The statements in this article are based on reliable sources and are repeated at the end of this article
Nuclear power plants are regarded as one of the most critical energy sources in the next era of mankind, after all, nuclear power plants have very low emissions during the operation stage, and can be regarded as a "green" energy source. In addition, nuclear power plants can provide baseload generation almost at full capacity, and can be relied on to supplement operations with peak shaving when renewable energy sources such as solar and wind and hydropower are not available.
But we also know that nuclear energy is not without harm, even if we do not consider safety issues such as the Fukushima crisis, it also has an important drawback, that is, it will produce "nuclear waste", according to the International Atomic Energy Organization's previous estimates, the world will produce about 10,000 tons of high-risk "nuclear waste" to be disposed of every year, and the continent needs to process about 3,000 tons per year, so how to deal with these nuclear wastes in the end? [Beer]
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Waste generation and disposal methods are subdivided internationally
Replace the fuel rods
Although we always like to use the metaphor of combustion, in fact, the reaction in an atomic furnace is not strictly "burning", but a more complex "nuclear reaction", in which the heavy element is hit and splits into two lighter elements, releasing energy, more neutrons and radiation at the same time. This process generates a large amount of heat energy, which is used to heat the water and produce steam, which ultimately drives the turbine to generate electricity.
So why is waste generated? The simple reason is that the process of this reaction is not "complete", and it usually does not convert all fissile material into energy. In a typical light-water reactor, only about 3%-4% of the fuel is consumed in the fuel cycle. The remaining uranium-238 and newly produced elements constitute the "spent fuel", which is more radioactive and has a half-life that can range from a few years to tens of thousands of years.
Scrap from temporary storage
At present, there are two main strategies for the mainstream treatment in the world, one is through simple treatment and then buried in the deep underground layer, which is a relatively conservative method. In this method, the waste that needs to be disposed of needs to be treated in advance to reduce the radioactivity level and temperature. Once cooled, they are encapsulated in corrosion-resistant containers and then transferred to a dry storage facility or transported directly to a predetermined geological disposal site.
Large storage tanks
The disposal process begins with the collection of individual waste tubes into a larger assembly. The component groups are then placed in cast-iron cans with a 5-centimeter-thick copper exterior – to protect the interior from corrosion – and penetrate deep into the underground part of the facility. There for storage, the tanks were moved to a tunnel area, where they were placed vertically in separately drilled cavities in the bedrock and surrounded by bentonite.
Large-scale treatment plants
This specially selected clay has the peculiar property of expanding when exposed to water, further sealing it in place. Once the area under each tunnel reaches capacity, they are backfilled with bentonite and sealed with concrete. Segregating waste from the biosphere ensures that it does not cause harm to people and the environment for hundreds of thousands or even millions of years. At present, deep geological disposal is considered to be the safest and most durable method for dealing with high-level radioactive waste.
FINNISH ONKALO Repository
Deep geological disposal facilities are typically located in stable rock formations hundreds to thousands of meters underground. For example, the ONKALO project in Finland is a recent example of this. The aim of the project is to build a deep geological repository for long-term sequestration of "high-level radioactive waste", which is expected to commence operations in 2025. You may wonder why it will only be operational in 2025, but I say it is the closest to being put into service? Because at present, human beings have not really built a deep geological treatment facility.
Schematic diagram of the ONKALO project
At this time, you may be curious, without such equipment, how to store the previous scrap? In fact, due to the huge investment and long lead time required for the construction of long-term geological disposal facilities, coupled with the challenges of technical and social acceptance, some countries are exploring the establishment of integrated temporary storage facilities as an intermediate option. The purpose of these facilities is to provide some safe sites for the centralized management and storage of spent nuclear fuel on a "temporary" basis until a final geological disposal solution is implemented.
The Yucca Mountain Repository, which has not yet been put into use
These transitional "integrated temporary storage facilities", which are typically designed to operate for decades, will have advanced safety technology to store waste bins and be located in low-risk areas, such as inland locations away from the coast and geologically stable areas, to reduce potential risks. The United States has one of the largest stockpiles of spent nuclear fuel in the world, with about 86,000 tons as of 2019, most of which are currently stored at nuclear power plant sites.
To deal with this hoarded waste, the United States is moving forward with two "temporary storage projects." However, some scholars have suggested that countries may be cautious in deciding whether to accept the establishment of integrated temporary storage facilities, fearing that so-called "temporary" storage could actually become a long-term storage situation if an eventual geological disposal site is not realized.
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How "recycling" is disposed of
The other approach is called "reprocessing", the logic of which is to treat "spent fuel" itself as a "resource" that has not been exploited. The principle is to extract incompletely burned uranium and plutonium, as well as other reusable isotopes, from spent fuel. These substances can be converted into new fuels or other forms of by-products that can be reused in the nuclear fuel cycle. In addition, "post-processing" can also reduce the volume and radioactivity of the final disposal.
After all, as a nuclear energy power, France has sufficient practical experience in this area, and this technology is more straightforward, also known as "nuclear fuel recycling", which should be said to be an advanced nuclear fuel management strategy. At the heart of this programme is the recovery and reuse of useful materials from nuclear fuel through chemical processing techniques and the conversion of surplus radioactive waste into a form that is easier to store for long periods of time.
To put it simply, the technology is "not complicated", as the fuel waiting to be processed is first cooled in a dedicated facility and then sent to a reprocessing plant. Here, a chemical separation process is used to extract the elements. The extracted uranium can be converted into new enriched uranium, and the extracted plutonium can be mixed with natural or depleted uranium to create new MOX fuel, which can then be sent back to nuclear reactors for further use.
Of course, this is only a model of treatment under ideal conditions, but in fact the post-processing process also generates new heavy element waste. These elements have a relatively long half-life and pose a greater threat to the environment. In order to safely manage these substances, advanced curing techniques, such as vitrification or ceramicization, are used to embed these radionuclides into a stable matrix to form solidified bulk waste. This reduces the volume of waste and, thanks to its chemical and physical stability, reduces the risk of radioactive material leaking into the environment.
By maximizing fuel efficiency, this reduces the amount of waste required for final disposal and minimizes hazards. It has to be said that this model is of great significance for achieving sustainable nuclear energy development and provides an important reference example for global spent fuel processing. However, the implementation of the program requires highly developed technology, strict security measures, and corresponding economic investments, so its promotion in different countries may be limited by various practical conditions.
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China that "walks on two legs".
Site selection of "Beishan No. 1".
In fact, the use of nuclear power is a latecomer, as China is in many other areas, but the current growth has reached a respectable level, but at the same time the pressure to deal with it has also increased. To deal with this complex problem, China did not choose any single route, but drew on the advanced experience of the international community to carry out a "two-pronged approach".
For example, the experiments related to the "large-scale deep geological reservoir" of the first method have been carried out for a long time, and there are clear steps and foundations, and the preliminary work has basically been completed. In 2021, construction began on a laboratory in Gansu Province to study and verify the feasibility of geological disposal of spent nuclear fuel in granite bedrock, located 560 meters below the Gobi Desert. The project is part of the continent's nuclear fuel cycle back-end management strategy to ensure the safe disposal of nuclear waste.
In the laboratory, participating scientists will conduct a series of experiments and evaluations, including a comprehensive study of the stability of the bedrock, the properties of barrier materials, hydrogeological conditions, and long-term environmental impacts. The results of these studies will help determine whether the site is suitable for the construction of a long-term geological disposal facility. If the results show that the site is suitable, then China may begin construction of a full-fledged geological disposal complex for spent nuclear fuel in the 2040s.
On the other hand, the mainland did not regard this plan as the final solution. The post-processing technology is also actively promoted, in fact, the mainland is currently going very deep in this work. A significant amount of financial and technical support has been invested in the relevant projects. By promoting the continuous development of various treatment technologies, we can effectively improve the utilization efficiency of spent fuel, increase the utilization rate from 1 percent to more than 90 percent, and "turn waste into treasure" in the true sense.
After all, this important international problem is even related to the development of human society in the future, after all, the traditional fossil energy is far from comparable to nuclear energy in terms of reserves and utilization rate, and as long as the problem of nuclear energy use is overcome, it will be able to better benefit mankind.
Resources:
[1] Guangming.com - 2020.01.20 "From 1% to 95%, "Eat Dry and Squeeze Clean" Nuclear Waste"
[2] Xinhua News Agency - 2023.04.21 "China-US-Germany Cooperation Makes New Progress in the Field of Nuclear Waste Disposal"