RU2070751C1 - Loop device for testing thermionic power-generating assemblies - Google Patents

Abstract

FIELD: thermionic energy conversion. SUBSTANCE: gas-control clearance in cesium channel near boundary of active part of power-generating assembly is profiled. EFFECT: provision for eliminating formation of additional cesium steam source (false thermostat). 1 dwg

Description

 The invention relates to a thermionic method of converting thermal energy into electrical and reactor thermophysics and can be used in laboratory and reactor studies of thermionic energy converters (TEC), thermionic and other fuel elements.

 Reactor tests of fuel elements, including thermionic power generating assemblies (EHS), are the most important stage in the development of the reactor and power plant. Such tests are carried out in research nuclear reactors (NR) using special loop devices (PU), often called loop channels (PC).

 Known PCs for reactor tests of EHS (Design and testing of thermionic fuel elements. V. V. Sinyavsky and other Atomizdat, 1981, pp. 24-28). The main purpose of the PC is to ensure close to the operating conditions of the EHS test conditions (heat dissipation, electrode temperatures, cesium vapor pressures, etc.). From this point of view, the following characteristic systems can be distinguished in a PC: ensuring energy release, heat removal, and temperature control; providing parameters of the interelectrode medium; output of electrical energy; monitoring and measuring the characteristics of EHS and PC systems.

 As a prototype we take a specific PU for testing the EHS of the Topaz reactor in the active zone of the first nuclear power plant (ibid., Pp. 27-28, Fig. 2.10).

 PU consists of a housing, inside of which there is a heat-discharge system (STS) cooled by the reactor coolant (water), made with the possibility of installing an EHS inside it. The STS, in turn, contains a temperature control system, which is a small gap (fractions of a millimeter), which can be evacuated or filled with gas (gas mixture). The collector temperature is controlled by changing the gas pressure or the ratio of the gas components in this gap. Current leads are isolated from the mass and removed from the cesium space through vacuum-tight metal-ceramic nodes. The reliability of the operation of such nodes is increased by creating around them from the outside a safety forevacuum or high vacuum cavity. The temperature conditions of the PU units are maintained either with the help of special built-in electric heaters, or due to radiation heat generation in the materials of these units.

 The weakest node of such a PC is the portion of the heat-release system near the boundary of the active (heat-generating) part of the EHS and its current output. This is due to the fact that at this place there is a sharp change in the density of the heat flux passing through the STS gas gap, and therefore, the temperature difference on it, all other things being equal, is proportional to the passing heat flux. This difference is especially significant when testing energetically stressed EHS. Since the STS is cooled by the reactor coolant (water) at approximately the same temperature along the entire PU, a significant difference in the temperature difference across the STS gas gap leads to a sharp decrease in the temperature of the inner wall of the cesium path near the boundary of the active part of the EHS current output. As a result, a section of the tract with a temperature below the temperature of the cesium vapor source may appear. The result is known - the formation of a “false” thermostat with the inability to continue normal test conditions. Such a case is considered in detail in the book of V.V. Sinyavsky "Methods for determining the characteristics of thermionic fuel elements", M. Energoatomizdat, 1990, p. 144.145, fig. 5-I. Therefore, when designing PU, the task is to prevent the temperature of the tract from falling below the temperature of the cesium vapor source.

, (1)
где d_н.т. диаметр несущей трубки;
T $\genfrac{}{}{0ex}{}{\text{min}}{\text{cs}}$ минимально допустимая температура цезиевого тракта;
Т_в температура охлаждающего теплоносителя;
λ_г коэффициент теплопроводности газа;
g(Z) погонная мощность тепловыделения.A PU is proposed comprising a housing inside which there is a source of cesium vapor, a cesium path and cooled by the coolant of the STS research reactor, made with the possibility of placing the tested EHS with current leads inside it, and inside the STS there is a gap filled with a gas or gas mixture, characterized in that the gap made profiled, and the gap width is selected by the ratio

, (1)
where d _nt diameter of the carrier tube;
T $\genfrac{}{}{0ex}{}{\text{min}}{\text{cs}}$ minimum allowable temperature of the cesium tract;
T _{at the} temperature of the cooling fluid;
λ _{g the} coefficient of thermal conductivity of the gas;
g (Z) linear heat dissipation power.

 The drawing shows a diagram of the PU. It contains a housing 1, inside of which there is a source of cesium 2 vapor, a cesium path 3 and STS 4. Inside the STS during testing, an EHS 5 is placed, consisting of separate EGE 6, each of which contains a fuel-emitter unit 7, a collector 8, and a jumper 9 The EHS has a collector insulation 10 and a cover common to all EGEs. The extreme EGEs have current leads 12 and 13, one of which is electrically insulated from the cover 11, passes inside the cesium path 3 and is led out of the cesium path 3 from the cesium path 3 to the safety cavity 15 STS 4 and there is a gap 16, which can be evacuated or filled with gas, for example helium, of different pressure (or a mixture of gases). This gap 16, which is placed along the EHS 5 and its current leads 12 and 13, is profiled opposite current leads 12 and 13 (sections of the gap 17 and 18, respectively). Outside STS 5 is cooled by the water of the reactor 19. The loopback device is also equipped with vacuum systems, gas supply, parameter measurements and others, which are not shown in the drawing.

 The device operates as follows.

After installing PU with EHS 5 in the cell of the research reactor, its power is raised to the required level. In the interelectrode gaps 20 of the EHS 5 from the source of steam of cesium 2 serves cesium vapor at operating pressure, the saturation temperature of which is equal to T _cs .

In the gap 16,17 and 18 serves gas with a pressure of P _g . Heat is generated in the fuel of unit 7, part of which is converted into electricity, and the non-converted part (≈ 90%) goes to the collector 8 and then passes through the gap 16 and is discharged to the coolant 19. As a result of the temperature difference in the gap 16, the collector temperature T _c ≥ T _cs . Through sections 17 and 18 of the gap along the current leads, the heat flux is much less (than heat generation due to fission of uranium nuclei). However, due to the profiling of the gap in sections 17 and 18, the temperature of the path inside which cesium vapor is located is higher than T _cs .

 Consider the system of heat balance equations for the PU section near the border of the fuel part of the EHS and the current output.

For radial heat transfer, the linear heat release density in the current output g (Z) will be the same (with some error), in the gap between the current output and the carrier tube (g ₁ ), in the carrier tube (g ₂ ), in the helium gap, which we need profile (g ₃ ), in the PC case (g ₄ ) and in the section the case the cooling medium (g _{5, the} value of g (Z) is defined as
q (z) = q _j + q _γ (2)
where g _j joule heat
q _γ heat release from g-capture in the material of the current output.

. (4)
Принимая значение температуры корпуса Т_к равным температуре охлаждающего теплоносителя T_в, а значение T $\genfrac{}{}{0ex}{}{\text{min}}{\text{cs}}$ как минимально допустимое значение температуры насыщения пара цезия при соответствующем давлении из (4), получим (1).With a slight error
g (Z) = g ₁ = g ₂ = g ₃ = g ₄ = g ₅ . (3)
Considering that we are not interested in the temperature difference between the current output and the carrier tube and the main temperature difference will be in the gas-controlled gap, we rewrite equation (3) in the form
g (Z) g ₃
or

. (4)
Taking the temperature value of the housing T _to equal the temperature of the coolant T _in , and the value of T $\genfrac{}{}{0ex}{}{\text{min}}{\text{cs}}$ as the minimum acceptable value of the saturation temperature of cesium vapor at the corresponding pressure from (4), we obtain (1).

As information confirming the effectiveness and technical feasibility of the proposed solution, we consider a typical PU for testing EHS at a current of 100 A, with an efficiency of about 10% at a temperature of cooling water of 40 ^o C and an operating pressure of cesium vapor of 4-6 mm Hg. corresponding T _cs ≈ 360 ^o C. A current output of 6 mm in diameter with a wall thickness of 1.5 mm is made of niobium, the γ-heating of which is 188 W / m. At a current of 100 A, the total linear power will be 425 W / m.

;
δ_возд/r_н.т.≥0,28.Consider 3 options for gas filling the adjustment gap: helium, a mixture of helium-nitrogen (50% to 50%) and air. The following values were obtained, respectively:
d _not / r _nt ≥ 2.63;

;
δ _air / r _nt ≥0.28.

For the latter case, at r _nt 12 mm we will have δ _air ≥ 3.36 mm. In the case of a smaller gap, condensation of cesium vapor on the inner wall of the carrier tube is possible with the formation of an additional source of cesium vapor ("false" thermostat).

 Thus, the proposed PU makes it possible to provide reliable tests of the EHS by eliminating the possibility of the formation of a “false” thermostat in the cesium path near the boundary of the active part of the EHS, where for structural and technological reasons, as a rule, it is impossible to install electric heaters of this section of the tract.

Claims (1)

A loop device for testing thermionic power generation assemblies, comprising a housing in which a cesium vapor source, a cesium path, and a heat transfer cooling system cooled by a research reactor coolant are arranged to accommodate a test thermionic emission assembly inside it with current leads, wherein the heat transfer system contains an annular gap filled with gas or a mixture of gases, characterized in that the gap is profiled, and the width of the gap opposite the current leads is selected from sheniya

where δ (Z) is the width of the annular gap filled with gas, in section Z, m;
d _nt internal diameter of the cesium tract, m;

minimum allowable temperature of the inner wall of the cesium path, K;
T _{in the} temperature of the coolant, K;
q (z) linear heat dissipation power inside the cesium path in section Z, W / m;
λ _g coefficient of thermal conductivity, gas, W / m • deg.