FR2466781A1 - DEVICE FOR MEASURING RADIOACTIVE PARTICLES (ISOTOPES) PRESENTED IN GASES - Google Patents

Abstract

Device for the integral measurement of radioactive isotopes and consisting of a turntable 3 driven by a control device 5 and having at least one opening 3b, 3c, 3d for housing the various filters 12, a supply container 6 for the filters which is arranged above the turntable 3, an inlet duct 7 for the gas provided on one side of the turntable 3, a detector 10 with an outlet duct for the gas provided on the other side of the turntable 3, a sheath 9 for ejecting the filters, a switching unit for stopping the control device 5 when the measuring position is reached and a limit value unit for controlling the change of the filters when a determined contamination of the latter is reached. (CF DRAWING IN BOPI)

Description

The present invention relates to a device

  for the measurement of the quantity of radioactive isotopes.

  When monitoring nuclear installations, particularly nuclear power plants, both waste water pollution and aerosol content and gas content are measured.

  rare outgoing air. It is also necessary to de-

  in addition, to detect the possible presence of radioactive iodine, since this constitutes a particular hazard

for the environment.

  During normal operation it is even

  detect concentrations of very low radioactive activity, which requires

  extremely sensitive detection. In the case of disturbance

  In addition, it must be possible to carry out

  and therefore the measurement range should cover several

  ten powers of ten. Aerosols (substances in addition to

  pension) and iodine are retained by special filters, which is why detectors measure the increase in

  the activity inside these filtering materials.

  It was found during disturbances

  have already been produced $ that the activity in the filters

  comes very important so that the range covered by the measuring device is insufficient. In this case the monitoring staff should therefore quickly replace the filters to allow integration

  perfect radioactivity escaping into the atmosphere.

  During disruptions the staff is however fully occupied by other problems which has the effect that the filters are not changed. Access to the place o

  the detectors equipped with filters are not

  is not possible or poses significant risks due to increased radioactivity. So we are

  faced with intolerable deficiencies in surveillance.

  The object of the present invention is therefore to eliminate these deficiencies and to make the measurement automatic so that it is possible to control perfectly and without

2466781 '

  handling all radioactive activities.

  These problems are solved in accordance with the

  by a measuring device which is characterized in that it comprises a turntable driven by a control device and having at least one opening for accommodating the various filters, a container

  supply for filters which is

  above the turntable, an inlet duct for the

  gas provided on one of the sides of the turntable, a detection

  with an outlet pipe for the gas provided on the

  side of the turntable, a sheath for ejecting the filters, a switching unit for stopping the control device when the measuring position is reached and a limit value unit for controlling the

  filter change when a determined contamination

born of these is reached.

  In a preferred embodiment of the invention,

  the turntable, the supply container,

  filters and the ejection duct are sealed in a pressure-tight manner which allows the

  measuring device outside the reaction chamber

  to which it is connected by a bypass duct or

  bypass to monitor the prevailing atmosphere in the

inside this enclosure.

  Various other features of the invention

  from the detailed description which follows.

  One embodiment of the subject of the invention is represented, by way of non-limiting example, to

attached drawings.

  Fig. 1 is a top view of a unit of measurement

  sure whose turntable has three positions

to house filters

  Fig. 2 is a section, on a larger scale,

  along the broken line A-B of FIG. 1.

  Fig. 3 is a top view of a turntable

  three positions for housing filters.

  Fig. 4 is a section of the turntable of the

Fig. 3.

  As is apparent from FIG. 1, a plate 2 of circular shape is fixed on a base plate 1 of

  square shape. A turntable O3 whose peripheral edge

  It is made in the form of a ring gear 3a and is housed between these two plates. A pinion 4, which is mounted on the output shaft of a driving device 5,

  meshes with the ring gear 3a. The device

  preferably consists of a motor-

  gearbox with limit switches. The turntable 3 has three circular openings 3b, 3c, 3d which

  are offset by 1200 from each other.

  A filter supply container 6 is attached to the cover plate 2 via a flange 6a above the opening 3b. A gas supply pipe 7 connected by a flange 7a to the

  source of the gas to be measured, is connected to the

  Cover 2 above the opening 3c.

  A detector is placed below the opening 3j. The outlet for the gas is provided laterally with respect to the detector and is connected by a conduit 8 and

  a flange 8a, to a vacuum generator creating a depression.

  An ejection sheath 9, extending obliquely downwardly to the right, is connected to

  the base plate 1 below the opening 3d.

  The section of fig. 2 shows the base plate 1, the cover plate 2, the turntable 3 located

  between these two plates, the ring gear 3a, the opening

  3b, 3c, 3d, the training device 5, the recess

  6 supply of filters, the flange 6a, the duct 7 with the flange 7a, the oblique sheath 9

  and detector 10. The detector is surrounded by a shield

  lead in order to shield it from parasitic rays.

  Filter elements 12, whose lower element 12a already rests in the opening 3b of the turntable 3, are stacked inside the supply container 6. Another filter element 12b rests in the opening 3c occupying the Measuring position above the sensor window 10a of the detector 10. A filter element 12c is represented in broken lines in the opening 3d just before it falls into the ejection duct 9. The plate 3 rotates around an axis 13 which is placed in the center and between the plates 1 and 2. The filter element 12b is shown in section and it is seen that it is composed of a carrier ring 121 whose underside is strongly rounded, of the Filter element proper 122 and mesh plates 123, 124 to absorb the forces produced by the gas stream. During the exposure time of filter 12b at

  gases, all the particles present in the gas of

  certain radioactive particles accumulate in the filter element 122 so as to allow the

  detector to perform an integration measurement.

  When the filter contamination reaches a

  limit value, which can be set, the device

  tration receives a control signal so that the

  and, as a result, also the contaminated filter element are moved anticlockwise by 1200 in a clockwise direction until the element

  The filter is located above the ejection duct 9.

  Thanks to the rounded lower surface of the support ring 121, the contaminated filter element slides inside.

  of the sheath 9 without pivoting. During this operation the

  The filter element for the measurement is conveyed through the opening 3b to the measuring position above the detector, while the unoccupied opening is placed under the supply container 6 to receive a new filter element. The driving device 5 or the turntable 3 comprises contacts cutting the motor supply circuit after each rotation of 1200 of the tray while waiting for the next control signal. The time during which the filter element is exposed to the measurement gas can extend over several weeks or months during operation without disturbance of the installation but in case of very significant failure

  this time can be reduced by several minutes.

  Fig. 3 shows the turntable 3 with its

  ring gear 3a and its openings 3b, 3c, 3d.

  Fig. 4 represents, in section, the turntable

3 of Fig. 3.

  Supervisory staff can be easily informed about the operation of the unit of measure by numbering the filter elements and remotely indicating the change of the filter elements and their

gas exposure time.

  Measuring devices of this type equipped with gas pump, flow regulator and shut-off valves

  are preferably inserted into the

  (bypass) of the reactor enclosure. Since this enclosure must be able to withstand, according to international standards, an overpressure of 5 bars at 1200C, the

  measuring device must also satisfy these requirements.

  ments. O-rings 14, 15, 16, 17, 18, 19

  sealing between the base plate and the cover plate and between these plates and the container

  supply, the ejection duct and the detector.

  Another sealing device, not shown, is

  provided on the pinion shaft 4. The supply container

  filters and the ejection duct must, in addition,

  have pressure-tight closures.

  Where necessary, in case of disturbance

  tions, to introduce under an overpressure, inside

  of the enclosure, new filter elements and removal of

  worm the irradiated filter elements, it does first

  close the shutoff valves of the bypass duct.

  It can be seen from the foregoing that

  filter change can not be a cause of unexpected

  for monitoring personnel, especially in case of failure A numbering of the filter elements in the order of their ejection, allows to determine the operation of

  installation. The selective measurement of radio

  active activity in the laboratory can contribute, to a considerable extent, to

breakdown.

  It is advantageous to visualize the flow of gas

  for the duration of the measure by integration and pre-

  see a regulator to keep the current steady

  zeux and to compensate for the clogging of the filters.

  According to another embodiment of the invention,

  the turntable may only have one opening

  but in this case the switching unit must be programmed so that the board executes at each

once a complete revolution.

  In order to control the proper functioning of

  measuring devices, it is possible to bring an emission

  reference transmitter in front of the detector after each change

  filter change or before each third change, which makes it possible to periodically carry out a control measurement of the detector. The reference issuer can be

  rotated in front of the detector window by electrical means.

  tromagnetic or it can be housed inside an additional recess of the turntable so that the detector delivers a control pulse during the

  passage of the reference transmitter.

  When using large filters such as those intended, for example, to measure iodine, the plateau

turning is thicker.

  Depending on the measurements to be made, the detector may consist of a scintillation counter or a

ionization chamber.

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Claims (12)

  1 - Device for the measurement by integration of radioactive particles present in gases by means of filters and a detector mounted upstream of a limit value unit, characterized in that the measuring device comprises a turntable (3) driven by a control device (5) and having at least one opening (3b, 3c, 3d) for accommodating the different filters (12), a supply container (6) for the filters which is arranged above the turntable (3), an inlet duct (7) for the gas provided on one of the sides of the turntable (3), a detector (10) with an outlet duct (8) for the gas provided on the other side of the turntable (3), a sheath (9) for ejection   filters, a switching unit to stop the dis-   Positive control (5) when the measuring position is reached and a limit value unit for controlling   the change of filters when a contamination de-   completed of these is reached.   2 - Device according to claim 1, characterized   characterized in that each filter unit (12) is composed of a filter element (122), a carrier ring (121)   and mesh plates (123, 124) reinforcing the sur- filter faces.   3 - Device according to claim 2, characterized   characterized in that the underside of the carrier ring (121) is strongly rounded so that the filter (12) can slide without tipping inside the sheath oblique ejection (9).   4 - Device according to claim 1, characterized   characterized in that the edge (3a) of the turntable (3) has a toothing in which meshes with a pinion (4) a gear motor (5).   Device according to claim 1, characterized   in that it is inserted into a   (bypass), equipped with a pump, the reaction chamber   in that the turntable with the pinion, the   filter supply container and ejector sheath   filters are insulated in a pressure-tight manner. if we.   6 - Device according to one of the claims   1 to 5, characterized in that the turntable has a single housing opening for the filter and in that the switching unit secures the turntable after each round.   7 - Device according to one of the claims   1 to 5, characterized in that the turntable (3)   three openings (Lb, 3c, 3d) offset by 120, in that the filter supply container (6), the detector (10) and the filter ejection sheath (9) are also shifted by 1200 relative to each other and that the switching unit each time, a rotation of 1200.   8 - Device according to one of the claims   1 to 5, characterized in that it comprises a remote display device for the indication of the number of   Contaminated filters used per monitoring period.   9 - Device according to one of the claims   1 to 5, characterized in that it comprises a device for   indicate the duration of the exposure of a filter.   Device according to claim 9, characterized   in that it includes an apparatus for measuring the   flow during the exposure time.   11 - Device according to claim 9, characterized   characterized in that it comprises a regulator for keeping the gaseous current constant and for compensating the fouling of the filter.   12 - Device according to one of claims 6 and   7, characterized in that the turntable has an additional recess in which a reference transmitter is housed and in that the switching unit triggers a calibration measurement after each filter change or   after every third change.   13 - Device according to one of claims 1 to   12, characterized in that the turntable is made of   to be able to receive voluminous and sensory filters   more suitable for the measurement of iodine.   14 - Device according to one of claims 1   at 13, characterized in that the detector is a scintillation counter.   - Device according to one of claims 1   at 13, characterized in that the detector is an ionization chamber.