Pipe adapted for transporting a fluid inside a nuclear power plant and method of assembling such a pipe

Abstract

The pipe (10) is adapted for transporting a fluid inside a nuclear power plant, the pipe (10) comprising: - an inner conduit (12) defining a flow path (18) through which the fluid flows, - an outer insulation layer (14) surrounding the inner conduit (12), an air gap (22) being provided between the inner conduit (12) and the outer insulation layer (14), and - at least one stopper (16) extending along a main axis (X-X') in said air gap (22). The stopper (16) is compressed radially between the inner conduit (12) and the outer insulation layer (14), the circulation of air through said stopper (16) being completely prevented.

Description

[0001] Pipe adapted for transporting a fluid inside a nuclear power plant and method of assembling such a pipe

[0002] The present invention relates to pipes adapted for transporting fluids inside a nuclear power plant, and in particular to the thermal isolation of such pipes.

[0003] In nuclear power plants, to transport fluids such as superheated water, it is typical to use pipes comprising an inner conduit surrounded by an outer insulation layer with a tolerated air gap in-between. The outer insulation layer is generally composed of a plurality of individual insulation parts arranged axially next to each other.

[0004] However, such pipes present some drawbacks.

[0005] Indeed, due to the convection generated by the temperature difference between the outer surface of the outer insulation layer and the air inside the air gap, an inhomogeneous airflow circulates inside this air gap.

[0006] Furthermore, said inhomogeneous airflow is rendered directional due to the forced airflow generated around the pipe by the ventilation system of the containment.

[0007] Therefore, due to this airflow, cold air is drawn into the air gap, while hot air is released outside said air gap.

[0008] This leads to an increased heat release in the immediate surrounding of the pipe and to critical heat loss.

[0009] One of the aims of the present invention is to reduce heat dissipation and critical heat loss inside a nuclear power plant.

[0010] To this end, the invention proposes a pipe adapted for transporting a fluid inside a nuclear power plant, the pipe comprising: an inner conduit defining a flow path through which the fluid flows,

[0011] - an outer insulation layer surrounding the inner conduit, an air gap being provided between the inner conduit and the outer insulation layer, and

[0012] - at least one stopper extending along a main axis in said air gap; wherein the stopper is compressed radially between the inner conduit and the outer insulation layer, the circulation of air through said stopper being completely prevented.

[0013] The stopper allows completely preventing the circulation of air in the air gap 22, thus preventing the formation of a convection airflow causing the heat dissipation. Therefore, thanks to the stoppers, the heat loss is reduced.

[0014] In other embodiments, the pipe comprises one or several of the following features, taken individually or in any technically feasible combination:

[0015] - the outer insulation layer surrounds the inner conduit in a concentric manner;

[0016] - the stopper comprises at least one ring-shaped element; - the ring-shaped element is made in one piece comprising two extremities, the piece being wrapped around the inner conduit and the two extremities being connected together by positive fit so as to prevent airflow;

[0017] - the ring-shaped element is formed in at least two parts, each one of these two parts comprising a first extremity and a second extremity, the two parts being arranged around the inner conduit, the first extremity of each of the two parts being connected together by positive fit with the second extremity of the other of the two parts;

[0018] - the stopper comprises at least two ring-shaped elements axially arranged next to each other along the main axis;

[0019] - the stopper is made of a first material, the first material being an elastic material with a Young’s modulus lower that 5 GPa;

[0020] - the stopper is made of a first material, the first material being stable at temperatures above 50°C and / or against neutron irradiation.

[0021] The invention also relates to a nuclear power plant comprising at least one pipe as described above.

[0022] The invention also relates to a method for assembling a pipe as described above, the method comprising the following steps: a. providing the inner conduit, b. arranging the stopper against the inner conduit, and c. arranging the outer insulation layer such that the stopper is compressed radially between the inner conduit and the outer insulation layer.

[0023] In other embodiments, the method comprises one or several of the following features, taken individually or in any technically feasible combination: in step a), the inner conduit is provided with the outer insulation layer surrounding the inner conduit, the method comprising an additional step b1 ) before step b) of removing the outer insulation layer;

[0024] - the method comprises an additional step a2) before step b1 ) of determining areas of the air gap having a critical heat loss, in step b) the stopper being arranged in one of said areas;

[0025] - the areas are determined as having a critical heat loss by temperature measurement using circumferentially arranged temperature sensors around the inner conduit.

[0026] The invention and its advantages will be better understood on reading the following description given solely by way of non-limiting examples and with reference to the appended drawings, in which:

[0027] - Figure 1 is a schematic longitudinal section of a pipe according to a first embodiment of the invention; - Figure 2 is a schematic cross-section of the pipe showed on Figure 1 ;

[0028] - Figure 3 is a schematic longitudinal section of a pipe before the assembling of the stopper;

[0029] - Figure 4 is a schematic cross-section of the pipe of Figure 3;

[0030] - Figure 5 is a schematic longitudinal section of a pipe according to a second embodiment of the invention;

[0031] - Figure 6 is a schematic cross-section of a pipe according to a third embodiment of the invention.

[0032] Figure 1 shows a part of a pipe 10 according to a first embodiment of the invention.

[0033] In particular, the pipe 10 is installed inside a nuclear power plant 1 1 .

[0034] More precisely, the pipe 10 is inside a nuclear reactor, such as a boiling and pressurized water reactor, and more precisely inside the containment of such a nuclear reactor.

[0035] The pipe 10 is adapted for transporting a fluid inside a nuclear power plant, and in particular inside the nuclear reactor.

[0036] The fluid transported inside the pipe 10 is for example superheated water, i.e. pressurized liquid hot water at a temperature between 100°C and 374°C.

[0037] As visible on Figure 1 , the pipe 10 comprises an inner conduit 12, an outer insulation layer 14 and at least one stopper 16.

[0038] The inner conduit 12 defines a flow path 18 through which the fluid flows, in particular along a main axis X-X’.

[0039] For example, the inner conduit 12 has a hollow cylindrical shape extending along the main axis X-X’.

[0040] More precisely, the inner conduit 12 comprises a wall 20 comprising an inner face 20A delimiting the flow path 18 and an outer face 20B.

[0041] The inner conduit 12 is preferably made of a material to be stable up to temperatures of 700°C.

[0042] In particular, the wall 20 of the inner conduit 12 is for example made of a material resistant to such high temperatures, resistant against abrasive water flow with velocities above 10m / s and also stable against neutron radiation. Said material is also preferably adapted to be used inside the containment of a nuclear reactor.

[0043] Such material is preferably stainless steel.

[0044] As visible on Figure 1 , the outer insulation layer 14 surrounds the inner conduit 12, preferably in a concentric manner, such that an air gap 22 is provided between the inner conduit 12 and the outer insulation layer 14. The outer insulation layer 14 defines for example an outer face 14A and an inner face 14B facing the outer face 20B of the wall 20 of the inner conduit 12.

[0045] In particular, the outer insulation layer 14 has a hollow cylindrical shape extending along the main axis X-X’, more particularly with an annular cross-section.

[0046] The outer insulation layer 14 is preferably at least partly removable, for example for local inspection at the point of use.

[0047] In this context, removable means that the layer can be removed and repositioned afterwards without modifying and / or destroying said layer.

[0048] Preferably, the outer insulation layer 14 is formed by a plurality of individual insulation parts 15A, 15B, in order to facilitate removal of this outer insulation layer 14.

[0049] As shown on Figure 1 , the individual insulation parts 15A, 15B are arranged next to each other along the main axis X-X’ and connected to each other so as to form the insulation layer 14.

[0050] Each of these individual insulation parts 15A, 15B has for example a hollow cylindrical shape extending along the main axis X-X’.

[0051] Each of these individual insulation parts 15A, 15B is for example a cup at least partly ridged and covered inside with one or more layers of an insulating material, such as foam or textile, and preferably adapted to be used inside the containment of a nuclear reactor.

[0052] Each of these individual insulation parts 15A, 15B is preferably removable, for example for local inspection at the point of use. In a preferred manner, each of the individual insulation parts 15A, 15B is removable independently of the other parts 15A, 15B. The air gap 22 is more precisely defined between the outer face 20B of the wall 20 of the inner conduit 12 and the inner face 14B of the outer insulation layer 14.

[0053] As shown on Figure 1 , the air gap 22 has for example a cylindrical shape, in particular with an annular cross-section.

[0054] The air gap 22 has, in particular, a thickness measured radially between the outer face 20B of the wall 20 of the inner conduit 12 and the inner face 14B of the outer insulation layer 14, comprised between 0,1 cm and 3 cm.

[0055] In this context, radially means perpendicular to the main axis X-X’ and axially means along the main axis X-X’.

[0056] Each stopper 16 extends along the main axis X-X’ in said air gap 22, and in particular over a certain axial length.

[0057] In particular, each stopper 16 divides the air gap 22 axially on both sides of the stopper 16, especially between a first part 22A on one side of the stopper 16 and a second part 22B on the other side of the stopper 16. Each stopper 16 is compressed radially between the inner conduit 12 and the outer insulation layer 14.

[0058] In particular, each stopper 16 is maintained by frictional pressure between the inner conduit 12 and the outer insulation layer 14.

[0059] In other words, the fixation of each stopper 16 is performed only by the compression of said stopper 16 between the wall 20 of the inner conduit 12 and the outer insulation layer 14, and more precisely between the outer face 20B of the wall 20 of the inner conduit 12 and the inner face 14B of the outer insulation layer 14.

[0060] Each stopper 16 has for example a cylindrical shape with an annular cross-section, as visible on Figure 2.

[0061] Each stopper 16 is configured so that the circulation of air through said stopper 16 is completely prevented.

[0062] In other words, each stopper 16 is configured such that there is no air circulation between the first part 22A and the second part 22B of the air gap 22.

[0063] Preferably, as visible on Figure 2, the cross-section of each stopper 16 completely seals the air gap 22 radially over a certain axial length.

[0064] In particular, the thickness of each stopper 16 is substantially equal to that of the air gap 22, such that no air can pass through.

[0065] Each stopper 16 has for example a length, measured along the main axis X-X’, between 3 cm and 20 cm.

[0066] Each stopper 16 is made of a first material, preferably an airtight material.

[0067] Preferably, this first material is stable at temperatures above 50°C and in a preferred manner up to 700 °C.

[0068] In a preferred manner, this first material is stable against neutron irradiation.

[0069] In this context, stable means that the first material remains in its stable state, in particular in its stable solid state with nonporous effects.

[0070] In an advantageous manner, this first material is an elastic material, in particular with a Young’s modulus lower that 5 GPa, and more preferably lower that 1 GPa, in particular in order to resist to technically induced vibrations inside the containment of the nuclear reactor.

[0071] This first material is for example rockwool enclosed by caramelized glass fabric.

[0072] In the specific embodiment shown on Figures 1 and 2, each stopper 16 comprises one ring-shaped element 24, preferably removable for example for local inspection.

[0073] In particular, in this embodiment, the ring-shaped element 24 is made in one piece 26 comprising two extremities 26A, 26B.

[0074] More particularly, the piece 26 comprises a central portion 27, preferably made of the first material, and two outer portions 28, preferably surrounding the central portion 27. More precisely, during use, the piece 26 is wrapped around the inner conduit 12, such that the two extremities 26A, 26B are connected together by positive fit, so as to prevent airflow.

[0075] In other words, the two extremities 26A, 26B are fitted into one another, so that the piece 26 is ring-shaped during use and preferably dense against airflow.

[0076] A method for assembling a pipe 10 as described above will now be described.

[0077] In a first step a), the inner conduit 12 is provided.

[0078] In particular, in this first step a), a pipe 10 without any stopper 16, as shown on Figure 3, is provided.

[0079] More precisely, the inner conduit 12 is provided with the outer insulation layer 14 surrounding the inner conduit 12, in particular in a concentric manner such that the air gap 22 is provided between the inner conduit 12 and the outer insulation layer 14.

[0080] In a preferred manner, as shown on Figure 3 and 4, a plurality of temperature sensors 28A, 28B, 28C are circumferentially arranged around the inner conduit 12, and more precisely installed against the outer face 20B of the wall 20 of the inner conduit 12 inside the air gap 22.

[0081] More preferably, as visible on Figure 4, three temperature sensors 28A, 28B, 28C are installed against the outer face 20B of the wall 20 of the inner conduit 12 at different positions, preferably in the same cross-section of the inner conduit 12.

[0082] Preferably, the method comprises an additional step a2) of determination of areas 30 of the air gap 22 with critical heat loss.

[0083] In particular, the areas are determined by temperature measurement using the temperature sensors 28A, 28B, 28C.

[0084] More precisely, the temperature TA, TB, Tcmeasured respectively by each of the temperature sensors 28A, 28B, 28C are compared to each other and to a reference temperature TREF.

[0085] The reference temperature TREF corresponds for example to the temperature of the fluid inside the flow path 18.

[0086] A difference between the measured temperatures and with the reference temperature T EF indicates in particular the circulation of an inhomogeneous airflow inside the air gap 22, and thus an area 30 with critical heat loss.

[0087] In particular, if the following equation is verified, it is determined that there is a circulation of an inhomogeneous airflow inside the air gap 22: The method comprises then an additional step b1 ) of removing the outer insulation layer 14.

[0088] More preferably, only the individual insolation elements 15B facing the areas 30, preferably for which a critical heat loss has been determined at step a2), are removed.

[0089] Thereafter, at least one stopper 16 is arranged against the inner conduit 12, preferably in one of the areas 30 determined as having a critical heat loss.

[0090] Preferably, one stopper 16 is arranged in each one of the areas 30 determined as having a critical heat loss.

[0091] In the specific embodiment shown on Figures 1 and 2, the piece 26 is wrapped around the inner conduit 12 and the two extremities 26A, 26B are connected together by positive fit to form the ring-shaped element 24.

[0092] Afterwards, the outer insulation layer 14 is arranged such that each stopper 16 is compressed radially between the inner conduit 12 and the outer insulation layer 14, as shown on Figure 1 .

[0093] More precisely, each individual insolation elements 15B removed in the additional step b1 ) are repositioned in their original position such that the stopper 16 is compressed between the inner conduit 12 and the corresponding individual insolation elements 15B.

[0094] Thanks to the stopper 16 according to the invention, the heat loss is reduced.

[0095] Indeed, each stopper 16 allows to completely prevent the circulation of air in the air gap 22, thus stopping the convection airflow and preventing the heat dissipation.

[0096] The reduction of heat dissipation in the containment of the nuclear reactor allows reducing the need for an intensive ventilation of said containment.

[0097] The heat loss is further reduced by the specific arrangement of the stoppers 16 in the areas 30 determined as having a critical heat loss.

[0098] Furthermore, said stoppers 16 are easy to install, even in existing pipes 10.

[0099] Moreover, these stoppers 16 may be installed and removed without dismantling the inner conduit 12.

[0100] The stoppers 16 are also reusable and could be dismantled and then reinstalled many times.

[0101] Moreover, the use of an elastic material for the stoppers 16 allows counteracting at least a part of the vibrations inherent to nuclear reactor operation, and also the variation in the size of the air gap. In a second embodiment of the invention showed in Figure 5, the pipe 10 differs from the one of the first embodiment only in that the stopper 16 comprises at least two ringshaped elements 24A, 24B axially arranged next to each other along the main axis X-X’.

[0102] More precisely, the two ring-shaped elements 24A, 24B are axially dense connected, in order to obtain a stopper 16 with a greater length leading to a greater airtightness.

[0103] Preferably, the two ring-shaped elements 24A, 24B are set against each other in such a manner that the extremity areas of both elements 24A, 24B are displaced against each other by angular rotation of said elements 24A, 24B.

[0104] In the specific example shown in Figure 5, the stopper 16 comprises two ring-shaped elements 24A, 24B, preferably removable for example for local inspection.

[0105] According to an alternative, the stopper 16 comprises more than two ring-shaped elements 24 axially arranged next to each other along the main direction X-X’.

[0106] In a second embodiment of the invention showed in Figure 6, the pipe 10 differs from the one of the first embodiment only in that the ring-shaped element 24 is formed in at least two parts.

[0107] In the specific example shown in Figure 6, the ring-shaped element 24 is formed in two parts, in particular a first part 34 and a second part 36.

[0108] In particular, each one of these two parts 34, 36 comprises a first extremity 34A, 36A and a second extremity 34B, 36B.

[0109] The two parts 34, 36 are for example arranged around the inner conduit 12, such that the first extremity 34A, 36A of each of the parts 34, 36 is connected together by positive fit with the second extremity of the other of the two parts 34B, 36B.

[0110] In particular, the first extremity 34A of the first part 34 is fitted into the second extremity 36B of the second part 36 and the first extremity 36A of the second part 36 is fitted into the second extremity 34B of the first part 34, in order to form the ring-shaped element 24.

[0111] According to an alternative, the ring-shaped element 24 is formed by more than two parts connected together according to the same principle.

Claims

CLAIMS1. Pipe (10) adapted for transporting a fluid inside a nuclear power plant, the pipe (10) comprising: an inner conduit (12) defining a flow path (18) through which the fluid flows,- an outer insulation layer (14) surrounding the inner conduit (12), an air gap (22) being provided between the inner conduit (12) and the outer insulation layer (14), and- at least one stopper (16) extending along a main axis (X-X’) in said air gap (22); characterized in that the stopper (16) is compressed radially between the inner conduit (12) and the outer insulation layer (14), the circulation of air through said stopper (16) being completely prevented.

2. Pipe (10) according to claim 1 , wherein the outer insulation layer (14) surrounds the inner conduit (12) in a concentric manner.

3. Pipe (10) according to claim 1 or 2, wherein the stopper (16) comprises at least one ring-shaped element (24; 24A, 24B).

4. Pipe (10) according to claim 3, wherein the ring-shaped element (24) is made in one piece (26) comprising two extremities (26A, 26B), the piece (26) being wrapped around the inner conduit (12) and the two extremities (26A, 26B) being connected together by positive fit so as to prevent airflow.

5. Pipe (10) according to claim 3, wherein the ring-shaped element (24) is formed in at least two parts (34, 36), each one of these two parts (34, 36) comprising a first extremity (34A, 36A) and a second extremity (34B, 36B), the two parts (34, 36) being arranged around the inner conduit (12), the first extremity (34A, 36A) of each of the two parts (34, 36) being connected together by positive fit with the second extremity (34B, 36B) of the other of the two parts (34, 36).

6. Pipe (10) according to any of claims 3 to 5, wherein the stopper (16) comprises at least two ring-shaped elements (24A, 24 B) axially arranged next to each other along the main axis (X-X’).

7. Pipe (10) according to any of claims 1 to 6, wherein the stopper (16) is made of a first material, the first material being an elastic material with a Young’s modulus lower that 5 GPa.

8. Pipe (10) according to any of claims 1 to 7, wherein the stopper (16) is made of a first material, the first material being stable at temperatures above 50°C and / or against neutron irradiation.

9. Nuclear power plant (1 1 ) comprising at least one pipe (10) according to any of claims 1 to 8.

10. Method for assembling a pipe (10) according to any of claims 1 to 8, the method comprising the following steps: a. providing the inner conduit (12), b. arranging the stopper (16) against the inner conduit (12), and c. arranging the outer insulation layer (14) such that the stopper (16) is compressed radially between the inner conduit (12) and the outer insulation layer (14).1 1 . Method according to claim 10, wherein in step a), the inner conduit (12) is provided with the outer insulation layer (14) surrounding the inner conduit (12), the method comprising an additional step b1 ) before step b) of removing the outer insulation layer (14).

12. Method according to claim 1 1 , wherein the method comprises an additional step a2) before step b1 ) of determining areas (30) of the air gap (22) having a critical heat loss, in step b) the stopper (16) being arranged in one of said areas (30).

13. Method according to claim 12, wherein the areas (30) are determined as having a critical heat loss by temperature measurement using circumferentially arranged temperature sensors (28A, 28B, 28C) around the inner conduit (12).

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