FR2520505A1 - ULTRASONIC TEMPERATURE SENSOR FOR MEASURING VERY HIGH TEMPERATURES - Google Patents

Abstract

THIS SENSOR CONTAINS A PROBE FORMED WITH A WIRE AND A PROTECTIVE SHEATH SURROUNDING THE PROBE AND SHAPED AS A TUBE. ACCORDING TO THE INVENTION, THE WIRELESS SENSOR 9 IS BRIEFLY MOVED LONGITUDINALLY FROM ITS REST POSITION AT REGULAR INTERVALS AND AGAINST THE FORCE OF A COMPRESSION SPRING 17. THE BONDING - NORMALLY INEVITABLE - OF THE WIRELESS SENSOR 9 TO ITS SLEEVE 6 IS THUS. PREVENT OR SUPPRESSED, EVEN AT HIGH TEMPERATURES. THE INVENTION IS APPLICABLE TO MEASURING TEMPERATURES IN NUCLEAR REACTORS.

Description

The invention relates to an ultrasonic temperature sensor, comprising a

  probe formed of a wire extended in length,

  a sheath formed of a tube surrounding the probe and a magnetic system

  by means of which, on the one hand, ultrasonic pulses are applied to one end of the filiform probe, on the other hand

  ultrasound echoes are transmitted from the

  positive electronic operating, with use of delay time between echoes of defined reflection points of the

  probe as a measure of the temperature to be measured.

  Ultrasonic thermometers are used to measure very high temperatures, above 15,000 C, such as exist for example in the fuel columns of nuclear reactors, such thermometers are known from the United States patent 4 020 692 for example The probe formed of a wire is protected against the environment by a protective tube or sheath At the temperatures at which these devices must operate, it can occur material transformations and diffusion phenomena that lead to the bonding of the filiform probe to its sheath and thus affect the propagation of the ultrasonic signal on the filiform probe The parasitic echoes that result can be superimposed on the measurement signals and

  compromising the exploitation of these In the past, this col-

  In the patent cited above, it was recommended that the thermometer be made unusable and replaced at elevated temperatures, so that it is recommended in the patent cited above to place spacers between the filiform probe and the sheath. where a signal reflection must take place or a parasitic echo may be tolerated Uncertainty about what goes to where the bonding may take place is thus suppressed However, such a provision is only

  applicable in a limited way because there is not always enough

  locations on the filiform probe o an echo can be tolerated.

  In addition, the spacers specifically favor unwanted gluing

of the probe in the sheath.

  Another solution to this problem is described in German patent application DE-OS 27 35 908. In this case, the thermal expansion of the filiform probe and the sheath is used to produce a relative movement relative to significant temperature variations between them. relative movements suppress the collages that may have occurred and thus make the thermometer usable again This process can not however be applied

  only if the temperature in the environment of the heat

  meter can be changed at regular intervals In the case of a thermometer for a nuclear fuel rod, such a change in temperature occurs only in case of shutdown

nuclear reactor.

  The aim of the invention is to indicate an ultrasonic thermometer

  sounds of the type indicated at the beginning but which prevents or suppresses

  between the sheath and the probe without the need for

  furrows or sudden changes in temperature.

  According to the invention, the wire forming the probe is mechanically lengthened backwards through the magnetic system and it ends on a moving part of a mechanical pulse generator which deliversperiodically thrust pulses having the effect that the filiform probe is briefly moved longitudinally from

  its rest position against the force of a compression spring.

  Longitudinal displacements of the probe are preferably carried out outside the measurement cycles and at regular intervals in time. Thus, the bridges that may have formed between the filiform probe and the sheath are broken rapidly or are punctured.

to form.

  Other features and advantages of the invention

  will be clearer from the following description of a

  preferred embodiment but not limiting, as well as the single figure of the accompanying drawing, which is an axial section of a

thermometer according to the invention.

  The drawing represents a fuel column of a

  nuclear reactor> consisting of a stack of cylindrical pellets

  jets of fuel 1 of circular section in a compression tube

  This tube has a 3 axis oriented vertically and is

  closed at the bottom by a terminal cap 4 At the top, the compression tube

  2 is welded to a plug 5 in which a tube 6 forming the sheath of the probe is fixedly mounted, coaxially, using a guide tube 7 of short length The sheath 6 passes through the entire stack of pellets and ends at a low distance

closure cap 4.

  Between the cap 5 and the highest fuel pellet 1 of the stack is a compression spring 8 which

  concentrically surrounds the guide tube 7 and allows the exchange

  height of the pellet stack as a result of changes

temperature.

  The tubular sheath 6 is traversed over its entire length.

  The wire shows constrictions where the echo is to be produced. The drawing shows only one

  only constriction 10, located just above the stack of pellets.

  The propagation time of ultrasonic pulses between this con-

  triction 10 and the lower end of the filiform probe allows

  to determine the average temperature of the pellet stack.

  Above the cap 5, the wire forming the transducer

  a magnetic system which is constituted by a permanent magnet 11 and an electromagnet 12. The coil of the latter is concentric with the axis 3. On the one hand, it receives the ultrasonic pulses which must travel through the filiform probe and serves measurement coil for the signals represented by the echoes The electronic operating circuit and the pulse generator have not been shown for simplicity They are connected to the coil by a connecting cable 13 The filiform probe is

  magnetostrictive material in the region of the magnetic system.

  The upper end of the filiform probe 9 is provided with a centering head 14 which is arranged axially movable

  in a tube 15 extending the fuel tube 2 upwards -

  which forms the thermometer body The centering head 14 constitutes at the same time the membrane or the moving part of a bellows 16 A spring 17 is supported on one side on the electromagnet 12 and on the other

  side on the centering head 14, which is pressed by this res-

  fate against stops 18 provided inside the tube 15 in

the absence of other forces.

  The bellows 16 is essentially cylindrical and terminates at the top with a plug 19 fixed in the tube 15 forming the body of the thermometer. The plug 19 is traversed by a capillary tube 20 through which pressure pulses are applied during operation to the bellows 16. , so that the centering head 14 is briefly moved axially from its rest position to each pulse. The pneumatic pulses applied to the bellows 16 are thus transformed into mechanical pulses.

  thrust and / or traction on the filiform probe 9.

  The bellows 16 is not coaxially disposed in the tube 15 forming the thermometer body but in a position

  slightly off-center, in order to leave room for

  For this reason, the bellows 16 is eccentrically attached to the centered head 14.

  tube 15 is closed at the top by a cover disc 21

  poured by the Able 13 and the capillary tube 20.

  During operation, pulses of pressure

  are applied at short or long time intervals, as required, to the capillary tube 20, each time causing a short longitudinal displacement of the filiform probe 9, so that any bridges formed between the probe and the sheath 6 are destroyed. Measurements of the temperature are of course not possible during the duration of the pulses of pressure As the latter do not last long, the thermometer is nevertheless

  available practically unlimitedly.

  It is also within the scope of the invention to replace

  place the bellows by another mechanical pulse generator,

  for example by an electromagnetic system In addition, the

  the probe may also have more than one constriction 10, for example in view of the temperature profile-survey over the entire height of the reactor core As there is no support between

  the wire forming the probe and the sheath, the thermometer according to the invention

  tion provides a strong local definition of such a profile.

Claims (3)

REVENDICATI O NS   An ultrasonic temperature sensor comprising a probe (9) formed of a wire extended in length, a sheath (6) formed of a tube surrounding the probe and a magnetic system (12) by means of which, on the one hand, , ultrasonic pulses are applied to one end of the filiform probe, on the other hand, ultrasound echoes   sounds are transmitted from the probe to an electronic device for   tation, using the delay time between echoes of defined reflection points of the wave as a measure of the temperature at   characterized in that the wire forming the probe (9) is   mechanically lined backwards through the magnetic system   tick (12) and ends on a moving part (14) of a generator   mechanical pulses (16) which periodically delivers pulses   thrust forces causing the filiform probe to be brief   moved longitudinally from its resting position to the   force of a compression spring (17).   Sensor according to claim 1, characterized in that   that the mechanical pulse generator is a cylindrical bellows   drique (16) which receives pneumatic pulses through a tube (20).   3 Sensor according to claim 2, characterized in that the axis of the bellows (16) is slightly offset relative to the axis (3) of the filiform probe (9) and in that the moving part or membrane (14) bellows forms a centering head which is   centered on the axis of the filiform probe.