Control device of gas pressure in fuel element of nuclear reactor

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.

 

The invention relates to a device for non-destructive control of the gas pressure inside the fuel rod of a nuclear reactor. The gas pressure inside the fuel rod is one of the parameters determining the safety of nuclear reactors, and therefore subject to control in the manufacturing process. The invention can also be used to measure the gas pressure inside the hermetic vessel without depressurization.

There is a method of determining the gas pressure in the sealed thin-walled products, which consists in the fact that the outer sheath of the product apply a heat pulse and measure its temperature at some distance from the point of application of the pulse [USSR Author's certificate No. 1306295, CL G01L 11/00. 1991].

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

A device for monitoring gas pressure in the fuel rod, which is taken as a prototype, in which the fuel rod is horizontal, the heater is made circular and its axis coincides 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 of the fuel element and at a distance of 0.25-2)Do from the center the ring and heater, where Do is the diameter of a controlled TVEL [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 for determining the pressure depends not only on the pressure under the membrane, but also from the movement of outdoor air, causing changes in temperature plots shell, controlled by sensors, from changes in thermal contact between the sensors and the shell, and also subject to variation due to statistical nature of convective flow of gas.

The technical result obtained by the implementation of this invention is to improve the accuracy characteristics of the gas pressure inside the fuel rod. This technical result is achieved due to the fact that the pressure control device of a gas in a fuel rod of a nuclear reactor containing an annular induction coil (inductor), the temperature sensors are located on one side of the heater at a distance close to the diameter of a fuel rod, on the opposite forming a membrane of a fuel rod is aligned perpendicular to the axis of the fuel rod, added insulation pads between the temperature sensors in the area of thermal contact, and the sensors have metal shoes in the form of a rectangular copper plates bent along the radius of the surface forming the sheath of the fuel element, p is covered insulating heat-conducting film, and elastic (e.g. rubber) coupling, and a unit of rotation of the fuel rod by 180° about its longitudinal axis together with the inductor, sensors and heat-insulating lining.

Figure 1 shows schematically the proposed device for controlling gas pressure in a fuel rod, which includes the collet 2 for fixing a fuel rod 1, a temperature sensor 3, the heater (coil) 4, the insulating dielectric lining 5, the rotation mechanism 6, boots of sensors 7 and the clutch 8.

The sensitive element of the temperature sensor 3 is a thermocouple junction, attached to Shoe 7 with convex sides. The concave surface of the Shoe in contact with the shell, covered with insulating heat-conducting film, which eliminates the influence of electrical noise measuring circuit of thermocouple.

Shoe 7 with thermocouple attached to the rack, which allows the clip to the shell of the fuel rod through the sleeve 8.

The device operates as follows.

Using collets 2 fix the position of the fuel rod 1 relative to the inductor 4 and the sensor 3. Simultaneously with the action of the gripper sensors 3 are insulating plates 5, which exclude the influence of external air flows in the sensor readings, and pressed to the shell of the fuel rod device for equal, with high accuracy, the efforts of the clamp. Made in the field, and measuring the initial temperature difference plots shell, to which is pinned sensors (Vd1), and absolute temperature, which shows one of the sensors (Vt1).

Then from the generator induction heating coil 4 serves short-term (approximately 1.0) high-frequency current and over time τ1 again measure the temperature difference (Vd2and the absolute temperature, which shows one of the sensors (Vt2). Calculate the differential difference Vdd1=Vd2-Vd1.

Next, to compensate for the effect on the convective flow of the asymmetry of the shell and items within the turning mechanism 6 rotate TVEL together with lining 5, the sensors 3 and the coil 4 at an angle of 180° and after rotation through a certain time τ2 measure the temperature difference (Vd3and the absolute temperature, which shows one of the sensors (Vt3). Calculate the differential difference Vdd2=Vd2-Vd3.

From the generator induction heating inductor 4 again served briefly (approximately 1.0) high-frequency current and over time τ1 again measure the temperature difference (Vd4and the absolute temperature, which shows one of the sensors (Vt4). Calculate the differential difference Vdd3=Vd3-Vd4. The rotation mechanism 6 rotate TVEL together with lining 5, the sensors 3 and the coil 4 by 180° is mainly what about the original position, again after time τ2 measure the temperature difference (Vd5and the absolute temperature, which shows one of the sensors (Vt5). Calculate the differential difference Vdd4=Vd5-Vd4.

Then to reduce the variation differential of the temperature difference plots of the shell due to the statistical nature of convective flow of the gas inside the fuel rod this cycle of operations is repeated, and then determine the sum of the differential values of the temperature difference plots shell Vdr=ΣVddi and absolute change in the temperature of the shell dVe=Vtk-Vt1.

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

P=[A·ln(Vdr·(C/dVe))-B] ·0.1 (MPa),

where a, b, C - calibration factors, the value of which is determined during calibration for a specific type of Fuel elements.

Experimental studies conducted on the proposed device, confirmed the effectiveness of the claimed technical solution and helped reduce measurement errors in 1,5-2 times. The characteristic dependence of Vd(curve 2), Vt(curve 1), obtained by the control pressure, is presented in figure 2.

These distinctive features in the proposed functional-structural unity is necessary and sufficient to provide the stated technical result.

The control device D. the effect of gas in the fuel rod of a nuclear reactor, containing an annular induction coil (inductor), the temperature sensors are located on one side of the heater at a distance close to the diameter of a fuel rod, on the opposite forming a membrane of a fuel rod is aligned perpendicular to the axis of the fuel rod, characterized in that the device additionally introduced heat-insulating lining between the temperature sensors in the area of thermal contact, the sensors have metal shoes in the form of a rectangular copper plates bent along the radius of the surface forming the shell of a fuel rod, covered with insulating heat-conducting film, and elastic (e.g. rubber) coupling, and a unit of rotation of the fuel rod by 180° about its longitudinal axis together with inductor, sensors and heat-insulating lining.



 

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