Device for detecting radiation and associated detection device

Abstract

A radiation-detecting device including at least two radiation detectors distributed in series along a support cable, each detector including an optically stimulated luminescence detection element which is optically coupled to at least one optical fiber, each optically stimulated luminescence detection element being held opposite a first end of the optical fiber by a mechanical part fixed to the support cable, the mechanical part being held in a flexible cable by a holding mechanism, second ends of each optical fiber leading to the same first end of the flexible cable.

Claims

1. A radiation-detecting device comprising: at least two radiation detectors distributed in series along a support cable, wherein each detector comprises an optically stimulated luminescence detection element which is optically coupled to at least one optical fiber, each optically stimulated luminescence detection element being held opposite a first end of the optical fiber by a mechanical part fixed to the support cable, the mechanical part being held in a flexible cable by holding means which comprises a carrier cylinder made of a deformable solid material on which the optical fibers are wound, second ends of each optical fiber leading to a same first end of the flexible cable.

2. The radiation-detecting device according to claim 1, wherein the mechanical part which encloses the support cable comprises a first bore and a second bore aligned with each other, the optically stimulated luminescence detection element being fixed in the first bore and the optical fiber being fixed in the second bore.

3. The radiation-detecting device according to claim 1, wherein the optical fibers are helically wound.

4. The radiation-detecting device according to claim 1, wherein the deformable solid material is a polymer.

5. The radiation-detecting device according to claim 1, wherein a plurality of optical fibers is coupled to a same optically stimulated luminescence detection element, the plurality of optical fibers being gathered in a capillary pipe as a beam of optical fibers.

6. The radiation-detecting device according to claim 1, further comprising a grease layer that covers an internal wall of the flexible cable.

7. The radiation-detecting device according to claim 1, further comprising a polymer layer that covers an external wall of the flexible cable.

8. The radiation-detecting device according to claim 1, wherein a single mode optical fiber containing a plurality of fiber Bragg gratings is fixed in the mechanical part, the optical fiber having an end leading to the first end of the flexible cable.

9. The radiation-detecting device according to claim 1, wherein the support cable is a multi-strand wire.

10. The radiation-detecting device according to claim 1, wherein the flexible cable is an interlocked metal hose.

11. The radiation-detecting device according to claim 1, wherein nominal diameter of the flexible cable is between 4 mm and 100mm.

12. The radiation-detecting device according to claim 1, wherein diameter of the core of a multimode optical fiber is between 100 m and 200 m.

13. The radiation-detecting device according to claim 1, wherein a second end of the flexible cable, opposite the first end, is closed by a tip.

14. The radiation-detecting device according to claim 13, wherein the tip comprises a microphone.

15. A radiation-detecting system in a facility, the system comprising: a radiation-detecting device and introduction means for introducing the radiation-detecting device into the facility, wherein the radiation-detecting device is a device according to claim 13, and wherein the introduction means comprises a turntable on which the flexible cable is wound, an injecting tube which opens into the facility and in which the tip of the flexible cable is engaged, and propulsion means for propelling the flexible cable into the facility.

16. The radiation-detecting detecting system according to claim 15, wherein the propulsion means comprises a motor and mechanical means connected to the motor and configured to rotate the turntable once a propulsion command is applied to the motor.

17. The radiation-detecting detecting system according to claim 15, wherein a multi-fiber connector fixed to the turntable connects both ends of the optical fibers to a measuring instrumentation configured to stimulate the optically stimulated luminescence detection elements and to read a luminescence which results from radiation exposure.

Description

BRIEF DESCRIPTION OF THE FIGURES

(1) Further characteristics and advantages of the invention will appear upon reading a preferential embodiment made in reference to the appended figures in which:

(2) FIG. 1, already described, represents a first radiation-detecting device according to prior art;

(3) FIG. 2, already described, represents a second radiation-detecting device according to prior art;

(4) FIG. 3 represents a schematic diagram of radiation-detecting device according to the invention;

(5) FIGS. 4A-4D represent detail views of the radiation-detecting device of the invention;

(6) FIGS. 5A and 5B represent elements for closing the radiation-detecting device of the invention;

(7) FIG. 6 represents a schematic diagram of a dose rate measuring instrumentation associated with the radiation-detecting device of the invention;

(8) FIG. 7 represents a radiation-detecting system in a facility, the system using a radiation-detecting device in accordance with the device of the invention.

(9) Throughout the figures, the same references designate the same elements.

DETAILED DISCLOSURE OF EMBODIMENTS OF THE INVENTION

(10) FIG. 3 represents a schematic diagram of essential elements which make up a radiation-detecting device according to the invention and FIGS. 4A-4D represent detail views of the detecting device of the invention.

(11) The device comprises a set of OSL detectors D.sub.i (i=1, 2, 3, etc.) placed in the flexible cable FL. The detectors D.sub.i are connected to each other using a support cable MB. Each detector D.sub.i is equipped with a beam of fibres F.sub.i. FIG. 4C represents a longitudinal cross-section view of a detector D. FIG. 4D represents a transverse cross-section view of the same detector.

(12) The flexible cable FL is preferentially an interlocked metal hose. The interlocked metal hose can be of the single lock or double lock type. The single lock hose has a greater flexibility and a higher internal/external diameter ratio than the double lock hose, but its mechanical strength is lesser.

(13) In practice, for dismantling applications, a double lock hose such as that represented, for example, in FIG. 4A is preferred. By way of non-limiting example, the double lock hose is made of stainless steel and can be chosen from a very wide range of nominal diameters, typically between 4 mm and 100 mm. In a particular embodiment of the invention, the hose has, for example, an inner diameter of 4.8 mm and an outer diameter of 8.5 mm. The minimum radius of curvature of the hose is 35 mm. Its weight per unit length is, for example, equal to 112 g/m. Other cables can also be used such as, for example, braid based flexible metal sheaths covered with a polyvinyl chloride (PVC) layer. Such metal flexible cables are made from a preformed stainless steel metal strip. Since such cables are likely to be submerged, a polymeric coating R is applied externally, for example by coating. The coating R has also the advantage of facilitating propulsion (reducing friction because of its smooth character) and decontamination (context of dismantling) operations. Among polymers usable for the coating, polyethylene (PE) is recommended by virtue of its temperature (up to 105 C. in its cross linked form) and radiation resistance, and its satisfactory chemical stability, in particular to acids used for clean-up.

(14) As has been mentioned previously, a support cable MB connects the detectors D.sub.i to each other. Unlike prior art (cf. U.S. Pat. No. 5,665,972), the support cable MB is not used to extend or insert the detectors inside a duct. Within the scope of the invention, the strain necessary to extend or insert the detectors in the ducts is applied to the single flexible cable FL. The latter can advantageously withstand a propulsion strain without buckling because, due to its diameter, its flexural rigidity moment is much higher than that of the support cable. Within the scope of the invention, the support cable MB is only used to connect the detectors and hold a constant gap between them.

(15) The overall space of the detecting device of the invention is mainly a function of the diameter of the beams of fibres (generally in the order of 200 m to 600 m), which diameter impacts the detection performance. A higher measuring capability can be reached by increasing the cable diameter or by reducing the diameter of the beams of collection fibres (typically 100 m). The volume occupied by a unit detector D.sub.i and the collected optical signal are two parameters being a function of the squared diameter of the flexible cable FL. Thus, at a constant flexible cable diameter, an increase in capability by a factor 4 (64 fibres), for example, can be reached for a reduction in the diameter of the beams by a factor 2. The signal reduction resulting from this reduction in diameter thus imposes to increase the exposure time by a factor 4 to preserve an identical signal to noise ratio. Within the scope of the invention, the optical fibres used to make a beam of fibres have a low diameter (typically 100 m to 200 m). It is thus advantageously possible to readily wind them and to reduce curvature stresses. By way of non-limiting example, an exemplary beam of fibres consisting of 7 fibres arranged according to a hexagonal arrangement is given in FIG. 4B. The fibres fb are assembled by gluing or inserted in a flexible capillary pipe K formed from a radiation resistant polymer, for example silicone, polyurethane, polyethylene or polypropylene. It is also possible to assemble a greater number of fibres with a reduced diameter, for example in beams of 19 fibres.

(16) Advantageously, the fibres fb have a low core/clad ratio in order to optimise light collection. The optical fibres are preferentially single mode ones, with a core diameter between 100 m and 200 m and have, for example, a numerical aperture NA between 0.22 and 0.48.

(17) It is also possible to use step-index multimode fibres or graded-index multimode fibres, coated with a hard polymer such as polyimide. This polymer is applied as thin films (a few tens of micrometers) and shows good radiation and temperature resistances.

(18) Most fibres are also coated with other acrylate or Tefzel type polymers which are then removed on the last centimeters to form the beam of fibres. By way of non-limiting examples, the following step-index multimode fibres can be used: core 200 m, clad 225 m, coating 500 m, NA=0.39, core 200 m, clad 230 m, coating 500 m, NA=0.48, core 200 m, clad 230 m, coating 500 m, NA=0.37 or 0.43.

(19) Regardless of the fibre type used, a hexagonal beam of fibres has a more reduced coverage than a single fibre having the external diameter of the beam. Thus, for a total area of 0.22 mm.sup.2 covered by seven fibres of a hexagonal beam, the area of a single fibre having the external diameter of the beam would correspond to 0.283 mm.sup.2. The area loss is thus about 30%. However, the rigidity of a fibre increases as a function of its cubed diameter. The hexagonal beam with 7 fibres then has a flexibility 27 times higher than that of a single fibre with an equivalent diameter and is thus much easier to wind inside the flexible cable.

(20) Moreover, for a given radius of curvature, the curvature stresses change in proportion to the diameter of the fibre. Thus, the stresses applied to the beam of fibres are three times more reduced than for a single fibre. In practice, the deformation applied to a fibre should remain very lower to one percent to reduce breaking risks. The curvature deformation corresponds to the diameter of the fibre divided by twice its radius of curvature. For a fibre with a 200 m diameter and a 30 mm minimum radius of curvature, the maximum deformation generated by the curvature is about 0.33%, which is acceptable.

(21) FIG. 4C represents a longitudinal cross-section view of a detector D.sub.i and FIG. 4D represents a transverse cross-section view of the flexible cable at a detector D.

(22) An OSL detector crystal 9 is placed facing the end of a beam of optical fibres F.sub.i. The detector crystal 9 and the beam of fibres F.sub.i are placed, facing each other, in two concentric bores of a clamp d. A first bore accommodates the beam of optical fibres F.sub.i and has consequently a diameter required to accommodate the beam of fibres, for example 0.6 mm. The second bore is threaded and accommodates a grub screw V, for example of stainless steel, which contains the detector crystal 9. The detector crystal 9 is fixed downhole, for example by an epoxy type glue having a satisfactory radiation mechanical resistance. The beam of fibres F.sub.i is also fixed in its mount, for example using an epoxy type glue. This method of coupling between the detector crystal 9 and the beam of fibres F.sub.i enables a very low air interval to be left between the crystal and the beam of fibres. It is also possible that the detector crystal 9 and the end of the beam of fibres F.sub.i are in contact of each other. In practice, there is a small air thickness of a few tens of micrometers between the detector crystal 9 and the end of the beam of fibres F.sub.i because of their surface state.

(23) Each clamp is, for example, machined in a stainless steel parallelepiped having dimensions of about 3310 mm.sup.3. The steel parallelepiped is, for example, machined by turning on a first part and pierced by a hole having a diameter equivalent to that of the support cable, for example a 1 mm diameter, on a second part. On this second part, the steel parallelepiped is also grooved on an entire half-length in order to form a clamp. The support cable MB is then engaged in the hole and the clamp is tightened on the support cable by two screws VR, for example, of stainless steel. Alternatively, it is possible to secure each clamp to the support cable MB by welding.

(24) By way of non-limiting example, the support cable MB consists of a stainless steel multi-strand wire (e.g. =1 mm), with an elastic modulus close to 200 GPa. A maximum tensile force in the order of 400N (40 kg), corresponding to a stress of 400 MPa, can thereby be applied within the 0.2% yield strain.

(25) To optimise the distribution of the beams of fibres in the flexible cable FL, the different clamps can follow each other with variable angular orientations, for example spirally, along the support cable MB.

(26) The length of the clamps can advantageously be designed as a function of the minimum curvature necessary to be ensured to the flexible cable FL. By way of non-limiting example, for a minimum radius of curvature desired to be 30 mm of a flexible cable FL with an internal diameter equal to 4 mm, the length of the linear segment should not exceed 20 mm. Clamps with a 10 mm length can thereby be chosen not to hinder the curvature of the flexible cable in use.

(27) FIG. 4D represents a transverse cross-section view of the flexible cable at a detector D. The beams of fibres F.sub.j, F.sub.k, F.sub.l, etc. which come from the respective detectors D.sub.j, D.sub.k, D.sub.l, etc. (not represented in the figure) are wound, preferably spirally wound, on a carrier cylinder S made of a deformable solid material, for example a foam cylinder, which surrounds the clamp d (the cylinder S is not represented in FIG. 3 for the sake of convenience).

(28) The beams of fibres F.sub.j, F.sub.k, F.sub.l, etc. are distributed on the carrier cylinder S which is positioned between the internal wall of the flexible cable FL and the clamp d. The internal wall of the cable FL is preferentially covered with a grease film G able to move the beams of fibres. The beams of fibres are wound on the carrier cylinder S before the detectors are mounted in the flexible cable FL. In use, the carrier cylinder S advantageously does not resist to movements of the fibres.

(29) In a particular embodiment of the invention, the fibre Bragg gratings B are photo-recorded in a conventional single mode fibre, which fibre is inserted in a capillary wound, in the manner of the beams of optical fibres, about the carrier cylinder S. Each fibre Bragg grating B is placed as close as possible to a detector crystal 9. In a known manner per se, the Bragg gratings are used for measuring the temperature of the detector crystals 9. Each fibre Bragg grating is photo-recorded at a different Bragg wavelength which enables its position in the hose to be identified.

(30) The flexural behaviour of the detecting cable of the invention is described hereinafter, in the case where the internal diameter of the flexible cable is, for example, equal to 4 mm. In this case, the difference in radius of curvature between two beams of fibres located at both ends of an internal diameter of the flexible cable aligned with the radius of curvature of the flexible cable is substantially equal to 4 mm.

(31) The beam of fibres farthest from the centre of the radius of curvature then travels a higher distance than the other beam of fibres, by substantially 25 mm for a full turn of the cable FL. Concretely, the worst case corresponds to the storage situation for which the flexible cable is always wound in the same direction (cf. FIG. 7). For winding a 20 m long cable on a storage turntable having a radius of 150 mm, 21 turns are necessary for winding the full cable on the turntable. The length offset between both beams of fibres located at both ends of the internal diameter of the cable is thereby substantially equal to 525 mm (i.e. 2125 mm).

(32) According to the preferential embodiment of the invention, the beams of fibres are helically wound about the axis of the flexible cable. For a given length of a rectilinear fraction of the flexible cable, each beam of fibre has consequently a length higher than the length of the rectilinear fraction of the cable. In the following of the description, the difference between the length of the beam of fibres and the length of the rectilinear fraction of the cable which corresponds thereto is called an overlength. In the case where the internal diameter of the cable is substantially equal to 4 mm, the helices have, for example, a pitch in the order of 50 to 60 mm. According to this configuration, the overlength obtained by helical winding is about 1.55 mm per pitch of 50 mm, that is an overlength of 31 mm/m which is then sufficient to wind the cable on a turntable having a radius of 150 mm without deterioration risk.

(33) The manufacture of the detecting device according to the invention will now be described. All the detectors D.sub.i and the beams of fibres F.sub.i are first wound on the carrier cylinder and covered with grease in order, on the one hand, to facilitate their insertion into the flexible cable and, on the other hand, to facilitate the movement of fibres inside the cable during subsequent decontamination operations. A wire puller as a rigid rod, having a length substantially equal to that of the flexible cable FL, is then connected to the support cable and introduced into the flexible cable, at a first end of the flexible cable. The flexible cable is held rectilinear upon introducing the wire puller. The wire puller is then pulled out from the flexible cable, at the end of the flexible cable which is opposite the first end, thus driving all the detectors D.sub.i inside the cable. Once all the detectors D.sub.i are placed inside the flexible cable, the wire puller is removed and a protective sealing tip is positioned at the end of the flexible cable which is located opposite to the end through which the beams of fibres come out. This tip is detailed below in reference to FIGS. 5A and 5B. At the sealing tip, the support cable MB is severed and the end thereof is preferentially left free. At the end of the flexible cable FL located opposite the tip, the beams of fibres F.sub.i, F.sub.j, F.sub.k, F.sub.l, etc., the capillary KP and the support cable MB are connected to a flange as detailed in reference to FIGS. 6 and 7 below.

(34) FIGS. 5A and 5B represent elements for closing the flexible cable.

(35) FIG. 5A represents an element for closing the flexible cable according to a first embodiment of the invention. By way of non-limiting example, the closing element is a steel plug EB which is welded to the end of the flexible cable FL. The steel plug is for dampening the cable shocks as it progresses in a duct.

(36) FIG. 5B represents an element for closing the flexible cable according to a second embodiment of the invention. The closing element according to the second embodiment of the invention comprises a microphone MC. A first part P.sub.1 of the closing element is a mount, preferentially of stainless steel, which is made integral with the flexible cable by welding and a second part P.sub.2 is a plug, preferentially of duralumin, consisting of a hemispherical head screw screwed to the mount. The microphone MC is inserted into a cylinder CY, preferentially of silicone, to protect it from shocks and embedded in a grease GR which ensures acoustical coupling with the plug. The microphone MC is connected to electrical wires AL. The electrical wires AL are for electrically powering the microphone and recovering the electrical signal delivered by the microphone. By way of non-limiting example, three electrical wires come out of the microphone and are connected, by welding, to three electrical wires present in the flexible cable FL. If necessary, the excess wires are wound. One of the power supply electrical wires can be electrically connected to a wire of the multi-strand cable in order to reduce the number of wires present in the flexible cable.

(37) The use of a closing element equipped with a microphone occurs, for example, upon extending a flexible cable in a pool. Within such a context, an ultrasound acoustical location can be implemented. The microphone is, for example, a miniature microphone known as MEMS (Micro-Electrical-Mechanical Systems) microphone. In a particular embodiment (not represented in the figures), several microphones can also be disposed in different locations inside the flexible cable the diameter of which is then adapted to the presence of the microphones. It is then possible to account for the extension of the cable under water. The location is achieved, in a known manner per se, by submerging at least three sound sources in the pool to be inspected. A possible mode of operation is to sequentially emit, by each source, a pulse periodical sound signal at an arbitrary frequency, for example close to 20 kHz, in order to reduce sound overlaps due to echoes on the walls. The three signals sequentially received by the MEMS microphone(s) accommodated in the flexible cable are then synchronised with respect to the respective emission signals in order to determine the time delays thereof. The distance between a microphone accommodated in the flexible cable and the local frame reference which carries the three sound sources is then determined from the three time delays measured and the known sound velocity in water.

(38) FIG. 6 represents a schematic diagram of a dose rate measuring instrumentation associated with the radiation-detecting device of the invention.

(39) The beams of optical fibres which come out from the end of the flexible cable FL located opposite the closing plug make-up a set of beams of fibres E. The beams of fibres of the set E are connected to an optical switch Q. The number of beams of fibres is equal to the number of detectors D.sub.i, for example 16. The optical switch Q is connected to an optoelectronic detection block 10. In a known manner per se, the optoelectronic detection block 10 contains a laser, a photomultiplier, an electromechanical shutter and filters for filtering a laser light before stimulating OSL detectors and the luminescence resulting from a detection, after collection by the beams of fibres (cf. Magne and al. Multichannel dosemeter and Al.sub.2O.sub.3 Optically Stimulated Luminescence fibre sensors for use in radiation therapyevaluation with electron beams Radiat. Prot. Dosim. 131(1), 2008, pp 93-99).

(40) The instrumentation described in FIG. 6 performs reading of the different detectors sequentially. For electronuclear applications, in dismantling and in radiation protection, readouts of ambient dose rates should be performed under exposure by uncontrolled permanent sources. For this reason, a prior reset is always made before exposure. The protocol occurs consequently in the following way: prior optical stimulation carrying out a prior reset of all the OSL detectors, stopping the prior optical stimulation and exposure of the OSL detectors during a time T defined by the user (a few minutes, hours, days, or even weeks or months), subsequent optical stimulation with reading of the OSL luminescences from the different OSL detectors and resetting all the detectors.

(41) In a known manner per se, the optoelectronic detection block 10 delivers, from the reading data of the OSL luminescence, dose rate data DB for each of the OSL detectors.

(42) A unit OSL signal detected by the block 10 consists of an OSL pulse and a base line. The base line is a signal which results from the contribution of different phenomena, namely: background noise of the OSL detector, fluorescence of the deep traps of the OSL detector crystal, scintillation and Cerenkov effect in the fibre which propagates the OSL pulse, which are a function of the radiating nature of the environment present about the flexible cable.

(43) The OSL pulse reaches an asymptotic minimum at the end of a reading time T.sub.OSL, once substantially all the traps present in the detector crystal have been emptied (typically 99.9%). A measurement of the mean value of the asymptotic minimum is then made on the last recording points. This mean value is then subtracted from the OSL pulsed signal throughout the period T.sub.OSL. The corrected signal which results from this subtraction is independent from the external disturbances and, in particular, from the Cerenkov effect. The corrected signal is then integrated on the entire time band and then weighted by a calibration coefficient to deduce therefrom the dose D integrated on the entire exposure time. The mean dose rate DdD is then estimated by dividing the dose D by the exposure time T:
DdD=D/T.

(44) The user can make a periodical acquisition sequence or a single measurement. In the case where the user makes several acquisitions periodically, the protocol is advantageously reduced to two phases (exposure and optical stimulation) since the optical stimulation makes resetting for the next measurement.

(45) Likewise, the user can make several measurements on several parallel cables for the purpose of saving time in the overall dosimetry of a facility. This option is particularly advantageous in a low dosing environment, with high exposure times (in the order of one day, or even one week or one month). In this case, the resetting operations are time-stamped for all the lines which are analysed in parallel.

(46) The disconnection of the flexible cable enables the operator to come out from the zone during the exposure phase. This phase has thereby little impact on the personnel exposure and its duration can be chosen as long as necessary, since the parallel operating mode enables time to be saved on reading.

(47) In a preferential embodiment of the invention, an OSL crystalline fibre with a 0.5 mm diameter and 5 mm length is an interesting trade-off. The dose resolution is estimated at about 0.7 mGy with Al.sub.2O.sub.3:C crystals. By way of non-limiting example, for an exposure time of 18 hours, the mean dose rate resolution is 0.7 mGy/18 h that is 40 Gy/h. Such a duration can then be obtained easily by triggering the integration at the end of the day at about 4 p.m. and by performing dose readings the following morning at about 10 a.m. Still by way of example, it is also possible to integrate, during an entire week (i.e. 168 hours), measurement data at the end of a clean-up worksite. The dose rate resolution is consequently in the order of 0.7 mGy/168 h, that is 4 Gy/h.

(48) The detecting device of the invention advantageously enables a high dynamics in terms of dose rate (5 to 7 decades) to be reached by virtue of the combination of the dose range (3 to 4 decades) and the exposure time range (2 to 3 decades).

(49) The interest of a 1-D sensitive cable is to make a readout of several measurements at different points (linear mapping of the activity) simultaneously in order to save time in dosimetry. Indeed, the readings can thereby be made simultaneously at different points and no longer sequentially as is the case by moving a point sensor on the entire scene to analyse.

(50) FIG. 7 represents a radiation-detecting system in a facility which uses a detecting device in accordance with the device of the invention. Generally, the facility can be a contaminated facility or a facility which, without being contaminated, is exposed to radiations. In the example of FIG. 7, the facility I is a contaminated facility which consequently has to be decontaminated.

(51) The facility to be decontaminated I comprises, for example, a duct 11 and a vessel 12 in which the duct 11 leads. The flexible cable FL equipped with detectors is introduced into the duct 11 from a non-contaminated zone ZA which is accessible to users. The flexible cable FL is introduced into the facility I using a propelling device which comprises an injecting tube 13, a motor 14 equipped with a control lever 15, a turntable 16 on which the flexible cable is wound and mechanical driving means 17 which connect the motor to the turntable. The turntable 16 is equipped with a multi-fibre connector 18 which connects both ends of the bent-out optical fibres which lead from the flexible cable to a measuring instrumentation. The measuring instrumentation comprises, for example, a multi-fibre optical cable 19, a multi-channel connector 20 and a measuring unit 21.

(52) The purpose is to make readouts of dose rate inside the duct and the vessel and thus, to follow-up the clean-up process. The facility I remains inaccessible as long as the clean-up is not ended.

(53) As is described below, the measurements occur in three phases.

(54) Phase 1: Cable Propulsion

(55) The operator has disconnected beforehand the multi-fibre optical cable 19 from the turntable. If he has forgotten to do so, the presence of the connector in its housing prevents the motor to be started up.

(56) The end of the flexible cable FL initially wound about the turntable 16 is engaged in the injecting tube 13. The injecting tube 13 is connected to the inlet of the duct 11. When the operator triggers the control lever 15 in the propulsion position, the rotation of the motor 14 is activated at a controlled speed and the mechanical driving means 17 rotate the turntable. The flexible cable FL is then propelled in the duct 11.

(57) Driving rollers are used for propelling the flexible cable. The driving pressure of the rollers is adjustable up to a maximum value depending on the cable strength. For example, for a cable resisting at 200 kg, the maximum strain could be limited to 50 kg in order to take a safety coefficient into account. In case of a blockage due, for example, to an unexpected decrease in the cross-section area of the duct, propulsion is naturally stopped and the cable is saved as soon as the reaction force is higher than the friction force. The operator should then stop the propulsion operation to analyse the blockage cause.

(58) When the cable is integrally extended, the core acting as a stop abutment collides with the injecting tube 13 and blocks the cable to avoid destroying the optical link adapted to the turntable hub. The driving rollers then slip and the operator has to shut down the motor and switch to neutral.

(59) Phase 2: Exposure and Rate Readout

(60) When the flexible cable reaches the wanted position, regardless of whether the cable is fully wound or not, the operator puts the motor to neutral.

(61) The operator then connects the measuring instrumentation 19, 20, 21 to the connector 18 accommodated in the turntable hub. As has been previously mentioned in reference to FIG. 6, the measuring instrumentation comprises means able to optically stimulate the OSL detectors. The optical stimulation of the OSL detectors can thus be made. Preferentially, the connection of the measuring instrumentation to the connector 18 deactivates the power supply to the motor and prevents the same to be rotated.

(62) The operator can then either leave the measuring instrumentation connected and wait for the exposure end, or disconnect the measuring instrumentation to make the optical stimulation of other flexible cables.

(63) In any case, at the end of the exposure time, the measuring instrumentation has to be connected to the connector 18 such that luminescences which result from the detection of nuclear radiations are read. In theundesiredcase where the operator forgets to connect the measuring instrumentation and still triggers the data acquisition, nothing happens since the flexible cable FL is not connected. The user then observes no signal and an error message appears on the screen informing him/her about the anomaly. The operator is then requested to connect the measuring instrumentation and to make a reading. Based on the luminescence data read, the calculating unit 20 calculates the dose rates.

(64) Phase 3: Cable Rewinding

(65) Once the luminescences are read, the operator again disconnects the multi-fibre cable 19 of the turntable which enables the motor to be rotated again. The operator can then trigger the rewinding of the cable on the turntable by actuating the level 15 in the rewinding position. This operation is made by rotating a second hub driving a belt which transmits the rotation strain to the turntable. The turntable is then rotated in the reverse direction to the direction of phase 1 and the flexible cable FL is rewound, preferentially in zigzag (combination of alternate rotational movement and translational movement) to distribute homogeneously the cable throughout the surface of the turntable. Other rewinding protocols can also be contemplated.

(66) It is advantageously possible to readily disconnect the measuring instrumentation of the flexible cable FL, regardless of whether it is in the propulsion/rewinding phase or in radiation exposure phase. The measuring instrumentation can then be reused to make measurements with other cables propelled beforehand in other ducts for the purpose of saving time in the follow-up of the contamination of the overall facility.

(67) Advantageously, temperature measurements can be made in parallel, if this turns out to be necessary, thanks to a single mode fibre present in the multi-fibre optical cable 19 and connected, via the connector 18, to the single mode fibre which contains the fibre Bragg gratings present in the flexible cable. Furthermore, when this turns out to be necessary, for example for measurements in a pool, an electrical connector (not represented in the figure) recovers the signal from the microphone(s) incorporated in the flexible cable FL.

(68) The multi-fibre optical cable 19 is connected to the connector 18 integral with the turntable. The optical cable 19 is disconnected during propulsion and rewinding phases given that the turntable is rotated during both these phases. In one embodiment, the optical cable 19 includes a core (two half-shells) screwed at the terminal part (at a few tens of centimeters from the end) which acts as a mechanical abutment. The unwinding of the cable, guided by a guide tube at the outlet of the turntable, is then naturally blocked when the core collides with the guide tube. In addition, a sensor for the presence of the plugged connector triggers a safety preventing the motor from being started up in case it is forgotten. The presence of the connector deactivates the motor power supply and thus prevents the same from rotating (and thus the optical cable from being destroyed).

(69) The logistic interest of the flexible cable equipped with OSL detectors of the invention will now be described.

(70) The utilisation of the 1-D cable of the invention enables time to be saved on the overall dosimetry of the facility investigated and consequently indirectly contributes to optimising the cost of a clear-up operation. This operating mode is particularly interesting from the logistic point of view in low dosing environments characterised by high exposure times (in the order of one day to one week).

(71) The user can made 1-D curvilinear readouts using a single cable. In this case, the 1-D cable can remain connected to its reading instrumentation or be disconnected, which enables the operator to come out from the zone during the exposure phase. By way of non-limiting example, for 16 simultaneous measuring points read out with a flexible cable, the total duration DT of a 1-D OSL dosimetry operation is:
DT=T+32T.sub.OSL, where

(72) T is the exposure duration (for example a few tens of minutes, several hours, several days or several weeks), and

(73) T.sub.OSL is the reading and reset duration of the OSL detectors (typically in the order of a few tens of seconds).

(74) The user can also carry out 2-D readouts by extending N 1-D flexible cables in parallel, for example 8 cables. In this case, the N 1-D cables are extended and simultaneously disconnected and the reset and reading operations are time-stamped for all the curves analysed in parallel. The total duration DT of the 2-D OSL dosimetry operation is then, for 16 simultaneous measuring points read out with a flexible cable:
DT=T+328T.sub.OSL, that is
DT=T+256T.sub.OSL.

(75) Let us consider a dose rate of 6 mGy/h. By assuming an exposure time of 2 hours, the OSL measurement resolution of the dose rate is substantially 0.25 mGy/h (SNR=24). The total duration of the OSL dosimetry operation is then 2.25 hours for 16 1-D measuring points and 4.1 h for 128 2-D measuring points. It is possible to compare these OSL dosimetry durations to the duration of a point (0-D) conventional dosimetry made using a miniature CZT detector (a few mm.sup.3) that can be inserted and moved in a duct. The acquisition duration is in the order of 15 minutes for a typical dose rate of 6 mGy/h (cf. A. Rocher, N. Blanc de Lanaute <<Caractrisations par spectromtrie gamma CdZnTe de la contamination des circuits des centrales nuclaires>>, Congrs SFRP 2013, Paris). Consequently, the dosimetry duration with the CZT detector is 4 hours (1615 minutes=4 h) in 1-D and 32 hours (12815 min=32 h) in 2-D.

(76) At an equivalent performance, the 1-D/2-D OSL dosimetry made with the device of the invention is thus quicker than the 0-D dosimetry made with a CZT detector. Moreover, the 0-D conventional measurement requires an operator permanently on stand-by duty since the readings are made sequentially. However, the OSL methodology relays on a nearly simultaneous reading mode of all the detectors at the same time in an automated manner. Thus, the presence of an operator is only required for triggering the OSL reading protocol.

(77) This parallel OSL methodology thus enables time to be saved in the dosimetry operation itself as well as in operator time.

(78) In parallel to the economic interest of the use of the detecting device of the invention, a linear mapping of the activity enables the statistical origin measurement uncertainty to be reduced, for a measurement time identical to that of a single moved detector. Indeed, let us consider a single point (0-D) detector delivering a dose rate measurement with a given uncertainty at the end of an exposure time T. A total time NT is thus required to analyse the N measuring points of the scene.

(79) However, let us consider now the case of the cable consisting of N detectors simultaneously exposed during the same exposure time T. The measurement statistics are then the same and the measuring time is reduced by a factor N. This same cable exposed during a duration NT thereby delivers a dose rate measurement with an uncertainty improved by a factor with respect to a single moved detector.

(80) With an identical dosimetry duration of a scene, the 1-D measurement thus enables the results of dose rate measurements to be improved. For 16 points, the measuring uncertainty is, for example, improved by a factor 4. For a plurality of 8 cables with 16 simultaneously exposed detectors, the measurement uncertainty is, for example, improved by a factor 11 with respect to a single detector.