RU2084044C1 - Thermal-emission converting reactor - Google Patents

Abstract

FIELD: nuclear power engineering. SUBSTANCE: device has core which is designed as set of thermal-emission electric-current generating channels and booster heat elements, which have system of heat- transmitting bridges which are located between fuel core and jacket of booster heat element. EFFECT: increased power. 6 cl, 9 dwg

Description

 The invention relates to energy with thermionic conversion of thermal energy into electrical energy and can be used to create thermionic nuclear power plants (NPPs) mainly for space purposes.

 In a thermionic converter reactor (TRP), both the generation of thermal energy during the fission of uranium nuclei and its direct conversion into electrical energy occur.

 The unit cell of the TRP is an electricity generating element (EGE), and the assembly unit is an electricity generating channel (EGE), which usually consists of series-connected EGE. The most widespread EGE and, accordingly, EGC coaxial type. In order to obtain the minimum TRP size and maximize the use of the core volume (ac) for the placement of EGCs and thus obtain the maximum electric power removed from the ac unit TRP, they use fast neutron reactors, where no moderator. However, the requirements of the minimum masses of a space nuclear power plant lead to the need for a further decrease in the volume of a.s. TRP, which is achieved by replacing part of the EGC with booster fuel rods.

 In Russia and in the USA [1, 2], studies were conducted on the development of nuclear power plants with an electric power of 25,250 kW for space stations rigidly mounted on a ship or connected to it by flexible communications. The peculiarity of these installations is that the number of EGCs in a.z. TRP is less than that required for nuclear criticality. Criticality is achieved through the use of booster fuel rods by replacing a part of the EGC or adding to the gas station. TRP booster fuel rods.

 Space TRP is characterized by the requirements of high specific energy-mass characteristics and the long operating time of the TRP in the forced mode, which can be achieved for a year or more. For such TRP, the temperature of the coolant, the cooling shell of the EGC and booster fuel rods can reach 1300 K or more. The temperature in the fuel material (TM) of the booster fuel rod will be even higher and depends on the thermophysical characteristics of the TM, the design features of the fuel rods and the modes of operation of the TRP. High values of heat density and temperature lead to intensive release of gaseous fission products (GPA) from HM. Isolation of a part of the GPA from a fuel cell leads to an increase in gas pressure inside the fuel cladding and can lead to its destruction. This circumstance requires the design of the booster fuel rod not only to satisfy the required critical parameters of the TRP, but also to have high resource life, which can be achieved by moving the GPA beyond the limits of the fuel rod and reducing the load on the cladding of the booster fuel rod from the swelling TM.

 The closest to the invention in technical essence is the TRP, the active zone of which consists of EGCs, some of which are replaced by booster fuel rods.

 The shell of the booster fuel rod experiences significant loads not only from the GPA emerging from the TM, but also from the mechanical contact of the interaction between the TM and the shell due to an increase in the diameter of the fuel core as a result of thermal expansion and radiation swelling. An increase in the diametrical gap between the fuel element and the cladding of the fuel element increases the resistance of the cladding of the fuel element, but it is limited by overheating of the fuel center. During operation, the resulting radial cracks in the coldest peripheral zones of the fuel expand. If the adhesion (friction) force between the cladding of the booster fuel element and the TM is sufficient, then a local deformation of the cladding occurs in the zones where radial cracks are located. During cyclic changes in power (starting and stopping the TRP), these voltages are not completely relaxed, and repetition of cycles leads to the destruction of the cladding of a fuel rod.

 The gap between the fuel element and the cladding of the booster fuel rod exerts strong thermal resistance to the heat flux coming from the fuel element to the cladding and thus leads to a significant jump in temperature in the fuel element.

 For oxide fuel, this can lead to a sharp increase in the mass transfer of HM from the heated zones and its condensation on the relatively cold cladding of the booster fuel element. Radial mass transfer can lead to a decrease in the gap between the core of TM and the cladding of the booster fuel rod until it disappears completely. Moreover, in the TM layer condensed onto the cladding, the temperature and, accordingly, its ductility drop sharply, which causes high stresses and deformation of the cladding of the booster fuel element.

Carbide-nitride fuel is more “hard” compared to oxide fuel, since it has higher thermal conductivity and correspondingly lower temperatures in HM. Under the conditions of high thermal loads occurring in booster fuel rods of TRP with fast neutrons, this circumstance leads to an adverse effect of the TM on the cladding. The core cracks into several segments. The segments wedged by the resulting crumbs are tightly pressed against the shell and, upon further swelling, cause local deformation in it, which leads to destruction [5]
The technical result achieved by using the invention is to increase the operability of the TRP by increasing the service life of the booster fuel rods by reducing the load on the cladding of the booster fuel rod due to thermal expansion and radiation swelling of the TM.

 The indicated technical result is achieved in a TRP containing an active zone composed of thermionic electricity generating channels and booster fuel elements having a gap between the fuel material and the cladding of the booster fuel element, an elastic system of heat-transfer bridges is introduced into the gap between the fuel material and the surface of the cladding of the booster fuel element.

 The system of heat transfer bridges is made of refractory metal or an alloy based on refractory metal.

 Tungsten, molybdenum, or alloys based on them are used as refractory metal.

 The system of heat transfer bridges can be made in the form of a perforated thin-walled cylindrical shell, covering the fuel material, cut along a generatrix and twisted into an overlap, on the outside of which, in the plane passing through the axis of the cylindrical shell, thin-walled plates connected along the generators of the cylindrical shell are located, the width of which exceeds the gap between the fuel material and the cladding of the booster fuel element.

 The system of heat transfer bridges can be made in the form of a grid twisted along a cylindrical surface and covering the fuel material, humiliated attached to it by radially directed segments of a thin wire, the length of which exceeds the gap between the fuel material and the shell of the booster fuel rod.

 The system of heat transfer bridges can be made in the form of an entangled system of thin wire filling the gap between the fuel material and the shell of the booster fuel element.

The proposal to implement a system of heat transfer bridges made of refractory metals W and Mo or alloys based on them appeared because these metals successfully combine the following important properties necessary for high efficiency and reliability of TRP (especially for a fast reactor):
1) high melting point;
2) high thermal conductivity;
3) good compatibility with TM in the considered temperature mode;
4) a low capture cross section (especially for Mo).

 The proposal to implement a system of heat transfer bridges in the form of a perforated thin-walled cylindrical shell cut along a generatrix, or in the form of a mesh does not prevent uniform swelling of the TM and the free exit of the GPA from the TM.

 In the drawing of FIG. 1 shows a structural diagram of the proposed TRP; in FIG. 2 structural diagram of the TRP booster fuel rod; in FIG. 3, 4, 5, 6, 7, 8, 9 detailing of individual nodes of booster fuel elements.

 TRP 1 contains an active zone 2, which is composed of EGC 3 and booster fuel rods 4. Outside 2, a lateral reflector 5 and end reflectors 6, 7 are placed. In the lateral reflector 5 there are placed CPS bodies 8, for example, in the form of rotary cylinders with neutron absorbing inserts 9. In FIG. 1 also shows tubes 10 for outputting the GPA to the switching chamber 11 of the TRP 1 and further to the reservoir-settling tank of the GPA 12. Booster fuel rods 4 (Fig. 2) contain a cladding 13 enclosing TM 14 with a gap 15 filled with a system of heat transfer bridges, shown in detail in FIG. 3, 4, 5, 6, 7, 8, 9.

 In FIG. 3, 8, the system of heat transfer bridges is made in the form of a perforated thin-walled cylindrical shell 16, cut along a generatrix and lap-twisted, as shown in FIG. 3. Thin-walled plates 17 connected to the shell 16 are located along the generators.

 In FIG. 4, 5, 9, the design of the heat transfer bridges is made in the form of a grid 18, twisted along a cylindrical surface and humbled by pieces of wire 19 radially attached to it.

 In FIG. 6, 7, the heat transfer bridges are made in the form of a tangled thin wire 20 filling the gap 15.

 Thermionic reactor converter operates as follows.

 After the assembly of the TRP 1 and its connection to all NPP systems, the necessary checks are carried out and, in space use, the TRP 1 as part of the NPP is put into space in a radiation-safe orbit.

 At the command of the Earth, the TRP 1 is automatically launched by turning the BPS bodies 8 located in the side reflector 5 with absorbing inserts 9 from the core 2. Upon reaching the criticality of the TRP 1, heat begins to be generated in the fuel material of the EGC 3 and booster fuel rods 4. The level of thermal power rises to the working one.

As a result of fission of the nuclei of U ²³⁵ , fission products are formed. A part of the gaseous fission products (the main volume of the GPA is krypton and xenon) is released from the TM 14 and enters the gap 15 formed by the TM 14 and the shell 13, and then through the tubes 10 it is discharged into the switching chamber 11 of the TRP 1, from where the GPA enters the settling tank 12. The remainder of the fission products is involved in the swelling of TM.

 In thermionic EGC 3, part of the thermal energy is directly converted into electricity, which is supplied to the consumer. The unconverted part of the heat of the EGC 3 and the heat of the booster fuel rods 4 are removed by the nuclear coolant carrier and discharged into space by radiation.

 Moreover, the thermal energy released in the TM 14 of the booster fuel element 4 is transmitted through a system of heat transfer bridges (Fig. 3, 4, 5, 6, 7, 8, 9) to the shell 13, cooled by the coolant of the nuclear power unit.

 As shown in FIG. 3, 8, thermal energy from ТМ 14 through perforated thin-walled shells 16, through thin-walled plates 17 enters the cladding 13 of the booster fuel rod 4 and then to the coolant of the nuclear power plant. Under the action of swelling TM 14, the lapped perforated shell 16 is slightly untwisted, not preventing the increase in the volume of TM 14. Thin-walled plates 17 made in the form of a foil are deformed without exerting noticeable force on the shell of the booster fuel rod 13. GPA exiting TM 14 through holes in the shell 16 freely enter the gap 15 and then through the tubes 10 into the switching chamber 11 of the TRP 1, from where the GPA enter the settling tank 12.

 As shown in FIG. 4, 5, 9, the thermal energy from the TM 14 along the grid 18 and the segments of the thin wire 19 falls on the shell 13 of the booster fuel rod 4 and then the heat carrier of the nuclear power plant is discharged into space by radiation. The grid 18 and pieces of thin wire 18 form an elastic system of heat transfer bridges that does not prevent the swelling of TM 14 and the GPA exit into the gap 15 and beyond beyond the TRP 1 into the settling tank 12.

 As shown in FIG. 6, 7, the thermal energy from the TM through a tangled thin wire 20 filling the gap 15 is transferred to the cladding 13 of the booster fuel element 4 and then is discharged into space using the nuclear power carrier. An elastic system of heat transfer bridges, in the form of a tangled wire 20, does not prevent the swelling of ТМ 14 and the GPA exit into the gap 15 and further from the booster fuel rod 4 through tubes 10 outside the TRP 1 to the settling tank 12.

As preliminary estimates show, the proposal to install an elastic system of heat transfer bridges in the booster fuel rods allows increasing the life and reliability of the thermionic converter reactor due to:
1) lowering the temperature in the fuel material of the TRP booster fuel rods;
2) a sharp slowdown in the process of "evaporation-condensation" of the fuel material in the booster fuel rods TRP;
3) a more stable open porosity in the TM, contributing to the unhindered exit of the GPA from the booster fuel rod;
4) prevent contact of the swelling TM with the cladding of the booster fuel element.

Claims (6)

 1. Thermionic reactor-converter containing an active zone composed of thermionic electricity generating channels and booster fuel elements having a gap between the fuel material and the cladding of the booster fuel element, characterized in that an elastic system of heat transfer bridges is introduced into the gap between the fuel material and the surface of the cladding of the booster fuel element.  2. The reactor Converter according to claim 1, characterized in that the system of heat transfer bridges is made of refractory metal or an alloy based on refractory metal.  3. The reactor-converter according to claim 2, characterized in that tungsten, molybdenum or alloys based on them are used as refractory metal.  4. The reactor-converter according to claim 1, characterized in that the heat transfer bridge system is made in the form of a perforated thin-walled cylindrical shell, covering the fuel material, cut along the generatrix and twisted overlap, on the outside of which are located in a plane passing through the axis of the cylindrical shell Thin-walled plates connected along the generatrices of the cylindrical shell, the width of which exceeds the gap between the fuel material and the cladding of the booster fuel element.  5. The reactor Converter according to claim 1, characterized in that the heat transfer bridge system is made in the form of a grid twisted along a cylindrical surface and covering the fuel material, humiliated attached to it by radially directed pieces of thin wire, the length of which exceeds the gap between the fuel material and a booster fuel cladding.  6. The converter reactor according to claim 1, characterized in that the heat transfer bridge system is made in the form of a tangled thin wire system filling the gap between the fuel material and the booster fuel cladding.

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