RU-2861391-C1 - FLUIDISED BED STRUCTURE OF SPHERICAL FUEL ELEMENTS IN CORE OF NUCLEAR REACTOR

RU2861391C1RU 2861391 C1RU2861391 C1RU 2861391C1RU-2861391-C1

Abstract

FIELD: nuclear industry. SUBSTANCE: invention relates to a fluidised bed structure of spherical fuel elements in the core of a nuclear reactor and can be used in fast neutron reactors with a heavy liquid metal coolant, such as lead or lead-bismuth. The fluidised bed structure of spherical fuel elements in the core of a nuclear reactor consists of spherical fuel elements containing a protective shell with nuclear fuel. The shell is solid and made of steel, and the nuclear fuel is in the form of individual granules. Inside the protective shell there is liquid lead and a free cavity containing gases. Wherein, the nuclear fuel together with the liquid lead form a layer located under the free cavity containing gases, such that the spherical fuel elements form a fluidised bed structure in the core of the nuclear reactor. EFFECT: reducing clogging of heat exchange channels, uniform burnup of nuclear fuel across the entire cross-section of the core, as well as ensuring safe operation of the reactor in the event of an emergency stop of coolant circulation. 3 cl, 1 dwg, 3 tbl

Inventors

Glazkov Vasilii Valentinovich
Tyvrovskii Maksim Vladimirovich
Tolpegin Artem Alekseevich

Dates

Publication Date: 20260505
Application Date: 20251219

Claims (4)

1. A fluidized structure of spherical fuel elements in the active zone of a nuclear reactor, consisting of spherical fuel elements containing a protective shell and nuclear fuel, characterized in that inside the protective shell there is liquid lead and a free cavity containing gases, the nuclear fuel together with the liquid lead form a layer located under the free cavity containing gases, while the spherical fuel elements form a fluidized structure in the active zone of a nuclear reactor when the conditions of the system of equations are met:
where n is the number of spherical fuel elements, pcs., - the volume of the shell in the spherical fuel element, , - the total volume of the shell in the active zone, , - the volume of nuclear fuel in a spherical fuel element, , - the total volume of nuclear fuel in the core, , - volume of the spherical fuel element, , - radius of the spherical fuel element, , - the volume of lead in the spherical fuel element, , - the volume of the free cavity in the spherical fuel element, , - thickness of the shell of the spherical fuel element, , - the mass of one spherical fuel element, , - density of the shell of the spherical fuel element, , - density of nuclear fuel, , - density of liquid lead, , - the buoyancy force of one spherical fuel element, , - acceleration of gravity, , - the difference between the weight of the body and the buoyant force for the entire system, .
2. A fluidized structure of spherical fuel elements in the active zone of a nuclear reactor according to paragraph 1, characterized in that the shell is one-piece and made of steel.
3. A fluidized structure of spherical fuel elements in the active zone of a nuclear reactor according to paragraph 1, characterized in that the nuclear fuel is in the form of individual granules.

Description

The invention relates to the field of nuclear energy, in particular to the design of fuel elements of the active zone of nuclear reactors, and can be used to reduce fouling of heat exchange channels and ensure additional safety in fast neutron reactors with a heavy liquid metal coolant, such as lead or lead-bismuth. A well-known model of spherical fuel elements for a high-temperature gas-cooled reactor (HTGR) [1] consists of a central fuel microsphere of uranium dioxide and a cladding with several layers of pyrolytic carbon and silicon carbide. The use of such fuel elements in gas-cooled reactors allows for the operation of fuel elements at elevated temperatures. In the HTGR reactor core, spherical fuel elements form a backfill; new elements are added from above the core, and spent elements are removed from below. A disadvantage of this technical solution is that the use of carbon fuel rod cladding significantly reduces the safety margin during a relatively long, thermally intense fuel cycle. During circulation, the spherical fuel rods rub against each other and against reactor structural elements. This leads to the formation of graphite dust, which can contaminate the coolant circuit and reduce the safety margin of the fuel rods. Cracks and fractures in the surface of the protective containment vessel are possible, followed by contamination with decay products of the original fuel material. The fuel rod cladding material adequately maintains the required thermal neutron spectrum in a high-temperature reactor (HTGR). However, in a fast neutron reactor, due to the properties of carbon, such fuel rods will introduce significant negative reactivity, making their use in this type of reactor unsuitable. A well-known design of a spherical fuel element for the HTR-10 gas-cooled reactor [2] consists of a spherical graphite body 60 mm in diameter, within which approximately 8,300 four-layer TRISO particles with a uranium dioxide core are dispersed. Each fuel microsphere, 500 μm in diameter, is successively coated with layers of porous pyrolytic carbon, inner dense PyC, silicon carbide, and outer dense PyC, which ensures the confinement of fission products at operating temperatures up to 1600°C. The fuel zone, 50 mm in diameter, is surrounded by a graphite cladding 4-6 mm thick, which performs protective and structural functions. A disadvantage of this design is the technological difficulty of ensuring consistent quality of multilayer coatings on an industrial scale. This is reflected in the relatively high content of free uranium (5.0 x 10 -5 in the first batch), which is a source of coolant contamination. When circulating in the core, the spherical fuel rods are subject to erosion, and mechanical stress can damage the outer cladding, exposing fuel particles. The graphite matrix effectively functions as a moderator in the thermal neutron spectrum, but the use of such spherical fuel rods in fast reactors is impossible due to the strong neutron absorption of carbon. The closest in technical essence to the proposed invention is the spherical fuel element [3]. The design of the spherical fuel element provides for a spherical hydrodynamically transparent cladding (SHGPO) located above the sealed cladding with a gap, which is connected to the cladding by heat-conducting struts. The cladding contains nuclear fuel in the form of a spherical pellet, with conical depressions on opposite sides along the axis, transitioning into a through hole. Heat is transferred from the pellet core to the struts by the spherical fuel element to the SHGPO. The SHGPO has a network of holes through which a coolant flows to the surface of the cladding, removing heat from all heating surfaces. A disadvantage of this technical solution is that the main heat-transfer struts are filled with heat-conducting gas under excess pressure. In the event of a fuel rod leak, this could result in the formation of highly thermally stressed fuel rod parts susceptible to overheating, followed by melting of the structural materials and "contamination" of the primary coolant with daughter products of the original fuel material. Furthermore, the use of spherical fuel rod backfill in a reactor with liquid metal coolant can lead to clogging of the heat-exchange channels due to the immobility of the entire system, as liquid metals corrode structural components. With this type of coolant backfill, the use of spherical fuel rods can lead to serious problems with fuel rod failure. The technical objective of the proposed invention is to create a design for a spherical fuel element as part of a fluidized structure in the active zone of a nuclear reactor for use in fast neutron reactors with a heavy liquid metal coolant, such as lead or lead-bismuth. The technical result consists in reducing the fouling of heat exchange channels caused by corrosion of structural elements, achieving uniform burnout of nuclear fuel across the entire cross-section of the active zone, and ensuri