Device for reducing nuclear fuel

Abstract

Device for reducing spent nuclear fuel, comprising a container for receiving nuclear fuel, wherein the device is configured to transmute long-lived radioisotopes of the nuclear fuel into radioisotopes having a significantly shorter half-life than the initial radioisotopes by interaction with fast neutrons.

Description

[0001] The invention relates to a device for reducing spent nuclear fuel. Nuclear reactors generate nuclear energy through the nuclear fission of radioisotopes in fissile material arranged in nuclear fuel assemblies within the reactor. After a certain lifetime, the nuclear fuel assemblies can no longer be used to generate nuclear energy because they no longer contain enough radioisotopes that decay upon excitation with neutrons and generate nuclear energy. The chain reaction can no longer be sustained, and the nuclear fuel assemblies must be replaced. Spent nuclear fuel assemblies can be partially reprocessed, but their disposal at the end of their service life poses a significant problem. Long-lived radioisotopes in spent nuclear fuel assemblies include transuranic elements and actinides, such as plutonium-239, uranium-235, uranium-238, and neptunium-237.These reaction products emit gamma radiation, in some cases for millions of years, or undergo spontaneous fission, emitting fast fission neutrons. These isotopes therefore pose a threat to the environment and must be shielded against the release of gamma and neutron radiation.

[0002] The object of the present invention is to provide a device with which the volume of spent nuclear fuel with a long half-life can be reduced.

[0003] The problem is solved by a device for reducing spent nuclear fuel with the features according to claim 1. The device according to the invention comprises a container for receiving nuclear fuel and is configured to transmute long-lived radioisotopes of the nuclear fuel into radioisotopes that have a significantly shorter half-life than the initial radioisotopes by interaction with neutrons, in particular fast neutrons.

[0004] Nuclear fuel primarily consists of decay products from spent nuclear fuel elements, which include, for example, minor actinides. Through interaction with fast neutrons, the radioisotopes of the minor actinides are transmuted into lighter radioisotopes that can have significantly reduced half-lives. Neutron-induced fission of americium-242 serves as an example. By emitting, for example, three neutrons, the americium atom decays into lighter fission products similar to those produced by the thermal fission of uranium-235 or plutonium-239. This allows the amount of long-lived radioisotopes to be reduced through transmutation into other radioisotopes. The transmuted radioisotopes include those with half-lives that are 100, 1,000, or 10,000 times shorter than those of the original isotopes.

[0005] To interact with the long-lived radioisotopes in the nuclear fuel and to excite nuclear fission processes during transmutation, fast neutrons with energies of, for example, 14 MeV are particularly important. These can originate from commercial nuclear reactors with fast neutron spectra for energy generation, or from specialized neutron sources such as a linear accelerator, a cyclotron, a subcritical reactor, or one or more easily manageable neutron sources based on neutron tubes, where the neutron flux intensity can be controlled by an electrical supply. The neutron tubes can operate, for example, on the principle of liquid confinement fusion (LCF) or on another principle.

[0006] According to one embodiment, the device is arranged in the reactor core of a nuclear reactor configured to generate fast neutrons. By arranging it in the reactor core, a sufficiently high neutron flux intensity can be maintained in the fuel container to generate transmutations on a large scale.

[0007] According to one embodiment, the container has a cylindrical, circular cylindrical, polygonal, or hexagonal cross-section. This shape allows for the efficient arrangement of several identical containers in a bundle or side by side, with one or more containers potentially housing neutron sources, such as neutron tubes. The neutron sources preferably emit neutrons radially symmetrical to the tube or container axis, enabling efficient interaction with nuclear fuel in one or more adjacent containers.

[0008] According to a further embodiment, the device has a feed device for nuclear fuel or radioisotopes, wherein the feed device is coupled to the container and configured to continuously feed the nuclear fuel or radioisotopes into the container. According to one embodiment, the nuclear fuel is in liquid, gaseous, or solid, particularly pourable, form, and the feed device is configured to feed nuclear fuel in liquid or solid, particularly pourable, form into the container.

[0009] According to one embodiment, the device includes a means of removing the nuclear fuel or radioisotopes from the container. In particular, the means of removing the nuclear fuel can be configured for liquid or solid, especially free-flowing, materials containing the nuclear fuel or radioisotopes.

[0010] According to one embodiment, the device includes a mechanism for separating fission products from the nuclear fuel. The fission products must be removed from the nuclear fuel after transmutation because they can contain a large quantity of neutron-absorbing isotopes that absorb the free neutrons needed for transmutation and prevent their use in the process.

[0011] According to the invention, a system for reducing spent nuclear fuel is also provided, comprising a device for reducing spent nuclear fuel as described above and a closed circuit in which the device is integrated, wherein the closed circuit is set up to supply nuclear fuel to a container and, after the interaction between the neutrons and the nuclear fuel, to discharge it from the container.

[0012] According to another embodiment, the system has one or more neutron sources configured to emit free neutrons that can interact with isotopes of the nuclear fuel.

[0013] According to one embodiment, the one or more neutron sources are selected from a group of neutron sources comprising: a neutron source configured to produce neutrons, in particular fast neutrons, with a kinetic energy of 1 MeV or more, with a kinetic energy between 1 MeV and 10 MeV, or with a kinetic energy of more than 10 MeV, in particular 14.2 MeV; a neutron source, in particular a neutron tube, in which the production of neutrons takes place by plasma-induced fusion processes in a material surface of the neutron source in contact with a plasma; a neutron source, in particular a neutron tube, operating according to the lattice confined fusion (LCF) principle; a neutron source comprising a nuclear fission reactor configured to produce fast neutrons; and a spallation source.Preferably, the neutron flux strength of the neutrons emitted by the neutron sources based on a neutron tube can be controlled by a power supply that is set up to operate the neutron source and to generate neutrons.

[0014] According to a further embodiment, the system comprises one or more first containers arranged next to the one or more neutron sources, wherein the one or more first containers are designed to hold a nuclear fuel capable of fission by interaction with neutrons, releasing thermal energy and, if applicable, neutrons.

[0015] According to another embodiment, the system comprises several containers arranged in a bundle and at least partially surrounding one or more neutron sources. Particularly in conjunction with neutron sources that have a substantially cylindrical shape and emit neutrons radially symmetrically, a particularly high transmutation efficiency can be achieved.

[0016] According to another embodiment, the containers have a cylindrical, circular cylindrical, polygonal or hexagonal shape in cross-section.

[0017] Further features, properties and advantages of the device according to the invention will become apparent from the following drawings, in which Fig. 1 shows a device for reducing spent nuclear fuel according to a first embodiment of the invention; Fig. 2 shows a reactor according to an embodiment of the invention, which forms part of a device for reducing spent nuclear fuel.

[0018] The embodiment of the device for reducing spent nuclear fuel is described below with reference to the figures.

[0019] The in Fig. The transmutation device shown in Figure 1 comprises a circuit including a transmutation device 10 and a conditioning device 12. The transmutation device 10 includes a neutron source 22, such as a nuclear reactor, a spallation source, or another type of reactor for generating fast neutrons, such as those used for power generation. The reactor is configured to emit a fast neutron field with neutrons in the range of more than 1 MeV or more than 10 MeV, in particular 14.2 MeV. This allows isotopes, such as minor actinides, to be transmuted into lighter isotopes.The circuit has a container 20 located near the neutron source 22 for holding nuclear fuel. Through interaction with fast neutrons from the neutron source 22, long-lived radioisotopes of the nuclear fuel are transmuted into radioisotopes with significantly shorter half-lives than the original radioisotopes. The fission products can have a half-life reduced by a factor of 100, 1,000, or 10,000 compared to the half-life of the original radioisotopes. The circuit also includes a conditioning device 12 configured to introduce isotopes, such as minor actinides, into the circuit. The conditioning device 12 is also configured to remove fission products resulting from the interaction with the fast neutron field from the circuit.The fission products in the reactor can have the effect of absorbing a large number of neutrons, which are then no longer available for the nuclear fission of isotopes in the nuclear fuel or for transmutation. This can lead to the reactor no longer being able to be kept running, as the number of neutrons produced is insufficient to sustain the chain reaction in the reactor due to the increased absorption by the fission products. Furthermore, a liquefaction device 18 for transmutation material is provided, with which transmutation material in solid form, such as MA, which originates from spent nuclear fuel rods, can be liquefied in order to circulate it through the cycle. For this purpose, one or more pumps (not shown) are used.

[0020] The conditioning device 12 is connected to a device 16 for supplying transmutation material, which in turn is connected to the liquefaction device 18 for the transmutation material in order to feed liquefied transmutation material into the cycle. However, the devices can also be configured for the supply and circulation of solid transmutation material, which, for example, has a pourable consistency. Furthermore, the conditioning device 12 is connected to a device 14 for the removal of fission products, with which the fission products separated by the conditioning device 12 are removed from the cycle. Transport devices, such as pumps or conveying systems, can be arranged in the cycle or in various components of the illustrated device to continuously circulate the nuclear fuel or radioisotopes or fission products through the cycle.to supply into them or to remove from them.

[0021] In Fig. Figure 2 shows a reactor that can form part of a device for reducing spent nuclear fuel. The in Fig. The hexagonal device shown in cross-section has 12 neutron sources 1 arranged around the edge inside it, which surround several containers 3.

[0022] The neutron sources 1 have a cylindrical shape, and neutrons are emitted from them in a substantially radially symmetrical manner. Cylindrical containers 3, designed to hold nuclear fuel, are arranged symmetrically to the reactor axis between and parallel to the neutron sources 1. This nuclear fuel can be, for example, mixed oxide fuel (MOX), consisting of a mixture of 80% uranium oxide (UO₂) and 20% plutonium oxide (PuO₂). Other mixture ratios or the use of uranium oxide alone are also conceivable. The neutron sources 1 can be formed by low-carbon reactor (LCF) systems, whose neutron emission can be controlled by the applied current. The neutron sources 1 shown, for example, have a total emission power of 43 × 10⁻⁶. 13n / s. Neutrons with an energy of 14.1 MeV can be generated using the neutron sources 1. The neutrons emitted from the neutron sources 1 collide with the nuclear fuel located in the containers 3 and cause a fission reaction of the isotopes in the nuclear fuel. The neutron sources 1 and the containers 3 are surrounded by a reflector 5 made of or containing graphite. Helium is used as the coolant. The total power generated during reactor operation is, for example, approximately 66 kW. The number and arrangement of the neutron sources 1, as well as the number and arrangement of the containers 3, can vary.

[0023] Furthermore, the in Fig. The device shown contains containers 7 arranged internally, which are intended for other materials that interact with the neutrons emitted by the neutron sources 1 and the nuclear fuels present in the containers 3, such as minor actinides (MA). The MAs can, for example, originate from spent fuel elements in nuclear reactors and can no longer be used as fuel in these reactors. By introducing these nuclear fuels containing MAs into the containers 7, the volume of the nuclear fuel material can be reduced by producing lighter isotopes through interaction with the free neutrons and by fission of the atomic nuclei. These lighter isotopes have a significantly shorter half-life (< 1000 years) than the original long-lived radioisotopes in the spent fuel elements.To treat the MA in the reactor with free neutrons, these are extracted from unusable nuclear fuel elements in a process and preferably fed into containers 7 in liquid form. The feed into containers 7 can also take place within a closed loop, as in [reference to diagram]. Fig. Figure 1 shows that, to implement a closed circuit, one or more pump devices, as well as one or more feed devices and separator devices, can be integrated into the circuit, as shown above with reference to Fig. 1 was described.

[0024] Furthermore, the in Fig.The reactor shown has two additional containers 9, designed to hold radioisotopes. These radioisotopes interact with free neutrons from the fuel-filled containers 3 and from the neutron sources 1 during reactor operation and can be transmuted into desired radioisotopes through decay reactions. These isotopes could include, for example, molybdenum-99, a fission product used in cancer diagnostics. Iodine-125 is another fission product already widely used in medicine. The produced radioisotopes can be used for specific applications, such as medical ones.

[0025] The number and arrangement of containers 3 for nuclear fuel, containers for radioisotopes, and containers 9 for transmutation processes, and their arrangement within the reactor, can vary, or only one type of container may be present. Containers 3 and 9 may also be of the same design, differing only in the material used for their filling. Containers 3 or 9 may be configured to hold radioisotopes in solid or liquid form. Furthermore, containers 3 or 9, or both types of containers, may be configured for the flow of radioisotopes in liquid form and connected, for example, to a fixed circuit or one or more pumping devices (not shown in the figure).

[0026] Numerous modifications can be made to an invention without altering its scope. Reference symbol list: 1 neutron source 3 containers for nuclear fuel 5 Reflector 7 containers for transmutation material 9 containers for radioisotopes 10 Transmutation device 12 Conditioning device 14 Device for the removal of fission products 16 Device for supplying transmutation material 18 Liquefaction unit for transmutation material 20 containers 22 neutron source

Claims

Device for reducing spent nuclear fuel, comprising a container (7, 20) for receiving a nuclear fuel, wherein the device is configured to transmute long-lived radioisotopes of the nuclear fuel into radioisotopes that have a significantly shorter half-life than the initial radioisotopes by interaction with fast neutrons. Device according to claim 1, wherein the container (7, 20) has a cylindrical, circular cylindrical, polygonal or hexagonal shape in cross-section. Device according to claim 1 or 2, wherein the device has a supply device (16) for nuclear fuel or for radioisotopes, wherein the supply device (16) is coupled to the container (7, 20) and is configured to continuously supply the nuclear fuel or the radioisotopes to the container (7, 20). Device according to one of the preceding claims, wherein the nuclear fuel is in liquefied form in the containers (7, 20). Device according to one of the preceding claims, wherein the device comprises a device (14) for removing the nuclear fuel or radioisotopes from the container (7, 20). Device according to one of the preceding claims, wherein the device comprises a device (12) for separating fission products from the nuclear fuel. System for reducing spent nuclear fuel, comprising a device according to one of the preceding claims and a closed circuit in which the device is integrated, wherein the closed circuit is configured to supply nuclear fuel to the container (7, 20) and to discharge it from the container (7, 20) after the interaction between the neutrons and the nuclear fuel. System according to claim 7, comprising one or more neutron sources (1, 22) configured to emit free neutrons which can interact with isotopes of the nuclear fuel. System according to claim 7 or 8, wherein the one or more neutron sources (1, 22) are selected from a group of neutron sources (1, 22) comprising: a neutron source comprising a neutron tube configured to produce neutrons with a kinetic energy of 1 MeV or more, with a kinetic energy between 1 MeV and 10 MeV, or with a kinetic energy of more than 10 MeV or of 14.2 MeV; a neutron source in which the production of neutrons is carried out by plasma-induced fusion processes in a material surface of the neutron source in contact with a plasma; a neutron source operating according to the lattice confined fusion (LCF) principle; a neutron source comprising a nuclear fission reactor configured to produce fast neutrons; and a spallation source. System according to one of claims 7 to 9, comprising one or more first containers (3) arranged next to the one or more neutron sources (1), wherein the one or more first containers (3) are configured to hold a nuclear fuel capable of fission upon interaction with neutrons, releasing thermal energy and neutrons. System according to one of claims 7 to 10, comprising several containers (3, 7, 9, 20) arranged in a bundle and at least partially surrounding one or more neutron sources. System according to one of claims 7 to 11, wherein the containers (3, 7, 9, 20) have a cylindrical, circular cylindrical, polygonal or hexagonal cross-section shape.

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