The present invention relates to a method and a plant for treating contaminating and/or contaminated material, in particular radioactive material deriving from decommissioning of activated and/or contaminated components of nuclear plants. The decommissioning of nuclear plants consists in the segmentation of the activated and/or contaminated components, such as the vessels and the internals of the nuclear reactors, in the insertion of the waste materials in special packaging containers and the transport thereof to the temporary or permanent storage. The segmentation operations are normally carried out in a dedicated and equipped tank/pool, all under water head for reasons of radiation protection of the operating personnel.

The personnel in charge of decommissioning normally stand on the edges or above the pool itself in order to be able to visually perform and control the operations of transferring and positioning the vessel and the internals in the segmentation cradle and the operations of gripping and transferring the segmented materials in a shielded-shuttle container, of closing the cap, of transferring the container to the conditioning station, etc.

At present, the dispersion of radioactive material in a segmentation pool of the aforesaid components results in an extensive water contamination and the need l to recover the dispersed material. The operation is definitely complex and involves the operating personnel being significantly exposed to ionising radiations, the dilation of the overall cutting times, costs, etc.

Generally, the segmentation of the components is carried out with mechanical cutting systems in the pool in remote conditions that give rise to dispersion of the chips and cutting residues and require frequent tool replacements, etc.

Other cutting methods and in particular the so-called AWJC (acronym for Abrasive Water Jet Cutter) have been instead almost abandoned, despite the greater efficiency of the segmentation process, precisely because of the presence of extensive contamination of the processing pool due to the radioactive iron powder mixed with the abrasive in the form of sludge.

The invention aims to make available a method and a plant for the direct treatment of the contaminating and/or contaminated material, in particular radioactive material from decommissioning of nuclear plants, which allows overcoming at least some of the drawbacks complained about with reference to the aforementioned known technique.

In particular, the method and the plant according to the invention are aimed at allowing an effective application of cutting methods AWJC without this leading to a dispersion of the residual processing sludges within the segmentation pool. Furthermore, the invention aims to provide a method and a plant for the direct treatment of the contaminating and/or contaminated material that ensures an optimal protection of the personnel in charge and an appropriate and concentrated storage of the processing residue. These technical problems are solved by the invention, by means of a method for treating contaminating and/or contaminated material, in particular radioactive material deriving from decommissioning of nuclear plants, comprising a step of cutting said material in a circumscribed environment by means of abrasive water jet technology and a step of recovering the abraded residue deriving from the cutting step. According to a preferred example of embodiment of the invention, the circumscription of the environment in which the cutting step is carried out is obtained by application to the surface subjected to abrasive water jet of at least one containment cap suitable for containing the cutting fluid formed by the mixture of cutting water, abrasive material and abraded residue, reducing the overall cutting times. Preferably, the method makes use of two abrasive water jets arranged on opposing sides of the piece to be cut so as to attack the surfaces of the piece from opposing sides, each abrasive water jet being circumscribed by a respective containment cap of the respective cutting fluid. Actually, even if a single abrasive water jet should be used, it is preferred that the surface to be cut is delimited on both its opposing surfaces by a respective cap so that the containment of the cutting fluid is guaranteed on both sides of the piece while it is being cut.

Preferably, the step of recovering the abraded residue is carried out by sucking and pumping from the cap(s) the cutting fluid towards a storage vessel.

In a preferred application example, the cutting step is carried out in a pool or segmentation tank under a water head and each cap hydraulically separates the tank water from the cutting fluid to prevent the contamination of the tank water, while limiting the infiltration of the water inside the cap.

In order to advantageously limit the amount of residue to be stored (water plus abrasive plus cutting powder plus infiltration water), a step of concentration of the abraded solid residue in the storage vessel is also preferably provided, eliminating the excess water.

This concentration step can for example be carried out by centrifugation of the cutting fluid, cyclonic separation, and/or mechanical filtration. It is preferred that the centrifugation step is carried out directly in the storage vessel by centrifugal stirring of the cutting fluid and at least partial separation of the cutting and infiltration water from the abrasive material and the abraded residue.

The step of sucking each containment cap is for example carried out by vacuum suction applied to the storage vessel. However, it is envisaged that this step can be carried out by direct pumping or by other per se known liquid transfer techniques.

A plant for treating contaminating and/or contaminated material, in particular radioactive material from decommissioning of nuclear plants according to the method of this invention comprises at least one cutting unit of said material by means of abrasive water jet technology and means for recovering the abraded residue deriving from the cutting step. The means for recovering the abraded residue deriving from the cutting step comprise at least one containment cap associated with the cutting unit and delimiting with a surface of the material to be cut a circumscribed volume suitable for containing the cutting fluid formed by the mixture of cutting water, abrasive material and abraded residue. Preferably, a unit for sucking and pumping from the containment cap the cutting fluid, including abrasive material and abraded residue, towards a storage vessel, is also envisaged. In an exemplary and preferred plant, said at least one containment cap is mounted on board a respective manipulator.

Separate manipulators can be used for the cutting unit and the containment cap, but it is envisaged that the manipulator of said at least one cap is the same one that controls over the movement of the cutting unit.

A preferred solution comprises two respective containment caps opposed to the positioning of the material to be cut so as to collect and contain the cutting fluid on both sides of the cut made in the material to be treated.

In one embodiment example, the plant comprises two opposing cutting units bearing the respective containment caps, each cutting unit taking care of the cutting of the material about half of its thickness.

The plant also comprises a respective storage vessel for each containment cap. In a preferred solution, the means for recovering the abraded residue deriving from the cutting step comprise a piping for the connection between each cap and the corresponding storage vessel and suction unit for pumping the cutting liquid from the containment cap towards the storage vessel associated therewith and preferably the suction unit comprises a vacuum line arranged to suck by vacuum the cutting fluid in the storage vessel. Alternatively, it is provided that the suction from the caps is carried out by one or more pumps. It is also provided that the storage vessel comprises a stirrer with motorised axis. This stirrer is used to concentrate the solid residue of the cutting fluid by centrifugal effect. By providing that the stirrer is made with a hollow (tubular) axis, it is possible to extract the liquid part of the cutting fluid from the vessel by sucking it through the hollow axis, substantially in the middle of the storage vessel. Where appropriate, an in-line filter can be provided that serves to remove the not separated solid residues by centrifugal effect.

The stirrer is preferably disposable with the storage vessel and is also used to mix the concentrated sludges in the storage vessel with cement mortar. It is envisaged that the suction from the caps is preferably carried out with "rotor canned" pumps. These pumps operate under wet conditions with all rotating components exposed in contact with the pumped fluid.

This eliminates the need for the sealing of the shaft by means of a packing gland or a mechanical seal, required for other pump types. The pumped fluid is used to lubricate the motor bearings and to cool the inside of the rotor. This so-called wet space is sealed off from the atmosphere or the motor winding by a non-magnetic high alloy steel box container. The container is statically sealed by means of O-ring seals.

The pump for sucking from the caps is preferably submerged in the pool and in an application example it is provided with suction with variable flow rate controlled by a valve as a function of the pressure measured in the caps themselves.

Preferably, the cutting and infiltration waters from the caps enter the collection vessel from below and outflow from the upper part, after the separation of the solids occurred by centrifugation by means of rotating blades.

In one embodiment example, the collection vessel may be placed outside the water level of the cutting pool, fed by the suction pump from the caps. This makes it possible to use conventional movement systems for centrifugation and stirring. In another embodiment example, a suction pump is provided from the storage vessel of the liquid clarified by centrifugation, it is also placed above the water level of the pool and is also of the rotor canned type.

According to one embodiment, a stilling zone, within which the separated solid material is deposited, is preferably realised in the lower part of the collection vessel.

In this embodiment, the water, after separation of the solid particles, is sucked from the upper part of the vessel by a pump preferably of the rotor canned type and sent to a filter for the separation of the remaining particles (e.g. of less than the micron in diameter), not separated as a result of centrifugation. This is useful for limiting the number of revolutions of the impeller of the stirrer, preferably below 1000 revolutions per minute. After filtration, the water is sent to the purification plant, present in the same nuclear plant during the dismantling step. The mixing of the separated solid inside the collection vessel is carried out by reverse rotation of the stirrer, which sets in motion a turbine placed on the bottom of the vessel, which is stopped during the centrifugation step but is subjected to rotation with the stirrer when the separated solid is to be suspended again. Preferably the turbine is actuated by a one-way rotation device, for example of the free-wheel type, so as to remain stationary during the rotation of the stirrer in one direction and to rotate solidly therewith in the opposite direction.

The features and advantages of the invention will best appear from the following detailed description of a preferred but not exclusive example of a plant for treating contaminating and/or contaminated material, in particular radioactive material from decommissioning of nuclear plants and of the relative operating method, given by way of non-limiting example with reference to the accompanying drawing in which:

- fig. 1 is an outline diagram of a plant according to the invention; - Fig. 2 is a partial diagram of an embodiment variant of the plant of Fig. 1.

The aforesaid plant is similarly suitable for treating different materials and more generally for the operations that generate cutting powders and abrasives that require disposal as special or toxic/harmful waste.

The plant preferably makes use of a segmentation pool, which is not represented as being conventional in itself, within which a water head is maintained. A contaminating and/or contaminated material is schematically indicated with 1, has a thickness 2 and is exemplarily delimited by two opposing surfaces 3 and 4.

The plant, represented in the diagram in Fig.l, comprises two opposing cutting units, indicated with 5 and 6, respectively facing the surfaces 3 and 4 and both including a robotic manipulator 7 that controls over the support and the displacement according to a programmed cutting logic, for example by means of a computerised numerical control system of each cutting unit 5, 6 in a preferably coordinated manner so as to maintain it substantially facing. It is also provided that both units 5, 6 are carried by a single manipulator, for example fork-like.

Each cutting unit preferably comprises an AWJC device 16 (acronym for

Abrasive Water Jet Cutting) fed by a pressurized water feed line 8 (or other per se known cutting fluid) and an abrasive supply line 9, typically granules of metallic or ceramic oxides, for example corundum or almandine. The cutting water in the line 8 is maintained at a pressure preferably comprised between 400 and 700 MP. The respective line 8 is selectively interceptable, by means of a first valve assembly 10 including a first and a second solenoid valve 11, 12. The second solenoid valve 12 is controlled by a feedback signal schematised with a line 13, according to the methods specified below.

Each cutting unit 5, 6 further comprises a respective containment cap 14, 15 which, when applied to the respective surface 3, 4 serves to circumscribe the environment in which the cutting step is performed by delimiting a circumscribed volume with the respective surface of the material to be cut. The cap 14, 15 is made of an abrasion-resistant material and serves to prevent the cutting fluid, including the pressurized water fed through line 8, the abrasive fed through the line 9 and the abraded material during the cutting step, as well as any splashes thereof and any infiltrations of water from the segmentation pool from being able to return and/or disperse into the segmentation pool contaminating the waters.

The caps 14, 15 as well as the material to be segmented are preferably maintained during all the aforementioned phases under water head, immersed in the segmentation pool.

The two units 5, 6 involve the cut for about half of the thickness 2. It is envisaged that the plant either includes a single cutting unit with respective cap, or two caps, one of which will be provided with an AWJC device, or that both caps are provided therewith and are placed in simultaneous or non- simultaneous operation. In all cases it is envisaged that during the entire cutting step the environment in which this step takes place is always circumscribed by the cap(s) 14, 15 to avoid contamination of the segmentation pool. For this reason, reference will be made in the appended claims to at least one cutting unit and at least one respective containment cap.

Each containment cap 14, 15 is fitted with a sealing ring 17 aimed to prevent leakages between the respective cap and the segmentation pool. Leakages towards the segmentation pool are also prevented by keeping the inside of the cap at a lower pressure than the outside in the manner that will be clarified below.

Each cap is preferably made of high-strength steels, such as ballistic steels of the Armox or Ramor 500 type, with a thickness preferably comprised between 2 and 30 mm and a hardness of 490-560 HBW. The caps are arranged symmetrically with respect to the element to be cut in order to collect the

"reflected" and "emerging" cutting fluids from the element itself.

Each cap 14, 15 is connected through pipe 18, preferably flexible, to a cutting fluid collection and treatment unit 19. It should be noted that in fig.l, for reasons of simplification and clarity, only the collection unit associated with the unit 14-16 is represented. Preferably, the connection of the pipe 18 to the collection unit 19 is selectively interceptable through a second valve assembly including a third manually operated solenoid valve 36 and a fourth remotely controlled solenoid valve 37, connected on the line 13. The cutting fluid collection and treatment unit comprises a storage vessel 20 for the residues derived from the corresponding cutting unit 15, 16 and a suction unit 21 placed between the cutting unit and the storage vessel 20. In an application example, the suction unit comprises a vacuum line 22 connected to the vessel 20 so as to reduce the pressure stability inside the vessel and with respect to the outside of the caps 14, 15. The vacuum line 22 is selectively interceptable by means of a valve 24, preferably an on-off solenoid valve with manual push-button control.

The suction unit thus allows not only the cutting fluid, including abrasive and abraded material, to be collected in the storage vessel 20, but also any water infiltration from the segmentation pool towards the caps. This avoids the spillage of the fluid and of the cutting residues into the segmentation pool preventing the contamination thereof.

The storage vessel 20 is preferably made of stainless steel and is, for example, of the type used for the conditioning with cement mortar of the liquid or semi- liquid radioactive waste with low/medium low activity by means of the process known as "in drum mixing and cementation".

The vessel 20 is preferably modified by adding one or more of the following components:

- a shield 25 suitable for providing a protective insulation towards the outside as a function of the treated material. The shield 25 also serves to isolate the storage vessel during its transfer out of the pool to an air conditioning unit (not represented). In addition, the shield 25 has the function of preventing the vessel from floating in the segmentation pool (when empty in whole or in part) and from rotating; - a sealing cap 26;

- a stirrer 27 preferably with motorised axis

- a connector 28 preferably with a quick coupling, e.g. of the swagelock type. The shield 25 is chosen as a function of the type and hazardousness of the material treated. In the case of radioactive material from decommissioning, a steel shield will preferably be adopted. The cap 26 serves to sealingly close the vessel 20 so that the same can be connected to a vacuum pump via the vacuum line 22 controlled by the valve 24. The axis of the stirrer 27 is preferably a hollow (tubular) shaft 30 fitted with vanes 28 and is preferably connected to a filtration system 29. By rotating the stirrer 27, the sludges of abrasive material and abraded residue are centrifugally concentrated towards the side wall of the vessel 20 so as to at least partially separate them from the process water which can thus be extracted by suction through the hollow shaft 30 and moved away from the container through an extraction line 31. The extraction can be advantageously achieved by means of an ejector 32 operated with pressurized water through a valve-controlled line. The cutting water is then sent to a treatment unit, not represented, through the extraction line 31.

A sensor is preferably placed in the storage vessel 20 and which is provided for measuring the level of the concentrated solid residue accumulated in the storage vessel 20 and for consequently driving the valves 12 and 37 through the line 13 intercepting the relative pipings when the vessel is to be considered full, that is, the solid residue has reached a predetermined level. After the vessel 20 has been filled, it is transferred to the cementation station (not represented); cement mortar for cementing the sludges concentrated with the "in drum mixing and cementation" system mentioned above is introduced into it with known methods. The stirrer 27 is then actuated and contributes to homogenising said mortar by being rotated in both directions until the partial hardening of the mortar occurs. It is therefore disposable remaining bonded to the vessel 20 after consolidation of the cement mortar and process sludges. In figure 2, the cutting fluid formed by the mixture of cutting water, abrasive material and abraded residue is sucked from the caps 14, 15 through a pump 40 preferably submerged in the containment pool 49 (i.e. under head) and preferably of the "rotor canned" type. These pumps operate under wet conditions with all rotating components exposed in contact with the pumped fluid.

This eliminates the need for the sealing of the shaft by means of a packing gland or a mechanical seal, required for other pump types.

The pumped fluid is used to lubricate the motor bearings and to cool the inside of the rotor. This so-called wet space is sealed off from the atmosphere or the motor winding by a non-magnetic high alloy steel box container. The container is statically sealed by means of O-ring seals.

The pump for sucking from the caps 40 is preferably submerged in the pool and in an application example it is provided with suction with variable flow rate controlled by a valve 41 as a function of the pressure measured in the caps themselves.

Preferably, the cutting and infiltration waters from the caps enter the collection vessel 20 from below, through a conduit 42 and outflow from the upper part through a conduit 43, after the separation of the solids occurred by centrifugation by means of the rotating blades of the stirrer 27.

In one embodiment example, the collection vessel 20 may be placed outside the water level of the cutting pool, fed by the suction pump from the caps 40. This allows the use of conventional movement systems for centrifugation and stirring, e.g. an electric motor 44. In a further embodiment example, a suction pump 45 is provided from the storage vessel of the liquid clarified by centrifugation, it is also placed above the water level of the pool and is also of the rotor canned type. The pump 45 is connected to the conduit 43. According to one embodiment, a stilling zone 46, within which the separated solid material is deposited, is preferably realised in the lower part of the collection vessel.

In this embodiment, the water, after separation of the solid particles by centrifugation through the stirrer 27, is sucked from the upper part of the vessel by the pump 45, it also preferably being of the rotor canned type and sent to a filter 47 for the separation of the remaining particles (e.g. of less than the micron in diameter), not separated as a result of centrifugation. This is useful for limiting the number of revolutions of the impeller of the stirrer, preferably below 1000 revolutions per minute. After filtration, the water is sent to the purification plant, present in the same nuclear plant during the dismantling step.

The mixing of the separated solid inside the collection vessel is carried out by reverse rotation of the stirrer, which sets in motion a turbine 48 placed on the bottom of the vessel, in the stilling zone 46, which is stopped during the centrifugation step but is subjected to rotation with the stirrer when the separated solid is to be suspended again. Preferably the turbine is actuated by a one-way rotation device, for example of the free-wheel type, so as to remain stationary during the rotation of the stirrer in one direction and to rotate solidly therewith in the opposite direction. The invention thus solves the proposed problem and achieves numerous advantages, including allowing the use of cutting units AWJC without producing contaminations of the segmentation pool, consequently increasing the efficiency of the cutting operations and the safety for the operators, concentrating the cutting sludges and consequently reducing the storage volume and finally automating the cutting and removal process of the abraded residues.