Patent Description:
A steam generator provided in a nuclear power plant or the like includes a plurality of heat transfer tubes. Each heat transfer tube is fixed to a tube plate provided within the steam generator. When dismantling the steam generator, it is necessary to remove the heat transfer tubes from the tube plate. Patent Document <NUM> discloses a configuration in which a heat transfer tube fixed to a tube plate is pulled out of the tube plate.

<CIT>, <CIT>, <CIT> and <CIT> disclose other examples of steam generators for nuclear power plants including a plurality of heat transfer tubes.

Incidentally, the heat transfer tubes are expanded outward in the radial direction in through-holes formed in the tube plate, and are pressed against the inner walls of the through-holes to be fixed. Therefore, it takes time and effort to pull out the heat transfer tubes from the tube plate. Moreover, the inner surface of the heat transfer tube may be contaminated with radioactive substances.

The present invention has been made to solve the above problems, and an object thereof is to provide a method for dismantling a steam generator capable of suppressing the spread of contamination on the inner surface of the heat transfer tubes.

In order to solve the above problems, a method for dismantling a steam generator according to the present invention is defined in claim <NUM>, and is a method for dismantling a steam generator including a tube plate, a plurality of heat transfer tubes, and welded portions. The tube plate has a plurality of through-holes. The plurality of heat transfer tubes are each inserted into the through-holes. The plurality of heat transfer tubes are fixed to inner wall surfaces of the through-holes. The welded portion fixes the heat transfer tubes and the tube plate to each other. The method for dismantling a steam generator includes a step of reducing a fixing force of the heat transfer tubes to the tube plate from which the welded portions are removed. The method for dismantling a steam generator includes a step of removing the heat transfer tubes from an inside of the through-holes.

A method for dismantling a steam generator not covered by the present invention is a method for dismantling a steam generator including a tube plate, a plurality of heat transfer tubes, and welded portions. The tube plate has a plurality of through-holes. The plurality of heat transfer tubes are each inserted into the through-holes. The plurality of heat transfer tubes are fixed to inner wall surfaces of the through-holes. The welded portion fixes the heat transfer tubes and the tube plate to each other. The method for dismantling the steam generator includes a step of performing trepanning processing with a diameter equal to or greater than an outer diameter of the heat transfer tube. The method for dismantling a steam generator includes a step of removing the heat transfer tubes from an inside of the through-holes.

According to the method for dismantling a steam generator of the present invention it is possible to suppress the spread of contamination on the inner surface of the heat transfer tube.

Hereinafter, a method for dismantling a steam generator according to an embodiment of the present disclosure will be described with reference to <FIG>.

As shown in <FIG>, a steam generator <NUM> at least includes a body portion <NUM>, a tube plate <NUM>, and a plurality of heat transfer tubes <NUM>. The body portion <NUM> is a tubular container extending in an axial direction Da. The tube plate <NUM> is arranged inside the body portion <NUM>. The tube plate <NUM> is arranged along a plane (for example, a horizontal plane) orthogonal to the axial direction Da. The tube plate <NUM> partitions the inside of the body portion <NUM> into upper and lower parts. As a result, in the body portion <NUM> of the steam generator <NUM>, a primary cooling water chamber <NUM> below the tube plate <NUM> and a secondary cooling water chamber <NUM> above the tube plate <NUM> are formed. The steam generator <NUM> illustrated in this embodiment further includes a partition <NUM>. The partition <NUM> divides the primary cooling water chamber <NUM> into an inlet side water chamber 14a and an outlet side water chamber 14b. Here, the first side of the tube plate <NUM> in the axial direction Da (the lower part of the paper in <FIG>) is the primary side, and the second side of the tube plate <NUM> in the axial direction Da (the upper part of the paper in <FIG>) is the secondary side.

The plurality of heat transfer tubes <NUM> are arranged in the body portion <NUM>. The plurality of heat transfer tubes <NUM> each have a pair of straight tube portions <NUM> and a curved portion 13t. The pair of straight tube portions <NUM> are formed at both end portions of each heat transfer tube <NUM>. Each straight tube portion <NUM> extends from the primary side to the secondary side. The curved portion 13t is formed in the intermediate portion of each heat transfer tube <NUM>. The curved portion 13t is formed by being curved in an inverted U shape. Both end portions of each heat transfer tube <NUM> (end portions 13b of each straight tube portion <NUM>) are fixed to the tube plate <NUM>.

As shown in <FIG>, a plurality of through-holes <NUM> penetrating in the axial direction Da are formed in the tube plate <NUM>. Each heat transfer tube <NUM> (more specifically, the straight tube portion <NUM>) is inserted into each through-hole <NUM>. In the through-hole <NUM>, the heat transfer tube <NUM> is expanded toward the outside in a radial direction Dr. As a result, each heat transfer tube <NUM> is pressed against and fixed to an inner wall surface 18i of the through-hole <NUM>.

The end portions 13b of each heat transfer tube <NUM> are arranged near a first surface <NUM> of the tube plate <NUM> (more specifically, slightly on the secondary side of the first surface <NUM>). The end portions 13b of each heat transfer tube <NUM> are bonded to the first surface <NUM> (and the inner wall surface 18i of the through-hole <NUM>) of the tube plate <NUM> by seal welding. That is, the steam generator <NUM> has a welded portion <NUM> for fixing the end portion 13b of the heat transfer tube <NUM> and the first surface <NUM> of the tube plate <NUM>. This steam generator <NUM> can be provided, for example, in a nuclear power plant.

As shown in <FIG>, the primary cooling water heated by the nuclear reactor (not shown) is introduced into the inlet side water chamber 14a of the primary cooling water chamber <NUM> of the steam generator <NUM>. The primary cooling water introduced into the inlet side water chamber 14a passes through the plurality of heat transfer tubes <NUM> exposed in the secondary cooling water chamber <NUM> and reaches the outlet side water chamber 14b of the primary cooling water chamber <NUM>.

Secondary cooling water is introduced into the secondary cooling water chamber <NUM>. The secondary cooling water is heated into steam by exchanging heat with the primary cooling water passing through the heat transfer tube <NUM> in the secondary cooling water chamber <NUM>. The steam generated in the secondary cooling water chamber <NUM> is sent to a turbine (not shown) installed outside the steam generator <NUM>. Further, the primary cooling water cooled by heat exchange with the secondary cooling water is sent to a nuclear reactor (not shown).

As shown in <FIG>, a method S1A for dismantling the steam generator <NUM> includes a step S2A of reducing the fixing force of the heat transfer tubes <NUM> and a step S3 of removing the heat transfer tubes <NUM>.

In the step S2A of reducing the fixing force of the heat transfer tubes <NUM>, the fixing force of the heat transfer tubes <NUM> expanded in the through-holes <NUM> of the tube plate <NUM>, from which the welded portion <NUM> is removed, with respect to the tube plate <NUM> is reduced. In this embodiment, for example, by heating the heat transfer tubes <NUM> to cause deformation in the heat transfer tubes <NUM>, the fixing force of the heat transfer tubes <NUM> to the tube plate <NUM> is reduced. Specifically, for example, the heat transfer tubes <NUM> are heated by a welding arc for tungsten inert gas (TIG) welding or a laser for laser beam welding. Then, the heat transfer tube <NUM> is heated. This heating causes the heat transfer tubes <NUM> to deform (for example, contraction of the heat transfer tubes <NUM> in the radial direction). Then, the fixing force of the heat transfer tubes <NUM> to the tube plate <NUM> is reduced. As means for heating the heat transfer tube <NUM>, for example, a burner, an electric heater, and the like may be used in addition to the welding arc and the laser. In a case where the end portions of the heat transfer tube <NUM> are sealed with a plug <NUM> inserted into the heat transfer tube <NUM>, the welded portions <NUM> including the plug <NUM> are removed.

In the step S3 of removing the heat transfer tubes <NUM>, as shown in <FIG>, the heat transfer tubes <NUM> of which the fixing force to the tube plate <NUM> has decreased in the step S2A of reducing the fixing force of the heat transfer tubes <NUM> are removed from the through-holes <NUM>. In this embodiment, the heat transfer tubes <NUM> are removed from the tube plate <NUM> by pulling out the heat transfer tubes <NUM> from the lower side of the tube plate <NUM> toward the primary side in the axial direction Da.

By performing such work on the plurality of heat transfer tubes <NUM>, the plurality of heat transfer tubes <NUM> are removed from the tube plate <NUM>.

In the method S1A for dismantling the steam generator <NUM> of the above embodiment includes the step S2A of reducing the fixing force of the heat transfer tubes <NUM> to the tube plate <NUM>, and the step S3 of removing the heat transfer tubes <NUM> from the through-holes <NUM>.

Therefore, according to the method S1A for dismantling the steam generator <NUM> of the embodiment, the heat transfer tubes <NUM> can be removed from the through-holes <NUM> after the fixing force of the heat transfer tubes <NUM> to the tube plate <NUM> is reduced. As a result, it is possible to suppress the spread of contamination on the inner surface of the heat transfer tube <NUM>. In addition, the heat transfer tubes <NUM> can be easily removed from the tube plate <NUM>.

In the above embodiment, in the step S2A of reducing the fixing force, the heat transfer tubes <NUM> are heated to deform the heat transfer tubes <NUM>, and the fixing force of the heat transfer tubes <NUM> to the tube plate <NUM> can be easily reduced.

In the above embodiment, in case where the end portions 13b of the heat transfer tube <NUM> are sealed with the plug <NUM>, the welded portion <NUM> is removed including the plug <NUM>. Accordingly, it becomes possible to efficiently remove the heat transfer tubes <NUM> and the plug <NUM> from the tube plate <NUM>.

Next, a second embodiment of the method for dismantling a steam generator according to this disclosure will be described. In the second embodiment described below, only the configuration of a step S2B for reducing the fixing force differs from that of the first embodiment, and thus the same parts as those in the first embodiment will be given the same reference numerals, and redundant description will be omitted.

As shown in <FIG>, a method S1B for dismantling the steam generator <NUM> includes a step S2B of reducing the fixing force of the heat transfer tubes <NUM> and the step S3 of removing the heat transfer tubes <NUM>.

In this embodiment, in the step S2B of reducing the fixing force of the heat transfer tubes <NUM>, the thickness of the heat transfer tubes <NUM> in the radial direction Dr is reduced. For this purpose, for example, as shown in <FIG>, an inner peripheral surface 13p of the heat transfer tube <NUM> is cut from the primary side of the heat transfer tube <NUM> with a drill <NUM> inside the through-hole <NUM> in the radial direction Dr. At this time, the outer diameter of the drill <NUM> to be used is set to be greater than the inner diameter of the heat transfer tube <NUM> and smaller than the outer diameter of the heat transfer tube <NUM>. As a result, the inner part of the heat transfer tube <NUM> in the radial direction Dr including the inner peripheral surface 13p is removed from the heat transfer tube <NUM>, leaving only the outer part 13x in the radial direction Dr.

In the step S3 of removing the heat transfer tubes <NUM>, the heat transfer tubes <NUM> having the cut inner peripheral surfaces 13p are removed from the through-holes <NUM>, as shown in <FIG>. In this second embodiment, similarly to the first embodiment, the heat transfer tubes <NUM> are removed from the tube plate <NUM> by pulling out the heat transfer tubes <NUM> from the primary side of the tube plate <NUM>.

By cutting the inner peripheral surface 13p of the heat transfer tube <NUM> in this manner, the rigidity of the heat transfer tube <NUM> decreases in the through-hole <NUM> of the tube plate <NUM>. Thereby, the fixing force of the heat transfer tube <NUM> to the tube plate <NUM> is reduced. The inner peripheral surface 13p of the heat transfer tube <NUM> is contaminated with radioactive substances contained in the primary cooling water. However, by removing the part including the inner peripheral surface 13p of the heat transfer tube <NUM>, the expansion of the contamination to the tube plate <NUM> can be suppressed.

The cutting of the inner peripheral surface 13p of the heat transfer tube <NUM> by the drill <NUM> may be performed over the entire length in the axial direction Da fixed to the through-hole <NUM> of the tube plate <NUM>, or may be performed only partially in the axial direction Da. For example, cutting of the inner peripheral surface 13p of the heat transfer tube <NUM> by the drill <NUM> may proceed in the axial direction Da, and cutting may be stopped when the heat transfer tube <NUM> rotates together with the drill <NUM>. Here, the reason why the heat transfer tube <NUM> rotates together with the drill <NUM> is that the fixing force of the heat transfer tube <NUM> to the through-hole <NUM> has decreased.

In the method S1B for dismantling the steam generator <NUM> of the second embodiment, the heat transfer tubes <NUM> can be removed from the through-holes <NUM> after the fixing force of the heat transfer tubes <NUM> to the tube plate <NUM> is reduced. As a result, it is possible to suppress the spread of contamination on the inner surface of the heat transfer tube <NUM>. In addition, the heat transfer tubes <NUM> can be easily removed from the tube plate <NUM>.

In the above embodiment, in the step S2B of reducing the fixing force, the inner peripheral surface 13p of the heat transfer tube <NUM> is cut inside the through-hole <NUM> in the radial direction Dr to reduce the thickness of the heat transfer tube <NUM> in the radial direction Dr. As a result, the rigidity of the heat transfer tubes <NUM> within the through-holes <NUM> of the tube plate <NUM> is reduced. Therefore, the fixing force of the heat transfer tubes <NUM> to the tube plate <NUM> can be easily reduced.

Next, a third embodiment of the method for dismantling a steam generator according to this disclosure will be described. In the third embodiment described below, only the configuration of a step S2C for reducing the fixing force differs from that of the first embodiment, and thus the same parts as those in the first embodiment will be given the same reference numerals, and redundant description will be omitted.

As shown in <FIG>, a method S1C for dismantling the steam generator <NUM> includes the step S2C of reducing the fixing force of the heat transfer tubes <NUM> and the step S3 of removing the heat transfer tubes <NUM>.

In this embodiment, in the step S2C of reducing the fixing force of the heat transfer tubes <NUM>, the thickness of the heat transfer tubes <NUM> in the radial direction Dr is reduced at part of the heat transfer tubes <NUM> in the circumferential direction Dc. For this purpose, for example, as shown in <FIG> and <FIG>, inside the through-hole <NUM> in the radial direction Dr, on the inner peripheral surface 13p of the heat transfer tube <NUM>, one or more grooves <NUM>, which are continuously connected to the heat transfer tube <NUM> in the extending direction (axial direction Da), are formed. In this embodiment, for example, three grooves <NUM> are formed at intervals in the circumferential direction Dc. The number of grooves <NUM> is not limited to three, and may be another number. Here, the grooves <NUM> may be formed over the entire length in the axial direction Da of the heat transfer tubes <NUM> fixed to the through-holes <NUM> of the tube plate <NUM>, or may be formed only partially in the axial direction Da.

By forming the grooves <NUM> on the inner peripheral surface 13p of the heat transfer tube <NUM> in this manner, the rigidity of the heat transfer tube <NUM> decreases in the through-hole <NUM> of the tube plate <NUM>. Thereby, the fixing force of the heat transfer tube <NUM> to the tube plate <NUM> is reduced.

In the step S3 of removing the heat transfer tubes <NUM>, similarly to the first and second embodiments, the heat transfer tubes <NUM> having the grooves <NUM> are removed from the through-holes <NUM>.

In the method S1C for dismantling the steam generator <NUM> of the third embodiment, similarly to the first and second embodiments, the heat transfer tubes <NUM> can be removed from the through-holes <NUM> after the fixing force of the heat transfer tubes <NUM> to the tube plate <NUM> is reduced. As a result, it is possible to suppress the spread of contamination on the inner surface of the heat transfer tube <NUM>. In addition, the heat transfer tubes <NUM> can be easily removed from the tube plate <NUM>.

In the third embodiment, in the step S2C of reducing the fixing force, the grooves <NUM> are formed on the inner peripheral surface 13p of the heat transfer tube <NUM> inside the through-hole <NUM> in the radial direction Dr, and the thickness of the heat transfer tube <NUM> in the radial direction Dr is reduced at part of the heat transfer tube <NUM> in the circumferential direction Dc. Thereby, the fixing force of the heat transfer tubes <NUM> to the tube plate <NUM> can be reduced.

Next, a fourth embodiment of the method for dismantling a steam generator according to this disclosure will be described. In the fourth embodiment described below, only the configuration of the step of removing the heat transfer tube <NUM> differs from that of the first embodiment, and thus the same parts as those in the first embodiment will be given the same reference numerals, and redundant description will be omitted.

As shown in <FIG>, a method S1D for dismantling the steam generator <NUM> includes a step S2D of reducing the fixing force of the heat transfer tubes <NUM> and a step S3D of removing the heat transfer tubes <NUM>.

In the fourth embodiment, in the step S2D of reducing the fixing force of the heat transfer tubes <NUM>, any one of the steps S2A to S2C of reducing the fixing force of the heat transfer tubes <NUM> in the first to third embodiments described above is performed. In the fourth embodiment, in the step S3D of removing the heat transfer tube <NUM>, as shown in <FIG>, the trepanning processing is performed with a diameter D2 equal to or greater than the outer diameter D1 of the heat transfer tube <NUM>. For this, for example, a cylindrical hole <NUM> is formed in the tube plate <NUM> outside the outer peripheral surface 13q of the heat transfer tube <NUM> in the radial direction Dr by using a cutting tool <NUM> having a diameter greater than the outer diameter D1.

By forming the cylindrical holes <NUM> by such trepanning processing, the heat transfer tubes <NUM> are separated from the tube plate <NUM>. Thereby, as shown in <FIG>, the heat transfer tubes <NUM> separated from the tube plate <NUM> can be removed from the tube plate <NUM>.

In the method S1D for dismantling the steam generator <NUM> of the fourth embodiment, the trepanning processing is performed with the diameter D2 equal to or greater than the outer diameter D1 of the heat transfer tube <NUM>. As a result, the heat transfer tubes <NUM> are separated from the tube plate <NUM>, and the fixing force of the heat transfer tubes <NUM> to the tube plate <NUM> is reduced. Therefore, the heat transfer tubes <NUM> can be easily removed from the tube plate <NUM>.

Further, in the fourth embodiment, the heat transfer tubes <NUM> are removed from the tube plate <NUM> after the fixing force of the heat transfer tubes <NUM> is reduced. As a result, it is possible to suppress the spread of contamination on the inner surface of the heat transfer tube <NUM>. In addition, the trepanning processing can be stably performed at a position near the inner surface of the through-hole <NUM>.

Next, a fifth embodiment of the method for dismantling a steam generator according to this disclosure will be described. In the fifth embodiment described below, the same reference numerals will be given to the same parts as those of the first to fourth embodiments, and redundant description thereof will be omitted.

As shown in <FIG>, a method S1F for dismantling the steam generator <NUM> includes a step S11 of performing trepanning processing and a step S12 of removing the heat transfer tubes <NUM>.

In this embodiment, in the step S11 of performing the trepanning processing, as shown in <FIG>, the trepanning processing is performed with a diameter D12 equal to or greater than an outer diameter D11 of the heat transfer tube <NUM>. For this, for example, a cylindrical hole <NUM> is formed in the tube plate <NUM> outside the outer peripheral surface 13q of the heat transfer tube <NUM> in the radial direction Dr by using a cutting tool <NUM> having the diameter D12 greater than the outer diameter D11. The cylindrical hole <NUM> is formed to penetrate from the first surface <NUM> to a second surface 12f of the tube plate <NUM>. By forming the cylindrical holes <NUM> by such trepanning processing, the heat transfer tubes <NUM> are separated from the tube plate <NUM>.

In the step S12 of removing the heat transfer tubes <NUM>, as shown in <FIG>, the heat transfer tubes <NUM> separated from the tube plate <NUM> are removed from the through-holes <NUM>. In this case, the heat transfer tubes <NUM> may be pulled out of the lower side of the tube plate <NUM> toward the primary side in the axial direction Da as in the first to fourth embodiments, or may be pulled out of the upper side of the tube plate <NUM> toward the secondary side in the axial direction Da.

In the method S1F for dismantling the steam generator <NUM> of the fifth embodiment, the heat transfer tubes <NUM> are separated from the tube plate <NUM> by forming cylindrical holes <NUM> by the trepanning processing. Therefore, it is possible to suppress the spread of contamination on the inner surface of the heat transfer tube <NUM>. In addition, the heat transfer tubes <NUM> can be easily removed from the tube plate <NUM>.

In addition, when removing the heat transfer tubes <NUM>, it is not necessary to remove the welded portions <NUM>, the plug <NUM>, and the like, in advance, and in this regard, the heat transfer tubes <NUM> can also be easily removed from the tube plate <NUM>.

Above, the embodiments of the present disclosure have been described in detail with reference to the drawings, but the specific configuration is not limited to the embodiments, and includes design changes and the like within the scope of the present disclosure.

For example, in the above fourth and fifth embodiments, the cylindrical holes <NUM> and <NUM> are formed in the tube plate <NUM> outside the outer peripheral surface 13q of the heat transfer tube <NUM> in the radial direction Dr by using the cutting tools <NUM> and <NUM> having the diameters D2 and D12 greater than the outer diameters D1 and D11, but the present disclosure is not limited thereto. The trepanning processing may be performed with the diameters D2 and D12 that are equal to or greater than the outer diameters D1 and D11 of the heat transfer tubes <NUM>. That is, the trepanning processing may be performed with the same diameters as the outer diameters D1 and D11 of the heat transfer tubes <NUM> to form the holes <NUM> and <NUM> along the boundary surfaces between the heat transfer tubes <NUM> and the through-holes <NUM>.

Further, the sequence of the procedure of the above method for dismantling the steam generator may be changed as appropriate.

The method for dismantling the steam generator described in each embodiment is ascertained as follows, for example.

There are provided the methods S1A to S1F for dismantling the steam generator <NUM> including the tube plate <NUM> having the plurality of through-holes <NUM>, the plurality of heat transfer tubes <NUM> each inserted into the through-holes <NUM>, and fixed to the inner wall surfaces 18i of the through-holes <NUM>, and the welded portions <NUM> fixing the heat transfer tubes <NUM> and the tube plate <NUM> to each other, the methods S1A to S1F including: the steps S2A to S4D of reducing the fixing force of the heat transfer tubes <NUM> to the tube plate <NUM> from which the welded portions <NUM> are removed; and the step S3 of removing the heat transfer tubes <NUM> from the inside of the through-holes <NUM>.

In the methods S1A to S1F for dismantling the steam generator <NUM>, the heat transfer tubes <NUM> can be removed from the inside of the through-holes <NUM> after the fixing force of the heat transfer tubes <NUM> to the tube plate <NUM> is reduced. Therefore, it is possible to suppress the spread of contamination on the inner surface of the heat transfer tube <NUM>. In addition, the heat transfer tubes <NUM> can be easily removed from the tube plate <NUM>.

In the step S2A of reducing the fixing force of the heat transfer tubes <NUM>, the fixing force of the heat transfer tubes <NUM> to the tube plate <NUM> may be reduced by heating the heat transfer tubes <NUM> to deform the heat transfer tubes <NUM>.

By heating and deforming the heat transfer tubes <NUM> in this manner, the fixing force of the heat transfer tubes <NUM> to the tube plate <NUM> can be easily reduced.

In the step S2B of reducing the fixing force of the heat transfer tubes <NUM>, the fixing force of the heat transfer tubes <NUM> to the tube plate <NUM> may be reduced by cutting the inner peripheral surface 13p of the heat transfer tube <NUM> inside the through-hole <NUM> in the radial direction Dr and reducing the thickness of the heat transfer tube <NUM> in the radial direction Dr.

By reducing the thickness of the heat transfer tube <NUM> in the radial direction Dr in this manner, the rigidity of the heat transfer tube <NUM> decreases in the through-hole <NUM> of the tube plate <NUM>. Accordingly, it becomes easier for the heat transfer tubes <NUM> to deform when a force is applied to the heat transfer tubes <NUM>. Therefore, the fixing force of the heat transfer tubes <NUM> to the tube plate <NUM> can be easily reduced.

In the step S2C of reducing the fixing force of the heat transfer tubes <NUM>, the fixing force of the heat transfer tubes <NUM> to the tube plate <NUM> may be reduced by forming the continuous grooves <NUM> in the extending direction of the heat transfer tube <NUM>, and reducing the thickness of the heat transfer tube <NUM> in the radial direction Dr at part of the heat transfer tube <NUM> in the circumferential direction Dc.

A step of performing trepanning processing with the diameter D2 equal to or greater than the outer diameter D1 of the heat transfer tube <NUM> after the step S2D of reducing the fixing force of the heat transfer tubes <NUM>, may be further provided.

In this manner, the heat transfer tubes <NUM> are separated from the tube plate <NUM> by performing the trepanning processing with the diameter D2 equal to or greater than the outer diameter D1 of the heat transfer tube <NUM>. Accordingly, it becomes possible to easily remove the heat transfer tubes <NUM> from the tube plate <NUM> after the fixing force of the heat transfer tubes <NUM> to the tube plate <NUM> is reduced.

In a case where the end portions 13b of the heat transfer tube <NUM> are sealed by the plug <NUM> inserted into the heat transfer tube <NUM>, the welded portion <NUM> is removed including the plug <NUM>.

By removing the plug <NUM> in the heat transfer tubes <NUM> together with the welded portions <NUM> in this manner, the heat transfer tubes <NUM> can be easily removed from the tube plate <NUM>.

There may be provided the method S1F for dismantling the steam generator <NUM> including the tube plate <NUM> having the plurality of through-holes <NUM>, the plurality of heat transfer tubes <NUM> each inserted into the through-holes <NUM>, and fixed to the inner wall surfaces 18i of the through-holes <NUM>, and the welded portions <NUM> fixing the heat transfer tubes <NUM> and the tube plate <NUM> to each other, the method including: the step S11 of performing trepanning processing with the diameter D12 equal to or greater than the outer diameter D11 of the heat transfer tube <NUM>; and the step S12 of removing the heat transfer tubes <NUM> from the inside of the through-holes <NUM>.

Accordingly, by forming the cylindrical holes <NUM> by such trepanning processing, the heat transfer tubes <NUM> are separated from the tube plate <NUM>. Therefore, it is possible to suppress the spread of contamination on the inner surface of the heat transfer tube <NUM>. In addition, the heat transfer tubes <NUM> can be easily removed from the tube plate <NUM>.

Claim 1:
A method (S1A-S1D) for dismantling a steam generator (<NUM>) including a tube plate (<NUM>) having a plurality of through-holes (<NUM>), a plurality of heat transfer tubes (<NUM>) each inserted into the through-holes (<NUM>), and fixed to inner wall surfaces (18i) of the through-holes, a plurality of plugs (<NUM>) inserted into each of the plurality of heat transfer tubes (<NUM>), and welded portions (<NUM>) fixing end portions (13b) of the heat transfer tubes (<NUM>) and the tube plate (<NUM>) to each other, the method comprising:
a step (S2A-S2D) of reducing a fixing force of the heat transfer tubes (<NUM>) to the tube plate (<NUM>) from which the welded portions (<NUM>) are removed; and
a step (S3, S3D) of removing the heat transfer tubes (<NUM>) from an inside of the through-holes (<NUM>),
characterized in that
in a case where the end portions (13b) of the heat transfer tube (<NUM>) are sealed by the plurality of plugs (<NUM>) inserted into the heat transfer tubes (<NUM>), the welded portions (<NUM>) are removed including the plugs (<NUM>).