RU2230378C2 - Thermionic conversion reactor - Google Patents

Abstract

FIELD: thermionic plants primarily for space engineering. SUBSTANCE: thermionic conversion reactor has neutron deflector; core assembled of power-generating channels with fuel elements filled with fissionable material. Power-generating channels with fuel elements disposed near deflector are filled with fissionable material based on isotopes having higher neutron breeding factor and are separated from deflector by minimum one layer of power-generating channels with fissionable material of lower breeding factor. Chosen as isotopes of higher neutron breeding factor are ²³³U, ²³⁹Pu., and ²⁴¹U. isotopes. Chosen as isotope of lower breeding factor is ²³⁵U. Proposed design ensures higher reactivity margin of reactor, heat-transfer field equalization throughout reactor core section, equalization of mean temperature of emitter cans over reactor core, and equal operating conditions for thermionic fuel elements. EFFECT: enhanced power characteristics and enlarged service life of reactor. 3 cl, 3 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 thermal energy is generated during the fission of ²³⁵ U nuclei in a fuel material (TM), and its direct conversion to electric. The unit cell of the TRP is an electricity generating element (EGE), and the assembly unit is the electricity generating channel (EGE), which usually consists of series-connected EGE. The most widespread EGE and, accordingly, EGC coaxial type. TRP are being developed on thermal, intermediate, and fast neutrons. In order to obtain the minimum TRP size and maximize the use of the core volume (a.z.) for placing an EGC and thus obtain the maximum electric power removed from a unit a.z. TRP, they use fast neutron reactors, where no moderator. Obviously, in order to ensure the same emission current density of the TRP removed from the emission surface, it is necessary that the emitter claddings of fuel elements in EGCs operate under approximately equal temperature conditions. For this, it is necessary to equalize the heat release by the volume of a.z. TRP. For reactors with a neutron reflector, there is a non-uniformity of heat release, and two maximums of heat release are observed: this is in the central part of the a.z. and a surge in heat generation at the periphery of the a.z. at the border with a reflector [1]. Physical profiling conducted to equalize the heat in the AC TRP, leads to an uneven distribution of TM in the volume of a.s. and, accordingly, to the unevenness of the load exerted on the emitter shells of fuel rods located in different places of the a.s. This is because the operating conditions of the fuel rods will be different. In fuel rods with a smaller amount of TM, the intensity of the formation of fission fragments (gaseous and solid) is lower and, accordingly, the pressure exerted by the swelling TM and fission fragments on the fuel cladding is lower. Hence, the performance of such thermionic fuel rods is higher compared to fuel rods in which there are more TMs. As studies [2, 3] show, in thermionic fuel rods with a lower TM content, this is especially true for high-temperature ventilated fuel elements with volatile TM (for example, UO ₂ ), the reliability of the removal of gaseous fission fragments beyond the fuel rod is higher. These circumstances lead to the uneven resource capacity of thermionic fuel rods in the core of the TRP. In addition, physical profiling is not always possible, especially for low-volume fast-neutron pulsed neutron diffusers. due to criticality problems, since the maximum possible amount of TM with the maximum possible enrichment for fissile material is laid in the EGC fuel rods of such TRPs.

Known TRP on fast neutrons, described in [4]. It contains a.z. and a reflector with reactor controls. In turn, A.Z. contains thermionic EGCs that provide the required value of electric power, and booster fuel elements (BEL), which are not electrically generating, but are added to the a.z. to ensure its criticality, since the volume fraction of fissile material in them is significantly higher than in EGC. BELs can be placed throughout the entire volume of a.z. EGCs and BELs contain a cooling system based on a liquid metal coolant, and BELs, in addition, can have an additional cooling system based on heat pipes. BELs, which actually contain only TM in the housing, can reduce the critical volume of a.z. and, consequently, the mass of the entire nuclear power plant. However, the introduction to a.z. BEL, in addition to lowering the efficiency of the nuclear power plant and increasing the size of the nuclear power plant due to the increase in the surface of the refrigerator-emitter, leads to an increase in the density of the critical load of TM in the TRP. This, in turn, increases the nuclear hazard in emergency situations with a launch vehicle during the launch of a spacecraft (SC) from a nuclear power plant into space.

Known thermionic reactor-converter, containing a reflector, an active zone, recruited from electricity generating channels with fuel rods filled with fuel material based on the ²³⁵ U isotope, described in [5] for nuclear power plants with an electric power level of 100 ... 150 kW. Two variants of such a TRP based on fast neutrons with a packet and monoblock core structure are considered. To ensure the adequacy of the reactivity margin for the campaign, a.z. TRP contain booster elements. The disadvantage of these options TRP is a significant unevenness of heat release in the A.Z. Thus, the average thermal power in peripheral EGCs adjacent to the reflector reaches ~ 12.6 kW (per one EGC), while the average thermal power in other EGCs is ~ 10.8 kW. As a consequence of this fact, an elevated temperature of the emitter shells in these EGCs and thus a decrease in the resource characteristics of EGCs and TRPs in general are observed. In addition, the use of BEL leads to a reduction in the total emission surface in the TRP, a decrease in the efficiency of the entire nuclear power plant, and an increase in the dimensions of the refrigerator-emitter and the nuclear power plant as a whole.

Close to the invention in technical essence can be considered TRP for the space nuclear power plant "Topaz" [6] with a useful electric power of ~ 6 kW. The TRP contains a reflector, an active zone drawn from electricity generating channels with fuel rods filled with fuel material based on the ²³⁵ U isotope. The active zone includes 5-element EGCs located in the holes of the moderator from zirconium hydride and is surrounded by a beryllium reflector. Reactor controls in the form of 12 beryllium rotary cylinders with sector neutron-absorbing boron carbide pads are located in the side reflector. The outer shells of EGCs are cooled by a heat carrier (eutectic alloy Na-K). Relatively large leakages of hydrogen from the moderator in the core, which falls into the interelectrode gaps, are observed and thereby contribute to the degradation of the electrical characteristics of the reactor, corresponding to a decrease in the initial conversion efficiency on average with a relative speed of (5-7) • 10 ^-3 % / h. In addition, a change in reactivity was noted in this TRP due to relatively large hydrogen leakages from the moderator (approximately 80-85% of the total change in reactivity). According to the results of flight tests, it was noted that the average rate of decrease in reactivity exceeded the values obtained from the corresponding ground tests.

The task is to increase the reactivity margin of the TRP, aligning the field of heat generation over the cross section of the gas station TRP, equalization of the average temperature of the emitter shells on the a.z. TRP, creation of equal conditions in the operation of a thermionic fuel rod and, thus, increase of the energy characteristics and resource of the TRP.

The task is achieved in a thermionic converter reactor containing a neutron reflector, an active zone drawn from electric generating channels with fuel rods filled with fuel material, electric generating channels with fuel rods near the reflector are filled with fuel material based on isotopes with a higher neutron reproduction coefficient and separated from the reflector by at least than a single layer of electricity generating channels with fuel material with a lower reproduction rate. The isotopes ²³³ U, ²³⁹ Pu, ²⁴¹ Pu were selected as isotopes with a higher neutron reproduction coefficient. The isotope ²³⁵ U is chosen as the isotope with a lower neutron reproduction coefficient.

The use of isotopes (U ²³³ , ²³⁹ Pu, ²⁴¹ Pu) with a higher neutron reproduction coefficient in fuel elements TM compared to TM based on isotopes with a lower neutron reproduction coefficient ( ²³⁵ U) is primarily due to the fact that it provides significantly more a high reserve of reactivity of TRP with the same proportion of fuel in the reactor [7, 8, 9, 10].

It is possible to align the heat release in the volume of a.z. TRP by varying in the fuel element the shares of TM with a higher and lower reproduction rate. Thermionic fuel rods adjacent to the reflector of at least one layer are filled with fuel material based on the ²³⁵ U isotope, the other part of the fuel rods is filled with fuel material in which the ²³⁵ U isotope is replaced in whole or in part by isotopes with a higher neutron reproduction coefficient, and the density of these isotopes in the fuel material of the fuel rods decreases, on average forming a smooth dependence, along the radius and length of the TRP active zone from the periphery to the center of the active zone, changing from the maximum value at the periphery of the active the first zone to zero in the center of the core. The arrangement of EGCs and fuel rods with TM based on isotopes with a higher neutron reproduction coefficient over the TRP active zone and the course of the change in the density of these isotopes along the radius and height of the a.s. first of all, it is explained by the curve of the distribution of heat release over the core characteristic of nuclear reactors [11].

Figure 1 shows the structural diagram of the proposed TRP. Figure 2 shows the cross section of the TRP with a monoblock structure of the active zone. Figure 3 - structural diagram of the EGC.

TRP 1 contains an active zone 2, which is composed of EGC 3, 4, a neutron reflector 5, in the lateral part of which are placed the control and protection system (CPS) 6, for example, in the form of rotary cylinders with neutron-absorbing inserts 7. EGCs 3, 4 represent serially connected assemblies of the EGE 8. The EGE 8 includes an emitter 11, a collector 12, and the emitter 11 is the sheath of the thermionic fuel rod 9, which encloses the fuel material 10. The EGC 3 with the fuel rods 9 are filled with TM based on the ²³⁵ U isotope. In the region of the active zone 2, about reflector 5, placed EGK 4 with a fuel rod 9 filled with TM based on isotopes with a higher neutron reproduction coefficient, which are separated from reflector 5 by at least one layer of EGC 3 with TM based on the ²³⁵ U isotope. Thermionic fuel rods 9 of EGC 3 adjacent to reflector 5, at least one layer are filled with TM 10 based on the ²³⁵ U isotope, for the other part of the EGC 4 fuel rods 9 are filled with TM 10 in which the ²³⁵ U isotope is replaced in whole or in part by isotopes with a higher neutron reproduction coefficient, and the density of these isotopes in the TM 10 of fuel rods 9 decreases, in average image I have a smooth dependence, changing from the maximum value at the periphery of the active zone 2 to zero in the center of the active zone 2 (in Fig. 2 this circumstance is expressed by the density of the hatching of the cross section of the EGC 4, gradually decreasing from the periphery of the a.z. 2 to its center).

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 6 located in the lateral reflector 5 with absorbing inserts 7 from the core 2. Upon reaching the criticality of the TRP 1, heat is generated in the fuel material of 10 fuel rods 9 of EGK 3 and EGK 4. Since fuel rods 9 of EGC 4 include fissile material based on isotopes with an increased neutron reproduction coefficient, compared with EGC 3, and are located in the zone of minimum heat release a.z. 2 TRP 1, which leads to equalization of heat generation along the radius of the a.s. 2, which causes uniform heating of the emitters 11 in the EGE 8. This circumstance leads to equalization of the operating conditions of the fuel rods 9 and EGE 8 throughout the TRP 1, which leads to an increase in the energy resource characteristics and efficiency of the TRP.

Thus, the proposed technical solution increases the reactivity margin of the TRP and allows you to:

to increase the electric power of the TRP, at a constant total thermal power of the TRP, due to a more uniform distribution of thermal power over the volume of the active zone of the TRP;

to obtain higher average specific energy characteristics, taken from a unit volume of the active zone of the TRP at a constant maximum temperature of the EGC emitters;

to obtain a higher efficiency of converting thermal energy into electrical energy in TRP due to a more uniform temperature distribution of the emitter shells of the EGE in TRP;

to increase the life of the TRP due to a more uniform in terms of volume AZ load distribution on the emitter cladding of EGE fuel rods from swelling fuel material;

to increase the share of structural materials, the relative share of porosity in the fuel elements of the EGE, which leads to an increase in the resource characteristics of EGC and TRP as a whole.

In addition, the use of the ²³³ U isotope instead of the ²³⁵ U isotope in a TM makes it possible not to change the physicochemical characteristics of the TM, in particular its compatibility characteristics with the material of the emitter cladding, to keep the share of the TM in the fuel rods unchanged, to achieve almost uniform thermal emission fuel rods with such nuclear profiling throughout active zone TRP.

LITERATURE

1. Samoilov A.G. Fuel elements of nuclear reactors. M .: Energoatomizdat, 1985, p. 15.

2. Kornilov V.A., Sukhov Yu.I., Yuditsky V.D. Method for calculating the temperature fields of a heterogeneous fuel core of a thermionic fuel element. Atomic Energy, 1980, Volume 49, no. 6, p. 393 and 394.

3. Kornilov V.A., Yuditsky V.D. Modeling of heat and mass transfer in the core of a thermionic fuel element. Atomic Energy, 1982, Volume 53, no. 2, p. 74-76.

4. Patent RU No. 2138096 C1. MKI H 01 J 45/00. Thermionic converter reactor. Publ. 09/20/99, Bull. No. 26.

5. Combined nuclear power plant "TEMBR" with a fast reactor neutron converter / V.I. Chitaykin, V.I. Ionkin, M.K. Ovcharenko and others // Fifth international conference "Nuclear energy in space", Sat reports./ Under the general ed. prof. I.I. Fedika, part 1. - Podolsk, Mosk. reg., 1999, p. 94.

6. The main tasks and results of flight tests of nuclear power plants under the program "Topaz" / I.P. Bogush, G.M. Gryaznov, E.E. Zhabotinsky et al. Atomic energy, vol. 70, no. 4, 1991, p. 214.

7. Handbook of Nuclear Physics./ Ed. Acad. L.A. Artsimovich. - M .: Fizmatgiz, 1963, p. 267 and 338.

8. Jacobs A., Kline D., Remick F. Fundamentals of nuclear science and reactors. - M .: Gosatomizdat, 1962, p. 61 and 188.

9. Zaimovsky A.S., Kalashnikov V.V., Golovnin I.S. Fuel elements of nuclear reactors. - M .: Gosatomizdat, 1962, p. 9.

10. Emelyanov V.S., Evstyukhin A.I. Metallurgy of nuclear fuel. - M .: Atomizdat, 1968, p. 12 and 298.

11. [1], p.16.

Claims (3)

1. Thermionic reactor-converter containing a neutron reflector, an active zone recruited from electricity generating channels with fuel rods filled with fuel material, characterized in that the electricity generating channels with fuel rods near the reflector are filled with fuel material based on isotopes with a higher neutron reproduction coefficient and separated from reflector with at least one layer of electricity generating channels with fuel material with a lower reproduction rate. 2. Thermionic reactor-converter according to claim 1, characterized in that the isotopes ²³³ U, ²³⁹ Pu, ²⁴¹ Pu are selected as isotopes with a higher neutron reproduction coefficient. 3. Thermionic reactor-converter according to claim 1, characterized in that the isotope ²³⁵ U is selected as the isotope with a lower neutron reproduction coefficient.

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