MACHINE FOR CLEANING THIN-WALLED PIPES CLOGGED BY CRYSTALIZED MATERIAL OR OTHER WASTE

Description

Object of the invention

[0001] The present invention relates to an installation or machine for removing and separating waste obstructing thin-walled pipes without damaging these pipes and without leaving a significant trace of this waste.

[0002] In particular, the invention relates, for example, to the treatment of pipes from a wastewater treatment (WWT) circuit, clogged by highly radioactive crystalline materials, especially boron, in a nuclear power plant. The invention may also find applications in other industrial sectors, such as steam boilers where the internal walls of heat exchangers may be coated with scale (e.g., magnetite).

[0003] The invention also relates to the uses of the aforementioned machine. State of the art

[0004] It is known to introduce boron into the primary circuit of a nuclear power plant in the form of boric acid (H₃BO₃). Boron is used as a neutron moderator, absorbing the neutrons produced during the fission reaction. Boric acid helps control the reactor's reactivity.

[0005] In a pressurized water reactor (PWR) nuclear power plant, the primary fluid is treated by a chemical and volumetric control circuit (CVC), a primary effluent treatment circuit (PEC), a pool water treatment and cooling circuit, and a wastewater treatment circuit (WWT). The secondary fluid is treated by a steam generator blowdown (SG) circuit.

[0006] The wastewater treatment circuit (TEU) drains all non-recyclable effluents. These are collected by the purge and vent circuit (RPE) and then directed to appropriate treatment facilities within the circuit.

[0007] Effluent treatment is tailored to its characteristics. Effluents are classified into four categories, which are collected and stored before treatment: wastewater, chemical effluents, floor drains, and service effluents. They may also be treated by evaporation.

[0008] The TEU treatment circuit consists of filters and demineralizers. The latter are mainly composed of ion exchange resins presented as mixed beds (cationic and anionic). They ensure the removal of undesirable chemical elements because they present a risk of corrosion of the primary circuit and fission products (Sources: Chr. Mérignac, Speciation of tritium and carbon 14 bound to organic molecules in liquid radioactive effluents from Nuclear Power Plants, Doctoral thesis, Univ. of Nantes, 2017; EP 0 497 641 B1).

[0009] One problem encountered is the clogging of the TEU evaporator due to boron (sassolite) crystallization in the pipes. Consequently, another issue arises: during corrective maintenance involving the dismantling and replacement of blocked pipe sections, the mixed metal / boron waste must be stored, pending treatment, in pre-concreted metal containers with color-coded strops according to the dose rate to facilitate future processing. There is no approved "mixed waste stream," and therefore, there is an unmet need in the current state of the art to separate the two types of waste to high purity levels. It is thus necessary to develop a suitable technique for the fine separation of the two types of waste (metal and boron).

[0010] Document FR 3 093 014 A1 discloses a mechanical vibratory assembly comprising at least one mechanical vibrator and at least one retaining means capable of receiving a circuit component, for example, a tube, and of maintaining said mechanical vibrator in direct contact with said circuit component. The invention also relates to a device for separating solid material contained within or on a circuit component, the device comprising a support plate and at least one mechanical vibratory assembly according to the invention. The invention also relates to a method for separating solid material contained within or on a circuit component.

[0011] US document 4,907,542 A discloses an improved cleaning system for a horizontal tube assembly that can perform remote automatic cleaning of the external surfaces of the tubes in the tube assembly without requiring human labor from workers who are forced to work in a limited space.The improvements lie in the fact that the cleaning system includes a main body cleaning section comprising a cleaning template for an external surface of a tube, a screw and a motor in combination to move the cleaning template back and forth in the axial direction of the tube, another motor to deflect the direction of the cleaning template, and a support plate to support the aforementioned elements; an upper cross section comprising a winding drum, lifting wires and a winding motor in combination to raise and lower the main body cleaning section to any arbitrary height, a movable roller to move in the axial direction of the tube, and a drive motor to drive the moving roller.The main body cleaning section further includes a sensor to detect the tube during its ascent and descent, and a push plate mounted on the main body cleaning section via an expandable and contractible cylinder. Preferably, the cleaning jig is equipped with pneumatic hammers to strike the outer surface of the tube. Objectives of the invention

[0012] The present invention aims to provide an efficient handling solution with a significant reduction in dosimetry for on-site operators compared to other cleaning or cutting solutions.

[0013] A particular aim of the invention is to limit hot spots during maintenance phases and a fortiori intervention times, reduce the volume of nuclear waste and limit the generation of so-called "non-residential" radioactive waste.

[0014] Another particular aim of the invention is to use the cleaning method not only in curative mode with treatment and sorting of associated radioactive waste but also in preventive mode to reduce system downtime and increase the operational availability of the power plant, through periodic campaigns at nuclear sites. Main characteristic elements of the invention

[0015] A first aspect of the present invention relates to a machine for cleaning a thin-walled pipe or conduit partially or totally blocked by crystallized waste, comprising a plurality of vibrating hammers transmitting vibrations in use to the external surface of said pipe or conduit so as to detach from the internal wall of the pipe and collect by gravity the crystallized waste in the form of aggregates or powder, characterized in that the machine comprises an external frame enclosing the vibrating hammers and ending at the bottom in a funnel or truncated pyramid with an evacuation opening for the waste.

[0016] According to preferred embodiments of the invention, the machine comprises at least one of the following features or an appropriate combination thereof: Each vibrating hammer comprises a fixed jaw and a movable jaw positioned to be diametrically opposed to the pipe or conduit, and a striker operated by a pneumatic or hydraulic cylinder in a direction perpendicular to the pipe or conduit; the external frame containing the vibrating hammers and the cylinders is mounted on a structure with flexible shock absorbers; the machine includes a waste collection drum positioned under said opening; the machine includes a closing hood.

[0017] A second aspect of the present invention relates to a use of the machine described above, for cleaning the internal surface of pipes or conduits made of metal, ceramic, plastic or stone, preferably less than 10mm thick, whose internal surface is covered or blocked by crystallized waste such as radioactive boron, mill scale, limestone or nitrate residues.

[0018] A third aspect of the present invention relates to a use of the machine described above, for cleaning the internal surface of metal pipes or conduits, preferably stainless steel or special steel, sealed by boron crystals, in an evaporator of a nuclear power plant wastewater treatment circuit.

[0019] A fourth aspect of the present invention relates to a use of the machine described above, for cleaning the internal surface of metal pipes or conduits, preferably stainless steel or special steel, clogged with scale, in an industrial boiler exchanger. Brief description of the figures

[0020] There figure 1 represents a perspective view, with the hood closed, of an embodiment of the machine for separating crystallized radioactive boron waste in a thin-walled metal tube, according to the present invention. figure 2represents a detailed view, hood open, of the machine shown on the figure 1 . Description of a preferred embodiment of the invention

[0021] One embodiment of the invention is shown in the Figures 1 And 2 This is a vibratory hammering machine 1 for processing sections of metal pipe 10 from a TEU evaporator, sealed with boron crystals, possibly in the presence of impurities. To clarify, the illustrated machine is suitable for processing sections of pipe cut for post-dismantling treatment, but the invention also relates to any variant that can be directly adapted to an operational pipeline.

[0022] Machine 1 comprises a casing or frame 12 which can be fitted with a cover 13 and which contains the functional components of the vibrating hammer. The casing 12 terminates at its lower part in a truncated pyramid 6 fitted with an opening (not shown) for the collection of boron waste into a collection drum 7.

[0023] During operation, the tube to be treated 10 is held by fixed jaws 8, preferably at least two in number. The vibrating hammer comprises strikers 2, preferably at least two in number, attached to movable jaws 3 and actuated by pneumatic cylinders 5. As a result of the vibrations generated, the crystallized boron detaches in the form of aggregates and / or powder which fall into the recovery drum 7.

[0024] The treatment machine is mounted on soft shock absorbers (silent blocks) 4. The use of a machine such as described above and of reduced size makes sense insofar as boron tends to accumulate in a localized manner in the pipes (hot spots).

[0025] The tubes to be treated are thin-walled tubes, for example DN 100 or 150 stainless steel tubes with a wall thickness of 5mm. The vibrating hammer and its actuator are designed to avoid deforming the tubes (no exceeding their elastic limit), which is obviously a requirement for preventive maintenance and allows for the removal of a maximum number of crystals (no crevices formed during treatment).

[0026] The tests carried out showed satisfactory separation of the crystallized boron from the stainless steel pipes. The surface of the internal pipework has slight asperities and a very thin, non-adherent layer of boron.

[0027] Advantageously, the cleanliness of the internal piping can be improved by passing it with a chimney sweeping brush.

[0028] According to advantageous forms of execution, the aforementioned separation technique will be implemented in a controlled area by optimizing the process with respect to dosimetry, optimizing handling, limiting the dispersion of boron dust by collecting boron residues as close as possible to the ends of the cylindrical tube and by implementing appropriate biological protections. List of reference symbols

[0029] 1. Cleaning machine 2. Impactor 3. Moving jaw 4. Flexible shock absorber (silent block) 5. Pneumatic cylinder 6. Funnel or pyramid-shaped waste collector 7. Collection drum 8. Fixed jaw 10. Pipe or conduit to be treated 11. Pipe fixing(s) 12. Machine frame 13. Cover

Claims

1. A machine (1) for cleaning a thin-walled pipe or conduit (10) partially or completely blocked by crystallized waste, comprising a plurality of vibrating hammers (2, 3, 5, 8) transmitting, when in use, vibrations to the external surface of said pipe or conduit (10) in such a way as to detach from the internal wall of the pipe and to collect by gravity the crystallized waste in the form of aggregates and / or powder, characterized in that it comprises an external frame (12) enclosing the vibrating hammers (2, 3, 5, 8) and ending downward in a funnel or truncated pyramid (6) with an opening for the evacuation of the waste.

2. The machine (1) according to claim 1, characterized in that each vibrating hammer comprises a fixed jaw (8) and a movable jaw (3) positioned to be diametrically opposed relative to the pipe or conduit (10) as well as a striker (2) actuated by a pneumatic or hydraulic cylinder (5) in a direction perpendicular to the pipe or conduit (10).

3. The machine (10) according to claim 1, characterized in that the external frame (12) enclosing the vibrating hammers as well as the cylinders are mounted on a structure with flexible dampers (4).

4. The machine (10) according to claim 1, characterized in that it comprises a waste recovery bin (7) positioned under said opening.

5. The machine according to any one of the preceding claims, characterized in that it includes a closure cap (13).

6. Use of the machine according to any one claims 1 to 5, to clean the internal surface of pipes or conduits made of metal, ceramic, plastic, or stone, preferably with a thickness less than 10mm, the internal surface of which is covered or blocked by crystallized or non-crystallized waste such as radioactive scale, calamine, limestone, or nitrate residues.

7. The use of the machine according to any one of claims 1 to 5, to clean the internal surface of pipes or conduits in metal, preferably stainless steel or special steel, blocked by boron crystals, in an evaporator of a waste effluent treatment circuit of a nuclear power plant.

8. The use of the machine according to any one of claims 1 to 5, to clean the internal surface of pipes or conduits in metal, preferably stainless steel or special steel, blocked by calamine, in an industrial heat exchanger.