RU2844148C1 - Radiation protection of space nuclear power plant - Google Patents

Abstract

FIELD: nuclear power engineering.

SUBSTANCE: invention relates to nuclear power engineering, particularly to shadow radiation protection of space nuclear installations designed to reduce the level of neutron and gamma radiation from a nuclear reactor to values acceptable for the payload of spacecraft. Proposed radiation protection of space nuclear power plant comprises container, layer of neutron-absorbing material and layer attenuating flux of quanta and neutrons. Inside the container there is a plate-type heat exchanger formed from successively welded and made in the form of corrugated plates, layers of material attenuating flux of gamma-quanta and neutrons. There are gaps between the plates which are filled on one side of the corrugated plates with a layer of neutron-absorbing material and on the other side with a heat carrier, wherein the outer surface of the container is coated with a layer of boron-containing material.

EFFECT: reduced absorbed dose of gamma-radiation and fluence of neutrons emitted by the space nuclear power plant reactor on the payload of the spacecraft.

5 cl, 2 dwg, 1 tbl, 1 ex

Description

Field of technology

The invention relates to the field of nuclear energy, in particular, to shadow radiation protection (SR) of space nuclear installations (SNIPs), designed to reduce the level of neutron and gamma radiation from a nuclear reactor to values acceptable for the payload of a spacecraft.

When designing any type of nuclear reactor, it is important to consider the need to protect the reactor components and the surrounding environment from the high flux of neutrons and gamma radiation produced by the nuclear reactor. In terms of radiation protection, there is a need for effective biological protection of spacecraft components, as well as the ability to protect other parts of the reactor, such as electronic systems. Reactive protection materials must provide protection against a wide range of high-energy radioactive particles, including alpha, beta, and gamma rays, neutrons, under thermal and vacuum conditions at short range and with minimal mass.

State of the art

A patent is known (RU 2761020 C2, published 02.12.2021 Bulletin No. 34, IPC C22C 27/04, B22F 3/12, G21F 1/08, C22C 29/06, G21C 11/02) which discloses a composition used to protect reactor components from nuclear radiation. The powder composition for protecting reactor components from nuclear radiation contains, in at.%: boron 21-41, iron 25-35, chromium 2-4, carbon 3-10, tungsten the rest. A method for manufacturing a component for protecting a reactor from nuclear radiation is also disclosed, which includes providing powders containing B, Fe, Cr, C and W in the above-mentioned quantity, grinding the powders with an organic binder to obtain a powder mixture, pressing and reaction sintering to obtain a sintered composition.

The disadvantage is that the heat generated in the shielding material is removed only by thermal conductivity and radiation, which can cause overheating of the RZ when operating together with the reactor. In addition, the patent does not disclose the design of the shadow protection device.

A patent is known (RU 2225649 C2, published 10.03.2004, Bulletin No. 25, IPC G21D 1/00, G21C 11/02), which discloses a shadow radiation shield consisting of a container with a material that effectively weakens the intensity of gamma radiation, which can be uranium-238, and a container with lithium hydride. Heat pipes are radially welded into the side shell of the container with uranium-238, while the evaporation section of the heat pipe is located inside the container, and the condensing section is placed in the shadow cone of the radiation shield. The free space of the container with uranium-238 is filled with a eutectic alloy, which can be NaK. The container with uranium-238 is connected via a tube to a compensation tank, which ensures thermal expansion of the eutectic alloy during operation of the nuclear power plant. The compensation tank is placed in a cavity formed by the spherical bottom of the container with lithium hydride and the end shell of the container with uranium-238. The feature of the invention is to increase the intensity of heat transfer between the radiation protection material and the environment, which serves to discharge excess heat.

The disadvantage of this proposal is that the use of lithium hydride in the composition of the KHPU with a high-temperature reactor leads to the decomposition of the hydride, the escape of hydrogen at a temperature above 400 °C in a vacuum and a decrease in the effectiveness of the protective properties of the device. In addition, the RP has a sufficiently large mass of the cooling system and uranium-238 to absorb the gamma radiation of the reactor.

The closest prototype is a patent (RU 2 069 898 C1, published 27.11.1996, IPC G21C 11/02), which discloses radiation protection containing a layer of lithium hydride made of composite material. In the central part of the protection there is a disk made of a material with high gamma-quantum attenuating properties. A flange made of a structural material is installed on the periphery of the disk. The thickness of the flange is selected from a dependence that takes into account, in particular, the dose of gamma quanta and the characteristics of the structural material. Radiation protection of the nuclear reactor facility, containing layers of neutron-absorbing material lithium hydride, enclosed in a shell, and a layer attenuating the flow of gamma quanta, characterized in that the layer attenuating the flow of photons is made composite, the central part in the form of a disk made of a material with high gamma-quanta attenuating properties, and the peripheral part in the form of a flange made of a structural material with worse gamma-quanta attenuating properties, but high strength characteristics, the thickness of the flange is selected taking into account the thicknesses of the metal structures of the containers with lithium hydride, at which their total thickness: the flange made of the structural material and the shell of the containers with lithium hydride.

The disadvantage of the above proposal is that the protection does not have a heat dissipation system, is limited by temperature to 400 °C, massive elements made of structural and heavy metal determine the large mass of the protection equipment.

Disclosure of the essence of the invention

The technical problem that the claimed invention is aimed at solving is ensuring that the level of neutron and *γ-radiation from a nuclear reactor with a high-flux, high-temperature nuclear reactor reaches values acceptable for the payload of a spacecraft.

The technical result consists in reducing the absorbed dose of *γ-radiation and the fluence of neutrons emitted by the KNU reactor on the payload of the spacecraft.

The specified technical result is achieved by radiation protection of the nuclear reactor facility, containing a container made of heavy metal, layers of neutron-absorbing material and layers of a material weakening the flow of quanta and neutrons, while inside the container there is a plate heat exchanger formed from successively welded and made in the form of corrugated plates layers of a material weakening the flow of gamma quanta and neutrons, between which gaps are formed, filled on one side of the corrugated plates with a layer of neutron-absorbing material, and on the other side with a coolant, while the outer surface of the container is covered with a layer of boron-containing material.

An additional technical result - an increase in the intensity of heat transfer between the RP material and the environment, which serves to discharge excess heat inside the RP, is achieved by pumping a coolant from the payload of the spacecraft to the KNU reactor, for example water, hydrogen, eutectic sodium-potassium alloy, through gaps in the RP layers. In an emergency (stopping the pumping of the coolant), by pumping a light component of the RP (liquid metal, lithium) through gaps between the RP layers and a special cooling system of the KNU reactor.

Brief description of the drawings

Fig. 1 shows a diagram of the longitudinal section of the radiation protection:

1 - heavy metal RZ container with a plate heat exchanger inside;

2 - layer of boron-containing material;

3 - corrugated plates made of heavy metal;

4 - gaps filled with light metal (shaded);

5 - light (liquid metal) metal;

6 - coolant of the KYAU;

Fig. 2 shows a hydraulic diagram of the movement of liquids in radiation protection, where the positions indicate:

5 - light (liquid metal) metal;

6 - coolant of the nuclear reactor.

7 - KNU reactor

8 - spacecraft (payload)

Implementation of the invention

The radiation protection of a space nuclear installation, Fig. 1, comprises a container 1 made of heavy metal, covered on the outside with a layer 2 of boron-containing material. Inside the container 1 there is a plate heat exchanger formed from successively welded and made in the form of corrugated plates layers of a material 3 that attenuates gamma quanta and neutron fluxes, between which gaps 4 are formed, filled on one side of the corrugated plates with a layer of neutron-absorbing material 5, and on the other side with a coolant CNAU 6.

The container 1 made of heavy metal can be made, for example, of niobium or uranium-238.

Layer 2 of boron-containing material can be made, for example, from boron carbide.

The material 3, which weakens the flow of quanta and neutrons, can be made of a heavy metal selected from niobium or uranium 238.

The layers of neutron-absorbing material 5 can be made of a light liquid metal, such as lithium.

The gaps 4 in each layer between the plates 3 are selected so that the mass of the light liquid metal, for example lithium, is 2 times less than the mass of the plates that make up the layers 3 of the heavy metal.

The mass of the layer of boron-containing coating 2 is selected based on the condition of the boron content by mass in an amount of at least 2% of the mass of the structural material (heavy metal).

The hydraulic diagram of the movement of liquids in the radiation protection is shown in Fig. 2, and is made as a plate heat exchanger for cooling the radiation protection and heating the coolant entering the KNU reactor.

The sequential alternation of the materials of the plates 3 and the liquids 5 and 6 increases the efficiency of the radiation protection compared to the prototype of the monoblock design of the reactor protection system. The cooling of the radiation protection system occurs due to the pumping of the coolant 6, and in an emergency, the liquid metal 5, which ensures a lower temperature inside the reactor protection system compared to the prototype and, consequently, the strength and durability of the radiation protection system of the high-flux reactor 7.

Permissible radiation loads on the electronic equipment of a spacecraft are:

- absorbed dose of *γ-radiation 5*10 ⁵ rad;

- fast neutron fluence (E>0.1 MeV) 1012 neutrons/cm2.

The neutron fluence in the KNU reactor is estimated at 10 ¹⁹ neutrons/cm ² and higher. The dose of *γ-radiation depends on the energy output of the KNU reactor and is 5*10 ⁸ rad and higher. /Manned expedition to Mars, edited by A.S. Koroteev, 2006, p. 135./

Description of the device operation

Example

As comparative neutron-physical calculations of the RP showed, the most promising results were demonstrated by the following materials: Nb - as a heavy and structural metal; Li - as a light metal; B ₄ C (boron carbide) - as a boron-containing coating material for the RP.

The results of neutron-physical calculations for the constructive conical shape of the prototype and this proposal are presented in the table. The calculations were performed for reactor 7 with a neutron flux in the center of the active zone of 10 ¹⁹ n/cm ² , and in front of the reactor core 10 ¹⁷ n/cm ² . For comparison, the authors of the proposed in this patent reactor core also provided a calculation of radiation protection based on zirconium hydride, which has a higher thermal stability, compared to lithium hydride (up to 800 ° C), with an additional structural element in the form of disks made of heavy metal between the reactor and the zirconium hydride block. / Mechanical Engineering. Encyclopedia. Editor-in-Chief, Academician of the Russian Academy of Sciences K.V. Frolov. Section IV. Calculation and Design of Machines. Volume IV-25. Mechanical Engineering of Nuclear Technology. Book 2. Volume Editor, Doctor of Technical Sciences E.O. Adamov. Moscow "Mashinostroenie" 2005. p. 527./

Calculations have shown that under identical design conditions and the diameters of the elements of the spacecraft 8 protected from radiation, the proposed layered RP has almost the same mass as the low-temperature RP, but a significantly more heat-resistant design. This is determined by the fact that the decomposition temperature of lithium hydride in a vacuum is about 400 °C, and the corrosion resistance temperature of niobium in liquid lithium is about 1200 °C.

In addition, the thermal calculations performed confirmed the achievement of acceptable temperatures on the protection materials when pumping the coolant of the KYAU in the gaps 6 between the layers of heavy metal. In the event of stopping the pumping of the coolant, heat removal is carried out by pumping light liquid metal 5 in the gaps 4.

Thus, the proposed design of the RP, meeting the conditions of the efficiency of attenuation of radiation flows, provides a neutron fluence of 10 n/cm on the payload, and a gamma radiation dose of less than 1x10 ⁵ rad, and allows obtaining minimum mass characteristics and maximum thermal stability in a vacuum. An additional function of the RP will be heating the coolant 6 of the CN before feeding it to the reactor 7 to increase the efficiency of the CN.

The body of the proposed RZ can be manufactured not only in the form of a cylinder, as shown in Fig. 1, but also in the form of a truncated cone to reduce weight if the diameters of the reactor and the payload of the spacecraft differ from each other. The truncated cone of the RZ body is located within the solid angle between the reactor cover and the flange of the protected object of the spacecraft.

Claims (5)

1. Radiation protection for a space nuclear installation, comprising a container, a layer of neutron-absorbing material and a layer of material attenuating the flow of quanta and neutrons, characterized in that a plate heat exchanger is located inside the container, formed from successively welded and corrugated plate layers of material attenuating the flow of gamma quanta and neutrons, between which gaps are formed, filled on one side of the corrugated plates with a layer of neutron-absorbing material, and on the other side with a coolant, while the outer surface of the container is covered with a layer of boron-containing material. 2. Radiation protection according to paragraph 1, characterized in that a heavy metal selected from niobium or uranium 238 is used as the material attenuating the flow of quanta and neutrons, a light liquid metal selected from lithium is used as the neutron-absorbing material, and, for example, boron carbide is used as the boron-containing material. 3. Radiation protection according to paragraph 2, characterized in that the ratio of the masses of heavy and light metals is 2:1, and the mass of the boron-containing material is not less than 2% of the mass of the heavy metal. 4. Radiation protection of a space nuclear installation according to paragraph 1, characterized in that the light liquid metal and the coolant of the nuclear reactor are pumped through the gaps between the layers of heavy metal in the radiation protection to reduce heat from the entire volume of the RP. 5. Radiation protection for a space nuclear installation according to paragraph 1, characterized in that the container made of heavy metal is made in the form of a cylinder or a truncated cone.