GB2175514A

GB2175514A - Apparatus for filtering radioactive slurry

Info

Publication number: GB2175514A
Application number: GB08612095A
Authority: GB
Inventors: Norbert Rohleder; Folkmar Schwarz
Original assignee: KARLSRUHE WIEDERAUFARBEIT; Wiederaufbereitungsanlage Karlsruhe Betriebsgesellschaft MbH
Current assignee: KARLSRUHE WIEDERAUFARBEIT; Wiederaufbereitungsanlage Karlsruhe Betriebsgesellschaft MbH
Priority date: 1985-05-24
Filing date: 1986-05-19
Publication date: 1986-12-03
Also published as: FR2582231B1; GB8612095D0; BR8602345A; DE3518718C2; JPS6224196A; DE3518718A1; BE904748A; FR2582231A1

Abstract

Apparatus for filtering radioactive slurry comprises a pressure housing with an upper inlet 61 and a lower outlet 101 for filtrate, divided by a removable filter in the form of a stack of filter discs clamped between support plates. The stack defines a central axial passage, closed at the lower end, from which slurry flows into spaces defined above each filter disc, the filtrate passing down through the discs and radially outwards through protective grid 97. After filtering, compressed gas is fed to inlet 61 to expel residual liquid, and housing cover 43 is withdrawn after unscrewing spindle 48 and pivotting yoke 49 sideways. The filter is then lifted from the housing by remote handling equipment, retaining all the solids within the spaces above the filter discs. <IMAGE>

Description

SPECIFICATION Apparatus for filtering a slurry of radioactive liquids charged with solids The invention relates to apparatus for filtering a slurry of radioactive liquids charged with solids comprising a pressurizable housing with a filter therein, a cover and feed means for the slurry, a collecting chamber provided at the bottom of the housing and a discharge for the filtrate.

In the reprocessing of irradiated nuclearfuel elements, fuel solutions are produced, which are cloudy and which contain a number of parts per thousand by weight of suspended insoluble components. The solids, being the dissolution residues, which are to be separated from the fuel solution, are zirconium particles and insoluble sludge of varying composition.

For the purposes of the further procedure, it is necessary for those solid components to be separated off before the solution passes into the extraction stage. That is achieved either by centrifuging or by filtration.

It is known to use what are referred to as bag filters with plastics filter agents for filtration purposes. However such bag filters do not have any retention effect in the micron and sub-micron range and they have only a small filter surface area per unit of volume, which adversely affects economic use thereof. In addition mechanical stability of a bag filter is not adequate in every case.

A further proposal in regard to filter apparatus for the stated purpose relative to high-quality steel candle filters which can be back-flushed. Such candle filters also provide for inadequate retention of solids in the sub-micron range. Furthermore, a disadvantage of candle filters is that they have only a limited service life as the clogged filter pores can be only partially cleaned by back-flushing.

German laid-open application (DE-OS) No.

31 36 905 discloses a pressure filter for separating residues from the wet-process incineration of Pubearing waste materials, which has a housing with a cover and a feed for the solution. Separation of the solids and the filtrate occurs in the housing. The arrangement has a filter cup in which a sieve basket is sealingly fitted. Formed between the sieve-like bottom plate of the sieve basket and the bottom of the filter cup is a collecting chamber or space for the filtrate, which can be carried away by way of a filtrate discharge connection sealingly through the bottom of the housing by means of the interior of the housing being pressurized or by a reduced pressure being generated at the filter discharge connection. That filter represents a single-plate horizontal filter and has a low rate of throughput.

The described filter apparatus give rise to difficulties when changing a charged filter insert because the concentrated radioactive solids can result in the radioactivity being entrained. As the operation of replacing a filter insert must be carried out by way of remote-controlled equipment, using the remote handling procedure, the danger of radioactive substances being entrained is particularly high.

When using the filter apparatus of the state of the art a filtered solid product is produced, which requires further expensive process steps and items of equipmentforfurther processing.

According to the invention there is provided apparatus for filtering a slurry of radioactive liquids charged with solids comprising a pressurizable housing with a filter therein, a cover and feed means for the slurry, a cOllecting chamber provided at the bottom of the housing and a discharge for the filtrate, wherein the filter comprises a plurality of horizontally disposed filter plates which are in superposed stacked relationship and which each carry a respective deep-layer filter agent which is effective into the sub-micron range, the feed of the slurry is effected centrally into the stack of the filter plates by way of a vertical central passage with which the intermediate spaces between the filter plates, which spaces lies above the respective filter agent layer, communicate, the filter plates are sealed off relative to each other at the outer periphery and outwardly have radial discharge openings for the filtrate, the central passage is fluidtightly closed off at the lower end by a plate, and the filtrate can be withdrawn in per se known manner by way of a filtrate line at the bottom of the housing.

Such filtering apparatus can be well suited for use in nuclear installations, can be satisfactorily replaced by a remote handling procedure and in that respect can minimize the entrainment of radioactive particles, while permitting a high rate ofthroughput with a very good degree of retention of very fine solid components.

The solids-charged radioactive liquid flows to the filter housing from above by way of the feed in the cover of the housing and is distributed from the centre by way of the central passage into the intermediate spaces between the filter plates. Athin filter cake is formed on the filter agent of the filter plates, by the solid matter being retained; an additional depth filtration effect is achieved by virtue of the choice of the filter agent. The filtrate flows through the filter agent and is removed radially outwardly. The filtrate collects in the lower part of the filter housing and is fed to its destination by way of a filtrate line.

If, after a prolonged period of operation, clogging of the filter pack is signalled by a rise in the feed or upstream pressure, the filter plate stack must be replaced by a fresh filter unit. For that purpose the cover of the filter housing is opened by a remote handling operation and the filter insert is lifted out of the filter housing by means of a lifting apparatus.

The radioactive waste is securely enclosed in the filter stack and can be conditioned in suitable containers and passed to a final storage location. A filter insert is fitted into the filter housing by operation in the reverse sequence, and the filter apparatus is closed again, to be ready for further operation.

In an advantangeous embodiment of the invention, the stacked filter plates are welded together to form a unit. The welding is done at the outer periphery and seals the filter plate stack outwardly with the exception of the radial discharge openings for the clarified filtrate. That arrangement ensures that the retained solid material remains securely enclosed in the filter stack. The welding gives the filter stack an enhanced level of mechanical stability which is found to be advantageous particularly in relation to remote handling.

In another embodiment of the invention, the filter insert comprises a plurality of superposed filter plate units. The individual filter plates or a plurality of superposed filter plate units can be secured between two clamping plates by way of a centrally disposed clamping pin or bolt That provides a filter insert which is easy to handle. The lower clamping plate may advantageously serve for sealing off the central passage. If the lower clamping plate is releasably connected to the clamping pin or bolt, that arrangement permits the filter holding means consisting of clamping plates and clamping pin or bolt to be re-used.

The upper handling plate can be provided with a handling eye for further simplified remote handling of the filter insert.

Preferably the upper clamping plate is loosely suspended in the filter housing with the edge portion of the upper clamping plate on a peripheral annular shoulder, with the inclusion of a seal and is loaded by a compression spring bearing against the cover, and has at least one bore in the region of the central passage which passes vertically through the filter insert.

The loosely inserted filter insert can be easily lifted out of the filter housing by operating at the handling eye on the upper clamping plate. The annular shoulder and the annular surface which lies thereon, of the upper clamping plate, sealingly separate the upper feed chamber or space of the housing from the remainder of the space defined by the housing.

Advantageously, the cover of the housing is provided with a positive receiving means for receiving a locking head of a screwthreaded pressure spindle which is guided in a clamping yoke member which is rotatably mounted laterally on the housing and the clamping yoke member has clamping projections for engaging under a flange on the housing.

Such a structure permits the cover to be locked and unlocked on the filter housing in a simple and operationally reliable manner, in a remote-handling operation.

In order to avoid losses of dissolved valuable substances in the filter cakes, such as for example uranium or plutonium, the filter insert can be flushed with suitable solvents. The residual liquid in the filter insert can also be urged out by introducing gas through a suitable feed line before the cover of the filter housing is opened and the filter insert is removed.

The invention can provide a compact filter insert through which the liquid to be filtered flows from the interior outwardly, with the filter insert retaining the solids therein. The radioactivity is not entrained.

There is no need for separate handling of concentrated solids sludges.

The invention can provide a filter apparatus which enjoys enhanced mechanical stability and which can have a long service life. A high throughput with at the same time a fine filtering action is to be considered as a further important advantage of the apparatus of the invention.

The invention generally solves the various kinds of technical problems involved in a filter apparatus for the stated use, within a structural unit.

Two embodiments of the invention are diagrammatically illustrated by way of example with reference to the accompanying drawings, from which per se known items of equipment have been omitted in the interests of clarity and in which:~ Figure 1 is a diagrammatic view of a first embodiment of filtering apparatus according to the invention including a filter insert which is fitted in a filter housing and which comprises a multiplicity of filter plates in superposed stacked relationship; Figure 2 is a sectional view on an enlarged scale of a portion of a stack of superposed filter plates of the embodiment of Figure 1 with a central feed and a discharge at the outside periphery; and Figure 3 shows a modified embodiment of filtering apparatus according to the invention with a filter insert comprising three filter plate units.

Referring to Figure 1, a filter housing 6 is closed by a cover 7 by means of flange screws 8. The cover 7 has a handling eye 9 and is connected by way of a feed 11 to a feed line 12 for a solids-charged fuel solution. The line 12 has a pressure measuring device 13 and is connected to a branch line 14 which communicates with a gas pressure source (not shown).

Disposed in the housing 6 is a filter insert 15 which is loosely hung in the filter housing 6 by way of an upper clamping plate 16 supported on a peripheral annular shoulder 17. Provided at the lower end of the filter insert 15 is a closed clamping plate 18 which is fixedly connected to a clamping pin or bolt 19. The plates of the filter stack 15 are held together between the two plates 16 and 18 by way of the clamping pin or bolt 19.

The upper clamping plate 16 has a handling eye 22 which is loaded by a compression spring 21 and is provided in concentric relationship with the clamping pin or bolt 19 with bores 23 which communicate with a vertical feed passage 24 disposed centrally in the filter stack 15.

Disposed beneath the clamping plate 18 is a collecting chamber 25 for the filtrate. The filtrate flows to its destination by way of a filtrate discharge line 26.

Referring to Figure 2, shown therein are superposed filter plates 31 of the filter insert 15, which carry pieces of a filter agent 32. The pieces of filter agent 32 are clamped at the outer periphery and adjacentto the vertical passage 24. Beneath each piece of filter agent 32 is disposed a respective discharge passage 33 defined by the respective filter plate 31. The discharge passages 33 terminate in radial discharge flow openings 34 in the outer peripheral surface of the filter insert 15.

Each filter plate 31 lying above a piece of filter agent 32 is provided on the underside with feed flow passages 35 which are incorporated therein and which communicate with the feed passage 24, at the ends of the passages 35 which are towards the centre.

The uppermost filter plate 31 has two concentrically disposed sealing rings 37 which seal the filter insert 15 against the upper clamping plate 16.

The mode of operation of the above-described apparatus is as follows: The solids-charged sludge or slurry of fuel solution flows to the filter housing 6 above the upper clamping plate 16 and passes through the bores 23 in the plate 16 and into the vertical central feed passage 24. From there the fuel solution is distributed from the centre onto the pieces of filter agent 32 on the filter plates 31. Athin filter cake is formed on each piece of filter agent 32 by the solid matter being retained, while the filtrate passes through the pieces of filter agent 32 into the discharge flow passages 33 and is carried away radially outwardly. The filtrate collects in the lower collecting chamber 25 of the filter housing 6 and flows to its destination by way of the filtrate discharge line 26.

The pieces of filter agent 32 comprise glass fibre cloth.

If the feed pressure at the pressure measuring device 13 on the line 12 rises, that signals clogging of the filter insert 15. When a predetermined limit pressure in the line 12 is reached, the feed is shut off and residual liquid in the filter insert 15 is urged out by supplying gas through the branch line 14.

Aftethatflushing operation or drying operation, the cover 7 of the filter housing 6 is opened by a remote handling operation and the loosely inserted filter insert 15 is lifted complete out of the filter housing 6 by means of a lifting apparatus, using the handling eye 22. The parts of the filter mounting such as the clamping plates 16 and 18 and the clamping pin or bolt 19, being parts which consist of steel with a high level of resistance to corrosion, are dismantled under remote control in a separate working station, and fitted into a new filter plate stack to provide a fresh filter insert 15.

After a fresh filter insert 15 has been fitted into the filter housing 6, the cover 7 is closed and the filter is again ready for operation.

The filter apparatus shown in Figure 3 comprises a housing 41 which is closed by a lockable cover 43.

The locking action is produced by way of a locking mechanism 45 which is mounted centrally above the cover 43 and which has a T-shaped receiving means or mounting 46 into which engages a locking head 47 of a screwthreaded pressure spindle 48 of a clamping yoke or stirrup member 49 mounted pivotably on the housing 41. The clamping yoke member 49 has two clamping projections 51 and 53 which engage under a flange 55 on the filter housing 41 in the locked condition. Mounted on the upper part of the clamping yoke member 49 is a guide 59 which is intended to guide an impact screw driving tool for actuating the spindle 48.

The filter housing 41 is laterally provided with a fixed claw member 60 for mounting in a frame or rack and in an upper region has a feed connection 61 forslurry to be filtered. Provided in the filter housing 41 is a peripheral annular shoulder 63 on which the edge portion of an upper clamping plate 64 is supported, with the inclusion of a peripheral sealing ring 67. The clamping plate 65 is fixedly connected to a handling eye 69 and is pressed downwardly onto the annular shoulder 63 by way of a springloaded pressure head 71. A clamping pin or bolt 73 terminates in the handling eye 69 and at its lower end has a female screwthread 75 into which is screwed a screwthreaded pin or bolt 77 of a lower clamping plate 79.Three filter plate stack units 81, 83 and 85 are arranged between the two clamping plates 65 and 79 in a condition of being firmly pressed together, the individual units each enclosing respective sealing rings 87.

The clamping pin or bolt 73 passes through a central vertical feed passage 89 which extends perpendicularly through the filter insert 91. In the region of the passage 89 the upper clamping plate 65 has bores 93 which connect the feed chamber or space 95 with the feed passage 89.

The filter insert 91 is surrounded over the major part of its length by a grid-like housing 97 which is provided with openings and which represents a further mechanical protection.

A collecting chamber 99 for the filtrate is provided beneath the filter insert 91. A filtrate discharge line 101 is disposed in the bottom of the filter housing 41.

The mode of operation in replacement of the filter insert 91 in Figure 3 is as follows: When the feed pressure rises, the feed is shut off.

By means of an impact screw driving tool, the screwthreaded pressure spindle 48 is turned by the tool engaging its actuating hexagon and moved upwardly. The clamping action of the cover 43 is thus removed. The clamping yoke member 49 is pivoted to the side whereby the clamping projections 51 and 53 come out of engagement with the flange 55 and the form-locking or positive locking head 47 of the screwthreaded pressure spindle 48 thus comes out of the T-shaped groove of the locking mechanism 45 on the cover 43. The cover 43 is then free and can be lifted away from the filter housing 41 by gripping it with a lifting tool so that the filter insert 91 is exposed and can be gripped. The lifting tool engages the handling eye 69 and lifts out the filter insert 91 and moves it to the conditioning apparntus: The operation of fitting a fresh filter insert 91 is carried out in the reverse sequence in that the cover 43 of the housing is fitted onto the filter housing 41 under remote control, the clamping yoke member 49 is pivoted into position over the cover 43 so that the positive-locking head 47 of the screwthreaded pressure spindle 48 engages into the T-shaped groove of the locking mechanism 45 and the clamping projections 51 and 53 engage under the flange 55 on the housing 41 and the spindle 48 is rotated, to move it downwardly, by way of an impact screw driving tool so that the cover 43 is fixedly clamped in position on the housing.

Claims

1. Apparatus for filtering a slurry of radioactive liquids charged with solids comprising a pressurizable housing with a filter therein, a cover and feed means for the slurry, a collecting chamber provided at the bottom of the housing and a discharge for the filtrate, wherein the filter comprises a plurality of horizontally disposed filter plates which are in superposed stacked relationship and which each carry a respective deep-layerfilter agent which is effective into the sub-micron range, the feed of the slurry is effected centrally into the stack of the filter plates by way of a vertical central passage with which the intermediate spaces between the filter plates, which spaces lie above the respective filter agent layer, communicate, the filter plates are sealed off relative to each other at the outer periphery and outwardly have radial discharge openings for the filtrate, the central passage is fluid-tightly closed off at the lower end by a plate, and the filtrate can be withdrawn in per se known manner by way of a filtrate line at the bottom of the housing.

2. Apparatus according to claim 1, which the stacked filter plates are welded together to form a unit.

3. Apparatus according to claim 2, in which the filter comprises a plurality of superposed filter plate units which are sealed off relative to each other.

4. Apparatus according to claim 1 or claim 3, in which the filter insert is arranged between two clamping plates which are interconnected by way of a clamping pin or bolt.

5. Apparatus according to claim 4, in which the upper clamping plate is provided with a handling eye.

6. Apparatus according to claim 4, in which the upper clamping plate is loosely suspended in the filter housing with the edge portion of the upper clamping plate on a peripheral annular shoulder, with the inclusion of a seal and is loaded by a compression spring bearing against the cover, and has at least one bore in the region of the central passage which passes vertically through the filter insert.

7. Apparatus according to claim 1, in which the cover of the housing is provided with a positive receiving means for receiving a locking head of a screwthreaded pressure spindle which is guided in a clamping yoke member which is rotatably mounted laterally on the housing and the clamping yoke member has clamping projections for engaging under a flange on the housing.

8. Apparatus for filtering a slurry of radioactive liquids charged with solids substantially as hereinbefore described and illustrated with reference to the accompanying drawings.