wall."

Hearing this, everyone else in the laboratory looked over.

Zhao Hongzhi asked: "How to say?"

Xu Chuan thought for a while, organized his words and then said: "Each D-T fusion will produce a 14.1 MeV neutron. Since neutrons are not charged, they cannot be restrained by a magnetic field and will directly bombard the first wall material and cause damage. "

"14.1 MeV is a very large energy. You must know that the atoms that are bound in the material are all kinds of chemical bonds, and their bond energies are approximately between 1 and 10 eV."

"In other words, the energy carried by a 14.1 MeV neutron is enough to break millions of ordinary chemical bonds, which will undoubtedly cause irreparable damage to the material."

"In a fusion reactor, high-energy neutrons are like bullets fired at materials, constantly hitting metal atoms, breaking the chemical bonds around them, forcing the atoms to leave their original positions, thus destroying the regular atomic arrangement."

"If you simply want to resist neutrons, perhaps structures made of materials such as beryllium gold, graphite, graphite and uranium 238 can do it. Aren't these materials used in nuclear fission reactors to reflect neutrons?"

"But if you put it in a controllable nuclear fusion reactor, it won't work."

"The reason is simple, because we need neutrons to make tritium self-sustaining, otherwise the currently stored tritium raw materials cannot support the commercial use of controllable nuclear fusion."

"So I personally think that instead of looking for a resistant material in metal materials, why not try other materials?"