GB2153275A

GB2153275A - Compaction of spent nuclear fuel cans

Info

Publication number: GB2153275A
Application number: GB08402549A
Authority: GB
Inventors: Harry Sullivan
Original assignee: BLACKSPUR ENGINEERING Ltd
Current assignee: BLACKSPUR ENGINEERING Ltd
Priority date: 1984-01-31
Filing date: 1984-01-31
Publication date: 1985-08-21
Also published as: GB8402549D0

Abstract

Hydraulic press apparatus (10) for compacting waste material eg. spent nuclear fuel cans (11) comprises a fixed frame (12), a movable cross head (13), a press crown (17) and three groups of piston/cylinder devices (22, 25; 23, 26; 21, 24) having their pistons (31 to 36) connected to the cross head (13) and their cylinders (21 to 26) secured to the press crown (17). A control means connects the first group of devices (22, 25) to hydraulic fluid in a reservoir which is pressurised initially by gas from gas accumulators to move the cross head (13) and a quill (14) secured thereto towards the frame base (12) to compact the waste (11) at a first high rate under a first high loading. Compaction then proceeds at a lower second rate at a lower second loading as the hydraulic fluid in the reservoir is pressurised by a pump. At two subsequent stages of compaction of the waste (11) at which resistance increases causing a pressure rise in cylinders (22, 25) the control means causes hydraulic fluid to be passed to the second group of devices (23, 26) and thence to the third group of devices (21, 24), the compaction rate reducing at each stage but the compaction force increasing. <IMAGE>

Description

SPECIFICATION Compaction apparatus and method This invention relates to a method of compacting material, in particular waste material, and to apparatus for use in performing the method.

It is known to compact waste material in order to minimise storage space required when it is impracticable to segregate the component parts or differing materials of the waste for reuse. Car bodies are a well-known examples of waste material which is compacted for disposal purposes after all reusable items have been removed therefrom. In such cases presses are provided which, usually by hydraulic means, subject the car body or other waste to a large, substantially constant compressive force until sufficient compaction is achieved. However certain waste materials are not readily compacted in this way. In particular spend fuel cans from nuclear power stations are not readily compacted using known compaction presses.

Various solutions to the problem of disposal of spent nuclear fuel cans have been proposed. Such cans, which may be up to 5 metres long by up to 1 metre in diameter and comprise dividers and bulkheads of a substantial construction within a stainless steel casing of approximately 1 Omm thickness, require a very large press if they are to be compacted in conventional manner. The size of the press, the amount of hydraulic fluid required and the size of the pipe work necessary to maintain sufficient fluid flow rate therethrough for such a press, render the compaction of such fuel cans by such means economically impracticable. It has been proposed to cut the cans by laser beam and encapsulate the cut cans in concrete for disposal at sea.However the cutting equipment is costly, it is doubtful whether successful cutting through the various layers of material in the cans could be achieved and unacceptable quantities of contaminated cutting gases and fine particles would be released by this method. In addition handling of the radio-active cut pieces presents a major problem, the use of robot machinery being a further expensive element in such a method. Abrasive water cutting has been proposed but the quantity of contaminated water resulting from such a process renders this method impracticable.

It is an object of the present invention to provide a method for use in the disposal of waste material such as spent nuclear fuel cans which is not, or is less, subject to the aforementioned disadvantages, and to provide apparatus for use in such a method. In particular it is an object of the present invention to provide a method of and apparatus for compaction of such waste material.

The invention provides a method of compacting waste material comprising applying to such material a first compressive load to compact said material at a first rate of compaction, and thereafter applying a second compressive load to compact said material at a second rate of compaction.

Preferably said second load and speed are lower than said first load and rate respectively. The method may comprise applying a third compressive load to compact said material at a third rate of compaction. Said third load is preferably higher than said second load and said third speed may be lower than said second speed. The method may also comprise applying a fourth compressive load to compact said material at a fourth rate of compaction. Said fourth load is preferably higher than said third load and said fourth speed may be lower than said third speed.

The invention also provides apparatus for use in performing the aforesaid method comprising a plurality of piston/cylinder devices mounted in parallel between a common frame and a common movable cross head, a source of pressure fluid and control means coupled with said source of pressure fluid and operable to connect a first group of piston/cylinder devices with said source of pressure fluid to move said cross head at said first rate of movement under a first loading and thereafter to move said cross head at said second rate of movement under a second loading.The control means may be operable to connect a second group of piston/cylinder devices with said source of pressure fluid when the pressure in said first group of cylinders exceeds a first predetermined value, and may also be operable to connect a third group of piston/ cylinder devices with said source of pressure fluid when the pressure in said second group of cylinders exceeds a second predetermined value. Each group of piston/cylinder devices may comprise one or a plurality of such devices, preferably each group comprises two such devices. Said plurality of piston/cylinder devices may comprise three groups of two devices in each group, said devices being equi-spaced around a central axis thereof and each device being diametrically opposed to the other device of its group.

Said source of pressure fluid may comprise a supply of hydraulic fluid and first pump means operable to maintain said hydraulic fluid under pressure. Said source of pressure fluid may also comprise gas accumulator means operable to apply pressure to said supply of hydraulic fluid and second pump means operable to charge said accumulator means with gas under pressure.

The apparatus may also comprise hydraulic fluid reservoir means whereby hydraulic fluid may be supplied to those of said piston/cylinder devices other than said first group whilst said first group is and prior to said second group being, connected to said source of pressure fluid. Said reservoir means may also supply hydraulic fluid to said third group of piston/cylinder devices whilst said first and second groups are and prior to said third group being, connected to said source of pressure fluid.

The apparatus may include first sensing means operable to detect said first predetermined pressure in hydraulic fluid in said first group of piston/cylinder devices, and may also include second sensing means operable to detect said second predetermined pressure in hydraulic fluid in said second group of piston/cylinder devices.

One embodiment of apparatus in accordance with the invention will now be described with reference to the accompanying drawings in which: Figure 1 is a diagrammatic side elevation, Figure 2 is a developed plan view of part of the apparatus, Figures 3 to 5 are sectional elevations on lines Ill-Ill; IV-IV and V-V respectively of Fig. 2 and Figure 6 is a graphical representation of pressure variation with quill travel in the apparatus of Figs. 1 to 5.

Referring now to Figs. 1 to 5 there is shown a hydraulic press apparatus 10 suitable for the compaction of spent fuel cans 11 from a nuclear power station, or other waste material. The apparatus 10 comprises a fixed frame or machine bed 1 2 and a movable cross head 1 3. Secured to the movable cross head 1 3 is a quill 1 4 and provided in a fixed platen 16 of frame 12 is a door 15. The frame 1 2 also comprises a press crown 1 7 connected to but spaced from the fixed platen 1 6 by six equi-spaced tie bars 41 to 46, only two being show in Figs. 1 and 2 for clarity.

The movable cross head 1 3 is slidable on tie bars 41 to 46 away from the press crown 1 7 and towards the fixed plate 1 6 in order that the quill 14 can compress the waste material 11. A container 1 8 of suitable massive proportions and which has a liner 1 9 of suitable material is secured to the fixed platen 1 6 and retains the waste material 11 during compaction. After such compaction the door 1 5 is opened and the compacted material 11 is passed onto a roller feed bed 20 and may be removed by means of an overhead crane 27.

The container 1 8 is housed in walling 28 forming a biological shield therearound and through which the quill 14 and tie bars 41 to 46 extend.

Movement of the cross head 1 3 is effected by displacement of six pistons 31 to 36 under hydraulic fluid pressure in their respective cylinders 21 to 26. Each piston 31 to 36 is secured to the cross head 1 3 and each cylinder 21 to 26 is secured to the press crown 17, the cylinders 21 to 26 being equi-spaced around a central axis 29 of the press 10. A mounting plate 30 assists in securing the cylinders 21 to 26 in their positions relative to each other. Cylinders 22 and 25, which are diametrically opposed to each other, form a first group of cylinders 22,25. cylinders 23 and 26 form a similarly disposed second group of cylinders 23, 26 and cylinders 21 and 24 form a similarly disposed third group of cylinders 21,24.

Supply pipes 37 for hydraulic fluid under pressure from a reservoir 39 are provided for the cylinders 21 to 26 and control means 38 includes valves (not shown) operable selectively to connect the cylinder groups 22,25; 23,26; and 21,24 to the pressure fluid. The control means 38 also includes a motor and first pump (not shown) operable to pressurise the hydraulic fluid from reservoir 39 and supply it to pipes 37 as required. Gas accumulators 40 are connected to control means 38 which includes a second pump (not shown), operable to pressurise gas in the accumulators 40, and further valves (not shown), operable to connect hydraulic fluid contained in the accumulators 40 with a supply line 47 itself connected to the first group of cylinders 22,25. The two fluids are disposed on opposed sides of a membrane of each accumulator 40 in conventional manner.

A prefil reservoir 48 is provided and connected by supply line 49 to the second group 23.26 and third group 21,24 of cylinders.

Operation of the press 10 is as follows.

Prior to compaction of waste material 11 the gas accumulators are pressurised by means of the second pump of control means 28. The cross head 1 3 is in the retracted position shown in Fig. 1 and the waste material 11 is placed inside container 1 8 via door 1 5 which is then secured in its closed position. On initial activation of the control means 38 the hydraulic fluid in gas accumulators 40, which is at a high pressure due to the gas pressure in the accumulators 40, is discharged rapidly into the first group 22,25 of cylinders. Since only two of the six cylinders are charged with the hydraulic fluid their pistons 32 and 35 are rapidly displaced, thereby moving the cross head 1 3 very rapidly towards the waste material 11. This provides a very high initial loading on the waste material due to the inertia of the cross head 1 3 and pistons 31 to 36 connected therewith. It is to be noted that all of the pistons are displaced even though only cylinders 22 and 25 are charged with pressurised hydraulic fluid. This initial blow causes the end of the fuel can or other waste material 11 to crumple rapidly in a concertina or bellows fashion in contra-distinction to the buckling in a random and uncontrolled manner such as would occur under a slowly rising compaction force provided by a conventional press. Since the accumulators 40 can be charged prior to operation of the press 10 a motor and pump of modest proportions can be used, whilst a considerable amount of stored energy can be released in a relatively short period, for example in 5 seconds.After this initial impact the press 10 continues to operate as a 'normal' hydraulic press but with only the first group 22,25 of cylinders being charged with hydraulic fluid under pressure from reservoir 39 via control means 38 and supply pipes 37. Since only two cylinders are being forcibly extended by the hydraulic fluid the advance of the cross head 1 3 may be rapid without unnecessarily large pipes 37 and valves in control means 38. During this second stage movement of cross head 1 3 the pistons 31, 33, 34 and 36 are also moving and the cylinders 21, 23, 24 and 36 draw in hydraulic fluid by gravity feed through supply pipes 49 from prefil reservoir 48.

Once the first stage A of the compaction of waste material 11, and the specific collapse pattern thereof established, the load thereon falls as shown in Fig. 6. In the absence of internal fittings such as are contained in spent nuclear fuel cans the collapsing force would be fairly constant, small variations thereof occurring as each successive fold is formed.

With the aforementioned internal fittings the variations of load will be greater but the average load during this second stage B of the compaction will be considerably less than that applied during the first stage A, and compaction, although rapid, will be at a slower rate than that during the first stage A.

Eventually there will be a sufficient degree of compaction of the waste material 11 for a marked increase in pressure of the hydraulic fluid in cylinders 22 and 25 to occur. This is sensed by sensors 50 and in response to a signal from such sensors the control means 28 connects the second group 23,26 of cylinders to the pressurised hydraulic fluid from reservoir 39. Since the cylinders 23 and 26 are already filled with hydraulic fluid from prefil reservoir 48 a rapid "switching" into operation of the cylinders 23 and 26 is effected.

During this third stage C of compaction the rate of compaction is less than that during the second stage B since four cylinders are being charged with pressurised hydraulic fluid, but the compressive load applied to the waste material 11 is higher. When an even greater degree of compaction of waste material 11 is reached, i.e. when it behaves very nearly as a solid body, the pressure of the hydraulic fluid in cylinders 23 and 26 will rise to a predetermined value which may be sensed by sensors 51. In response to a signal from sensors 51 the control means 28 connects the third group 21,24 of cylinders to the pressurised hydraulic fluid from reservoir 39. Again since cylinders 21 and 24 are already filled with hydraulic fluid from prefil reservoir 48 a rapid "switching" into operation of cylinders 21 and 24 is effected.

During the fourth stage D of compaction the rate of compaction is less than that during the third stage C since all six cylinders are now in operation, but the load applied to the waste material is now equal to the maximum which can be applied by the press 1 0. Such load should be that required to finalise compaction of the waste material 11.

By means of the invention the provision of a large and costly piston/cylinder device adequate to provide the requisite high final compaction load is avoided. Also since only two or four of the cylinders are operational during all but the last compaction stage, the large rates of flow required by a multiple piston/cylinder device arrangement in which all devices are operational throughout are avoided, so that rapid early compaction is achieved simply and efficiently. Such high rates of flow would require prohibitively large pipe work, valves, pumps and motors whereas in the present case relatively modestly sized apparatus can be used.

Claims

1. A method of compacting waste material comprising applying to such material a first compressive load to compact said material at a first rate of compaction, and thereafter applying a second compressive load to compact said material at a second rate of compaction.

2. A method according to claim 1 wherein said second load is less than said first load.

3. A method according to claim 2 wherein said second speed is less than said first speed.

4. A method according to claim 3 comprising thereafter applying a third compressive load to compact said material at a third rate of compaction.

5. A method according to claim 4 wherein said third load is greater than said second load.

6. A method according to claim 5 wherein said third speed is less than said second speed.

7. A method according to claim 6 comprising thereafter applying a fourth compressive load to compact said material at a fourth rate of compaction.

8. A method according to claim 7 wherein said fourth load is greater than said third load.

9. A method according to claim 8 wherein said fourth speed is less than said third speed.

1 0. Apparatus for compacting waste material comprising a plurality of piston/cylinder devices mounted in parallel between a common frame and a common movable cross head, and control means adapted to be coupled with a source of pressure fluid and operable to connect a first group of piston/cylinder devices with said source of pressure fluid to move said cross head at a first rate of movement under a first loading and thereafter to move said cross head at a second rate of movement under a second loading.

11. Apparatus according to claim 10 wherein said pressure fluid is hydraulic fluid.

12. Apparatus according to claim 10 or claim 11 comprising first sensing means operable to detect a first predetermined pressure in said first group of piston/cylinder devices.

1 3. Apparatus according to claim 1 2 wherein said control means is operable to connect a second group of piston/cylinder devices with said source of pressure fluid when the pressure in said first group of cylinders exceeds said first predetermined value.

1 4. Apparatus according to claim 1 3 comprising second sensing means operable to detect a second predetermined pressure in said second group of piston/cylinder devices.

1 5. Apparatus according to claim 1 3 wherein said control means is operable to connect a third group of piston/cylinder devices with said source of pressure fluid when the pressure in said second group of piston/ cylinder devices exceeds said second predetermined value.

1 6. Apparatus according to any one of claims 10 to 1 5 wherein the or each group of piston/cyiinder devices comprises two such devices.

1 7. Apparatus according to claim 1 5 comprising three groups having two piston/cylinder devices in each group, said devices being equi-spaced around a central axis of said apparatus.

1 8. Apparatus according to claim 1 7 wherein each device is diametrically opposed to the other device of its group.

1 9. Apparatus according to claim 11 or any claim dependent thereon comprising first pump means operable to provide said source and to maintain said hydraulic fluid under pressure.

20. Apparatus according to claim 1 9 further comprising gas accumulator means operable to apply pressure to said source of hydraulic pressure fluid.

21. Apparatus according to claim 20 comprising second pump means operable to charge said accumulator means with gas under pressure.

22. Apparatus according to claim 1 5 or any claim dependent thereon wherein said pressure fluid is hydraulic fluid, comprising hydraulic fluid reservoir means and means operable to supply hydraulic fluid from said reservoir means to those of said piston/cylinder devices other than said first group whilst said first group is and prior to said second group being connected to said source of pressure fluid.

23. Apparatus according to claim 22 wherein said supply means is operable to supply hydraulic fluid from said reservoir means to said third group of piston/cylinder devices whilst said first and second groups are and prior to said third group being connected to said source of pressure fluid.

24. A method of compacting waste material substantially as hereinbefore described.

25. Apparatus for compacting waste material substantially as hereinbefore described with reference to and as illustrated in the accompanying drawings.