JPH0643247A - Collimation means of gamma ray beam emitted by edge section of irradiated fuel element inspected by detector - Google Patents

Abstract

PURPOSE: To quickly measure the intensity of γ-rays through a fixed apparatus, while protecting a person by moving two rollers touching an inclination path on the lower surface of a joint and setting a collimation slit between a fixed base part and a movable part. CONSTITUTION: Two vertical couplers 30, 32 traversing the channels 34, 36 made vertically in a supporting part 26 are moored, at the base part thereof, in a movable part 28 and coupled, at the top part thereof with a coupling part 38 mounted on the supporting part 26. The lower surface of the coupling part 38 comprises two oppositely inclining paths 44, 46 and two rollers 48, 50 and when the rollers 48, 50 are turned oppositely by means of a stepping motor 52, the coupling part 38 is elevated or lowered to set the movable part 28 at a desired height through the couplers 30, 32. Since a collimation slit 20 of 0.1-10mm high is provided in the horizontal direction, the fuel element region can be determined visually, and the intensity of γ-ray can be measured.

Description

Detailed Description of the Invention

[0001]

FIELD OF THE INVENTION The present invention relates generally to methods of inspecting irradiated fuel elements from a nuclear reactor which must be stored and / or reprocessed during their outages.

[0002]

No matter how the method is adapted to such irradiated fuel, once such fuel leaves a nuclear power plant reactor, each fuel element may be characterized by a certain number of individual criteria. is necessary. One of the aforementioned criteria essential for its identification is the special burnup, ie the degree of fissile material depletion spent by the fissile material in the reactor during that time. This special burnup provides, among other things, direct information about the properties of the radioactive elements present in the fuel element and about their inverse proportions.

Traditionally, information about a particular burnup is obtained based on the measurement of the gamma radiation flux emitted by a fuel element and specialized software is used to reprocess the flux data. is doing. When storing spent fuel elements of different types and coming from different types of reactors in this way, the gamma-ray flux emitted by the different fuel elements depends on the type of element, the reactor type, the It may be very different as a result of the residence time and the time spent by the element being activated in the pool in which it was first placed. In addition, the fact that the gamma ray fluxes emitted in this way are very high fluxes and they have variable values does not facilitate the measurement.

In addition, the emitted gamma radiation is the basis on which the overall fuel element reprocessing process is determined,
Must be accurate. In general, it is the knowledge of the specific burnup of each fuel element that justifies or does not justify its subsequent reprocessing.

According to the state of the art, the gamma flux emitted by a fuel element is the gamma flux with which it is desired to move vertically in the pool and to measure it by a horizontal edge or region of limited thickness. It is measured by inspecting with a gamma detector across a collimator that defines the shape of the beam. The biological protection required for this is provided by the concrete structure and the lead shield.

[0006]

In the known structure,
The collimating slit has a limited thickness in the horizontal direction, which is this thickness which determines the thickness of the inspected fuel element region, and in the horizontal direction has a substantially trapezoidal shape, the long side of which The edges are opened in the vicinity of the fuel element to be observed and the short edges emerge on the actual gamma radiation detector. In the known device, such a collimator is formed from a slit with an adjustable aperture rather than a remote. This feature has led to a number of drawbacks, including the drawbacks described below. When moving from inspecting a first type fuel element to inspecting a second type fuel element, it is always possible to change the setting of the slit and change its opening in order to adapt it for each particular bundle. is necessary. However, in order to carry out such a modification, it is necessary to completely remove the collimator, which is very complicated and is particularly long and expensive.

It is an object of the present invention to provide means for collimating a beam of gamma rays emitted by an irradiated fuel element which is to be examined by a detector,
The invention also ensures the measurement of the strength of a gamma source with a high and variable flux level, while allowing a movable collimator with an adjustable slit and guaranteeing overall biological protection, The measurements are taken immediately and the corresponding devices are fixed and suitable for ensuring the protection of humans.

[0008]

SUMMARY OF THE INVENTION The present invention therefore resides in a gamma ray beam collimating means for collimating the gamma ray beam emitted by an irradiated fuel element region being inspected by a detector. Within the sleeve connecting the observation chamber formed therein and having the active part of the detector and the vertical axis in which the fuel element to be observed is movable in vertical translation, a constant vertical spacing above it. Fixed rigid base part on which another rigid fixed support part rides, -in the space between the two mentioned fixed parts, connected in their upper part to the connecting part resting on said support part A rigid part that is vertically movable by means of a vertical connection, a suspension of said connection, each being arranged around each connection in a vertical channel of said support part. Device for guiding in translation, -from two rollers with a transverse axis lying in the upper horizontal plane of said support part and in contact with one of two ramps inclined in the opposite direction of the underside of said connection part The two rollers mentioned above for causing a vertical translation of the movable part and thus for setting the height of the collimation slit resulting from the vertical spacing between the basic part and the movable part. The present invention relates to gamma ray collimating means comprising means for symmetrically moving in opposite directions.

As in the prior art, the collimator slit generally has a trapezoidal shape in the plane with a wide side towards the fuel element and a narrow side towards the detector, which is the fixed base and the fixed side. It is constituted by a space between it and a part which is movable perpendicular to the base, so that its thickness can be adjusted in the vertical direction by any means that is easily used.

According to an important feature of the invention, there are two rollers with a transverse axis which lie on the upper horizontal surface of the support part.
It is secured to one nut, each nut engaging a thread located at the end of a rod that is rotated by a stepping motor, the two threads having opposite directions.

According to another feature of the invention, the upper surface of the vertically movable part and the lower surface of the supporting part are fitted with their vertical fittings in order to oppose the presence of a straight path between said supporting part and said movable part. Has an acceptable complementary staircase or step appearance.

The invention is explained in more detail below with reference to non-limiting examples and with reference to the accompanying drawings, in which:

[0013]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT FIG. 1 shows that a vertical axis 2 formed in a concrete structure 4 does not form part of the invention and is movable in vertical translation within the axis of the axis 2 by means not shown. A fuel element 6 is shown.

Within the concrete structure 4 there is an observation chamber 8 containing a detector 10 and actuation logic 12, the sensing part 10 of the detector being enclosed in a radiation protection enclosure 14 so that said chamber 8 is enclosed. The person using the structure may be approached.

A sleeve 1 is provided between the vertical axis 2 and the observation chamber 8.
6 is cut into the concrete 4 and its one part 16a is fixed and has a first half 18 of the collimating slit and the second part 16b of the sleeve 16 is the second part of the collimating slit.
It houses a mechanism for adjusting the vertical size of half 20.

FIG. 2 shows in plan view the corresponding elements of FIG. 1 and shows the trapezoidal shape of the collimating slit connecting the shaft 2 and the fuel element 6 to the detector 10. This collimating slit is in two fixed parts 18 and 22 and one part which is horizontally movable. In the plan view of FIG. 2 one can see the trapezoidal shape of the three parts 18, 20, 22 of the collimating slit, the wide side of which on the right side of FIG.
2 and its narrow side on the left side of FIG. With reference to FIG. 3, a mechanism will be described which is accommodated within the portion 16b of the sleeve 16 and thereby adjusts the desired height of the collimation slit 20 to the desired value according to the present invention.

FIG. 3 shows a fixed base portion 24 which is located within the sleeve 16b and is made of, for example, solid steel. Above the fixing part 24 is arranged a rigid support part 26 which is fixed in relation to the concrete structure 4. A movable part which moves in a vertical translation between the two latter parts 24 and 26 and which can define the height of the collimating slit within the narrow limits resulting from the presence of the two fixed parts 24 and 26. There are 28. This movable part 28 moves in the following way. Two vertical connections 30,32 traversing channels 34,36 formed perpendicularly to the support part 26 are anchored in the movable part 28 at their base and resting on the support part 26 at their top. Connected to portion 38. In the vertical channels 34, 36, the guides 40, 42 ensure centering of the couplings 30, 32 during vertical movement within the channels 34, 36 and the support portion 26.

The vertical movement of the connecting members 30 and 32 can be performed by the movable portion 2.
Correlationally causes a vertical movement of 8 and therefore the height of the collimator slit 20 occurs in the following way.
The lower part of the connecting part 38 is constituted by two ramps 44, 46 and two rollers 48, 50 which are inclined in opposite directions, which rollers are explained in more detail in connection with FIG. Is located between the upper horizontal part of the support part 26 on one of the two ramps 44, 46, each of which is capable of rolling with respect to each other, and is perpendicular to the plane of FIG. . The stepping motor 52 is associated with FIG. 4 to cause the rollers 48, 50 to rotate in opposite directions and to raise or lower the connecting portion 38 as a result of whether they move away from or toward each other. Provided in connection with the mechanical device described, thus causing vertical translation of the movable part 38.

Referring now to FIG. 4, one possible embodiment of the drive mechanism for rollers 48 and 50 will be described. The drawing shows the sleeve 16b and the stepping motor 52 of FIG. This stepping motor has oppositely directed threads and has a nut 6 respectively.
It drives a horizontal shaft 54 which carries two screws 56, 58 with which 0, 62 engage. These two nuts support the rollers 48 and 50 of FIG. 3 on the transverse axis 64 for the first roller and the transverse axis 66 for the second roller. If the rod 54 rotates under the influence of the stepping motor 52,
It is self-evident that the two nuts 60, 62 are translated simultaneously when moving in opposite directions, ie towards or away from each other. In both cases, they also drive in the opposite direction, in relation to the ramps 44, 46, the rollers 48 and 50 which cause the desired height movement of the connecting part 38 and finally of the movable part 28.

Returning to FIG. 3, it should be noted that the movable part 28 and the support part 26 avoid the formation of a possible straight leakage path for gamma radiation from the axis 2 to the observation chamber 8 of the entire apparatus. Complementary stairs or steps 60,7
It has 0,72. These stairs 6
The heights of 8, 70, 72 are calculated in such a way that the above-mentioned nested receptacle is still present when the height of the collimation slit (20) is at a minimum.

Thus, according to the invention, it is possible to obtain a deformable collimator which allows a complete fuel element area to be viewed in the horizontal direction with a height of, for example, between 0.1 and 10 mm, to the desired value. Is set according to the height given to the slit 20.

As noted above, the present invention is a gamma beam collimating means for collimating the gamma ray beam emitted by an irradiated fuel element region inspected by a detector, formed within a concrete protective structure. And in the sleeve connecting the observation chamber with the active part of the detector and the vertical axis in which the fuel element to be observed is movable in vertical translation-another rigid at a certain vertical spacing above it. Rigid rigid base part on which the fixed support parts rest, -in the space between the two mentioned fixed parts, by means of vertical couplings which are connected in their upper part to the connecting parts resting on said support parts. A vertically movable rigid part, -in a vertical translation of said connections, each arranged around each connection in a vertical channel of said support part Device for internal use-a device consisting of two rollers with a transverse axis lying in the upper horizontal plane of the support part and in contact with one of two ramps inclined in the opposite direction of the underside of the connection part -Reversing the two rollers mentioned above in order to cause a vertical translation of the movable part and thus to set the height of the collimation slit resulting from the vertical spacing between the basic part and the movable part. It has a high and variable flux level whilst allowing a movable collimator with adjustable slits and guaranteeing overall biological protection, as it is configured with means for symmetrically moving A means for collimating the gamma ray beam can be provided which guarantees a measurement of the intensity of the gamma source.

[Brief description of drawings]

1 is a vertical front view showing a complete viewing device for a fuel element movable in its axis using a detector via collimating means according to the invention, FIG.

FIG. 2 is a plan view showing a collimator means having the same height as a collimator slit.

FIG. 3 is a cross-sectional view showing details of vertical moving means for a part that is vertically movable with respect to a fixed base.

FIG. 4 is an explanatory diagram showing a method of moving a plurality of rollers to cause vertical translation of a movable part.

[Explanation of symbols]

 2 vertical axis 4 concrete structure 6 fuel element 8 observation room 10 detector 16 sleeve 20 collimation slit 24 fixed base portion 26 support portion 28 movable portion 30 connection body 32 connection body 34 vertical channel 36 vertical channel 38 connection portion 40 guide device 42 Guide device 44 Slope 46 Slope 48 Roller 50 Roller 52 Stepping motor 54 Horizontal shaft 56 Screw 58 Screw 60 Nut 62 Nut 68 Stair (step) shape appearance 70 Stair (step) shape appearance 72 Stair (step) shape appearance

Claims (4)

[Claims] 1. A gamma-ray beam collimating means for collimating a gamma-ray beam emitted by an irradiated fuel element region examined by a detector (10), formed in a concrete protective structure (4) and In a sleeve (16) connecting an observation chamber (8) having the active part of the detector and a vertical axis (2) in which the fuel element (6) to be observed is movable in vertical translation, A fixed rigid base portion (2) on which another rigid fixed support portion (26) rides at a constant vertical spacing above it.
4),-in the space between the two mentioned fixed parts, by means of vertical couplings (30, 32) connected in their upper part to the connecting part (38) resting on said support part (26) A rigid part (28) that is movable in the vertical direction, a vertical channel (34,3) of the support part (26).
6) A guide device (40, 42) in the vertical translation of the connections (30, 32), which is arranged in each case around each connection, in the horizontal plane above the support part (26). A device comprising two rollers (48, 50) with a transverse axis and in contact with one of two ramps inclined in the opposite direction of the lower surface of the connecting part (38), the movable part (28) ) And thus the height of the collimation slit (20) resulting from the vertical spacing between the basic part and the movable part. ) To move symmetrically in the opposite direction (52, 54, 5)
6, 58, 60, 62), and a gamma ray collimating means. 2. The two rollers (48, 50) are fixed to two nuts, each nut being located at the end of a rod (54) driven by a stepping motor (52). , 58) engaging the two threads in opposite directions, the gamma ray collimating means according to claim 1. 3. A vertically nested housing for the upper surface of the vertically movable part (28) and the lower surface of the support part (26) to oppose the presence of a straight path between the support part and the movable part. Appearance of complementary staircase shape (68,
70, 72).
The gamma-ray collimating means according to any one of items 1. 4. The collimating slit (20) has a trapezoidal shape in the plane of its width and its length, with its long side directed towards the fuel element (6) and said small side. Gamma-ray collimation means according to any one of claims 1 to 3, characterized in that it is aimed at the detector (10).