GB2408142A

GB2408142A - Floating platform

Info

Publication number: GB2408142A
Application number: GB0326693A
Authority: GB
Inventors: Keith Johnson; Kenneth George Jackson
Original assignee: RWE Nukem Ltd
Current assignee: Nuvia Ltd
Priority date: 2003-11-15
Filing date: 2003-11-15
Publication date: 2005-05-18
Anticipated expiration: 2023-11-15
Also published as: GB2408142B; GB0326693D0

Abstract

A remote controlled floating platform (1) for use on a liquid the platform comprising one or more floats (51) supporting a base (55), which platform is provided with a mast (4) extending below the liquid. Such a platform may also be provided with a crane (2) and can be used for moving containers of radioactive waste (6) within the liquid. The platform may also be provided with a suction system for removing radioactive debris from the liquid on which the platform floats.

Description

Floating Platform The present invention relates to a platform which can

float on a liquid and which can be used to lift objects within the liquid and/or remove debris from the liquid.

Certain types of radioactive waste are stored in open containers which are kept underwater. This has the advantage that heat produced by the decay of relatively short-lived radioactive isotopes in the waste is dissipated in the water and thus the fuel does not overheat. The water also acts as a shield for the radiation produced by the waste. However, over time the water in which the containers are stored may become mildly radioactive as a result of corrosion of the fuel and containers may fall over causing debris to collect in the water. Any debris such as sludge forming or collecting in the water, for example arising from corrosion of the fuel, will typically be radioactive. The water and its contents can therefore pose a risk in the event that an earthquake were to occur, as this could imperil the structure containing the water; typically the water is in the form of an artificial pond within a containment such as a wall, and if the wall were to break, water and debris could escape into the environment.

Such artificial ponds are typically equipped with an overhead crane system which enables the containers to be moved within the water. However, the crane is not necessarily able to lift containers which have fallen over and is not adapted to remove debris from the water.

In addition, crane maintenance is dangerous as it takes place over the water and thus personnel working on the crane have a reduced working time in order to avoid receiving an excessive dose of radiation.

The present invention aims to address these problems by providing a system for moving and righting containers, or for removing debris, such as sludge, from the water or making it safe, which is portable and thus can be maintained away from the water and is easily decontaminated.

Accordingly, the present invention provides a remote controlled floating platform for use on a liquid which may be radioactive, the platform comprising one or more floats supporting a base, which platform is provided with a mast extending below the liquid surface. In particular the present invention provides a remote controlled floating platform for use on a liquid, the platform comprising one or more floats supporting a base, which platform is provided with a mast extending below the liquid surface and a crane for lifting objects within the liquid. In a further embodiment the present invention provides a remote controlled floating platform for use on a liquid the platform comprising one or more floats supporting a base, which platform is provided with a mast and the mast is provided with a suction system. The mast is preferably also provided with a liquid jet system.

The invention also provides a method of removing radioactive debris from a liquid, which method comprises capturing the debris by means of a suction system and depositing the debris in a container which container is under the level of the liquid and wherein the suction means is provided on a mast extending into the liquid from a floating platform. In a preferred embodiment, the method further comprises disturbing the sludge by means 3 of a liquid jet and the jet means is also provided on the mast.

The invention further provides a method of moving a radioactive object within a liquid which method comprises attaching a crane attachment to a waste container in the liquid by means of a manipulator arm provided on a mast extending into the liquid from a floating platform and lifting the object by means of a crane provided on the said floating platform.

The platform comprises a base mounted on one or more floats. In a preferred embodiment the base is mounted on 2 or 4 floats. Where four floats are used, the floats may be placed in any orientation relative to one another but are preferably all aligned with one another if the floats have a longitudinal shape. In a preferred embodiment there are small floats fore and aft and two longer floats, one under either side of the platform, which are parallel to one another. In a particularly preferred embodiment, the outermost floats are moveable and can be jacked apart to increase the stability of the platform.

In this embodiment, lifting and lowering operations would typically take place while the floats are jacked apart.

The floats are then brought closer together when moving the platform through restricted spaces in order for the platform to pass through narrow passages or gateways.

Typically, the platform would not be used to lift underwater objects with the floats close together but could be used to transport an object by moving the platform. Typically the floats are jacked apart before lowering the object. The floats and/or the base of the platform may also be profiled so as to accommodate any equipment that passes on one side or the other the floats during operation of the platform. In a preferred embodiment the platform has an opening that is - 4 - substantially central in the platform and through which the crane operates.

The crane is adapted to lift objects, in particular containers of radioactive waste, within the liquid on which the platform is floating. The crane may be provided at platform level and may be unable to lift containers out of the liquid. In one embodiment, the crane is a four wire hoist. This typically has the advantage of increasing the stability of the platform.

The objects moved by the crane are typically containers of radioactive waste but may also include other radioactive objects, such as individual objects emitting a, or y radiation, particularly or y radiation.

The floating platform is typically provided with a radiation tolerant vision system comprising a number of pan and tilt cameras mounted below the liquid level (waterline). Preferably the vision system also comprises cameras mounted above the liquid level. The underwater mast is typically provided with at least one camera. The camera sensitivity is usually chosen to provide a high degree of visibility even in poor conditions. Lights may also be provided on the platform and/or under the liquid, for example on the underwater mast, in order to improve visibility.

Image enhancing software is typically used to ensure the clarity of the pictures produced by the vision system.

The mast is typically provided with a manipulator arm in the liquid and/or a jet and suction system for removing debris. - 5 -

A manipulator arm may be used to attach the crane, via a grapnel or similar attachment to a radioactive waste container or a radioactive object, for example a waste container that is on its side. The container can then be lifted by the crane. The vision system enables remote control of the manipulator arm to connect the crane to the container successfully. The manipulator arm enables connection of the crane to a container even if the container has fallen over, for example onto its side.

The position of the top of the container is detectable via the vision system.

The attachment on the end of the crane is typically designed so that the crane may be connected to and disconnected from an upright container without the use of the manipulator arm on the mast. Alternative attachments can be provided to connect the crane to other objects.

The mast extends below the base of the platform into the liquid and can be moved vertically with respect to the platform. For example, the mast may be moved by means of a cable passing over a pulley located above the uppermost point of the mast when it is fully raised.

The mast may be provided with a suction means for removal of sludge. Preferably it is provided with a jet means and a suction means. In this embodiment the sludge, for example sludge lying on the floor, is broken up and/or mobilised by directing the jet at the sludge and then removed by suction. The combination of sludge and liquid can then be pumped into a storage container.

However, preferably the sludge is concentrated using a cyclone apparatus and then the sludge is transferred into a container and the liquid is returned to the pond.

Typically the container is already positioned in the - 6 - liquid and therefore contains liquid, in order to weigh it down. The liquid is displaced by the sludge as it enters the container. The outlet of the container is typically provided with a non-return valve. The inlet is typically fed with pressurised feed from the cyclone.

Overfilling of the container may be avoided by controlling the output from the cyclone and ceasing filling a container after a specified time.

Alternatively, the container may be observed using the vision system and filling stopped when sludge is seen to be exiting via the outlet valve due to having displaced all the liquid.

The floating platform is typically provided with a propulsion system. This may take the form of pressurized liquid jets. For example, the platform might have four jets. In one embodiment at least one jet is pivotable, and where the jets can pivot fewer jets may be needed.

Alternatively, the platform may be provided with thrusters, for example in the floats. The thrusters may be pivotable. Typically, a platform could be provided with four thrusters, however fewer may be appropriate especially where pivotable ones are used.

The floating platform is provided with a power source. In one preferred embodiment this is in the form of electric power provided via an umbilical cord linking the platform to an installation at one side of the pond.

For example, the power cable may be provided from an overhead boom that can travel alongside the pond so as to enable the platform to receive power at all points within the pond. The platform may be provided with any other suitable power source such a generator or batteries.

However, these have the disadvantage that the power source equipment requires regular maintenance which can only be undertaken when the platform is removed from the - 7 - pond in order to enable the radiation dose to maintenance workers to be kept to an acceptable level.

Both power and control signals may be provided via the umbilical cord. Alternatively, control signals may be provided by radio. All of the operations performed by the platform can be controlled remotely including moving the platform within the pond, lifting and lowering objects using the crane, manipulating objects under the liquid using the manipulator arm and removing sludge from the liquid.

Typically the floating platform is equipped with integral recovery systems such as secondary drives for the crane and mast so that if any one system fails on the platform the platform can still be recovered safely from the pond for repair elsewhere. For example, secondary drives could be used to raise the crane or mast if the primary drive fails when the crane is lowered. In addition, a second platform may be deployed in order to recover a first platform where a drive has failed. For example, the manipulator arm may be equipped with cutting apparatus. In the event that the drives on the crane fail while the crane is attached to something, the manipulator arm from the same platform or a different one may be used to cut the crane wires in order to free the crane thereby enabling the first platform to be recovered and repaired.

The floating platform and all equipment attached to it is typically designed so as to be easily decontaminated. The materials used to construct the platform and its equipment are radiation tolerant. A preferred material is stainless steel where suitable.

The floating platform is installed in the pond using a crane situated outside the pond. Typically the platform is provided with a suitable fixing so that the platform may be lifted into position and then disconnected easily.

A floating platform of the invention and specific operations performed using it will now be described by way of example and with reference to the drawings filed herewith, in which Figure 1 is a schematic diagram showing a floating platform positioned over a container of radioactive waste; Figure 2 is a schematic diagram showing the use of the manipulator arm to connect the crane to the container; Figure 3 is a schematic diagram showing the use of the crane to lift the container; Figure 4 is a schematic diagram showing the floating platform supporting the container in a position suitable for transporting the container; Figure 5 is a schematic diagram showing a floating platform according to the present invention to a larger scale than in Figures 1-4; Figure 6 is schematic plan view of a floating platform according to the present invention seen from below in the direction of arrow A in Figure 5; and 9 - Figure 7 is a schematic diagram of the jet and suction system which may be provided on the mast of the floating platform.

Figure 1 shows a floating platform 1 positioned over a container of radioactive waste 6 which is located underwater and which is lying on its side. The floating platform 1 is provided with a crane 2 which has an attachment 3 suitable for connecting to the container 6.

The platform is also provided with a mast 4 which extends under the water and is provided with a manipulator arm 5 at its lower end.

As shown in Figure 2, in use the crane lowers the attachment 3 to the level of the container 6. The manipulator arm 5 is used to connect the attachment 3 to the container 6.

The mast 4 and manipulator arm 5 are then withdrawn as shown in Figure 3. The crane 2 is then used to lift the crane attachment 3 and move the container 6 into an upright position. The container is then lifted, as shown in Figure 4, to a height at which it can be transported by means of the platform while avoiding any danger of collision with any other waste containers in the water.

Figure 5 shows a more detailed view of a floating platform according to the present invention. The structure of the platform comprises a number of floats 51, of which two are shown, which support a base 55. The base 55 is provided with a crane 2 for raising and lowering an attachment 3 in the water. The base also supports a structure 54 encasing a mast 4 which is raised and lowered in the water by means of a cable 52 passing over a pulley means 53 located on the top of the structure 54. The mast 4 is provided with a manipulator arm 5 which may be used as shown to connect the crane attachment 3 to a container of radioactive waste 6 resting on the bottom 57 of the pond in which the floating platform is deployed. The bottom 57 of the pond is typically covered with sludge 56. Power is supplied to the floating platform via an overhead boom arrangement 58 on which is mounted an electric cable (not shown).

Figure 6 shows a plan view of a floating platform according to the present invention seen from below the base in the direction of arrow A in Figure 5. The platform comprises a base 55 supported by four floats 51.

On each float is mounted a jet 61 which is used to move the platform into position. The base also has an opening 62 through which the mast 64 passes. The base also has a further opening 65 through which the four wires 63 of the crane pass.

Figure 7 shows a flow diagram of one embodiment of the jet and suction system for removing sludge from the bottom of the pond. The sludge 71 is broken up and mobilised by a jet 72 located on the mast (not shown) and is then sucked up by a suction means 73 driven by a pump 74. The mixture of sludge and liquid is pumped to a cyclone 75 and separated into sludge and liquid. The liquid leaves the cyclone via outlet 78 and is returned to the liquid in the pond. The sludge leaves the cyclone via the outlet 77 and is transferred to a container 76.

The container 76 is on the bottom of the pond and is filled with liquid to weigh it down. The pump 81 pumps the sludge from the cyclone into the container through an inlet port. The sludge displaces liquid from the container through a one way outlet valve 80. The liquid is returned to the pond. The cyclone is typically operated to produce a solid: liquid ratio of about 10-25% sludge, preferably 15-20% sludge. The container 76 may be transported within the pond using a crane 2 provided on a platform 1 as shown in Figures 1 to 5. - 12

Claims

Claims 1. A remote controlled floating platform for use on a liquid the

platform comprising one or more floats supporting a base, which platform is provided with a mast extending below the liquidy5 'a
2. A platform according to claim 1 wherein the platform is provided with a crane for lifting objects within the liquid.
3. A platform according to claim 1 wherein the mast is provided with a suction system.
4. A platform according to claim 3 wherein the mast is further provided with a liquid jet system.
5. A platform according to any one of claims 1 to 4 wherein the mast is provided with a manipulator arm in the liquid.
6. A platform according to any one of claims 1 to 5 wherein the platform is provided with a below liquid vision system.
7. A platform according to any one of claims 1 to 6 wherein the platform is provided with a vision system.
8. A platform according to claim 4 wherein the liquid jet and suction system further comprises a cyclone.
9. A method of removing radioactive debris from a liquid, which method comprises capturing the debris by means of a suction system and depositing the debris in a container which container is under the level of the - 13 liquid and wherein the suction means is provided on a mast extending into the liquid from a floating platform.
10. A method according to claim 9 where the debris is disturbed by means of a liquid jet and the jet means is provided on the mast.
11. A method according to claim 9 wherein the debris is concentrated by means of a cyclone before deposition in the container.
12. A method according to claim 11 wherein the liquid is in a pond and liquid separated in the cyclone is returned to the pond.
13. A method according to any one of claims 9 to 12 wherein the debris is sludge.
14. A method according to any one of claims 9 to 13 wherein the container is moved by means of a crane provided on the floating platform.
15. A method of moving a radioactive object within a liquid which method comprises attaching a crane attachment to an object in the liquid by means of a manipulator arm provided on a mast extending into the liquid from a floating platform and lifting the object by means of a crane provided on the said floating platform.
16. A method according to claim 15 which method comprises moving the object in a horizontal direction by means of moving the floating platform after lifting the object.
17. A method according to claim 16 which method further comprises lowering the object to the floor by means of - 14 the crane and detaching the crane from the object by means of the manipulator arm.
18. A method according to claim 15 wherein the object is a container of radioactive waste.
19. A floating platform substantially as hereinbefore described with reference to any of the drawings.
20. A method of moving containers of radioactive waste substantially as hereinbefore described.
21. A method of removing radioactive debris from a liquid substantially as hereinbefore described.

15813 TpR C J Talbot-Ponsonby Agent for the Applicant