RU2766322C1 - Autonomous nuclear power plant - Google Patents

Abstract

FIELD: nuclear reactors.

SUBSTANCE: invention relates to a molten salt nuclear reactor and can be used to generate electrical energy for remote areas and islands of the Arctic. The installation consists of an outer and an inner shell, the space between which is filled with heat-insulating material in the form of an inert gas. An active zone is located inside the inner case, which includes graphite blocks of a moderator with channels for molten-salt fuel in the form of molten-salt fuel rods (FLs) and blocks of a thermoelectric generator. The lower part of molten salt FLs is located in the channels of the graphite stack of the moderator of the core, which has channels for emergency discharge of fuel salt from the core into the volume between the inner and outer housings in the lower part of the graphite stack of the moderator and reflector. The upper part of the molten-salt FLs comes out of the inner case into cylindrical steel sleeves fixed outside on the upper cover of the reactor, on the outer wall of which blocks of thermoelectric generator modules are fixed. Moreover, the excess of reactivity is compensated by the neutron absorber rods, which form four CPS channels. The liquid salt fuel circulates in the molten salt FL, heating up in the lower part of the core and transferring heat in the upper part to the inner, "hot" junction of thermoelectric modules of the thermoelectric generator, and the "cold", external junction of these modules is cooled by seawater in the case of an underwater nuclear power plant. installation or additional heat carrier.

EFFECT: increasing the efficiency and reducing the volume of molten salts in the installation.

1 cl, 1 dwg

Description

The proposal relates to the production of electrical energy for hard-to-reach territories and islands of the Arctic using an unattended molten-salt nuclear reactor (ZSR). Specifically, the proposal refers to a reactor with a capacity of 1-5 MW, cooled by sea water, with an active zone in the form of a molten salt melt and graphite, and a thermoelectric converter of thermal energy into electrical energy.

State of the art

Known autonomous nuclear power plant (patent RU 2741330), which consists of external and internal buildings, the space between which is filled with heat-insulating material in the form of an inert gas. Inside the inner case there is an active zone, including graphite blocks of the moderator with channels for liquid salt fuel and channels around the active zone with heat pipes with thermoelectric generators inserted into them. A gas tank is located on the cover of the reactor vessel, inside the gas tank there is a gas absorber with a dispenser that supplies fuel salt to liquid-salt fuel elements. Fuel rods are external pipes, the ends of which are plugged from below, and welded to the upper fuel salt collector from above. The pipes have internal pipe inserts installed coaxially with a gap with open ends, and the fuel salt circulating in the liquid-salt fuel elements is cooled from the outside by an additional liquid-salt coolant without fuel circulating both in the channels of the graphite blocks of the core moderator and in the channels of the side and bottom reflectors.

One of the disadvantages of this scheme is that the liquid salt fuel is enclosed in fuel elements connected by a collector and transfers heat to heat pipes with TEGs using an additional, intermediate fuel-free coolant that fills the entire reactor space.

The closest in technical essence to the claimed invention is a design diagram of a high-temperature molten-salt reactor (HTZhSR) (M.V. Kovalchuk, B.B. Chaivanov, S.S. Abalin, O.S. Feinberg "Nuclear energy source for the Arctic", VANT Ser. Fizika yadernykh reaktorov, 2018, issue 1), which proposes a scheme of a single-loop 1-5 MW HRTHS with circulating fuel based on molten metal fluoride salts. Fuel salt fills the entire reactor space, including the core, consisting of graphite blocks of the moderator with holes for the passage of fuel salt, a traction section above the core, and a lower section, in which there are heat pipes (HP) with their own coolant, the lower part of which is heated by fuel salt , and in the upper part the heat is transferred to the units of the thermoelectric generator (TEG) outside the reactor vessel with its own external cooling. At the same time, the closest in technical essence to the scheme of the core itself is the structural scheme of the core of a liquid-salt reactor (ZHR) for medical purposes (Tataurov A.L., Feinberg O.S. Liquid-salt reactor for large-scale production of ⁹⁹ Mo, Atomic Energy, 2017, t 122, No. 5, pp. 249-252), which is a masonry of twenty-one graphite blocks of the moderator with holes with a radius of 4 cm, which are liquid-salt channels.

One of the main disadvantages of this scheme is the relatively large fissile material load of the entire reactor facility (RP), which is many times greater than the load of the reactor core itself.

The technical problem to be solved by this invention is the improvement of the concept of a low-power nuclear power plant with a FSR and a thermoelectric generator (TEG) with a power of up to 500 kW (el) with a service life of 5-10 years or more with circulating fuel based on molten salts metal fluorides.

Disclosure of the essence of the invention

The technical result of the claimed invention is the improvement of the heat transfer scheme from liquid salt fuel to thermoelectric generators (TEG) without any intermediate coolant, which leads to an increase in the efficiency of the TEG and to a significant decrease in the volume of molten salts in the installation.

To achieve a technical result, an autonomous nuclear power plant is proposed, consisting of outer and inner cases, the space between which is filled with a heat-insulating material in the form of an inert gas, an active zone is located inside the inner case, including graphite blocks of the moderator with channels for liquid salt fuel in the form of liquid salt fuel elements, representing external pipes, the ends of which are muffled from above and below, and internal pipe inserts installed with a clearance with open ends, and thermoelectric generator units located outside above the top cover of the reactor, while the lower part of the liquid-salt fuel elements is located in the graphite masonry channels of the core moderator having in the lower part of the graphite stack of the moderator and reflector channels for emergency draining of the fuel salt from the core into the volume between the inner and outer casings, and the upper part of the liquid-salt fuel rods goes out of the inner casing into cylindrical steel sleeves fixed on the outside on the top cover of the reactor, on the outer wall of which blocks of modules of the thermoelectric generator are fixed, while the excess reactivity is compensated by neutron absorber rods forming four CPS channels, the lower part of which is located in the channels of the graphite stack of the moderator and reflector of the core, and the upper one is in cylindrical steel sleeves, fixed on the outside on the top cover of the reactor, located in the space of the outer protective case, where the electrical unit is located, including the switch of thermoelectric generators and power supply of the CPS, while the molten salt fuel circulates in the molten salt fuel element, heating up in the lower part of the core, and transferring heat in the upper part to the internal, "hot" junction of thermoelectric modules (TEM) of the thermoelectric generator, and the "cold", external junction of these modules is cooled by sea water, in the case of an underwater placement of a nuclear power plant, or by additional heat transfer teletel in the case of ground-based placement of a nuclear power plant for inclusion in the heating system of the settlement.

Brief description of the drawings

The figure shows a diagram of an autonomous nuclear power plant, where:

1 - External vessel of the reactor;

2 - Inner vessel of the reactor;

3 - Thermal insulation (inert gas)

4 - Graphite laying of the moderator and reflector;

5 - Channels for emergency discharge of the melt;

6 - External tube of TVEL;

7 - Inner pipe insert (the arrow shows the direction of movement of liquid salt fuel);

8 - Inverter;

9 - Top cover of the reactor;

10 - Steel sleeves;

11 - Blocks of thermoelectric generators (TEG);

12 - External coolant (intake water, the arrow shows the direction of movement);

13 - External protective case;

14 - Four CPS channels with neutron absorber rods;

15 - Electrical unit, including the TEG switch and CPS power supply.

Implementation of the invention

An autonomous nuclear power plant, the diagram of which is shown in the figure, includes a stack of twenty-one graphite moderator blocks 4 with holes with a radius of 4 cm, which are liquid-salt channels, in our case, fuel rods. Liquid-salt fuel rods are placed in the lower part into the cylindrical channels of the graphite masonry of the moderator and reflector 4 with a radius of 4 cm, and from above they exit the inner vessel 2 through the top cover of the reactor 9 into the upper protective housing 13, where each fuel rod is placed in its steel sleeve 10, on which the blocks are placed thermoelectric generators TEG 11.

Liquid-salt fuel rods are external pipes 6 with an outer diameter of 7 cm, the ends of which are muffled from below, and internal pipe inserts 7 of circular cross section with a radius of 2 cm of the Field type pipe. Such liquid-salt fuel elements are filled with molten fuel salt and operate in the thermosiphon mode: the lower part of the fuel element is located in the reactor core, where, when heated, the fuel salt rises up the annular gap of the fuel element to the top of the core, and then, after a special inverter 8, enters the inner tube the insert 7 of the upper part of the TVEL above the core, rises to the overflow zone and turns down into the annular gap of the TVEL, where it gives off heat to the TEG 11 blocks located on special steel sleeves 10 fixed on the top cover of the reactor, into which the upper parts of the TVELs enter.

As a fuel salt, a fuel composition of the molar composition 66LiF-34BeF ₂ +x(UF4+ ^ThF4 ) is used, where x is the mole fraction of 235U of 20% enrichment, which changes during burnout. The melting point of the fuel salt is 458°C. A natural requirement for the operating conditions of such a reactor is to minimize the load on fissile elements and use low-enriched nuclear fuel. These criteria are met by the VTZhSR scheme, in which U-233 burnup is compensated by its production from Th-232, previously added to the fuel salt in the form of ThF ₄ Graphite, including pyrographite, glassy carbon, is used as a structural material in the core, neutron moderator and reflector 4 SU-2000 and glassy carbon composite material. Among domestic grades of graphite, graphite grade GSP (graphite bound by pyrocarbon), which is used for the manufacture of spherical shells of fuel elements of high-temperature gas-cooled reactors, meets all the requirements for working under the conditions of the ZhSR to the greatest extent. The starting load of ²³⁵ U (with 20% enrichment and a UF ₄ fraction of 1.12 mol.%) in the core is 7.8 kg, and the annual make-up will be ~350 g per 1 MW, i.e. the total load per work for 10 years will be just over 10 kg.

In the space of the upper protective housing 13, an electrical unit 15 is mounted, including the TEG switch and CPS power supply.

In case of damage to the walls of the liquid-salt fuel element and possible leakage of fuel salt from it, in the lower part of the graphite masonry of the moderator and reflector 4 and the inner case 2 there are through channels 5 for emergency draining of the fuel salt into the volume between the inner case 2 and the outer case 1 to prevent the formation of uncontrolled additional critical masses .

Thermoelectric generator (TEG) 11 is a set of twenty-one TEG blocks in the form of an assembly of tubular thermoelectric modules (TEM), which are a set of twelve thermopiles (TB) strung one on top of the other on the wall of a cylindrical steel sleeve 11. "Hot" junction The TB is heated from the liquid-salt TVEL through the gas gap between the TVEL wall and the wall of the steel cylindrical sleeve 10. The “cold” junction of the TB is cooled by outboard water within the outer protective housing 13, when the installation is located underwater, or by an additional cooling circuit for inclusion in the heating system of the settlement.

Thus, by transferring heat from liquid salt fuel directly to TEG 11 blocks without "extra" intermediate heat carriers, the temperature at the "hot" junction of the TEM increases and, as a result, the efficiency of TEG 11 increases.

The space between the outer 1 and inner 2 cases is filled with an inert gas.

Excess reactivity is compensated by neutron absorbing rods 14, which form four CPS channels, the lower part of which is located in the channels of the graphite masonry of the moderator and reflector of the active zone 4, and the upper part is in cylindrical steel sleeves 10 located in the space of the outer protective housing 13 and fixed on the outside on the top cover reactor 9.

With a given geometry of the core, its dimensions, temperature design mode and the selected thermal-hydraulic scheme for cooling the reactor plant, a thermal power of about 1 MW (thr.) is achieved, providing electrical power from 50 to 100 kW (depending on the specific design of the TEG with its own efficiency transformations). A further increase in power is achieved by increasing the number of fuel rod units with TEG units. So, for example, even with the same diameter of the reactor vessel, adding 12 or 18 additional channels along the periphery of its core to the existing 21 fuel channels, the reactor power will increase to ≈1.5 or ≈2 MW, respectively.

Claims (1)

Autonomous nuclear power plant, consisting of outer and inner casings, the space between which is filled with a heat-insulating material in the form of an inert gas, inside the inner casing there is an active zone, including graphite blocks of the moderator with channels for liquid salt fuel in the form of liquid salt fuel elements, which are external pipes, ends which are muffled from above and below, and internal pipe inserts installed with a clearance with open ends, and thermoelectric generator units located outside above the top cover of the reactor, characterized in that the lower part of the liquid-salt fuel elements is located in the channels of the graphite stack of the core moderator, which has at the bottom parts of the graphite masonry of the moderator and reflector channels for emergency draining of fuel salt from the core into the volume between the inner and outer casings, and the upper part of the liquid salt fuel rods goes out of the inner casing into cylindrical steel sleeves fixed on the outside to the upper to the reactor cover, on the outer wall of which blocks of thermoelectric generator modules are fixed, while the excess reactivity is compensated by neutron absorbing rods forming four CPS channels, the lower part of which is located in the channels of the graphite masonry of the moderator and reflector of the core, and the upper part is in cylindrical steel sleeves, fixed outside on the upper cover of the reactor, located in the space of the outer protective housing, where the electrical unit is located, including the switch of thermoelectric generators and power supply to the CPS, while the molten salt fuel circulates in the molten salt fuel element, heating up in the lower part of the core and transferring heat in the upper part to the internal one, "hot", junction of thermoelectric modules (TEM) of thermoelectric generator, and "cold", external, junction of these modules is cooled by outboard water in case of underwater location of nuclear power plant or by additional coolant in case of ground location of nuclear power plant. oh power plant for inclusion in the heating system of the settlement.

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