GB2225152A

GB2225152A - Apparatus for treating compounds in a liquid and in particular having a bucket wheel rotating in a vessel and supply and discharge pipes for compounds

Info

Publication number: GB2225152A
Application number: GB8922547A
Authority: GB
Inventors: Didier Saudray; Brigitte Lorrain
Original assignee: Commissariat a lEnergie Atomique CEA
Current assignee: Commissariat a lEnergie Atomique et aux Energies Alternatives CEA
Priority date: 1988-10-25
Filing date: 1989-10-06
Publication date: 1990-05-23
Anticipated expiration: 2009-10-06
Also published as: JPH02259498A; GB2225152B; JP2860909B2; FR2638102B1; FR2638102A1; GB8922547D0

Abstract

Apparatus for treating compounds particularly irradiated nuclear fuel in a corrosive liquid of the type having a vessel (1), a mobile structure (5) carrying a wheel (4) with buckets (12), as well as part of a supply chute (43) and discharge chute for the compounds to be treated, another part of the chutes being fixed to the vessel (1). Several arrangements are proposed for reducing the splashing of liquid and foam and for improving sealing with respect to the outside and in particular a construction, fittable to at least one chute, for connecting parts (43, 44) by guide means (53, 54) and abutment means (48, 55). <IMAGE>

Description

Apparatus for treating compounds in a liquid and in particular having a bucket wheel rotating in a vessel and supply and disc harRe pipes for compounds.

DESCRIPTION The invention relates to an apparatus for treating compounds in a liquid. This apparatus has a vessel, a bucket wheel rotating in the vessel and supply and discharge pipes for the compounds.

An apparatus of this type is described in French Patent 79 30 952. It is a dissolver for irradiated nuclear fuel contained in rods or needles following the passage of the bundles of rods and their gratings into a shear, which has cut them up into sections with a length of a few centimetres, called shells.

The shells then reach the dissolver and via a supply chute or channel, which passes them into the vessel, travel to a bucket immersed in boiling nitric acid. The fuel is gradually dissolved.

The wheel then undergoes a sequential rotation bringing the buckets containing shells gradually out of the liquid. The shells are drained before being discharged into a discharge channel or chute, which passes them to a rinsing apparatus.

The apparatus described in this earlier-dated Patent has functioned satisfactorily, but various improvements have been thought out since its manufacture. The aim of these improvements is to improve the operation of the apparatus with respect to safety, regularity of dissolving, complete discharge of the shells out of the dissolver and maintenance. The main problem is associated with the dangerous nature of the treated products and the violence of the dissolving reactions. The dissolving of the oxide contained in the shells produces nitrous vapours, which when given off in gaseous form leads to pressure rises, spattering of liquids and foams. It is therefore necessary to limit to the greatest possible extent discharges of acid and dissolving products by the interstices at the vessel openings.However, it is difficult to reduce these interstices, because the vessel is assembled with a mobile structure carrying the wheel and part of the discharge and supply chutes. In view of the large dimensions of the apparatus, said assembly is far from easy and it is not easy to align with one another the chute parts located on the vessel and on the mobile structure.

The bubbling of the acid also has the disadvantage of agitating the shells in the buckets, so that they drop out of the latter.

Thus, in the earlier-dated Patent, a bubble elevator is provided making it possible to recycle to the buckets the shells which have dropped to the bottom of the vessel and which had slid onto the sloping bottom so as to arrive at the mouth of the elevator. Apart from the shells, small debris is encountered, called fines, which can be deposited at various locations of the apparatus.

The apparatus described in the earlier-dated Patent also does not have appropriate means for completely emptying the acid contained in the vessel, particularly when said acid contains too many impurities.

Thus, an essential objective of the invention is to obtain the maximum confinement of the solution within the vessel. This objective is firstly achieved by a particular construction of the chutes subdivided into an external part integral with the vessel and an internal part connected to the mobile structure.

This construction makes it possible to ensure a precise adjustment of the connecting surfaces of the two parts and can be adopted for the supply chute, the discharge chute or both such chutes, if appropriate. Various means make it possible to limit spattering and splashing of froth, foam and liquid.

Thus, greater operating safety is achieved and the emergent parts become dirty less rapidly. Rinsing means can also be added in order to increase this advantage.

Another objective of the invention is to better maintain the shells in the buckets. This objective is achieved to a certain extent by reducing spattering, i.e. the turbulence of the liquid.

However, mechanical confinement means for the shells in the buckets are also provided.

Finally, effective means are provided for emptying the acid and extracting or recycling the debris and particles which have dropped from the buckets.

In its more general form, the invention relates to an apparatus for treating compounds in a liquid having a vessel partly filled with liquid, a structure which is mobile with respect to the vessel, a rotary wheel carrying buckets supported by the mobile structure, a pipe for supplying the compounds to be treated to the buckets and a pipe for discharging the treated compounds out of the vessel, at least one of the pipes being subdivided and constituted by a part within the vessel and connected to the mobile structure and an external part integral with the vessel, whereby the mobile structure can assume with respect to the vessel an operating position for which the subdivided pipe parts form an extension of one another, characterized in that the inner part of at least one of the subdivided pipes is connected to the mobile structure by a connection offering a clearance and in that the vessel and each mobile inner part are provided with guidance means for bringing together the mobile inner part and the corresponding outer part and abutment means for keeping the said parts in an extension of one another.

The mobile inner part is advantageously connected to the mobile structure by an articulation having a clearance in an engagement direction corresponding to a displacement of the mobile structure towards the operating position.

Guidance means can be constituted by lugs cooperating with rails.

It is also possible to add deflecting flaps located between the corrosive liquid and the connecting surfaces, in order to limit spattering.

The mobile structure can be advantageously provided with a solid or perforated cover member covering the opening of the buckets immersed in the acid and filled with shells.

The invention is described in greater detail hereinafter relative to non-limitative embodiments and the attached drawings, wherein show: Fig. 1 an overall front view of the apparatus.

Fig. 2 a front view of the central part of the apparatus.

Fig. 3 a side view of the supply chute and the central part.

Fig. 4 a side view of the discharge chute and the central part.

The described construction comprises a certain number of elements identical or similar to those of the earlier-dated Patent referred to hereinbefore and reference should be made to the text thereof for more complete explanations of these elements.

The dissolving apparatus firstly comprises (fig. 1) a stainless steel vessel 1, whose bottom 2 slopes. Vessel 1 is partly filled with the boiling etching solution e.g. containing nitric acid up to a level 3. Vessel 1 has an oblong horizontal section roughly enveloping the wheel 4. The apparatus is shown in the operating position and it can be dismantled into two parts, one of which is essentially constituted by the vessel 1 and the other by a mobile structure 5, which firstly comprises a cover 6 placed on the top of vessel 1 when the apparatus is in the operating position. Vessel 1 and cover 6 are provided on their adjustment bearing surface with a hydraulic guard 7 forming a packing with respect to nitrous vapours.

Cover 6 carries a support part 8 on which are installed rollers 9 making it possible to support wheel 4. A main shaft 10 terminated by a pinion 11 traverses the cover 6 and makes it possible to rotate wheel 4 by meshing in a toothed ring thereof. The means used and the performance of the operation are as in the aforementioned Patent. Thus, if wheel 4 comprises twelve buckets 12, designated here 12a to 12L, the wheel 4 can be rotated by 1/12 turns, whilst defining the sequence times compatible with the constraints of the process. Rotation takes place here in accordance with arrow 13 in counterclockwise direction. Buckets 12 have front and rear walls 14 and 15 with cut faces. Each of these walls has a forwardly oriented ledge or edge respectively 16 and 17 on either side of opening 18. This arrangement prevents any premature discharge of shells following dissolving, when the buckets 12 are raised out of the acid and tilted over.

The front and rear walls 14,15, as well as the bottom 19 of buckets 12 are perforated and the diameter of the perforations is a few millimetres. However, the side walls 20 and 21 of buckets 12, which are close to the side walls of vessel 1, are solid in order to limit movements and spattering of acid and foam into this reduced space.

A central part 30 (cf. also fig. 2) is attached to support 8 and is located in the centre of the hollowed out wheel 4. The central part 30 comprises two parallel walls 31,32, which are substantially circular and between which extend hopper plates.

A supply hopper or funnel 33 is defined by a left-hand, outer plate 34, which borders the side plates 31,32 over part of their circumference and by a right-hand, outer plate 35. The outer plates 34 and 35 are in each case inclined towards one another and separated by an opening 65. A discharge hopper or funnel 36 is defined by the apex of the right-hand outer plate 35, by a radial plate 37 inclined towards the previous plate and by a bottom 38 connnecting these two plates and inclined towards one of the side walls 32. The radial plate 37 and the bottom 38 separate the two hoppers 33,36. Thus, the discharge hopper 36 overhangs the supply hopper 33 and is completely separate therefrom. The second side wall 32 has two orifices 39,40 respectively issuing into the supply hopper 33 and at the bottom of the discharge hopper 36.A horizontal bar 41, parallel to the second side wall 32 and fixed thereto by means of support clamps 42, is located not far from the latter in front of the first opening 39. An inner mobile part 43 of a supply chute for the shells is connected to the central part 30 via bar 41, in accordance with an arrangement characteristic of the invention and which will now be described.

For constructional reasons, the chutes or channels for supplying the shells to the vessel and for discharging the treated shells must pass through the wall of vessel 1. In order to be able to introduce wheel 4 in a vertical engagement direction, it is consequently necessary to subdivide them and construct them in two-part form, namely an inner part connected to the mobile structure and an outer part, whose end is welded to vessel 1. These parts are designated 33,34 for the supply chute. In the earlierdated Patent, the aligning or placing in a precise extension of one another with a very reduced clearance of the two parts 43 and 44 was made difficult, because the inner part was rigidly connected to the mobile structure and the manufacture and handling of such large parts cannot be very accurate.

The mobile part 43 of the supply chute firstly comprises (cf.

fig. 3) a connecting surface 45 into which opens the pipe 46, which must extend that of the outer part. Connecting surface 45 forms an edge of a connecting member 47 provided with a lower abutment surface 48 and two tabs 49 perforated by a vertically elongated hole 50. Bar 41 passes through the two elongated holes 50, the inner part 43 of the supply chute being articulated with respect to the central part 30, whilst still having an essentially vertical clearance with respect thereto.

Thus, pipe 46 passes through the first opening 39 and issues into the supply hopper 33, after which it curves and becomes vertical by a lower end 51, which terminates just below level 3. This arrangement permits a better guidance of the shells towards a bucket 12a beneath supply hopper 33. However, it is then necessary to provide slots 52 above level 3, in order to prevent vapour overpressures in pipe 46. It has been found that the slots 52 with a relatively large cross-section and which are located on the lower end 51, just above level 3, are not greatly exposed to dirtying and clogging by the oxide. Advantageously slots 52 open towards the outer plates 34,35, because the supply hopper 33 is wider in this direction, which makes it possible to limit the splashing and spattering of acid, froth and foam.

The support member 47 comprises two lateral lugs 53, whilst two rails 54 are positioned within vessel 1 on either side of the opening defined by the fixed part 44 of the supply chute. During the assembly of the dissolver, the lugs 53 are placed between the wall of vessel 1 and a respective rail 54 and they are gradually moved towards the same, because the substantially vertical rails 54 are closer to the wall of vessel 1 in the downwards direction. The connecting surface 45 is consequently brought towards the wall of the vessel 1 and is finally engaged against the same. A bracket 55 is provided on the wall of vessel 1 and serves as an abutment for the lower surface 48 of support member 47.Thus, it is ensured that the pipes of the inner and outer parts 43 and 44 are in an extension of one another and without any signifcant clearance, no matter what the fitting position of the central part 30, due to the connection between bar 41 and the elongated holes 50. The continuity of the pipe obtained completely eliminates the risks of the passage of shells and oxide between the wheel 4 and vessel 1.

As can be seen in fig. 4, the second opening 40 is provided with an inner part 60 of a discharge chute for the shells following the treatment thereof. The inner part 60 is extended in the operating position by an outer part of said same chute integral with vessel 1.

There is no respective adjustment of the two chute parts 60,61, as for the supply chute, so that there is a clearance between them. In order to prevent the splashing of liquid towards the outer part 61 of the discharge chute, deflecting flaps 62 occupy part of the space between the second side wall 32 and the vessel 1, thus breaking the acid splashes and returning them to the face opposite to the outlet. The deflecting flaps 62 are fixed to the second side wall 32 between the acid and the connecting zones of the two parts 60,61, overhanging the buckets 32 and in order to improve the trickling and draining of the acid received, are inclined towards vessel 1 and have different lengths, decreasing in length towards the top.These deflecting flaps 62 are particularly valuable in the represented embodiment, where the discharge chute is positioned above the buckets 12b and 12c immersed in the acid and in which continuous dissolving takes place, which leads to turbulence at this point. Side wall 32 is open between the deflecting flaps 62.

A latticed cover member 63 is positioned between side walls 31 and 32 and extends (fig. 2) above the openings 18 of buckets 12b and 12c and at a limited distance therefrom, in order to prevent or reduce the passage of the shells out of the buckets 12b and 12c. A solid cover member would also have been effective, but would have reduced the circulation of acid and would therefore have been prejudicial to the dissolving process. This cover member can also have an inspection hatch, so that action can take place within the facing bucket when the cover is removed.

A collar 64 adjacent to cover member 63 is located immediately below the opening 65 of supply hopper 33. It covers the periphery of opening 18 of bucket 12a into which the shells are introduced at this time to reduce or eliminate liquid splashing caused by the escape of reaction gases outside the loading hopper, the opening defined by the collar 64 having to have a projected surface inscribed in the opening of the bucket in order to reduce or eliminate the dropping of shells alongside bucket 12a.

However, it is inevitable in practice that shells will be located outside the buckets. These shells must be recycled with the aid of a bucket elevator 66 shown in fig. 1 and constituted by a pipe 67 entering the interior of vessel 1 by an opening in cover 6, a vertical suction pipe 68 extending to the bottom 2 of vessel 1 and more specifically into the lowest part 69 of said bottom, a box for degassing the solution and ensuring its passage to an oblique recycling pipe 70 connecting the suction pipe 68 by its upper end and the supply hopper 33 by its lower end as a result of a hole made in the first side wall 31 facing the lower end of the oblique recycling pipe 70.

This bubble elevator 66 is original, because it is supplied by two air pipes. A normal supply pipe 71 provides it with a constant flow of 11 m3/hour in the present case, which is adequate for the intake or admission of the shells which have dropped to the bottom of vessel 1. However, the bubble elevator 66 is also supplied by an additional air supply pipe 72 on which is placed a flow variator 73, such as an automatically regulated electro valve. The maximum flow rate of this additional air 3 supply pipe 72 is much higher and can reach 50 to 60 m /hour.

A manometer 74 is installed in the atmosphere of vessel 1 and controls the flow variator 73.

Due to the sudden discharge of nitrous vapours whenever shells are loaded, the pressure reduction or vacuum prevailing in the atmosphere of the vessel 1 becomes much lower whenever shells are charged or loaded. The air flow passing through the bubble elevator is then instantaneously reduced to combat said pressure rise and then the air supply is reestablished at a high rate, which makes it possible to bring colder acid into the reaction zone.

However, in order to limit irregularities of the operation of the apparatus, the heating circuit for the solution, which comprises a double bottom 81, into which is introduced the hot vapour which condenses to heat the solution, is not supplied at constant pressure as in the known apparatus, but at a constant mass flow from a system equipped with a flow regulating device 75. The oxide charging periods vary the heat exchange during a cycle, which can be explained by the fact that with a vapour supply regulated to constant pressure, the condensed vapour flow and therefore the heating are not uniform and tend to increase during the charging periods, which is prejudicial to the operating safety, there being an increase in reactivity and therefore liquid turbulence and spattering.

In order to form a barrier to the froth and foam which could form on the inner face of vessel 1, coils 76 are provided slightly above the level 3 and traversed by a cooling fluid. The foam condenses level with coil 76 and drops again.

A device for emptying vessel 1 is also provided. Under normal conditions, the acid is regularly replenished by a supply means and is able to flow out via an overflow 77. However, a total emptying can be advantageous in order to completely remove all the suspended fines and clean the bottom of the vessel, where debris of various sizes tends to accumulate, despite the bubble elevator 66.

Thus, a siphon 78 is located in the vicinity of the suction pipe 68 of the bubble elevator 66. Siphon 78 issues very close to the lowest point 69 of vessel 1 and passes out of the latter above level 3. When the apparatus is stopped, a first siphon described in the earlier-dated Patent makes it possible to almost entirely empty the vessel. There then remains a dead volume of a few or a few dozen litres, whose content is not sucked up by the first siphon. It is constituted by a residual liquid containing a very large amount of fines deposited by gravity.

It is for this reason that an air injection pipe 80 is provided, which issues close to siphon 78. The air is injected at the moment of emptying and restores the fines into suspended form by bubbling, so that they can be discharged. At the same time, the arrival of water through pipe 79 makes it possible to rinse the bottom 2 and move the accumulateddebris towards siphon 78.

Account has also been taken of the circumstance where already treated shells drop from the buckets 12 before reaching the discharge hopper 36. This case is represented by bucket 12e in the drawing, which occupies a median height position, where it is horizontal. It can be seen that bucket 12e contains too many shells, which can drop despite the guard constituted by the rear ledge 17. Thus, between the central walls 31,32 is provided a curved wall 91 positioned facing the opening of bucket 12e and a control plane 90 leading in front of the end of the rear ledge 17 of the immediately lower bucket 12d. Thus, the dropped shells pass immediately into said bucket.

Various other improvements can also be proposed. Thus, the seal between cover 6 and main shaft 10 can be ensured by a hydraulic joint 94. Another hydraulic joint 95 can be positioned between the bubble elevator 66 and cover 6. The bubble elevator 66 can then be made dismantlable from the cover 6 so that it can be changed. Pipe 70 is integral with vessel 1 and then terminates at a limited distance from the side wall 31 in front of an opening thereof and the acquired velocity projects virtually all the recycled mixture into the supply hopper 33.

It should be noted that the left-hand outer plate 34 is interrupted, so that the supply hopper 33 is open upwards in front of two buckets 12i and 12j which are empty at this time, which allows a greater release volume for the gases and foam.

Rinsing devices are also provided. An acid rinsing pipe 97 for pipe 46 of the inner part 43 of the supply chute is provided, in order to prevent its dirtying by fines detached from the shells during their dropping. There is also a water rinsing pipe 98 striking the area of the wheel 4, which has just passed out of the acid bath in order to remove therefrom the fines deposited thereon before reaching the rollers 9 and pinion 11. Finally, there is a water rinsing pipe 99 for the fixed part 61 of discharge chute, so as to prevent its dirtying by fines.

Thus, the wheel dissolver according to the invention offers numerous improvements compared with the prior art construction.

Claims

1. Apparatus for treating compounds in a liquid having a vessel (1) partly filled with liquid, a structure (5) which is mobile with respect to the vessel, a rotary wheel (4) carrying buckets (12) supported by the mobile structure (5), a pipe (43,44) for supplying the compounds to be treated to the buck ets (12) and a pipe (60,61) for discharging the treated com pounds out of the vessel (1), at least one of the pipes being subdivided and constituted by a part (43,60) within the vessel (1) and connected to the mobile structure (5) and an external part (44,61) integral with the vessel (1), whereby the mobile structure (5) can assume with respect to the vessel (1) an operating position for which the subdivided pipe parts form an extension of one another. herein the inner part (43) of at least one of the subdivided pipes is connected to the mobile structure (5) by a connection offering a clearance (41,50) and wherein the vessel (1) and each mobile inner part (43) are provided with guidance means (53,54) for bringing tog ether the mobile inner part and the corresponding outer part (44) and abutment means (48,55) for keeping the said parts in an extension of one another.

2. Apparatus for treating compounds according to claim 1, wherein the inner mobile part (43) is connected to the mobile structure (5) by an articulation (41,50) having a clearance in an engagement direction corresponding to a dis placement of the mobile structure (5) towards the operating position.

3. Apparatus for treating compounds according to claim 2, ''ere'n in-that the guide means are constituted by lugs (53) and rails (54) essentially parallel to the engagement direc tion, one of these said means being carried by the mobile inner part (43) and the other by vessel (1), means (53) carr ied by the inner mobile part (43) passing between means (54) carried by vessel (1) and the latter.

4. Apparatus for treating compounds according to either of the claims 2 and 3, wherein the abutment means incorporate a bracket (55) on vessel (1).

5. Apparatus for treating compounds according to any one of the claims 1 to 4. wherein deflecting flaps (62) are positioned between the liquid and the connection zones of at least one of the subdivided pipes (60,61).

6. Apparatus for treating compounds according to any one of the claims 1 to 5, wherein the mobile structure (5) carries a wall (32) separating the buckets from a wall of the vessel carrying the outer part of at least one sub divided pipe.

7. Apparatus for treating compounds according to either of the claims 5 and 6. wherein the deflecting buckets (62) are carried by the separating wall (32).

8. Apparatus for treating compounds according to any one of the claims 1 to 7, in which the inner part (43) of the supply pipe extends into the liquid when the mobile structure (5) is in the operating position, characterized in that slots (52) are formed in the inner part of the supply pipe above the liquid.

9. Apparatus for treating compounds according to claim 8, wherein the slots (52) are oriented in the largest dimension of a space defined by a hopper (33), which surr ounds the inner part (43) of the supply pipe.

10. Apparatus for treating compounds according to any one of the claims 1 to 9, w:ere'.n the mobile structure comprises a cover member (63) at least partly covering the opening of buckets (12b,12c) immersed in the corrosive liquid and containing compounds.

11. Apparatus for treating compounds according to one of the claims 1 to 10, wherein the mobile structure comprises a collar (64) between the supply pipe (43,44) and a bucket (12a) located beneath the supply pipe, the collar covering the peripheral part of the bucket opening.

12. Apparatus for treating compounds according to any one of the claims 1 to 11, comprising a bucket elevator (66), char acterized in that it comprises a gas flow variator (73) supplying the elevator in response to the readings of a manometer (74) measuring the pressure of the atmosphere in the vessel above the liquid.

13. Apparatus for treating compounds according to any one of the claims 1 to 12 having a means for heating the liquid by a vapour circuit (81) along vessel (1), characterized in that it comprises a means (75) for supplying vapour at a constant mass flow rate.

14. Apparatus for treating compounds according to any one of the claims 1 to 13, wrer'ei it comprises a cooling liquid coil (76) on the vessel above the liquid.

15. Apparatus for treating compounds according to any one of the claims 1 to 14, wflereiri it comprises a siphon (78) for emptying the vessel.

16. Apparatus for treating compounds according to claim 15, in which the vessel has a sloping bottom (2), wherein the siphon issues close to the lowest point (69) of bottom (2) of vessel (1).

17. Apparatus for treating compounds according to claim 16, wherein a gas injection pipe (80) issues close to the siphon (78) at the bottom of the vessel.

18. Apparatus for treating compounds according to any one of the claims 1 to 17, wNI+erQin it comprises a rinsing pipe (79) issuing at the bottom of the vessel.

19. Apparatus for treating compounds according to any one of the claims 1 to 18 wherein it comprises means (97,99) for rinsing the wheel and pipes.

20. Apparatus for treating compounds according to any one of the claims 1 to 19, wner-,sl the buckets are perforated, except in the portions (20,21) close to the vessel.

21. Apparatus for treating compounds according to any one of the claims 1 to 20, wiper'erin the mobile struc ture comprises a wall (91) facing the opening of a loaded bucket (12e).

22. Apparatus for treating compounds substantially as hereinbefore described with reference to the accompanying drawings.