EP4148162A1 - Coating method and device for forming a barrier layer to increase imperability and corrosion resistance, coating and container for embedding and sealing radioactive bodies for final storage, and method for producing the container - Google Patents

Abstract

Within the scope of the present invention, a coating method for forming a barrier layer 21 to improve the impermeability and corrosion resistance on a surface 11 of a body, in particular a radioactive body such as a fuel element, is specified, having the following steps: heating the surface 11 to be coated to a coating temperature ; Supplying hydrocarbon 69 to the surface 11 to be coated while maintaining the surface 11 to be coated at the coating temperature until a barrier layer 21 of amorphous carbon is formed on the surface 11 to a predetermined thickness. Furthermore, a device for forming the barrier layer and a coating and a container for embedding and sealing radioactive bodies 1, in particular radioactive reactor fuel elements, for disposal and a method for producing the container are specified.

Description

The present invention relates to a coating method and a device for forming a barrier layer to increase impermeability and corrosion resistance according to the subject matter of claims 1 and 4, and a coating according to the subject matter of claim 8. The invention also relates to a container for embedding and sealing radioactive bodies for disposal according to the subject matter of claim 13, and an associated method for producing the container according to the subject matter of claim 14.

During the operation of nuclear reactors, operational, radioactive waste in the form of radioactive bodies such as spent fuel elements is regularly generated. The high-energy radiation that emanates from such radioactive waste can endanger people and the environment for many hundreds of thousands of years. According to forecasts by the German Federal Office for the Safety of Nuclear Waste Management, a total of around 27,000 cubic meters of highly radioactive waste will remain in Germany alone after the planned shutdown of the last German nuclear power plant in 2022.

This radioactive waste must be isolated from the biosphere for extremely long periods of time due to the long half-lives and the resulting long-term radiation activity. This is to be achieved by transporting the waste to a repository. In order to be able to implement safe final storage while complying with the required isolation from the biosphere over the necessary ultra-long periods of time, the radioactive waste is enclosed in containers. The containers must meet extremely high requirements in terms of impermeability and corrosion resistance, so that the least possible escape of radionuclides through diffusion processes can be guaranteed over the entire storage period, and the penetration of moisture and associated corrosion of the container can be prevented.

Various concepts for processing radioactive waste such as fuel assemblies are known from the prior art. The current conventional concepts provide for the provision of waste containers for disposal, which are made of steel, cast materials such as GGG40 or concrete. Such waste containers can be reinforced by additional layers of reinforcement. The radioactive waste is then placed in the waste container, optionally in the form of suitable containers.

For example, the DE 10 2010 003 289 A1 a container for radioactive bodies and waste such as fuel elements, in which the radioactive bodies are provided with a metal shell and placed in a matrix of graphite and an inorganic binder. The DE 10 2018 114 463 A1 discloses a container for radioactive material formed from sintered silicon carbide.

The known concepts from the prior art for the containment of radioactive waste are still in need of improvement, in particular with regard to corrosion resistance and impermeability to prevent the escape of radionuclides over the required ultra-long storage periods. In addition, some of the known concepts are not mastered on a production scale or can only be implemented with considerable expenditure of energy and money.

Against this background, the object of the present invention is the containment of radioactive materials, as is required for upgrading the repository is to be further improved both with regard to the corrosion resistance and impermeability of the enclosure and with regard to the cost-effectiveness of the measures required for this.

This object is achieved by a coating method having the features of claim 1, a device having the features of claim 4, a coating having the features of claim 8, and a container having the features of claim 13 and a method according to the subject matter of claim 14 Preferred developments of the invention result from the dependent claims.

• Erhitzen der zu beschichtenden Oberfläche auf eine Beschichtungstemperatur;
• Zuführen von Kohlenwasserstoff an die zu beschichtende Oberfläche bei gleichzeitigem Halten der zu beschichtenden Oberfläche auf der Beschichtungstemperatur, bis an der Oberfläche eine Barriereschicht aus amorphem Kohlenstoff mit einer vorgegebenen Dicke ausgebildet ist.

In particular, the object is achieved by a coating method for forming a barrier layer to improve impermeability and corrosion resistance on a surface of a body, in particular a radioactive body such as a fuel element, having the following steps:

• heating the surface to be coated to a coating temperature;
• supplying hydrocarbon to the surface to be coated while maintaining the surface to be coated at the coating temperature until an amorphous carbon barrier layer having a predetermined thickness is formed on the surface.

A central aspect of the present invention consists in the surprising finding that a barrier layer of amorphous carbon can be formed on the surface of a body to be coated by merely heating the surface to be coated to a suitable coating temperature and, while maintaining the coating temperature, hydrocarbon to the surface to be coated is guided. As the hydrocarbon is supplied to the surface maintained at the coating temperature, the hydrogen content in the hydrocarbon decreases, particularly as hydrogen atoms are split off from the hydrocarbon. The remaining carbon accumulates successively as amorphous carbon in thin layers of a few nanometers on the surface to be coated.

The barrier layer produced using the coating method according to the invention consists of carbon and forms an amorphous carbon phase which has a quasi-isotropic layer structure. The barrier layer produced according to the invention has excellent impermeability or extremely low permeability and thus effectively prevents the passage of atomic or molecular substances through the barrier layer. In the context of the present invention, the term “amorphous carbon” denotes the above-described carbon phase which forms on the surface of a body to be coated when the coating method according to the invention is carried out.

The thickness of the barrier layer of amorphous carbon produced in this way increases steadily as the duration of the supply of hydrocarbon increases, while at the same time the surface to be coated is kept at the coating temperature. A desired layer thickness of the barrier layer can thus be set in a simple manner by appropriately adjusting the coating duration. The coating duration is the length of time during which the hydrocarbon is supplied to the surface to be coated while at the same time maintaining the surface to be coated at the coating temperature.

The use of the coating method according to the invention is particularly advantageous for forming a barrier layer on radioactive bodies such as fuel elements, since the barrier layer effectively prevents the escape of radionuclides or gases that are produced during the decay of radionuclides in the fuel elements. The barrier layer according to the invention is also characterized by high chemical inertness and extreme hardness. In this way, in particular, the corrosion resistance and the mechanical stability of radioactive elements can be improved.

Bodies of any geometry can be coated with the coating method according to the invention. In the special case of the coating of fuel elements, both spherical fuel elements, such as those used in pebble bed reactors, and rod-shaped fuel elements, such as fuel rods, can be provided with a barrier layer. The coating method according to the invention enables the barrier layer to be applied to radioactive fuel elements in an extremely economical and simple manner. The barrier layer Due to its properties mentioned, in particular its excellent impermeability, high chemical inertness and corrosion resistance as well as extreme hardness, it forms an ideal starting point for the further assembly of the fuel elements provided with the barrier layer for disposal.

The coating method according to the invention is conceptually extremely simple to implement. Only means for heating the surface to be coated to the coating temperature and means for (continuously) supplying the hydrocarbon are required. The coating method according to the invention can also be used on a production scale without any problems due to the simple conceptualization and does not cause high costs, since neither the means required for heating the surface to be coated and for supplying the hydrocarbon, nor the hydrocarbon as the starting material for the coating involve high costs.

In the sense of the present invention, the improvement of the impermeability is to be understood as the achievement of the lowest possible permeability, in particular for gases and radionuclides.

The heating of the surface to be coated is not subject to any particular restriction. It is particularly advantageous to carry out the heating in such a way that only the surface to be coated (and possibly lower-lying areas of the body which has the surface to be coated) is heated directly, while the supplied hydrocarbon in the vicinity of the surface to be coated is heated indirectly via the heated surface is heated. Particularly preferred heating methods are therefore inductive heating of the surface to be coated, if the surface to be coated has sufficient conductivity, and heating by means of electromagnetic radiation, in particular by means of microwave radiation.

The supply of hydrocarbon to the surface to be coated is also not subject to any particular restriction. It is only necessary to ensure that sufficient quantities of hydrocarbon are supplied. In the case of long coating times in particular, it is also preferable for hydrocarbons to be fed in continuously, so that there are always sufficient quantities of unused hydrocarbons on the surface to be coated.

It is particularly preferred to feed in the hydrocarbon in the liquid phase, ie to use liquid hydrocarbon in the process step of feeding in hydrocarbon. As a result, the supply of hydrocarbon to the surface to be coated can take place more efficiently since the amount of hydrocarbon on the surface to be coated is increased. The liquid hydrocarbon can be supplied, for example, by placing bodies with the surface to be coated in a bath of liquid carbon. Alternatively, the surface to be coated can be flushed with liquid hydrocarbon.

The coating temperature can be maintained at a substantially constant value, or within a suitable range of values. The coating temperature should be chosen so that the aforementioned elimination of hydrogen atoms from the molecules of the hydrocarbon and the attachment of the carbon atoms to the surface to be coated takes place.

In a preferred embodiment of the invention, the coating temperature is 400°C or more. The value of the coating temperature is particularly preferably in a range between 500°C and 800°C, more preferably between 600°C and 700°C, even more preferably between 640°C and 660°C.

If the coating temperature is too low, no carbon will be deposited on the surface to be coated, or the process will have low efficiency. The minimum coating temperature value depends on the hydrocarbon used. Values of 400°C or higher are sufficient for most hydrocarbons, which are in the liquid phase at atmospheric pressure and represent a preferred form of carbon source for the coating process of the invention, to initiate the deposition of carbon on the surface to be coated.

Values for the coating temperature which are too high are particularly problematic when using liquid hydrocarbons, since the hydrocarbons supplied can evaporate on the surface to be coated, which impairs the efficiency of the coating process. Allow for the preferred ranges of values for the coating temperature a particularly efficient implementation of the coating method according to the invention.

As already noted, in order to maintain the coating temperature, it is sufficient to maintain the temperature of the surface to be coated within a suitable temperature range, such as within the ranges specified as preferred. It is not absolutely necessary to keep the coating temperature at a (substantially) constant value during the supply of hydrocarbon in order to carry out the coating method according to the invention.

As already mentioned, the duration of the coating depends on the desired thickness of the barrier layer. It is preferred to provide a minimum coating time of 30 minutes. In general, it can be assumed that a layer of up to 5 mm per hour can be produced with the coating method according to the invention.

In principle, any chemical compound of hydrogen and carbon can be used as the hydrocarbon in the context of the present invention. For reasons of simpler supply to the surfaces to be coated, preference is given to chemical compounds of carbon and hydrogen which are liquid when supplied to the surface to be coated. (Liquid) hydrocarbons which comprise hydrocarbon chains are particularly preferred. According to a preferred embodiment of the invention, the (liquid) hydrocarbon contains molecular hydrocarbon, preferably hydrocarbon chains, where the hydrocarbon molecules have between 9 and 22 carbon atoms. The hydrocarbon chains can be branched or unbranched. These hydrocarbons are readily available, are liquid under normal conditions and have proven to be particularly advantageous in carrying out the coating process.

In one possible embodiment of the invention, an untreated petroleum distillate from the refining of petroleum or natural gas is used as the hydrocarbon.

The coating process is particularly efficient when the hydrocarbons mentioned are used. The use of the hydrocarbons mentioned also offers the advantage that substances can be used as the starting product for the barrier layer, which are inexpensive and in many cases arise as a waste product in petrochemistry or polymer chemistry. This increases the economics of the coating method according to the invention.

It is further preferred that the supply of hydrocarbon to the surface to be coated while maintaining the surface to be coated at the coating temperature is carried out in a reactor space. It is furthermore preferred that gases which are formed when the hydrocarbon is fed to the surface to be coated at the coating temperature are discharged from the reactor space.

In the coating process according to the invention, hydrogen gas is formed which is formed by hydrogen atoms which are split off from the hydrocarbon molecules on the surface to be coated when the surface is at the coating temperature. Venting this gas increases the safety of the coating process. In addition, the discharged hydrogen gas can be collected for further use.

• ein Reaktorgehäuse zur Aufnahme der zu beschichtenden Körper und zur Aufnahme von Kohlenwasserstoff;
• eine Heizvorrichtung zur Erhitzung der Oberflächen der zu beschichtenden Körper;
• einen Temperatursensor zur Bestimmung der Temperatur der Oberflächen der zu beschichtenden Körper;
• eine Steuereinheit, die dazu ausgebildet ist, die Heizvorrichtung derart zu steuern, dass die mittels des Temperatursensors bestimmte Temperatur der Oberflächen der zu beschichtenden Körper auf einer vorgegebenen Beschichtungstemperatur oder innerhalb eines vorgegebenen Beschichtungstemperaturbereichs gehalten wird.

The object of the invention is further achieved by a device for forming a barrier layer to improve the impermeability and corrosion resistance on a surface of one or more bodies, such as rod-shaped or spherical fuel elements

• a reactor housing for containing the bodies to be coated and for containing hydrocarbon;
• a heater for heating the surfaces of the bodies to be coated;
• a temperature sensor for determining the temperature of the surfaces of the bodies to be coated;
• a control unit that is designed to control the heating device in such a way that the temperature of the surfaces of the body to be coated, determined by means of the temperature sensor, is kept at a specified coating temperature or within a specified coating temperature range.

The device according to the invention is preferably used to carry out the coating method according to the invention described above.

With the device according to the invention, the same advantages can be achieved as have already been described in connection with the coating method according to the invention. Features of the device, in particular those relating to adjusting the temperature of the surface of the body to be coated to the coating temperature and the supply of hydrocarbon, can be transferred to the coating method according to the invention. Features of the coating method according to the invention can also be transferred to the device according to the invention by configuring the device in such a way that it is designed and suitable for carrying out the corresponding method features of the coating method. Just as the device according to the invention is preferably designed and used for carrying out the coating method according to the invention described above, it is preferred that the coating method according to the invention is carried out with a device according to the invention. The present invention also includes the use of the device according to the invention for carrying out the coating method according to the invention.

The reactor housing serves to accommodate the body to be coated and the hydrocarbon. The reactor housing represents a simple way of realizing the supply of hydrocarbon to the surfaces to be coated and of keeping the surfaces to be coated in contact with hydrocarbon during the coating process. The feed can be achieved in that the bodies with the surface to be coated are placed in the reactor housing together with the hydrocarbon. The reactor housing can consist of a metallic or ceramic material, but is not subject to any special restrictions with regard to the choice of material or geometry. Preferably, the reactor housing is configured to be lockable, to enable the coating process to be carried out safely. Preferably, the reactor housing is substantially gas-tight and configured to withstand high pressures.

The device according to the invention can be used to coat a surface to be coated of a single body with a barrier layer of amorphous carbon by only placing a body with a surface to be coated in the reactor housing. Likewise, with the device according to the invention, the simultaneous coating of several bodies is possible, in that several bodies are placed in the reactor housing. If bodies to be coated and their surfaces are mentioned in relation to the device according to the invention and the coating method, this always also includes the case of a single body with a surface to be coated.

It is preferred that the reactor housing is movably mounted and can be set in motion in such a way that bodies to be coated that are accommodated in the reactor housing are set in motion and/or held. On the one hand, this ensures that the body to be coated is constantly mixed with the hydrocarbon. This improves the supply of hydrocarbon to the surfaces to be coated. On the other hand, the mobile mounting - and the associated movement of the body to be coated in the reactor housing - can promote a uniform thickness of the resulting coating over the entire surface of the body to be coated, since the movement of the body to be coated causes bearing points on the bottom of the Reactor housing are avoided to which no hydrocarbon can be supplied. The movable mounting of the reactor housing is particularly advantageous in the preferred variant in which the hydrocarbon is supplied in the liquid phase, since the movement of the reactor housing causes continuous mixing and circulation of the hydrocarbon and the body to be coated.

The movable mounting of the reactor housing is not subject to any particular restriction. It is only necessary to ensure that the reactor housing can be set in motion during the operation of the device in such a way that the bodies to be coated can be set in motion. The movable storage can be realized, for example, by a storage is provided, on which the reactor housing is mounted in such a way that it can be set in a wobbling motion. For this purpose, the reactor housing can be mounted, for example, on a point or an axis, so that the reactor housing mounted in this way can be kept in a wobbling motion during the coating process. If the reactor housing is designed to be closable, for example as a closable drum, it is preferred that the reactor housing can be driven to rotate about an axis. If the reactor housing is configured as a closable drum, the reactor housing is preferably mounted such that it can rotate about the drum axis and can be driven via this axis. A temporary or continuous movement of the body to be coated within the reactor housing can also be ensured with this embodiment. This improves the uniformity of the applied barrier layer and increases the efficiency of the coating process.

It is also preferred that the device has a hydrocarbon feed line for introducing the hydrocarbon into the reactor housing. In this way, a controlled supply of hydrocarbons can be ensured during the operation of the device. The feed is in fluid communication with the reactor housing to allow the introduction of the hydrocarbon into the reactor housing. The feed can be connected to a reservoir for hydrocarbon. The feed can have a valve with which the feed of hydrocarbon can be metered.

The device, in particular the reactor housing, preferably has a gas discharge line for discharging gases, in particular gases produced during coating, from the reactor housing. As explained in connection with the coating method according to the invention, gases are produced during the coating process, in particular hydrogen gas, which is produced from the hydrogen atoms split off during the coating process. In order to avoid an excessively high concentration of hydrogen gas within the reactor housing during operation of the device, it is therefore advantageous to provide a gas discharge line at the reactor housing.

According to a further preferred embodiment, the device has an outlet for discharging fluids from the reactor housing. In combination with the hydrocarbon feed line that is preferably present, a (continuous) exchange of the hydrocarbon in the reactor housing can thus be implemented especially when the hydrocarbon is fed in the liquid phase. This improves the efficiency of the device. It is preferred that the vent is in fluid communication with a valve capable of controlling the discharge of fluids from the reactor housing.

According to a preferred embodiment, the heating device is formed by a microwave source. This enables selective heating of the surfaces to be coated without direct heating of the hydrocarbon at the same time. This improves the efficiency of the device. If the surfaces to be coated have sufficient conductivity, the heating device can alternatively or additionally have an induction heater which is designed to heat the surfaces to be coated. In this case, the induction heating is designed to generate an alternating magnetic field in the reactor housing, which induces eddy currents in the material of the surfaces to be coated, causing the surfaces to be coated to heat up.

It is also preferred that the temperature sensor is formed by a spectral-optical temperature sensor or a pyrometer. This enables non-contact determination of the temperature of the surfaces to be coated.

With the coating method according to the invention and the device according to the invention described above, it is possible to form a barrier layer on the surfaces of bodies, which has excellent properties in terms of impermeability, corrosion resistance and mechanical stability. This barrier layer can form part of a coating for embedding and sealing radioactive bodies, in particular radioactive fuel elements, with which the radioactive bodies can be prepared for disposal. Such a coating also achieves the object of the invention.

• eine Barriereschicht aus amorphem Kohlenstoff zur Verbesserung der Impermeabilität und Korrosionsbeständigkeit, vorzugsweise hergestellt mittels des obenstehend beschriebenen Beschichtungsverfahrens, vorzugsweise unter Verwendung der oben beschriebenen Vorrichtung;
• eine Moderatorschicht zur Abschirmung von Neutronen, die einen Moderator, vorzugsweise Borcarbid, B₄C, enthält; und
• eine Stabilisatorschicht zur Verbesserung der mechanischen Stabilität.

Within the scope of the present invention, a coating is therefore also specified which is suitable for embedding and sealing radioactive bodies, in particular radioactive reactor fuel elements, for disposal. The coating according to the invention has the following:

• an amorphous carbon barrier layer for improving impermeability and corrosion resistance, preferably produced by means of the coating method described above, preferably using the apparatus described above;
• a moderator layer for shielding neutrons, containing a moderator, preferably boron carbide, B ₄ C; and
• a stabilizer layer to improve mechanical stability.

With the coating according to the invention, a sealing of radioactive bodies is achieved which can be produced on a production scale at low cost and with little effort. With the coating according to the invention, the radioactive bodies can be prepared in an optimal manner for disposal. The combination of the layers provided according to the invention ensures in particular that the extremely high requirements with regard to impermeability and corrosion resistance are met, so that the least possible escape of radionuclides through diffusion processes can be guaranteed over the entire storage period, and the penetration of moisture and associated corrosion can be prevented .

A core aspect of the coating according to the invention is the barrier layer made of amorphous carbon, which due to its properties, in particular the excellent impermeability and corrosion resistance, makes a significant contribution to the solution of the object according to the invention. The advantages of the barrier layer described in relation to the coating method according to the invention and the device according to the invention can also be achieved with the coating according to the invention, which contains the barrier layer.

It is noted in this connection that the barrier layer according to the invention has proven to be particularly advantageous when used on radioactive bodies such as fuel elements. On the one hand, this is due to the fact that fuel elements usually have a graphite surface. The graphite surface proves to be particularly advantageous when carrying out the coating method according to the invention, in particular when using the device according to the invention, because the graphite surface can be heated particularly easily with the heating methods and devices described above. In addition it has been found that the barrier layer made of amorphous carbon according to the invention adheres particularly well to graphite surfaces. On the other hand, the barrier layer made of amorphous carbon according to the invention has a particularly good resistance to the radioactive radiation emitted by the fuel elements. As a result, the impermeability and corrosion resistance that can be achieved with the barrier layer is not excessively impaired by the radiation activity of the fuel elements.

In order to achieve the desired properties of the barrier layer for disposal, it is preferred that the barrier layer has a thickness of more than 0.5 mm. The barrier layer preferably has a thickness between 0.5 mm and 5 cm, more preferably between 0.1 cm and 4 cm, even more preferably between 0.2 cm and 3 cm, more preferably between 0.5 cm and 2 cm more preferably between 0.8 cm and 1.2 cm.

The coating according to the invention also has a moderator layer. This is used to decelerate and shield high-energy neutrons that occur during the decay processes of the radioactive body. For this purpose, the moderator layer contains a moderator, which is preferably formed by boron carbide, B ₄ C. The moderator is embedded in the moderator layer.

According to a preferred embodiment of the invention, the moderator layer contains a chemically bonded ceramic and/or a geopolymer. Inorganic binders are referred to as geopolymers, in particular amorphous aluminosilicates, the polymeric structure of which can be described by spatial networks without long-range crystallographic order. From a chemical point of view, geopolymer is a condensation product of purely inorganic starting components. Geopolymers are used as a concrete substitute and, compared to concrete, are more environmentally friendly during production and are more resistant to chemicals and heat. Due to the excellent chemical resistance and the inorganic, quasi-ceramic composite structure, no surface corrosion is to be expected.

Geopolymers are therefore of considerable advantage as a matrix for the moderator layer, since they meet the high demands on material durability, as required for the coating of radioactive bodies that can be disposed of. In addition, geopolymers offer advantages in terms of processing, since geopolymer-based substances can be processed just like cement-based substances, in particular can be cast. Overall, a geopolymer-based moderator layer is preferred from environmental aspects as well as with regard to the achievable material properties and processability.

In this context, it is also preferred that the proportion of boron carbide in the moderator layer is between 50% by weight (percent by weight) and 70% by weight. In this way, both the moderator properties of the boron carbide and the material properties of the moderator layer can be optimized. According to this preferred embodiment, the moderator layer preferably has a thickness of 5 mm or more, particularly preferably 15 mm or more. This ensures that the moderator layer has a sufficient moderator effect.

According to a further preferred embodiment of the invention, the moderator layer contains a titanium or nickel compound to which boron carbide is added as a moderator. The proportion of boron carbide is preferably between 50% by weight and 78% by weight. It is further preferred that, according to this embodiment, the thickness of the moderator layer is 2 mm or more, more preferably 5 mm or more. A good moderator effect and excellent mechanical and long-term stability of the moderator layer can also be ensured with this embodiment of the moderator layer.

The coating according to the invention also has a stabilizer layer. This serves to improve the mechanical strength of the coating. This improves the handling of radioactive bodies with a coating according to the invention, in particular during transport and transport to a repository, and the long-term stability of the coated radioactive bodies.

The choice of material for the stabilizer layer is not subject to any particular restriction. The only important thing is that the material is suitable for increasing the mechanical stability of the container. All materials that have good mechanical stability and long-term stability are therefore suitable. Possible materials for the stabilizer layer include, for example, cast materials such as GGG40, concrete, reinforced concrete, steel, lead or other materials that are used in the encapsulation of radioactive bodies.

According to a preferred embodiment of the invention, the stabilizer layer has, in particular as a binder, a chemically bonded ceramic and/or a geopolymer. It is also preferred that the stabilizer layer contains fibers, preferably glass fibers and/or carbon fibers, preferably with an average fiber length of between 2 cm and 3 cm, for mechanical reinforcement. The proportion of fibers in the stabilizer layer is preferably between 20% by volume and 60% by volume. A stabilizer layer with excellent mechanical properties and excellent long-term stability can thus be produced in an environmentally friendly and economical manner. A knitted fabric or woven fabric can also be used instead of the fibers.

According to a further preferred embodiment, the coating has a fourth layer, which is preferably applied to the stabilizer layer. According to the invention, the fourth layer serves to further improve the mechanical stability of the coating. The fourth layer preferably has a geopolymer and a fabric, in particular glass fiber fabric, to further improve the mechanical stability.

The sequence of the layers described within the coating according to the invention is not subject to any special restriction. The barrier layer made of amorphous carbon is preferably applied directly to the surface of the body to be embedded and sealed. The barrier layer is preferably followed by the moderator layer and the moderator layer by the stabilizer layer. Further (intermediate) layers can be provided within this layer sequence.

The coating according to the invention is therefore also fundamentally not limited to the layers described. The coating may have additional layers, such as layers of lead for additional stabilization and shielding. According to a further preferred embodiment, the coating has a layer of silicon-infiltrated boron carbide. This layer preferably has a thickness of 3 mm or more. In addition to the moderator effect provided by the boron carbide, silicon-infiltrated boron carbide has the advantage that this material is gas-tight. As a result, the sealing effect of the coating according to the invention can be further improved. In the The preferred layer sequence described above, the layer of silicon-infiltrated boron carbide is preferably arranged between the moderator layer and the stabilizer layer.

In a preferred embodiment, the silicon-infiltrated boron carbide layer is provided as a box or coffin which is filled with a mixture of geopolymer and boron carbide to form the moderator layer. This simplifies the manufacture of the layers.

The coating according to the invention can be used to coat individual radioactive bodies such as fuel elements and thus condition them for disposal. From an economic point of view, it is preferable to provide a number of radioactive bodies with the coating according to the invention in such a way that a package with a number of radioactive bodies can be formed which can be used for final storage of the enclosed radioactive elements. Such a container, which comprises the coating according to the invention, also achieves the object of the invention.

Therefore, within the scope of the present invention, a container for embedding and sealing radioactive bodies, in particular radioactive reactor fuel elements, for final disposal is also specified. According to the invention, the container has one or more radioactive bodies which are provided with the coating according to the invention described above.

In this case, the barrier layer is preferably attached to the radioactive body(s). The moderator layer is preferably on or outside the barrier layer and the stabilizer layer is preferably on or outside the moderator layer. If a fourth layer according to the invention is provided, it is preferred that this is applied to the stabilizer layer.

The features and advantages described in the context of the coating according to the invention can also be transferred to the container according to the invention.

• Ausbilden einer Barriereschicht aus amorphem Kohlenstoff zur Verbesserung der Impermeabilität und Korrosionsbeständigkeit auf einer Oberfläche mindestens eines radioaktiven Körpers, beispielsweise eines Brennelements, vorzugsweise mittels des obenstehend beschriebenen Beschichtungsverfahrens,
• Bereitstellen einer ersten Halbumschalung mit mindestens einer Vertiefung, in der der mindestens eine radioaktive Körper platzierbar ist;
• Einbringen des mindestens einen radioaktiven Körpers mit aufgebrachter Barriereschicht in die mindestens eine Vertiefung;
• Herstellen einer zweiten Halbumschalung auf der ersten Halbumschalung derart, dass die erste Halbumschalung und die zweite Halbumschalung eine Moderatorschicht ausbilden, die den mindestens einen radioaktiven Körper mit aufgebrachter Barriereschicht vollständig umgibt;
• Herstellen einer Stabilisatorschicht, die die Moderatorschicht zumindest teilweise, vorzugsweise im Wesentlichen allseitig, umgibt.

A method for producing a container, in particular the container described above, is also specified within the scope of the invention. The process of manufacturing the container includes the following steps:

• forming a barrier layer of amorphous carbon to improve impermeability and corrosion resistance on a surface of at least one radioactive body, for example a fuel element, preferably by means of the coating method described above,
• providing a first half casing with at least one depression in which the at least one radioactive body can be placed;
• introducing the at least one radioactive body with an applied barrier layer into the at least one depression;
• producing a second half-encapsulation on the first half-encapsulation in such a way that the first half-encapsulation and the second half-encapsulation form a moderator layer which completely surrounds the at least one radioactive body with an applied barrier layer;
• Production of a stabilizer layer which surrounds the moderator layer at least partially, preferably essentially on all sides.

The method according to the invention for producing a container represents a conceptually simple and economical possibility for producing the container according to the invention. The same advantages can be achieved with the method according to the invention for producing the container as have already been described in connection with the container according to the invention. Again, it is pointed out that the features described in the context of the container according to the invention also apply to the method of production according to the invention and can be used accordingly. Features of the container, in particular those relating to the composition and properties of the various layers of the container, can be transferred to the method according to the invention by using appropriate materials and producing the layers in such a way that corresponding properties of the container produced are achieved. Features of the method according to the invention can also be transferred to the container according to the invention.

The order of the process steps is not limited to the order claimed and presented above. In particular, the stabilizer layer or part of the stabilizer layer can already be produced before the second half casing is produced.

In principle, the container according to the invention can only contain a single radioactive body. In this case, the first half casing has only one indentation. If the container includes, as is preferred, several radioactive bodies, the first half casing has a corresponding number of indentations. If several radioactive bodies or cavities are mentioned in relation to the container, the case of a container with only one radioactive body or cavity is always referred to.

It is preferred that the first half-shell and the second half-shell contain a geopolymer and boron carbide, B ₄ C, the proportion of boron carbide preferably being between 50% and 70% by weight. As a result, a moderator layer can be formed from the two half shells, which has the same advantages as were described in relation to the container according to the invention.

It is also preferred that the stabilizer layer contains a binder such as a chemically bonded ceramic and/or a geopolymer, and fibers, preferably glass fibers and/or carbon fibers, preferably with an average fiber length of between 2 cm and 3 cm, for mechanical reinforcement. The proportion of fibers in the stabilizer layer is preferably between 20% by volume and 60% by volume. A stabilizer layer can thus be formed which has the effects and advantages described in relation to the container according to the invention. Again, a knitted fabric or woven fabric can also be used instead of the fibers. When producing the bundle, it is particularly preferred to initially apply the knitted or woven fabric to the bundle by winding when producing the stabilizer layer and then to fill the winding with a binding agent, preferably concrete or geopolymer.

It is further preferred that the provision of the first half casing comprises a casting of the first half casing from a mixture containing geopolymer and boron carbide. This represents an easy-to-implement possibility for the production of the first half casing the first half-enclosure particularly easy to implement a desired geometry and dimensioning of the first half-enclosure.

The production of the second half casing preferably comprises casting the second half casing from a mixture containing geopolymer and boron carbide. The production of the second half casing preferably takes place when the first half casing has not fully hardened. As a result, a particularly good material connection can be created between the two half casings that form the moderator layer.

With regard to the first half casing and its production or provision, it is preferred that the shape of the depressions is essentially adapted to the shape of the radioactive body. This makes it particularly easy to introduce the radioactive bodies into the depressions. The shape of the recesses is preferably designed such that after the radioactive bodies have been introduced into the depressions, a gap remains between the depressions and the introduced radioactive bodies. This has the advantage that when the second half casing is subsequently produced by casting, liquid material of the second half casing penetrates into the gap and thus creates a form fit between the two half casings. This improves the mechanical stability of the moderator layer and the cohesion between the two half-encasings.

It is also preferred that the production of the stabilizer layer includes casting the stabilizer layer, preferably from a mixture containing geopolymer and fibers, preferably glass fibers and/or carbon fibers, preferably with an average fiber length of between 2 cm and 3 cm. The production of the stabilizer layer can be carried out in a single process step or divided into several steps. Likewise, the production of the stabilizer layer can be interrupted by other process steps.

For example, it may be advantageous to first cast only a portion of the stabilizer layer after the first half wrap is provided but before the second half wrap is made. In this case it is preferred that a part of the stabilizer layer is made in such a way that it partially surrounds the first half-shell, such that a surface of the half-shell, in which the recesses are formed, is not surrounded by the stabilizer layer. The stabilizer layer is preferably produced at a point in time when the first half casing has not fully hardened, for example at a point in time when the first half casing has reached approximately 30% of its final strength. As a result, a particularly good material connection can be achieved between the first half sheathing and the stabilizer layer.

Correspondingly, it is preferred that a further part of the stabilizer layer is formed, in particular by casting, once the second half-shell is made. In turn, it is particularly preferred that the further part of the stabilizer layer is formed before the second half-encasing has fully cured in order to improve the connection between the second half-encasing and the stabilizer layer.

Alternatively, it is possible to first completely form the moderator layer by producing the two half shells before subsequently producing the stabilizer layer.

According to a further preferred development of the method according to the invention, two bundles are formed according to the above method with essentially identical geometry, ie identical dimensions of the individual components of the bundle. The two bundles are designed in such a way that the stabilizer layer partially surrounds the moderator layer in such a way that the bundles have an essentially flat connecting surface on which a region of the moderator layer is circumscribed by a region of the stabilizer layer.

The two essentially identically designed containers are then assembled in a further method step in such a way that the flat connecting surfaces come into contact with one another. As a result, a container is produced from two partial containers, the outer layer of which is formed entirely by a stabilizer layer.

According to a further preferred development of the method according to the invention, first two essentially identical partial containers are formed by means of a passage the first four method steps (formation of a barrier layer; provision of a first half casing with at least one depression; introduction of the at least one radioactive body into the at least one depression; production of a second half casing on the first half casing in this way). These two partial containers are placed or stacked on top of each other and together surrounded by a barrier layer. The barrier layer is preferably surrounded by casting. Also according to this development, a container is produced from two partial containers, the outer layer of which is formed entirely by a stabilizer layer.

In a further process step, a fourth layer is preferably applied to the stabilizer layer on the bundle produced. The fourth layer serves to further improve the mechanical stability of the container. The fourth layer preferably has a geopolymer and a glass fiber fabric for mechanical stabilization. Preferably, the fourth layer is made by casting.

The invention is also described below with regard to further details, features and advantages, which are explained in more detail with reference to the figures. The features and feature combinations described below, as shown below in the figures of the drawing and described with reference to the drawings, can be used not only in the combination specified in each case, but also in other combinations or on their own, without departing from the scope of the invention.

Fig. 1

eine schematische Schnittansicht einer Vorrichtung zum Ausbilden einer Barriereschicht auf zu beschichtenden Körpern gemäß einem Ausführungsbeispiel der vorliegenden Erfindung;

Fig. 2

die Vorrichtung aus Fig. 1 während eines Beschichtungsvorgangs;

Fig. 3

eine schematische Schnittansicht einer Vorrichtung zum Ausbilden einer Barriereschicht auf zu beschichtenden Körpern gemäß einem weiteren Ausführungsbeispiel der vorliegenden Erfindung;

Fig. 4

die Vorrichtung aus Fig. 3 während eines Beschichtungsvorgangs;

Fig. 5a

eine schematische Schnittansicht eines radioaktiven Körpers mit einer Beschichtung gemäß einem Ausführungsbeispiel der vorliegenden Erfindung;

Fig. 5b

eine Detailansicht des gepunktet eingezeichneten Bereichs in Fig. 5a;

Fig. 6a-f

schematische Darstellungen von Verfahrensschritten zur Herstellung eines Gebindes gemäß einem Ausführungsbeispiel der vorliegenden Erfindung, zur Einbettung und Versiegelung kugelförmiger Körper, in perspektivischer Ansicht;

Fig. 7a-f

schematische Darstellungen der in Fig. 6a-f gezeigten Verfahrensschritte in Draufsicht;

Fig. 8a-f

schematische Darstellungen der in Fig. 6a-f gezeigten Verfahrensschritte in einer Schnittansicht;

Fig. 8g

eine schematische Schnittansicht eines Gebindes mit einer vierten Schicht gemäß einem Ausführungsbeispiel der vorliegenden Erfindung;

Fig. 9a-f

schematische Darstellungen von Verfahrensschritten zur Herstellung eines Gebindes gemäß einem Ausführungsbeispiel der vorliegenden Erfindung, zur Einbettung und Versiegelung stabförmiger Körper, in perspektivischer Ansicht;

Fig. 10a-f

schematische Darstellungen der in Fig. 9a-f gezeigten Verfahrensschritte in Draufsicht;

Fig. 11a-f

schematische Darstellungen der in Fig. 9a-f gezeigten Verfahrensschritte in einer Schnittansicht;

Fig. 12a-e

schematische Schnittansichten von Verfahrensschritten zur Herstellung eines Gebindes gemäß einem weiteren Ausführungsbeispiel der Erfindung.

Here show:

1

a schematic sectional view of a device for forming a barrier layer on bodies to be coated according to an embodiment of the present invention;

2

the device off 1 during a coating operation;

3

a schematic sectional view of a device for forming a barrier layer on bodies to be coated according to a further embodiment of the present invention;

4

the device off 3 during a coating operation;

Figure 5a

a schematic sectional view of a radioactive body with a coating according to an embodiment of the present invention;

Figure 5b

a detailed view of the dotted area in Figure 5a ;

Fig. 6a-f

schematic representations of process steps for producing a container according to an embodiment of the present invention, for embedding and sealing spherical bodies, in a perspective view;

Fig. 7a-f

schematic representations of the in Fig. 6a-f shown process steps in plan view;

Fig. 8a-f

schematic representations of the in Fig. 6a-f shown method steps in a sectional view;

8g

a schematic sectional view of a bundle with a fourth layer according to an embodiment of the present invention;

Fig. 9a-f

Schematic representations of process steps for producing a container according to an embodiment of the present invention, for embedding and sealing rod-shaped bodies, in a perspective view;

Fig. 10a-f

schematic representations of the in Fig. 9a-f shown process steps in plan view;

Fig. 11a-f

schematic representations of the in Fig. 9a-f shown method steps in a sectional view;

Fig. 12a-e

schematic sectional views of method steps for producing a container according to a further embodiment of the invention.

1 shows a schematic view of a device for forming a barrier layer on bodies to be coated according to an embodiment of the present invention. The device is particularly suitable for carrying out the method according to the invention for forming a barrier layer for improving impermeability and corrosion resistance on a surface of a body.

The device according to 1 has a reactor housing 61 . The shape of the reactor body 61 is not particularly limited. In the embodiment according to 1 the reactor housing 61 is box-shaped or cuboid-shaped and can be closed.

A heat source 63 is arranged inside the reactor housing 61 and is designed to heat surfaces of bodies to be coated which can be accommodated in the reactor housing 61 . The heat source 63 is preferably constituted by a microwave source or induction heating. The arrangement of the heat source 63 is in 1 only indicated schematically. Depending on the configuration, the heat source 63 is arranged in such a way that surfaces to be coated can be heated at practically any position within the reactor housing 61 .

Also located inside the reactor housing 61 is a temperature sensor 64 which is designed to detect the temperature of the surfaces of the body to be coated. The detection preferably takes place without contact. Therefore, the temperature sensor 64 is preferably formed by an optical temperature sensor, in particular a thermal sensor or a pyrometer.

The heat source 63 and the temperature sensor 64 are in communication with a control unit 65 as indicated by the dotted lines is. The control unit 65 can, as in 1 shown, may be located inside the reactor housing 61, or outside. The specific design of the communicative connection is not subject to any particular restriction and can be implemented using wired or wireless technology. The control device 65 is designed to control the heat source 63 on the basis of the temperatures of the surfaces of bodies to be coated detected by the temperature sensor 64, as is described in more detail below.

The device also has a hydrocarbon feed line 66 which is designed to introduce hydrocarbons into the interior of the reactor housing 61 . In order to enable a controlled and controllable supply, the hydrocarbon supply line 66 has a (controllable) valve. A drain 68 is provided on the reactor housing 61 in order to be able to drain hydrocarbons located inside the reactor housing 61 out of the reactor housing 61 . The drain 68 is also valved to open and close the drain 68 as needed.

In order to be able to discharge gases produced during a coating process from the reactor housing 61, the reactor housing has a gas discharge line 67 which is also provided with a valve in order to be able to control the discharge of gas. While the coating process is being carried out, gas, in particular hydrogen gas, is produced continuously as carbon is deposited on the surfaces to be coated. With a closed reactor housing, it may be advantageous to maintain a slight positive pressure in the reactor housing 61 in order to increase the efficiency of the coating process. For this purpose, a pressure sensor (not shown) can be provided in the interior of the reactor housing, the valve of the gas discharge line 67 being controlled on the basis of the pressure values determined in this way in order to set a desired overpressure in the reactor housing 61 . If the reactor housing 61 is designed as an open housing, the gas discharge line 67 can be dispensed with.

in the in 1 In the exemplary embodiment shown, the reactor housing 61 is mounted on a bearing 62 in such a way that the reactor housing 61 can be set in a wobbling motion about the support point on the bearing 62, as shown schematically in FIG 1 is indicated by arrows. Drive devices (not shown) can be provided to trigger the wobbling movement. Alternatively can the reactor housing 61 can be passively tumbled by the movement of moving components contained within the reactor housing 61 during a coating operation.

In order to carry out a coating method according to the invention for forming a barrier layer on surfaces of bodies to be coated, the bodies 1 whose surface 11 is to be coated are placed in the reactor housing 61 . This is schematic in 2 shown showing the device 1 during a coating process. The bodies 1 to be coated, which are shown as circular in the schematic sectional view, are spherical or cylindrical and each have a surface 11 on which a barrier layer 21 made of amorphous carbon is to be formed.

The device according to the invention and the method according to the invention are particularly suitable for the coating of radioactive bodies, for example fuel elements. Fuel bundles are typically spherical or rod-shaped. At the in 2 The bodies 1 shown are therefore preferably spherical or rod-shaped (reactor) fuel elements, the surface 11 of which is formed by a graphite surface.

The surfaces 11 of the bodies 1 to be coated are heated in the reactor housing 61 by means of the heat source 63, preferably without contact. If a microwave radiation source is used as the heat source 63, in the case of fuel elements as the body 1 to be coated, essentially only the surface 11 is heated due to the low penetration depth of microwaves in graphite. The same applies when using an induction heater as the heat source 63, with which primarily the graphite surface 11, but not the radioactive core of the fuel elements, is heated.

The heat source 63 is preferably designed such that the surrounding hydrocarbon 69 is not heated by the heat source 63 but only indirectly via the heated surfaces 11. This is the case when using a microwave radiation source or induction heating.

The temperature of the heated surfaces 11 is recorded by the temperature sensor 64 and output to the control unit 65 . This controls the heat source 63 so that the temperature of the surfaces to be coated 11 on a preset coating temperature or within a range of values suitable as the coating temperature. For the sake of simplicity, only one coating temperature is mentioned below, which means both a discrete coating temperature and a coating temperature interval.

Before, during or after the heating of the surfaces 11 to the coating temperature, hydrocarbon 69 is conducted into the interior of the reactor housing 61, so that the body 1 to be coated is completely surrounded by hydrocarbon 69. As a result, hydrocarbon 69 is supplied to the surfaces 11 to be coated, while these are kept at the coating temperature by means of the heat source 63, the temperature sensor 64 and the control unit 65. In 2 the hydrocarbon 69 is shown in the liquid phase. The coating process can thus be carried out particularly efficiently. In principle, however, the use of hydrocarbons in other phases is also possible.

The continuous supply of hydrocarbon 69 to the surfaces 11 to be coated can be improved in that the reactor housing 61 is set in motion continuously or at intervals such that the bodies 1 to be coated in the reactor housing 61 are also set in (rolling) motion. This will be in the in Figures 1 and 2 shown embodiment achieved by the bearing 62, which allows the reactor housing 61 to wobble around the support. Drive devices (not shown) or spring elements (not shown) cause the wobbling movement to be maintained actively or passively. The movement of the body 1 to be coated within the reactor housing 61 continuously circulates the hydrocarbon 69 and mixes the body 1 to be coated with the hydrocarbon 69 so that fresh hydrocarbon 69 is always supplied to the surfaces 11 to be coated. Furthermore, due to the movement in the reactor housing 61, the bodies 1 to be coated do not have any support points to which no hydrocarbon 69 can reach.

To further improve the supply of hydrocarbon 69 to the surfaces 11 to be coated, fresh hydrocarbon 69 can also be fed into the Reactor housing 61 are introduced, and old hydrocarbon are discharged via the outlet 68.

During the coating process, the surfaces 11 to be coated are kept at the coating temperature, while at the same time hydrocarbon 69 is fed to the surfaces 11 to be coated. At the heated surface 11, hydrogen atoms detach from the molecules of the supplied hydrocarbon 69 and carbon accumulates on the surfaces 11 to be coated. As a result, a barrier layer made of amorphous carbon is formed on the surfaces 11 to be coated. The thickness of the barrier layer increases as the duration of the coating process increases. The hydrogen formed from the hydrocarbon 69 on the surfaces 11 to be coated rises as a gas in the interior of the reactor container 61 . This can be discharged via the gas discharge line 76 and optionally collected for further use.

Figures 3 and 4 show a schematic sectional view of a device for forming a barrier layer on bodies to be coated according to a further exemplary embodiment of the present invention. The functioning of the in Figures 3 and 4 The device shown essentially corresponds to that in Figures 1 and 2 device shown; components with the same effect are marked with identical reference symbols. Therefore, only deviating characteristics of the in Figures 3 and 4 device shown received.

The device according to Figures 3 and 4 has, instead of a box-shaped reactor housing, a drum-shaped reactor housing 61, which is parallel at the ends to the plane of FIG Figures 3 and 4 is locked. The reactor housing 61 is mounted to be rotatable about the drum axis, as indicated by the arrow on the upper left outside of the reactor housing in FIG Figures 3 and 4 is indicated. The drum axis is coupled to a drive (not shown) in order to be able to rotate the reactor housing 61 .

4 shows the device 3 during a coating process. Spherical or rod-shaped bodies 1 with a surface 11 to be coated, preferably spherical or rod-shaped fuel elements with a graphite surface, are accommodated in the reactor housing 61 . Your surface 11 is using the heat source 63, the temperature sensor 64 and the controller 65 on Coating temperature (or within a coating temperature range) maintained while the reactor housing 61 is filled with hydrocarbon 69. To improve the supply of hydrocarbon 69 to the surfaces 11 to be coated, the reactor housing 61 is rotated at intervals or continuously in order to achieve thorough mixing of the hydrocarbon 69 and the body 1 to be coated.

After the body to be coated 1 in the devices according to Figures 1 to 4 were kept at the coating temperature for a predetermined time while hydrocarbon 69 was supplied to the surfaces to be coated 11, an amorphous carbon barrier layer is deposited on the surfaces to be coated 11, which has excellent impermeability and corrosion resistance, and is particularly insusceptible to radioactive radiation, is gas-tight and does not allow diffusion of radionuclides through the barrier layer. If a barrier layer designed in this way is formed on radioactive bodies that are to be processed for disposal, the barrier layer can form the starting point for the construction of a multi-layer coating for embedding and sealing the radioactive bodies, which represents an optimal packaging of the radioactive bodies for disposal.

Such a coating is shown schematically in Figure 5a shown. A radioactive body 1 is shown with a (graphite) surface 11 on which a barrier layer 21 made of amorphous carbon is formed, which is preferably formed according to the coating method described above and/or using the devices described above. The barrier layer 21 has a thickness of more than 500 μm in order to provide an optimal barrier against the escape of radionuclides and other contaminating substances from the radioactive body 1.

A moderator layer 31 is formed on the barrier layer 21 and serves to moderate neutrons from the radioactive body 1 . The moderator layer 31 contains a moderator, preferably boron carbide, B ₄ C. The moderator can be embedded in a binder matrix, which preferably consists of geopolymer. Alternatively, the moderator forms part of a metal alloy, preferably a titanium or nickel compound. A ceramic compound containing boron carbide is also conceivable. Here, boron carbide a corresponding ceramic material are added, the mixture is then cold-pressed and sintered at approx. 1700 °C.

Depending on the configuration of the moderator layer 31 and the proportion of the moderator in the moderator layer, the thickness of the moderator layer 31 is at least 2 mm and up to 50 cm.

According to a specific exemplary embodiment, the moderator layer 31 is produced from a mixture containing boron carbide, B ₄ C and geopolymer, the proportion of boron carbide in the mixture being 50-70% by weight.

A stabilizer layer 41 is applied to the barrier layer 31 and serves to mechanically stabilize the coating. The stabilizer layer 41 preferably contains fibers such as glass fibers or carbon fibers for reinforcement, which are embedded in a matrix which preferably consists of geopolymer. The thickness of the stabilizer layer is preferably between 1 cm and 50 cm.

According to a specific embodiment, the stabilizer layer 41 is made from a mixture containing geopolymer and carbon fibers with a length of 2-3 cm, the proportion of carbon fibers in the mixture being 20-60% by volume. According to a further specific exemplary embodiment, the stabilizer layer 41 consists exclusively of geopolymer without any further additives.

Figure 5b shows the in Figure 5a dotted-framed detail in a schematic enlargement to clarify the layer structure of the coating again. the inside Figures 5a and 5b The layer structure shown can be supplemented by further layers on the stabilizer layer 41 and/or by intermediate layers between the barrier layer 21 and the moderator layer 31, or between the moderator layer 31 and the stabilizer layer 41.

The coating according to the invention for embedding and sealing radioactive bodies in particular can be implemented extremely easily and economically in the form of containers in which several radioactive bodies are preferably enclosed in such a way that all radioactive bodies are provided with a coating described above. These containers can go directly to final storage be spent, or be included in disposal containers for further reinforcement. From the point of view of the encapsulated radioactive elements, the layer structure of the containers corresponds to that in Figures 5a and 5b shown layer structure.

In the following, a method for producing the bundles is described with reference to Figures 6 to 11 described. Figures 6 to 8 show the production of bundles for spherical fuel elements. Figures 9 to 11 show the production of bundles for rod-shaped fuel elements.

Figures 6 to 8 represent schematic process steps for the production of a container for the final storage of radioactive, spherical bodies. Fig. 6a-f show the process steps in a perspective view, Fig. 7a-f show the process steps in a plan view of the container, and Fig. 8a-f show the process steps in a schematic sectional view.

For the production of a container according to this exemplary embodiment, the radioactive bodies 1 to be encapsulated or sealed are first provided with a barrier layer 21 made of amorphous carbon, for example by means of with reference to FIG Figures 1-4 described coating process.

A first half wrap 31a which will later form part of the moderator layer 31 is provided. Figures 6a, 7a and 8a Figure 13 shows the first half-shell 31a made of a material suitable as moderator layer 31, for example a mixture of geopolymer and boron carbide, or of a titanium or nickel compound with boron carbide. The first half casing 31a has indentations 32 on an upper side, which is preferably substantially flat. Projections 33 can be formed on the underside of the first half sheathing, which make it easier to form the stabilizer layer 41 in a later stage of the method.

After the provision or production of the first half casing 31a, the radioactive bodies 1 to be encapsulated, which are provided with the barrier layer 21, are introduced into the recesses 32. Figures 6b, 7b, and 8b 12 show the first half-enclosure 31a with radioactive bodies 1 placed therein. The barrier layer 21 formed on the surface 11 of the radioactive bodies 1 is at the right radioactive body in FIG Figure 8b shown.

The depressions 32 have a shape that is substantially complementary to the shape of the radioactive bodies 1 to form a stable seat for the radioactive bodies 1 . As in particular in Figure 8b As can be seen, the depressions 32 are shaped in such a way that a gap 34 remains on all sides between the inserted radioactive bodies 1 and the depressions 32 .

Figures 6c, 7c and 8c 12 illustrate the formation of a first part of the stabilizer layer 41. Around the first half-shell 31a is formed a first shell 41a made of a material suitable as the stabilizer layer 41, for example a mixture of geopolymer and fibers. The first shell 41a is formed so as to partially enclose the half shell 31a. The first casing 41a is formed so that the area of the first half casing 31a in which the recesses 32 with the radioactive bodies 1 accommodated therein are formed is not covered by the first casing 41a.

The advantage of the projections 33 on the first half casing 31a results when the first casing 41a is produced by means of casting: the projections 33 ensure that the first half casing 31a is stable when the first casing 41a is cast and not on the liquid material of the first casing 41a floats up. Preferably, the first shell 41a is cast before the first half shell 31a is fully cured to achieve a good bond between the layers.

After fabricating the first wrap 41a, the first half wrap 31a is completed into a moderator layer 31. FIG. this is in Figures 6d, 7d and 8d shown. Since the first shell 41a is formed so that it does not cover the surface of the first half shell 31a with the cavities 32 and radioactive bodies 1 accommodated therein, a second half shell 31b can now be formed on said surface. The first half casing 31a and the second half casing 31b together form the moderator layer 31 of the coating for the radioactive bodies 1 in the container. The material of the second half encapsulation 31b corresponds to that of the first half encapsulation 31a and is therefore also suitable for forming a moderator layer 31, as is also the case with the identical hatching of the elements with the reference symbols 31, 31a and 31b in FIG Figures 5-11 is expressed.

The second half casing 31b is in the in Figures 6-8 shown embodiment made by casting. This allows the material of the second half casing 31b to fill the gaps 34 between the depressions 32 and the radioactive bodies 1 accommodated therein in order to create a stable and form-fitting connection between the half casings 31a, 31b.

After the formation of the second half shell 31b, the stabilizer layer 41 is further supplemented. this is in Figures 6e, 7e and 8e shown. In the area adjoining the outer edges of the second half casing 31a and the first casing 41a, a second casing 41b is produced, which also consists of a material suitable for the stabilizer layer (as is again indicated by the uniform hatching of the elements 41, 41a and 41b in Figures 5 to 11 is displayed).

After the in Figures 6e, 7e and 8e shown method step can be formed on the top of the container (not shown) third shell made of a stabilizer layer-suitable material to close the container so that the radioactive elements 1 essentially on all sides of a coating with a layer structure according to Fig. 5a-b are surrounded.

However, in order to be able to increase the number of radioactive bodies 1 per container, it is preferable to use two of the Figures 6e, 7e and 8e to connect the container shown to form a combined container. this is in Figures 6f, 7f and 8f shown. Two essentially identically designed bundles are placed together with the surface on which an area of the moderator layer 31, namely the upper side of the second half shell 31b, is circumscribed by an area of the stabilizer layer 41, namely the upper side of the second shell 41b, and connected to one another. As in the sectional view in Fig. 8f is recognizable, this results in a combined container with a compared to the containers according to Figures 6e, 7e and 8e twice the number of radioactive bodies 1, each essentially all sides with a coating with a layer structure according to Fig. 5a-b are provided.

According to a further exemplary embodiment of the present invention, two bundles are first produced in that radioactive bodies 1, which are provided with the barrier layer 21 made of amorphous carbon, are placed in the depressions 32 of the first half casing 31a according to Figures 6b, 7b and 8b be inserted.

Subsequently, the second half shell 31b is formed to form the moderator layer 31 . Two such bundles, which only have the radioactive bodies 1 with the barrier layer 21 and the moderator layer 31, are placed on top of one another with the surfaces of the second half shell 31b and cast together with the stabilizer layer 41 to form a combined bundle.

This is schematic in Fig. 12a-e shown. First, a barrier layer 21 made of amorphous carbon is formed on the (radioactive) bodies 1 to be encapsulated. Then two first half casings 31a with depressions 32, in which the radioactive bodies 1 provided with a barrier layer 21 can be placed, are provided or produced ( 12a ). The radioactive bodies 1 provided with a barrier layer 21 on their surface 11 are then introduced into the depressions 32 of the two first half shells 31a ( Figure 12b ). A second half encapsulation 31b is then formed on the first half encapsulations 31a in such a way that the first half encapsulation 31a and the second half encapsulation 31b each form a moderator layer 31 ( Figure 12c ). The partial containers formed in this way are stacked or placed next to each other ( Figure 12d ). This arrangement is surrounded by a stabilizer layer 41, preferably cast around it, in order to form a container according to the invention ( Figure 12e ).

For further mechanical stabilization, the bundles can be enclosed in a further, fourth layer, which further increases the mechanical stability and which preferably consists of geopolymer with a glass fiber fabric embedded therein. this is in 8g shown schematically, the fourth layer being denoted by reference numeral 51 . The fourth layer 51 can comprise a knitted or woven fabric, which is first wound onto the bundle, and a binding agent such as a geopolymer, with which the bundle is cast around after the knitted or woven fabric has been wrapped around it.

That regarding Figures 6-8 The processes described for spherical radioactive elements and the resulting containers are also used in a completely analogous manner for the packaging of rod-shaped radioactive bodies for disposal. Figures 9-11 represent schematic process steps for the production of a container for the final disposal of radioactive, rod-shaped bodies. Fig. 9a-f show the process steps in a perspective view, Fig. 10a-f show the Process steps in plan view of the container, and Fig. 11a-f show the process steps in a schematic sectional view. Corresponding elements are in Figures 9-11 with the same reference numbers as in Figures 6-8 designated.

The only essential difference is in the shape of the radioactive elements 1 and accordingly in the shape of the corresponding recesses 32 in the first half-enclosure 31a. As in the case of the spherical radioactive elements, the container according to the embodiment of Figures 9-11 surrounded by a fourth layer 51, as in 8g shown.

The number of fuel elements per bundle, as specified in the Figures 6 to 11 is shown can be adjusted as needed by forming a corresponding number of depressions 32 in the first half shell 31a.

The containers are in Figures 6 to 11 shown as a cuboid. The shape of the container is not subject to any particular restriction. In order to avoid breaking edges or corners of the container during transport and transfer to a disposal facility, the container can be designed with rounded edges and corners, or have an overall oval or spherical outer contour, in accordance with the Figure 5a shown schematic representation.

Reference List

1

radioactive body

11

(to be coated) surface

21

barrier layer

31

moderator layer

31a

first half wrap

31b

second half wrap

32

deepening

33

head Start

34

gap

41

stabilizer layer

41a

first changeover

41b

second switch

51

fourth layer

61

reactor housing

62

storage

63

heat source

64

temperature sensor

65

control unit

66

hydrocarbon feed line

67

gas discharge

68

indulgence

69

hydrocarbon

Claims (15)

Coating method for forming a barrier layer (21) to improve the impermeability and corrosion resistance on a surface (11) of a body, in particular a radioactive body such as a fuel assembly, comprising the following steps: • heating the surface (11) to be coated to a coating temperature; • supplying hydrocarbon (69) to the surface (11) to be coated while maintaining the surface (11) to be coated at the coating temperature until an amorphous carbon barrier layer (21) of a predetermined thickness is formed on the surface (11). . The coating method according to claim 1, wherein the coating temperature is 400°C or higher and preferably between 500°C and 800°C, more preferably between 600°C and 700°C, even more preferably between 640°C and 660°C. Coating method according to Claim 1 or 2, in which the hydrocarbon (69) is constituted by hydrocarbons, in particular hydrocarbon chains, having between 9 and 22 carbon atoms. Coating method according to one of the preceding claims, in which the supply of hydrocarbon (69) to the surface (11) to be coated is carried out in a reactor space while the surface (11) to be coated is kept at the coating temperature at the same time, and in which the resulting gases, in particular hydrogen, be discharged from the reactor space during the supply of hydrocarbon (69) to the surface to be coated. Device for forming a barrier layer to improve the impermeability and corrosion resistance on a surface (11) of one or more bodies, such as rod-shaped or spherical fuel elements, in particular using a coating method according to one of Claims 1 to 4, having: • a reactor housing (61) for accommodating the body to be coated and for accommodating hydrocarbon (69); • a heating device (63) for heating the surfaces (11) of the bodies to be coated; • a temperature sensor (64) for determining the temperature of the surfaces (11) of the body to be coated; • a control unit (65) which is designed to control the heating device (63) in such a way that the temperature of the surfaces (11) of the body to be coated, determined by means of the temperature sensor (64), is kept at a specified coating temperature or within a specified coating temperature range becomes. Apparatus according to claim 5, wherein the reactor housing (61) is movably mounted and can be set in motion in such a way that in Reactor housing (61) accommodated bodies to be coated are set in motion and/or held. Apparatus according to claim 5 or 6, comprising: a carbon feed line (66) for introducing the hydrocarbon (69) into the reactor housing (61); and or a gas discharge line (67) for discharging gases, in particular gases produced during coating, from the reactor housing (61); and or a drain (68) for discharging liquids from the reactor housing (61). Coating for embedding and sealing radioactive bodies (1), in particular radioactive reactor fuel elements, for disposal, having: • a barrier layer (21) made of amorphous carbon to improve impermeability and corrosion resistance, preferably produced by means of a coating method according to any one of claims 1 to 4; • a moderator layer (31) for shielding neutrons, containing a moderator, preferably boron carbide, B ₄ C; and • a stabilizer layer (41) to improve the mechanical stability. Coating according to claim 8, wherein the barrier layer (21) has a thickness between 0.5 mm and 5 cm, preferably between 0.1 cm and 4 cm, more preferably between 0.2 cm and 3 cm, more preferably between 0.5 cm and 2 cm, more preferably between 0.8 cm and 1.2 cm. Coating according to Claim 8 or 9, in which the moderator layer (31) contains a geopolymer, in which the proportion of boron carbide is preferably between 50% by weight and 70% by weight, and/or in which the thickness of the moderator layer (31) is preferably 5 mm or more, more preferably 15 mm or more. Coating according to Claim 8 or 9, in which the moderator layer (31) contains a titanium or nickel compound, the proportion of boron carbide preferably being between 50% by weight and 78% by weight, and/or the thickness of the moderator layer (31 ) is preferably 2 mm or more, particularly preferably 5 mm or more. Coating according to one of claims 8 to 11, wherein the stabilizer layer (41) contains fibers, preferably glass fibers and/or carbon fibers, preferably with an average fiber length of between 2 cm and 3 cm, for mechanical reinforcement, and the proportion of fibers in the stabilizer layer (41) is preferably between 20% and 60% by volume; wherein the stabilizer layer (41) preferably contains a geopolymer; and wherein the thickness of the stabilizer layer (41) is preferably 1 cm or more. Container for embedding and sealing radioactive bodies (1), in particular radioactive reactor fuel elements, for disposal, having one or more radioactive bodies (1) which are provided with a coating according to one of Claims 8 to 12. Method for producing a container according to Claim 13, comprising the following steps: • Forming a barrier layer (21) made of amorphous carbon to improve the impermeability and corrosion resistance on a surface (11) of at least one radioactive body (1), for example a fuel element, preferably by means of a coating method according to one of claims 1 to 4, • Providing a first half casing (31a) with at least one recess (32) in which the at least one radioactive body (1) can be placed; • introducing the at least one radioactive body (1) with the applied barrier layer (21) into the at least one depression (32); • Manufacture of a second half-encapsulation (31b) on the first half-encapsulation (31a) in such a way that the first half-encapsulation (31a) and the second half-encapsulation (31b) form a moderator layer (31) which forms the at least one radioactive body (1) with an applied barrier layer (21) completely surrounds; • Production of a stabilizer layer (41) which at least partially surrounds the moderator layer (31). The method according to claim 14, wherein the shape of the at least one depression (32) is essentially adapted to the shape of the at least one radioactive body (1), the shape of the recess (32) preferably being designed in such a way that after the introduction of the at least a radioactive body (1) in the at least one depression (32), a gap (34) remains between the depression (32) and the radioactive body (1).

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