RU2399970C2 - Control device of gas pressure in fuel element of nuclear reactor - Google Patents

Abstract

FIELD: power industry.

SUBSTANCE: invention refers to control devices of gas pressure in fuel element of reactor. Device containing annular induction heater (inductor), temperature sensors located on one side of the heater at the distance close to fuel element diametre on opposite generatrixes of fuel element cover coaxially perpendicular to fuel element axis; in order to improve accuracy characteristics of pressure measurement there additionally introduced are heat-insulation patches between temperature sensors in thermal contact zone; sensors have metal shoes in the form of rectangular copper plates bent along the radius of surface generatrix of fuel element cover, covered with electrically insulating thermally conductive film, and flexible (for example rubber) couplings; there also introduced is the device of turning the fuel element through 180° relative to its longitudinal axis together with inductor, sensors and heat-insulation patches.

EFFECT: improving accuracy measurement characteristics of gas pressure inside fuel element.

Description

The invention relates to devices for non-destructive testing of gas pressure inside a fuel element (fuel element) of a nuclear reactor. The gas pressure inside the fuel rod is one of the parameters that determine the safety of nuclear reactors, and therefore must be controlled during their production. The invention can also be used to measure the gas pressure inside the sealed vessels without their depressurization.

A known method of determining the gas pressure in sealed thin-walled products, which consists in the fact that a thermal pulse is applied to the outer surface of the product shell and its temperature is measured at a distance from the point of application of the pulse [USSR Author's Certificate No. 1306295, class. G01L 11/00. 1991].

The disadvantage of this method is that the heating is carried out using an overhead heater, which does not provide the necessary reproducibility of heating the shell, and the excited convective gas flows have a low power.

A device for controlling the gas pressure in a fuel rod is known, which is taken as a prototype in which the fuel rod is horizontal, the heater is circular, its axis coinciding with the axis of the controlled fuel rod, and the sensors are located on one side of the heater, one above and the other below the axis Fuel rod and at a distance of (0.25-2) Do from the center of the ring heater, where Do is the diameter of the controlled fuel rod [USSR Author's Certificate No. 1316446, cl. G21C 17/06. 1985].

A disadvantage of the known device is that the temperature difference from the sensors, which determines the pressure, depends not only on the pressure under the shell, but also on the movement of outside air, causing temperature changes in the sections of the shell controlled by the sensors, on the change in thermal contact between the sensors and the shell, and also subject to scatter due to the statistical nature of convective gas flows.

The technical result obtained by the implementation of this invention is to improve the accuracy of the measurement of gas pressure inside the fuel rod. The specified technical result is achieved due to the fact that in the device for monitoring the gas pressure in the fuel rod of a nuclear reactor containing an annular induction heater (inductor), temperature sensors located on one side of the heater at a distance close to the diameter of the fuel rod, on the opposite forming shell of the fuel rod coaxially perpendicular to the axis of the fuel rod, heat-insulating linings between temperature sensors in the zone of thermal contact are additionally introduced, and the sensors have metal shoes in the form of rectangular honey s plates bent radially cladding surface forming a coated electrical insulating heat-conducting film, and the elastic (e.g., rubber) sleeve and has a rotation device TVEL 180 ° about its longitudinal axis together with the inductor, the sensors and the insulating plates.

Figure 1 schematically shows the proposed device for monitoring the gas pressure in the fuel rod, which includes a collet 2 for fixing the fuel rod 1, temperature sensors 3, heater (inductor) 4, insulating dielectric pads 5, rotation mechanism 6, shoes of sensors 7 and couplings 8.

The sensitive element of the temperature sensor 3 is a thermocouple junction fixed to the shoe 7 from the convex side. The concave surface of the shoe in contact with the shell is covered with an insulating heat-conducting film, which eliminates the influence of electrical noise on the measuring circuit of thermocouples.

The shoe 7 with a thermocouple is attached to the rack, with the help of which the clamp is pressed against the fuel rod shell through the coupling 8.

The device operates as follows.

Using the collet 2, the position of the fuel rod 1 relative to the inductor 4 and the sensors 3 is fixed. Simultaneously with the action of the collet, the sensors 3 are included in the heat-insulating linings 5, which exclude the influence of external air flows on the readings of the sensors, and are pressed to the fuel rod shell with a device that provides equal, high accuracy clamping force. Measure the initial temperature difference of the sections of the shell to which the sensors are pressed (V _d1 ), and the absolute temperature, which shows one of the sensors (V _t1 ).

Then, a high-frequency current is supplied briefly (about 1.0 s) from the induction heating generator to the inductor 4 and after a certain time τ1 the temperature difference (V _d2 ) and the absolute temperature, which is shown by one of the sensors (V _t2 ), are measured again. The differential difference V _dd1 = V _d2 -V _{d1 is} calculated.

Further, to compensate for the influence on the convective flows of the asymmetry of the shell and the elements inside the rotation mechanism 6, the fuel rods are rotated together with the plates 5, sensors 3 and inductor 4 through an angle of 180 °, and after rotation after a certain time τ2, the temperature difference (V _d3 ) and the absolute temperature, which shows one of the sensors (V _t3 ). The differential difference V _dd2 = V _d2 -V _{d3 is} calculated.

From the induction heating generator, the high-frequency current is again briefly (approximately 1.0 s) applied to the inductor 4 and after a certain time τ1 the temperature difference (V _d4 ) and the absolute temperature, which is indicated by one of the sensors (V _t4 ), are measured again. The differential difference V _dd3 = V _d3 -V _{d4 is} calculated. The rotation mechanism 6 rotates the fuel rod together with the plates 5, sensors 3 and inductor 4 180 ° back to its original position, again after time τ2 the temperature difference (V _d5 ) and the absolute temperature, which is shown by one of the sensors (V _t5 ), are measured. The differential difference V _dd4 = V _d5 -V _{d4 is} calculated.

Then, to reduce the scatter in the values of the differential temperature difference of the cladding sections due to the statistical nature of the convective gas flows inside the fuel rod, this cycle of operations is repeated, after which the sum of the differential values of the temperature difference of the cladding sections Vdr = ΣVddi and the absolute change in the shell temperature dV _e = V _tk -V _t1 .

The gas pressure in the fuel rod is determined by the formula:

P = [A · ln (Vdr · (C / dV _e )) - B] · 0.1 (MPa),

where A, B, C are calibration coefficients, the value of which is set during calibration for a specific type of fuel elements.

Experimental studies conducted on the proposed device, confirmed the effectiveness of the claimed technical solutions and ensured a decrease in measurement error by 1.5-2 times. Typical dependences V _d (curve 2), V _t (curve 1) obtained during pressure control are presented in FIG. 2.

These distinctive features in the proposed functional-structural unity are necessary and sufficient to ensure the claimed technical result.

Claims (1)

A device for monitoring the gas pressure in a fuel element (fuel element) of a nuclear reactor, comprising an annular induction heater (inductor), temperature sensors located on one side of the heater at a distance close to the diameter of the fuel element, on the opposite forming shells of the fuel element coaxially perpendicular to the axis of the fuel element, characterized in that heat-insulating linings between temperature sensors in the zone of thermal contact are additionally introduced into the device, the sensors have metal shoes in the form of rectangular copper plates astin, bent along the radius of the surface forming shell of the fuel rod, covered with an insulating heat-conducting film, and elastic (e.g. rubber) couplings, and there is also a device for turning the fuel rod 180 ° relative to its longitudinal axis along with an inductor, sensors and heat-insulating plates.

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