Device for monitoring pressure in a nuclear reactor fuel element

Abstract

The invention relates to devices for monitoring the pressure of a gas inside the sealed cladding of a fuel element and can be used, in particular, during the fabrication of fuel elements for nuclear reactor fuel assemblies. The present device for monitoring the pressure of a gas inside the sealed cladding of a nuclear reactor fuel element comprises, arranged on a fixed frame, fuel element conveying rollers with a clamping and releasing mechanism, a fuel element stopping member, a measuring unit which is disposed inside a housing and rotates relative to the longitudinal axis of a fuel element, fuel element position sensors, one of which is disposed before the measuring unit and another of which is disposed after the measuring unit, and a control and data processing system. The measuring unit comprises clamps with elastic elements for fastening and centering a fuel element, pyrometers for contactlessly measuring the temperature of the fuel element, one of which is disposed above the fuel element and the other of which is disposed below the fuel element, an inductive heater for heating the fuel element, and a ventilation system for cooling the fuel element in the period between temperature measurements. The technical result of the invention is that of improving the efficiency of the fabrication process and providing more accurate measurement of the pressure of a gas inside the sealed cladding of a fuel element.

Description

[0001] NUCLEAR REACTOR FUEL PRESSURE CONTROL DEVICE

[0002] AREA OF TECHNOLOGY

[0003] The invention relates to devices for monitoring gas pressure inside the sealed shell of fuel elements (fuel rods) and, in particular, can be used in the production of fuel rods for fuel assemblies of nuclear reactors.

[0004] LEVEL OF TECHNOLOGY

[0005] To improve heat exchange between the fuel element cladding and the fuel, its internal volume is filled with an inert gas - helium - before welding the second plug. Helium has high thermal conductivity, which allows for efficient heat transfer from the fuel to the cladding and the reactor coolant. Ensuring helium pressure in the fuel elements of the fuel assembly in accordance with the documentation requirements leads to equalization of thermal fields and reduces the likelihood of failures and emergency situations. High coolant pressure can lead to mechanical damage to the fuel element cladding in the compensation volume zone; helium pressure inside the fuel element helps prevent such accidents.

[0006] In order to ensure a high-quality fuel element manufacturing process, it is necessary to monitor the absolute gas pressure inside the sealed fuel element shells in automated production lines to avoid deviations from the specified parameters. In addition, it became necessary to monitor the absolute gas pressure in the fuel elements using automated acceptance of products from the production line units and a contactless method of measuring the gas pressure in order to exclude damage to the fuel element shell. A device for monitoring the gas pressure in a fuel element (FE) of a nuclear reactor is known, which contains a ring inductive heater (inductor), temperature sensors located on one side of the heater at a distance close to the diameter of the FE, on opposite generatrices of the FE shell coaxially perpendicular to the FE axis.The device additionally includes heat-insulating pads between the temperature sensors in the thermal contact zone; the sensors have metal shoes in the form of rectangular copper plates bent along the radius of the surface generatrix of the fuel element shell, covered with an electrically insulating heat-conducting film, and elastic (e.g. rubber) couplings; there is also a device for rotating the fuel element by 180° relative to its longitudinal axis together with the inductor, sensors and heat-insulating pads (RU 2399970, published 20.09.2010).

[0007] The disadvantage of this device is the use of heat-insulating pads between the temperature sensors in the thermal contact zone and the metal shoes, which leads to a significant delay in heat transfer from the fuel element to the sensors and errors in temperature measurement due to the high heat capacity of the elements used.

[0008] The KDG-VVER gas pressure monitoring unit is known, which contains two replaceable measuring heads designed to monitor the gas pressure in fuel rods, metal collet clamps of the fuel rod cladding, an induction heating unit, temperature sensors, a motor for rotating the measuring heads, panels used for convenient dismantling and mounting of replaceable measuring heads, an electropneumatic automation unit, and an industrial computer. The operating principle of the unit is based on the excitation of convective gas motion in the product and measuring the increment of the cladding temperature. Convective gas motion in the fuel rod is created by heating the annular region of the cladding in the area of ​​the compensation volume. The increment of the cladding temperature is converted into a change in the resistance of two thermistors (Operating Manual 2309-0048 RE, 2012). The disadvantage of this unit is the additional installation work required to replace one type of measuring head with another type.Another disadvantage is the use of resistance thermometers placed in glass shells, which have constant contact with the fuel element housing, which increases the error in measuring the fuel element shell temperature.

[0009] A method is known for monitoring gas pressure in a fuel element of a nuclear reactor, in which the fuel element is placed horizontally, inserted into a ring induction heater, a thermal pulse is generated that excites a convective flow of gas in the fuel element, the change in temperature is measured by temperature sensors pressed against the shell, and the gas pressure is calculated based on the magnitude of the change in temperature.Before measurements, shoes and couplings are installed on the sensors, the sensors are pressed to the casing opposite to each other, one from above, the other from below, heat-insulating pads are installed between the sensors and the temperature difference shown by the sensors is measured, then a thermal pulse is applied and after a certain time tl the temperature difference is measured again, after which the fuel element is turned together with the pads, sensors and induction heater by an angle of 180° and after the turn the temperature difference is measured after a certain time t2, then a second thermal pulse is applied and the temperature difference is measured after a time tl, then the fuel element is turned together with the pads, temperature sensors and induction heater by an angle of 180° back to the original position, the temperature difference is measured again after a time t2, the cycle is repeated several times, after which the obtained results are mathematically processed, as a result of which the value of the gas pressure inside the fuel element is determined (RU 2408098, published 27.12.2010 G.).

[0010] The disadvantage of this method is that the temperature is measured by temperature sensors pressed against the shell, which can lead to gradual heating of the shoes and couplings installed on the sensors due to the heat capacity of the materials during the cyclic supply of thermal pulses to the fuel element shell and, consequently, to an increase in the error in measuring the gas pressure.

[0011] A method is known for monitoring gas pressure in a fuel element of a nuclear reactor, which consists in applying a thermal pulse to the fuel element cladding, exciting a convective gas flow, and using sensors, measuring the cladding temperature increment corresponding to the convective component of heat transfer in the region of developed convective flow of gas filling the fuel element, by which the gas pressure is determined. Additionally, the cladding heating temperature is measured simultaneously with the measurement of the cladding temperature increment corresponding to the convective component of heat transfer, wherein both measurements are performed by the same temperature sensors, and the value of the gas pressure is determined taking into account the correction of the measured cladding temperature increment based on the results of monitoring the cladding heating temperature (RU 2109259, published 20.04.1998).

[0012] The disadvantage of this method is the need to introduce compensating corrections to the temperature measurement due to the increment of the half-sum of the fuel element cladding temperatures due to the wear of the contact pads during industrial vibrations in production conditions.

[0013] DISCLOSURE OF INVENTION

[0014] The objective of the invention is to create a device for operational monitoring of gas pressure inside the sealed casing of a fuel element, allowing the temperature of the fuel element casing to be determined in a contactless manner to prevent damage to it.

[0015] The technical result of the invention is: increasing the efficiency of the technological process and increasing the accuracy of measuring the gas pressure inside the sealed shell of the fuel element.

[0016] The technical result is achieved by a device for monitoring the gas pressure inside the sealed shell of a nuclear reactor fuel element, which contains rollers located on a fixed frame for moving the fuel element with a compression and release mechanism, a stop for stopping the fuel element, a measuring unit located in the housing and rotating relative to the longitudinal axis of the fuel element, fuel element position sensors, one of which is located in front of the measuring unit, the other is located after the measuring unit, a control and data processing system.

[0017] In this case, the measuring unit contains clamps with elastic elements for fixing and centering the fuel element, pyrometers for contactless measurement of the fuel element temperature, one of which is located above the fuel element and the other is located under the fuel element, an inductor for heating the fuel element, and a ventilation system for cooling the fuel element in the period between temperature measurements.

[0018] The pyrometers are equipped with special glasses. The ventilation system consists of nozzles that form a directed air flow around the fuel element in the measurement zone. The measuring unit rotates relative to the longitudinal axis of the fuel element using a pneumatic rotation drive. As a control and data processing system, it contains a controller, where, according to a special algorithm, the measured temperature values ​​are converted into the value of gas pressure in the fuel element.

[0019] LIST OF DRAWINGS

[0020] The invention is explained with drawings.

[0021] Figure 1 shows the general diagram of the device.

[0022] Figure 2 shows the arrangement of optical pyrometers.

[0023] IMPLEMENTATION OF THE INVENTION

[0024] The operation of the device for monitoring the gas pressure inside the fuel element shell is based on measuring the shell temperature using non-contact optical pyrometers with the conversion of the fuel element shell temperature to the ambient temperature.

[0025] The equipped and sealed fuel element 1 arrives at the loading position in the device. At the signal from the fuel element position sensor 2, the rotating rollers 3 compress the fuel element and move it to the measuring unit 4. The fuel element moves to the stop 5. At the signal from the position sensor 6, the fuel element is fixed by centering clamps 7 with elastic elements 13, which ensure the fixation and centering of the fuel element in the measuring unit, and also prevent damage to the sealed fuel element shell. The compression rollers 3 are unclenched. Before starting the temperature determination cycles, the pyrometers determine the surface temperature of the fuel element shell at a given position through built-in special glasses 11. According to a special algorithm, the inductor 8, at the signal from the controller, heats up the annular region of the shell and measures the temperature with pyrometers 9.On command from the controller, using the pneumatic rotation drive 10, all elements of the measuring unit located in the housing are rotated by a calculated angle relative to the longitudinal axis of the fuel element, the cladding is heated and the temperature is measured again. In the intervals between measurements, according to a special algorithm, the ventilation system through the stop 5 with built-in nozzles blows on the fuel element cladding to bring its surface to the ambient temperature. The transmitted values ​​of the measured temperatures and their increments are processed in the controller according to a special algorithm. The final result of the measurement processing is accepted as the value of the absolute pressure in the fuel element, registered and displayed on the controller operator panel. Upon completion of the measurement, on command from the controller, the centering clamps 7 move apart and the crimping rollers 3 move the fuel element to the unloading position. The fuel element that has passed the test is unloaded and the next fuel element is loaded.Fuel elements that do not meet the absolute gas pressure requirements are removed from the production flow.

[0026] Thus, the proposed device provides operational control of gas pressure inside the sealed shell of a nuclear reactor fuel element, and also increases the measurement accuracy.

Claims

CLAUSE OF THE INVENTION 1. A device for monitoring the gas pressure inside the sealed casing of a nuclear reactor fuel element, comprising rollers located on a fixed frame for moving the fuel element with a compression and release mechanism, a stop for stopping the fuel element, a measuring unit located in the housing and rotating relative to the longitudinal axis of the fuel element, fuel element position sensors, one of which is located in front of the measuring unit, the other is located after the measuring unit, a control and data processing system, wherein the measuring unit contains clamps with elastic elements for fixing and centering the fuel element, pyrometers for contactless measurement of the fuel element temperature, one of which is located above the fuel element and the other is located under the fuel element, an inductor for heating the fuel element, a ventilation system for cooling the fuel element in the period between temperature measurements, 2. The device according to item 1, characterized in that the pyrometers are equipped with special glasses.

3. The device according to item 1, characterized in that the ventilation system consists of nozzles that form a directed air flow around the fuel element in the measurement zone.

4. The device according to item 1, characterized in that the measuring unit rotates relative to the longitudinal axis of the fuel element using a pneumatic drive.

5. The device according to item 1, characterized in that as a control and data processing system, it contains a controller, where, according to a special algorithm, the measured temperature values are converted into the value of the gas pressure in the fuel element.

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