RU2122750C1 - Nuclear power system operating process - Google Patents

Abstract

FIELD: nuclear power engineering; nuclear power systems incorporating two or more reactors. SUBSTANCE: minor actinides are extracted from spent fuel, granulated, and granules are uniformly mixed up with aluminum granules to form fuel mixture from these ingredients that contains 12 - 13.5 atom percent of minor actinides and is used as first charge of fast homogeneous reactor; after this fuel mixture is charged in reactor core and melted therein, reactor is brought to critical state and minor actinides are burned out; part of burnt-out fuel is discharged from circulating circuit and fission products are removed, core is refueled with fuel mixture to maintain its critical condition as well as with aluminum, and minor actinide content of fuel mixture is brought to 3 - 3.5 atom percent; this minor actinide content is maintained in reactor core up to end of actinide burn-out process at level attained; in addition, starting fuel assembly is placed in reactor core for melting fuel mixture, and reactivity control elements are partially and/or fully brought out of core; in addition, reactor core container is heated for melting fuel mixture; upon extracting minor actinides from radioactive fuel Al+MA alloy is produced from these actinides and aluminum which is granulated before charging it into reactor core. EFFECT: provision for burning out highly radioactive and long-living products of fuel irradiation (minor actinides), reduced mass of spent plutonium and radioactive wastes subject to disposal. 4 cl, 1 dwg

Description

 The invention relates to nuclear engineering, in particular, to a method for operating a nuclear energy complex consisting of two or more reactors.

 A known method of operating a nuclear power complex is that the active zone of a fast neutron reactor with a liquid metal coolant is loaded with nuclear fuel from an alloy of uranium with plutonium, secondary nuclear fuel is generated from it, which is then used in a thermal neutron reactor (Kessler G. Nuclear Power Engineering Translation from English. - M.: Energoizdat, 1986, p. 182).

 One of the most significant drawbacks of this method is the need to include in the process chain the manufacture of fuel elements for thermal neutron reactors for the chemical processing of secondary fuel in order to remove fission products from it, because chemical processing is a technically complex, expensive and requiring special safety measures process. In addition, since chemical processing is carried out at special chemical plants, transportation costs for the transportation of secondary fuel from storage facilities of nuclear power plants (NPPs) to plants and vice versa increase, and the cost of compliance with measures to ensure radiation safety during transportation increases.

 During the operation of this complex, as well as at any of the current reactors, one of the most radioactive and long-lived elements is formed in nuclear fuel - minor actinides (MA), due to which the already difficult problem of processing and disposal of radioactive waste is repeatedly complicated. .

 This complex uses heterogeneous reactors, which further complicates and increases the cost of the fuel cycle, as In addition to factories for the chemical processing of secondary fuel, it is necessary to have a complex and very expensive automated line for the production of fuel assemblies with secondary fuel, which has great activity and energy release.

 The closest in technical essence and the achieved result to the proposed technical solution is a method of operating a nuclear energy complex, which consists in the fact that spent fuel from thermal and / or fast nuclear reactors is loaded in the form of granules into a fast homogeneous reactor with a liquid metal coolant equipped with reactivity control organs and a container-type core with a perforated bottom, then the fuel in the core is melted and through holes in the bottom of the container and outputted from the area again granulated and fed through the circulation circuit to the input of the active zone (patent of RF N 2031455, cl. G 21 C 1/00, 3/42, 1990).

 The use of a fast homogeneous reactor with a liquid metal coolant in this energy complex allows us to exclude chemical processing from the secondary fuel production process and simplify the manufacturing technology of fuel elements.

 However, this complex also has drawbacks. One of the most significant drawbacks is that this complex does not allow the burning of minor actinides (neptunium, americium, curium) in secondary fuel, therefore, this method does not solve, at least partially, the problem of environmental safety of nuclear energy.

 In addition, in this complex during operation of a fast reactor accumulates excess fuel containing plutonium, as well as volatile and gaseous fission products. In the light of the cessation of the arms race, an increase in the quantity of plutonium is undesirable because it is unclear, firstly, where and how to reliably bury the produced plutonium, and secondly, how to ensure, in the light of international treaties, its non-proliferation, i.e. the safety of an ever-increasing mass of plutonium.

 As for the fission products (PD), their presence in the circulation circuit leads, due to the difficulty in retaining gaseous substances in general and the great length of the circuit in particular, to the danger of PD entering outside the nuclear power plant.

 The task to which the invention is directed is to increase the safety of nuclear energy and, including environmental safety.

 The technical result achieved using the present invention is the destruction (burning) of highly radioactive and long-lived products of irradiation of nuclear fuel - minor actinides, reducing the mass of accumulated plutonium and radioactive waste to be disposed of.

 The specified technical result is achieved by the fact that in the method of operating the nuclear energy complex, which consists in the fact that spent fuel from thermal and / or fast reactors is loaded in the form of pellets into a fast homogeneous reactor with a liquid metal coolant equipped with reactivity control organs and a container-type core with perforated bottom, then the fuel in the core is melted and removed through the holes in the bottom of the container from the zone, granulated again and circulated around five are fed to the entrance of the active zone, minor actinides (MA) are extracted from the spent fuel, granulated, then MA granules are mixed uniformly with aluminum granules and a fuel mixture containing 12-13.5 at.% MA is formed from these ingredients for the initial loading a fast homogeneous reactor, after loading this fuel mixture into the core and melting it, bring the fast homogeneous reactor to a critical state and burn out the MA, some of the burned fuel is unloaded from the circulation loop and The fission products are added, the core is charged with the fuel mixture (to maintain the criticality of the reactor), as well as aluminum, and the MA content in the fuel mixture is adjusted to 3-3.5 at. %%, after which the MA content in the active zone of the fast homogeneous reactor is maintained up to the end of the MA burning process at the achieved level, in addition, for the fuel mixture to melt into the active zone of a fast homogeneous nuclear reactor, the starting fuel assembly is placed and / or the reaction control organs are partially and / or completely removed from the active zone vnosti furthermore to melt the fuel mixture is carried out heating the container core rapid homogeneous nuclear reactor, in addition, after extracting MA from irradiated fuel from them and aluminum manufactured Alloy Al + MA, which is before loading into the core of rapid homogeneous nuclear reactor is granulated.

 The invention is illustrated using a thermohydraulic circuit of a fast homogeneous nuclear reactor with a liquid metal coolant, shown in FIG. one.

 A fast homogeneous nuclear reactor contains a container-type core 1. The walls of the container 2 can be made cooled by "pure" sodium circulating in a separate circuit (not shown in the drawing).

 Launcher assembly 3 and reactivity control elements 4 are placed in container 2.

 Openings 6 are made in the bottom 5 of the container 2 and a gas chamber 7 is located under the bottom 5, which, when the reactor is in operation, is filled with some neutral gas, for example argon, ending in a sodium pool 8.

 The gas chamber 7 is connected to a device 9 for supplying "clean" gas and - through a pipe 10 - with a device for cleaning from gaseous and volatile fission products 11.

 The pool 8 through a dispersed heat exchanger 12 is in communication with a vortex hydroclone 13 connected to the active zone 1, and using a pipe 14, which is equipped with a normally open valve 15, with an intermediate heat exchanger 16.

 The intermediate heat exchanger 16 is followed by a low-pressure manifold 17, which is in communication with the sodium collection chamber 18 above the active zone 1 and, through a circulation pump 19, with a high-pressure manifold 20, to which injections 21 of the fuel circulation circuit and other devices are connected.

 To enter the fuel into the circulation circuit on the pipeline 22, leading from the high pressure manifold 20 to the hopper 23 with the "fresh" fuel connected to the dispersed heat exchanger 12, a valve 24 is installed.

 The burned-out fuel is removed into the hopper 25 for storing spent fuel through a pipeline (not indicated in the drawing), "embedded" in the circulation circuit in the area between the dispersed heat exchanger 12 and the vortex hydrocyclone 13.

 A bypass pipe 26 with a normally closed valve 27 is also extended to the bunker 25.

 The nuclear power complex is operated as follows.

 During operation or at the end of the campaign of any of the fast or thermal neutron reactors, partially or completely burnt fuel is unloaded from them. Minor actinides are separated from the components of this fuel (for example, in a smelting bath), which are then granulated to obtain homogeneous fuel in a "cold" solid state and for transporting fuel with a coolant. Here, or immediately before loading fuel into a homogeneous fast reactor, MA granules are uniformly mixed with aluminum (Al) granules and a fuel mixture containing 12-13.5 at. %% MA is obtained, the rest is Al, for initial loading into a fast homogeneous reactor with liquid metal coolant.

 This composition of the fuel mixture is due to the fact that when the MA content is less than 12 at. % of the fuel mixture in the core volume does not reach criticality, whereas when the MA value is more than 13.5 at.%, the reactivity becomes excessively high, which leads to unjustified complication and cost of the reactor control and protection system.

 To reduce the number of operations to obtain fuel of the required composition, carried out directly at the industrial site of a nuclear power plant, the process of manufacturing the fuel mixture can be carried out in the factory. In this case, the Al + MA alloy is first made containing 12-13.5 at. %% MA, the rest is Al, and then it is granulated.

 Then, before starting the reactor, the container 2 of the active zone 1 is filled with granules of the fuel mixture MA + Al containing 12-13.5 at. %% MA, the rest is Al.

 The fuel is introduced into the circulation circuit hydraulically by opening the valve 24. Fuel from the hopper 22 is fed by a sodium stream into the dispersed heat exchanger 12, and from it into the core 1, after which the valve 24 closes.

 The cooling circuit (not shown) of the container 2 of the core 1 may be provided, for example, with an electric heater (not shown). Hot sodium, heated by an electric heater, is supplied to the container 2 and heated and melts the fuel granules through the walls. The initial melting of the fuel can also be achieved using the launch assembly 3 and / or reactivity control 4, which can be completely and / or partially removed from the core 1.

 The fuel melted in the core 1 through holes 6 in the bottom 5 of the container 2 flows in thin jets into a gas chamber 7 filled with argon, where, under the influence of gravity, the fuel jets burst into droplets. Drops of liquid fuel fall into the sodium pool 8, granulate without the use of any auxiliary equipment, and heat the sodium. The high temperature of liquid fuel and the large surface of jets and droplets of liquid fuel contribute to the efficient exit of gas and volatile fission products in gas chamber 7. Connecting to it a cleaning system for gas and volatile fission products 11 can significantly increase the safety level of a fast reactor and the nuclear power complex as a whole.

 From the pool 8, the fuel granules are again discharged through the dispersed heat exchanger 12 to the vortex hydrocyclone 13 through the dispersed heat exchanger 12, where they are separated from the heated sodium, which goes into the intermediate heat exchanger 16 and transfers heat to the secondary circuit there.

 Granules of fuel, together with a small part of sodium (volume fractions of fuel and coolant are approximately equal), are lowered (through the chamber for collecting sodium 18) to the upper part of the active zone 1, limited by the level of molten fuel, and enter the molten fuel of the active zone 1. Sodium, as the lighter fraction (sodium is several times lighter than fuel), floats and is diverted from the chamber 18 to the low pressure collector 17, and the fuel granules move down the core 1 from the top by gravity and melt.

 From the intermediate heat exchanger 16, the cooled sodium through the low pressure manifold 17 enters the circulation pump 19, from it into the high pressure manifold 20, and from there the sodium enters the injections 21 of the fuel circuit and other devices, and in particular the hopper 23 for feeding the reactor “fresh” fuel.

 If necessary, fuel with burned-out MA and containing solid and, partially, gaseous and volatile fission products is diverted to the hopper 25, for which purpose a pipeline 26 is opened by a normally closed valve 27 and the pipeline 14 is closed by a normally open valve 15, as a result of which sodium discharges the fuel granules into a hopper 25 for storing spent fuel (from where it can be sent for reprocessing), after which the valves 15 and 27 are brought into normal condition.

 In the process of operation of a fast homogeneous reactor, not only is the reactor fed with “fresh” fuel of the initial composition and PD removal, but also the formation of more efficient fissile uranium and plutonium isotopes in the core is critical. Therefore, in order to ensure the equilibrium composition of the fuel in the active zone 1, the MA content in it is gradually reduced to 3-3.5 at. %% MA, and the volume of the active zone 1 released from MA is filled with aluminum.

 With this composition of the fuel mixture, the reactor enters a stationary mode of operation with excess reactivity close to zero. A further decrease in the content in MA fuel, i.e. less than 3 at. %%, leads to the fact that the fuel mixture in the core does not reach criticality, while when the MA content is more than 3.5 at. %%, a high excess reactivity appears, which leads to a decrease in reactor safety.

 After the fuel mixture reaches the specified equilibrium composition, i.e. MA content of 3-3.5 at. %%, the operation of a homogeneous fast reactor with a liquid metal coolant may continue until all actinides currently stored in the reserve are burned.

Claims (4)

 1. The method of operation of the nuclear energy complex, which consists in the fact that spent fuel from thermal and / or fast nuclear reactors is loaded in the form of granules into a fast homogeneous reactor with a liquid metal coolant equipped with reactivity regulators and a container-type core with a perforated bottom, then the fuel in the core it is melted and taken out of the zone through openings in the bottom of the container, granulated again and again fed to the core inlet along the circulation loop in that the spent fuel removed from minor aktivoidy (MA), granulated them, then uniformly stirred MA granules with granules of aluminum and is formed from a fuel mixture of these ingredients, containing 12 - 13.5 at. %% MA, for the initial loading of a fast homogeneous reactor, after loading this fuel mixture into the active zone and its melting, the fast homogeneous reactor is brought to a critical state and MA is burned, some of the burned fuel is unloaded from the circulation loop and fission products are removed, the core is loaded fuel mixture to maintain its criticality, as well as aluminum, and bring the MA content in the fuel mixture to 3 - 3.5 at. %%, and then maintain the MA content in the active zone of fast homogenization reactor to the end of the process of burning MA at the achieved level.  2. The method according to claim 1, characterized in that in order to melt the fuel mixture in the active zone of a fast homogeneous reactor, a starting fuel assembly is placed and / or reactivity control organs are partially and / or completely withdrawn.  3. The method according to claim 1, characterized in that for melting the fuel mixture, the container of the active zone of a fast homogeneous nuclear reactor is heated.  4. The method according to claim 1, characterized in that after the extraction of minor actinides from the irradiated fuel, an Al + MA alloy is made from them and aluminum, which is granulated before loading into the active zone of a fast homogeneous nuclear reactor.