RU2630893C1 - Reactor assembly with variable neutron spectrum - Google Patents

Abstract

FIELD: electricity-producing industry.

SUBSTANCE: heat transport main circuit system is equipped with the system of gas supply into the bottom mounting sockets, where the FA bottom nozzles are installed, and also with the injector for the gas priming into the heat transfer in the shape of the size-defined gas bubbles in water: of a size, which is greater than critical size to exclude the bubbles collapse, and of a size, which is lower than the fuel lattice spacing difference and the fuel element diameter for the exclusion of the gaseous cavities formation in the FA. The reactor assembly is supplied with the degassing system for removing gas from the heat transfer into the gas supply system for the gas multiple uses. It can be, for example, helium - the chemically inactive gas with high thermal conductivity - in the function of the gas.

EFFECT: possibility of the local correction of the in-reactor-core flux spectrum.

5 cl, 3 dwg

Description

The invention relates to nuclear power plants, and more particularly to reactor plants with nuclear water-cooled reactors with pressurized water and with technical means of influencing reactivity.

The VVER-1000 reactor installation is known, containing a complex of systems and elements, including a reactor with an active zone and systems directly connected with it, necessary for its normal operation, emergency cooling, emergency protection and maintaining it in a safe condition (F.Ya. Ovchinnikov, V. V. Semenov, “Operational modes of pressurized water reactors.” - M .: Energoatomizdat, 1988, Fig. 11.5 on pages 284-286, as well as pages 55 and 11). The core consists of fuel assemblies (FAs), a coolant moderator, and reactivity reactors.

The duration of the campaign is ensured by the loading of fissile materials, i.e. the creation of a full reactivity margin, which is largely offset by the introduction of boric acid into the reactor coolant in the initial period of the campaign and with a decrease in its concentration to 0 during the campaign. The necessary concentration of boric acid in the coolant is provided by the system of replenishment of the coolant with a solution of boric acid at the beginning of the campaign and the dilution of the reactor coolant with clean water during the campaign.

The disadvantage of this technical solution is the absorption of excess neutrons by a boron isotope ¹⁰ B in the coolant, i.e. there is an inefficient use of neutrons for fission of uranium nuclei and generation of energy.

The closest in technical essence (prototype) is a reactor installation (I.N. Vasilchenko and others. Design and development studies of VVER active zones with spectral regulation, abstracts of the 7th ISTC "Ensuring the safety of nuclear power plants with VVER", Podolsk, 17-20 May 2011, p. 68-69, report on the SD “Materials of the Conference of the 7th ISTC”, section 3 http://www.gidropress.podolsk.ru/files/proceedings/mntk2011/autorun/index-ru.htm), containing a complex of systems and elements, including a reactor with an active zone consisting of fuel assemblies, a coolant moderator and reactivity reactors, and systems directly connected with the reactor that are necessary for its normal operation, emergency cooling, emergency protection and maintenance in a safe condition.

In this device, the duration of the campaign is ensured by the loading of fissile materials, i.e. the creation of a full reactivity margin, which is compensated by a change in the water-uranium ratio (VLO) during the campaign and the use of boron regulation with harmful neutron absorption is excluded.

Channels are placed in the fuel assemblies in which displacers are installed in the initial period of the campaign to reduce the VLO, which, as the fissile nuclides burn out, are removed from the channel with its filling with water and an increase in the VLU. The first disadvantage of this device is the limited spatial area of regulation, the second disadvantage is the difference in spectrum in height when moving the displacer. These drawbacks are due to the fact that in a heterogeneous lattice with water cavities (channels, gaps between fuel assemblies), the spectrum will be variable along the cross section of the fuel assemblies, and when displacers move, the region of spectrum change is determined by its location relative to the displacer. In practice, the region of a fuel assembly with an unregulated or unregulated spectrum is implemented in an array of fuel rods remote from the channels with displacers by a distance comparable to and greater than the diffusion length (2.9 cm in water) and the deceleration length L _m = (6τ) ^0.5 ( τ - age, for water L _m = 14 cm).

The presence of water interlayers between fuel assemblies ~ 0.4 cm, as well as 4 or more rows of fuel rods in the area between the channels with propellants and the presence of channels for displaced propellants (∅28 ... 29 mm) create conditions for a variable spectrum along the fuel assemblies cross section and limited area with an adjustable spectrum near the channels with propellants.

The disadvantage of this reactor is the significant non-uniformity of energy release in the fuel rods over the cross section of the fuel assemblies, and the efficiency of spectral regulation is not large. As a result, fuel economy is up to 12% and 2 times less than the expected savings of 25% according to the estimate obtained for the “close” grid (F. Ran et al. Handbook of Nuclear Energy Technology. Translated from English by V. A. Legasov M.: Energoatomizdat, 1989, p. 344-345).

The purpose of the invention is the creation of a reactor installation that allows locally (within energy-stressed fuel assemblies) to regulate the neutron flux spectrum in the reactor core.

This goal is achieved by the fact that in a reactor installation containing a primary coolant system and a reactor with internals having lower and upper landing sockets in which fuel assemblies are installed with lower and upper end parts, according to the invention, the primary coolant system is provided with a gas supply system in the lower landing nests.

As a result of regulation of the neutron flux spectrum, fuel consumption is improved, which is understood as the fullest use of fissile isotopes of both primary and accumulated (secondary) during burnup (RZ Aminov and other WWER nuclear power plants: Modes, characteristics, efficiency. M: Energoatomizdat, 1990, pp. 53-55).

According to an embodiment, the gas supply system has an injector installed in the lower landing socket of the internal devices.

According to an embodiment, the primary coolant system has a coolant degassing system made after the fuel assemblies.

The fuel assemblies (8) may have a cover (12) connecting the lower (6) and upper (7) end parts.

The invention is illustrated by drawings, where:

in FIG. 1 shows a primary coolant system with a gas supply system and a degassing system;

in FIG. 2 is a diagram of internals with a gas supply system to the lower landing jacks;

in FIG. 3 - fuel assembly with a cover connecting the lower and upper end parts.

The reactor installation is equipped with a primary coolant system (1), contains a reactor (2) with internals (3), which have lower (4) and upper (5) landing sockets. The fuel assemblies (8), respectively, with the lower (6) and upper (7) end parts are installed in the indicated sockets (4 and 5).

The primary coolant system (1) is equipped with a gas supply system (9) to the lower landing sockets (4). The gas supply system (9) has an injector (10) installed in the lower landing socket (4) of the internal devices (3). Helium, for example, gas with high thermal conductivity, can be used as a gas.

The primary coolant system (1) has a degassing system (11) of the coolant located in the circuit and made after the fuel assemblies (8).

Fuel assemblies (8) can be equipped with a cover (12) connecting the lower (6) and upper (7) end parts, or used without a cover.

части активной зоны для организации годичной кампании ВВЭР-1000 и четырехгодичной кампании топлива. На вход в ТВС по системе теплоносителя первого контура подается водяной теплоноситель, не содержащий борной кислоты. Из системы подачи газа (9) через инжектор (10) подается в ТВС газ, например гелий, равномерно распределенный по сечению на входе ТВС в виде пузырьков определенного размера (d), который больше минимального критического размера, при котором пузырьки не могут образовываться или продолжительно существовать в жидкости из-за эффекта схлопывания пузырей, и менее характерного размера в дистанционирующей решетке (Δ) для исключения разрушения пузырька при прохождении через решетку и последующего схлопывания или образования в решетке локальной газовой полости: Δ≤D-d_твэла, D – шаг топливной решетки, d_твэла - диаметр твэла. Размер пузырька определяется разностью давления газа и жидкости, коэффициентом поверхностного натяжения жидкости и рассчитывается по уравнению Лапласа. Объемная доля газа в потоке воды задается требуемым ВУО: ВУО~1 в начале кампании; ВУО~2 в конце кампании (Р.З. Аминов и др. АЭС с ВВЭР: Режимы, характеристики, эффективность. М.: Энергоатомиздат, 1990, стр. 53-59).The operation of the reactor installation of the present invention is as follows. At the initial moment of the campaign, the reactivity margin is maximum and is ensured by loading fresh fuel assemblies into the active zone instead of burnt fuel assemblies, for example, they are replaced

parts of the core for organizing the VVER-1000 annual campaign and the four-year fuel campaign. At the entrance to the fuel assembly through the primary coolant system, an aqueous coolant that does not contain boric acid is supplied. From the gas supply system (9) through the injector (10) gas is supplied to the fuel assembly, for example, helium uniformly distributed over the cross section at the fuel assembly inlet in the form of bubbles of a certain size (d), which is larger than the minimum critical size at which bubbles cannot form or last exist in the liquid due to the effect of collapse of the bubbles, and a less characteristic size in the spacer lattice (Δ) to prevent destruction of the bubble when passing through the lattice and subsequent collapse or formation of local gases in the lattice th cavity: Δ≤Dd _{fuel element,} D - Step fuel lattice, d _{fuel element} - the diameter of the fuel element. The size of the bubble is determined by the difference in gas and liquid pressure, the coefficient of surface tension of the liquid and is calculated by the Laplace equation. The volume fraction of gas in the water flow is specified by the required HLW: HLW ~ 1 at the beginning of the campaign; VUO ~ 2 at the end of the campaign (RZ Aminov et al. VVER nuclear power plants: Modes, characteristics, efficiency. M: Energoatomizdat, 1990, p. 53-59).

Therefore, the volume fraction of gas bubbles should be equal to or less than 0.5 in the water-gas medium.

At the initial moment of the reactor campaign, the gas flow is maximum and decreases to 0 as it burns out during the campaign. An inert, non-inactivated gas is used, mainly with high thermal conductivity, for example, helium. After fuel assembly due to mixing, partial or complete dissolution of helium in the coolant occurs and its subsequent separation in a special bypass part of the circuit by reducing its pressure and reaching the saturation state. Next, helium is collected in a container and fed through a compressor (not shown in the drawing) to the input of the fuel assembly, in which it is necessary to tighten the neutron spectrum (fresh fuel assembly) or stored in the ballast tank.

The use of helium gas with high thermal conductivity (3 times higher than the thermal conductivity of water vapor and 2 times less than the thermal conductivity of water) in the form of bubbles directed in the flow of the coolant will lead to additional mixing of the water and improve heat transfer. The limiting solubility of helium in water is ~ 3.5 cm ³ / g (Collection of reports "Thermophysics - 89", Obninsk, 1992, pp. 381-393).

The use of sheathed fuel assemblies or case-free fuel assemblies allows one to change the neutron deceleration at the interface between fuel assemblies, thereby achieving more efficient fuel use.

The use of the claimed invention in comparison with known devices provides fuel economy of about 2 times greater than the effect of fuel economy in the prototype device.

Claims (5)

1. A reactor with a variable neutron spectrum, comprising a primary coolant system and a reactor with internals having lower and upper landing sockets, in which fuel assemblies are installed respectively by lower and upper end parts, characterized in that the primary coolant system is provided with a supply system gas to the lower landing nests. 2. The reactor installation according to claim 1, characterized in that the gas supply system has an injector installed in the lower landing socket of the internal devices. 3. The reactor installation according to claim 1, characterized in that helium is used as the gas. 4. The reactor installation according to claim 1, characterized in that the primary coolant system has a coolant degassing system made after the fuel assemblies. 5. The reactor installation according to claim 1, characterized in that the fuel assembly has a cover connecting the lower and upper end parts of the fuel assembly.

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