Steam generator coolant header with U-shaped tubes of a horizontal heat-exchange bundle and methods of its manufacture

Abstract

This invention relates to electric power industry, and can be used in horizontal steam generators for nuclear power plants (NPP) with a water-water energetic reactor (VVER). We claim a steam generator primary circuit coolant header with U-shaped tubes of a horizontal heat-exchange bundle designed as a thick-wall welded vessel with a perforated central cylindrical part designed so as to allow installation and fastening of a U-shaped heat-exchange tube bundle in the same, wherein the tubes are grouped into banks and separated by vertical inter-tubular tunnels, a lower cylindrical part designed so as to allow welded connection with the steam generator vessel connection pipe, and an upper cylindrical part with a conical adapter to the flange connection of the manhole with a lid, wherein primary circuit header outer diameter D.sub.head in the central part is selected based on formula. The technical result of the invention involves assurance of strength of the header wall bridges between holes for fastening of heat-exchange tubes and leaktightness of heat-exchange tube connections with the header assuming that the outer surface of the perforated header part is more efficiently (fully) used for tubing.

Claims

1. A steam generator primary circuit coolant header comprising: a horizontal heat-exchange bundle of U-shaped tubes, wherein the U-shaped tubes are grouped into banks and separated by vertical inter-tubular tunnels; a thick-wall welded vessel with a central cylindrical part perforated with holes configured for installation and fastening of the heat-exchange bundle therein, the central cylindrical part having a drilling area exceeding an area of holes by at least 20%, wherein a lower cylindrical part of the welded vessel is configured for welded connection with a steam generator vessel of the steam generator primary circuit, wherein an upper cylindrical part of the welded vessel comprises a conical adapter configured for flanged connection to a manhole with a lid, and wherein the primary circuit header has an outer diameter D.sub.head in the central cylindrical part configured in accordance with the following ratio: $2.Math.\left[\frac{\left(d+5.5\right).Math.\left(n_1+n_2\right)}{}+100\right]D_{\mathrm{head}}2.Math.\left[\sqrt{2}.Math.\left(n_1-1\right).Math.S_{}+\frac{\sqrt{2}}{2}.Math.B_2-\frac{\sqrt{2}}{4}.Math.\left(n_1+n_2\right).Math.S_{}-R_{}.Math.\mathrm{tg}\left(\frac{}{8}\right)+100\right]$ where: S.sub.h is a spacing between U-shaped tubes in the horizontal heat-exchange bundle, mm, B.sub.2 is a width of the heat-exchange bundle opposite to the coolant header, mm, d is an outer heat-exchange tube diameter, mm, n.sub.1 and n.sub.2 respectively indicate a quantity of tubes in the horizontal row of smaller and bigger heat-exchange tube banks, mm, R.sub.b is a minimum bend radius of the U shaped tubes, mm, and holes for fastening of heat-exchange tubes in the perforated central cylinder part of the header are staggered so that a distance between edges of a adjacent holes is not less than 5.5 mm.

2. A header according to claim 1, wherein the U-shaped tubes are seamless solid-drawn austenitic stainless steel pipes.

3. A header according to claim 1, wherein the U-shaped tubes of the heat-exchange bundle are grouped into banks separated by 100 to 250 mm wide vertical inter-tubular tunnels.

4. A header according to claim 1, wherein the flanged connection of the conical adapter to the manhole, with a lid, is equipped with a sealing gasket made of expanded graphite.

5. A header according to claim 4, wherein the sealing gasket of the flange connection comprises of pressed expanded graphite foil reinforced with a stainless steel strap.

6. A header according to claim 1, wherein holes of the perforated central cylindrical part includes a drilling area having holes there through, the drilling area limited at the bottom by a symmetrical wedge with a flat point.

7. A header according to claim 6, wherein the drilling area is limited at the bottom by a polyline in the shape of a wedge with a flat point, and a length of the flattened area is not less than 3.Math.(d.sub.hole+6) mm, where d.sub.hole is the hole diameter.

8. A method of manufacture of a steam generator primary circuit coolant header with U-shaped tubes of a horizontal heat-exchange bundle, the method comprising: fabricating two complex forgings and U-shaped heat-exchange tubes, assembly and welding of the forgings, drilling holes in a header central cylindrical part such that a drilling area exceeds an area of holes by at least 20%, assembly of a heat-exchange bundle of U-shaped heat-exchange tubes by grouping the U-shaped tubes into banks separated by vertical inter-tubular tunnels, fastening each U-shaped tube in holes of a primary circuit header by rolling and welding on a header internal surface, wherein a primary circuit header outer diameter D.sub.head in the central part is selected based on the following ratio: $2.Math.\left[\frac{\left(d+5.5\right).Math.\left(n_1+n_2\right)}{}+100\right]D_{\mathrm{head}}2.Math.\left[\sqrt{2}.Math.\left(n_1-1\right).Math.S_{}+\frac{\sqrt{2}}{2}.Math.B_2-\frac{\sqrt{2}}{4}.Math.\left(n_1+n_2\right).Math.S_{}-R_{}.Math.\mathrm{tg}\left(\frac{}{8}\right)+100\right],$ where: S.sub.h is a spacing between heat-exchange tubes in the horizontal heat-exchange bundle, mm, B2 is a width of the heat-exchange bundle opposite to a coolant header, mm, d is a outer heat-exchange tube diameter, mm, n.sub.1 and n.sub.2 respectively indicate a quantity of tubes in a horizontal row of a smaller and a bigger heat-exchange tube banks, mm, R.sub.b is a minimum bend radius of the heat-exchange bundle tubes, mm, and the drilled holes for fastening of heat-exchange tubes are staggered in the central cylindrical part of the header so that a distance between edges of the adjacent holes is not less than 5.5 mm.

9. A method according to claim 8, wherein the U shaped tubes are secured in the holes in the central part of the header by the steps of: round-welding of tube ends on inner surfaces of the headers, followed by hydraulic expansion of the U-shaped tubes, and mechanical curling near the external surfaces of the headers until a gap between the headers and the heat-exchange tubes is closed.

10. A method according to claim 8, further comprising arranging heat exchange bundles evenly from the bottom upwards with vertical gaps between adjacent tubes not exceeding the vertical spacing of tubes in the bundle.

11. A method according to claim 8, wherein during primary coolant header installation into the steam generator pressure vessel, a height of a drilling area does not exceed the arrangement limits set for the upper row of heat-exchange bundle tubes.

12. A method according to claim 8, wherein during fabricating, U-shaped tube bend radii are at least 60 mm, and preferably at least 100 mm.

13. A heat carrier header of a primary circuit of a horizontal steam generator for nuclear power plants, the heat carrier header comprising: a horizontal heat-exchange bundle of U-shaped tubes, wherein the U-shaped tubes are grouped into banks and separated by vertical inter-tubular tunnels; and a central cylindrical part comprising a drilling area exceeding an area of holes by at least 20%; an outer diameter D.sub.head of the central cylindrical part configured according to the following ratio: $2\left[\frac{\left(d+5.5\right)\left(n_1+n_2\right)}{n}+100\right]D_{\mathrm{head}}2\left[\sqrt{2}\left(n_1-1\right)S_{}+\frac{\sqrt{2}}{2}{B}_2-\frac{\sqrt{2}}{4}\left(n_1+n_2\right)S_{}-R_{}\mathrm{tg}\left(\frac{n}{g}\right)+100\right]$ where: S.sub.r is a pitch between heat exchange tubes in the horizontal row of a heat exchange bundle, mm; B.sub.2 is a width of the heat exchange bundle duct located opposite the heat carrier header, mm; d is outer diameter of heat exchange tubes, mm; n.sub.1 and n.sub.2 is a number of tubes in a horizontal row of a smaller and a larger bundle of heat exchange tubes, respectively, mm; R.sub.r is a minimum bend radius of tubes in a heat exchange bundle, mm, wherein heat exchange tubes are arranged in the central cylindrical part of the header in staggered order so that the horizontal distance between edges of adjacent tubes on the inner surface of the header is at least 5.5 mm.

14. A header according to claim 13, further comprising a conical adapter to a manhole equipped with a sealing gasket of expanded graphite.

15. A header according to claim 13, wherein the sealing gasket comprises pressed expanded graphite foil reinforced with a stainless steel strap.

Description

LIST OF FIGURES AND DRAWINGS

(1) FIG. 1 shows a sectional view of the primary circuit coolant header vessel.

(2) FIG. 2 shows a cross-section of the primary circuit coolant header vessel drilling area in the central cylindrical part of the header.

(3) FIG. 3 shows a cross section detail of the primary circuit coolant header vessel drilling area.

(4) FIG. 4 shows a section of the steam generator assembly comprising two primary circuit coolant headers with U-shaped heat-exchange tubes grouped into banks and separated by vertical inter-tubular tunnels.

(5) FIG. 5 shows a section detail of the coolant header with heat-exchange tubes inserted therein.

(6) FIG. 6 shows a diametrical development of the primary circuit coolant header vessel.

(7) FIG. 7 shows a cross section of the horizontal steam generator vessel.

(8) FIG. 8 shows insertion of a heat-exchange tube in a hole in the header side wall.

CORROBORATION OF ACTUAL REDUCTION TO PRACTICE

(9) As shown in FIG. 1, horizontal steam generator primary circuit coolant header 1 has a body in the form of a thick-shaped vessel. The central cylindrical part 2 of the header has deep holes 3 shown in FIGS. 2 and 3 in section that are used to secure heat-exchange tube 4 ends therein as shown in FIGS. 4, 5 and 8. The lower cylindrical part 5 of the header is designed as shown in FIG. 7 with a possibility to connect with the steam generator vessel 7 connection pipe 6 by welding, and the upper part 8 of the header has a flange connection for access inside. It is designed with a conical adapter 9 to the flange connection of the manhole with its lid 10.

(10) Header 1 has its central cylindrical part 2 with a large number of perforated holes 3 designed so as to allow to install and secure a bundle of U-shaped heat-exchange tubes 4 grouped into banks 11 and 12 and separated by vertical inter-tubular tunnels 13 in the said holes 3. Holes 3 are staggered on the central cylindrical part 2 of the header.

(11) The holes 3 in the central cylindrical part 2 of the header vessel 1 fill its external surface are from the bottom to the top. The limits of the upper and lower rows of holes 3 are shown by horizontal dash-dot lines in FIG. 1. In FIG. 5 showing header 1 development on the outer diameter, the said drilling area 14 is shown limited at the bottom by a polyline 15 in the shape of a symmetrical wedge. The wedge limiting the drilling area at the bottom has a flat point 16 with a horizontal section. The horizontal section size is at least 3(d.sub.hol+6) mm. The availability and size of the horizontal section are required to eliminate the stress riser in the header vessel area and increase header vessel strength and reliability.

(12) The flange connection of the manhole with its lid is equipped with a thermal expanded graphite sealing gasket 17.

(13) The assembly method for a steam generator comprising a primary circuit coolant header 1 with U-shaped tubes 4 of a horizontal heat-exchange bundle includes prefabrication of two complex forgings. The first one is designed to form lower 5 and central 2 cylindrical parts of the header 1 vessel. The second forging forms flanged upper conical part 8 of the header 1. Then the forgings are assembled and welded. Two-layer anti-corrosion build-up 18 is applied to the header vessel internal surface. In addition, the specified number of U-shaped heat-exchange tubes are manufactured. Holes 3 are drilled under the established procedure in the central cylindrical part 2 of the header 1, the heat-exchange bundle is assembled with U-shaped heat-exchange tubes 4 grouped into banks 11 and 12 separated by vertical inter-tubular tunnels 13. Each heat-exchange tube 4 is inserted in its corresponding hole 3 in header 1 vessel. Tubes 4 are secured in the primary circuit header holes by rolling followed by round-welding (ring welding) of the tube 4 end to the header 1 internal surface. The said ring weld joint 19 is shown in FIG. 8. Then hydraulic expansion of each heat-exchange tube 4 is performed over header wall thickness L with mechanical curling near the external surface of header 1 until the gap between the header vessel and the heat-exchange tubes 4 is closed.

(14) In order to ensure strength of the header 1 wall bridges 19 between holes 3 with fastened heat-exchange tubes 4 and leak-tightness of the said heat-exchange tube connections with the header, as well as to ensure more efficient use of the outer header surface perforated for tubing, it is required to properly select the outer diameter D.sub.head of the header in its central part (drilling area).

(15) For this purpose, the following empiric relation is used:

(16) $2.Math.\left[\frac{\left(d+5.5\right).Math.\left(n_1+n_2\right)}{}+100\right]D_{\mathrm{head}}2.Math.\left[\sqrt{2}.Math.\left(n_1-1\right).Math.S_{}+\frac{\sqrt{2}}{2}.Math.B_2-\frac{\sqrt{2}}{4}.Math.\left(n_1+n_2\right).Math.S_{}-R_{}.Math.\mathrm{tg}\left(\frac{}{8}\right)+100\right],$

(17) where: S.sub.h is the spacing between heat-exchange tubes in the horizontal heat-exchange bundle row, mm,

(18) B.sub.2 is the width of the heat-exchange bundle opposite to the coolant header, mm,

(19) d is the outer heat-exchange tube diameter, mm,

(20) n.sub.1 and n.sub.2 indicate the quantity of tubes in the horizontal row of the smaller and bigger heat-exchange tube banks, accordingly, mm,

(21) R.sub.b is the minimum bend radius of the heat-exchange bundle tubes, mm.

(22) Measurements of the correlation parameter are shown in FIGS. 2-4.

(23) Holes 3 for fastening of heat-exchange tubes 4 are staggered in the central cylinder part of the header, and the distance between edges of the adjacent holes 3 shall not be less than 5.5 mm along the inner surface of the header. When header 1 is installed in steam generator vessel 7, the height of its drilling area 14 shall not exceed the arrangement limits set for the upper row of heat-exchange bundle tubes in the steam generator.

(24) When the coolant header is assembled with a heat-exchange tube bundle to be inserted in the holes 3 drilled in the central part 2 of the header, heat-exchange tube bend radii shall be at least 60 mm, and preferably at least 100 mm to ensure eddy current testing and quality control of this assembly.

(25) The claimed assembly is operated as part of the horizontal reactor plant steam generator of the nuclear power plant.

(26) Primary coolant heated in the reactor is supplied to the inlet header 1 of the primary circuit coolant. From the inlet header 1, the coolant is supplied to heat-exchange tubes 4 grouped into bundles 11 and 12, passes through them while transferring the heat through the walls of heat-exchange tubes 4 to the secondary circuit coolant, i.e. to the boiler water, and is collected in the outlet or collecting header 20 of the primary circuit coolant. The coolant is returned to the reactor from the outlet header 20 by a circulating pump. The steam generator vessel 7 is filled with boiler water to a certain level above the heat-exchange tube bundle which is to be maintained during operation. Feed water is supplied to the steam generator through connection pipe 21 for feed water supply and the feed water input and distribution device. The feed water flowing out of it is mixed with the boiler water and heated to the saturation temperature. The heat transferred from the primary coolant is spent on boiler water evaporation and steam generation in the inter-tubular space of the steam generator. The generated steam is ascending to the separation part of the steam generator comprising a free volume, separation devices or a combination thereof. After passing the separation part of the steam generator, the steam has the design rated humidity. Then it is removed from the steam generator through steam removal devices comprising steam removal connection pipes 22 and overhead perforated sheets installed in front of them. The steam generated by the steam generator is further used in steam-power process cycle of electric power generation.

(27) During steam generator operation, primary circuit coolant header connection with the U-shaped heat-exchange bundle tubes is the assembly which primarily requires assurance of inter-circuit density, as any loss of tightness leads to ingress of primary coolant radioactive water into the secondary circuit steam-water coolant circulating through the turbine and other structural components of the NPP reactor plant with potential radioactive substance release into the environment.

(28) The claimed technical solution relating to the steam generator coolant header design with U-shaped tubes of horizontal heat-exchange bundle and its manufacture method establishes the following technical result: assurance of the guaranteed strength of the header wall bridges between the holes for fastening of heat-exchange tubes, leak-tightness of heat-exchange tube connections with the header assuming that the outer surface of the perforated header part is more efficiently used for tubing.

EXAMPLE 1

(29) A steam generator is manufactured with in-line arrangement of tubes. The horizontal spacing between heat-exchange bundle tubes is S.sub.h=27 mm. To form a heat-exchange bundle, 18 mm heat-exchange tubes are used. The minimum bend radius of tubes is R.sub.b=120 mm. Number of heat-exchange tubes in a horizontal row of each bank is n.sub.1=n.sub.2=44. The width of tunnels between tube banks is B.sub.1=B.sub.2=220 mm.

(30) $D_{\min }=.Math.\left[\frac{\left(d+5.5\right).Math.\left(n_1+n_2\right)}{}+100\right]=1517\mathrm{mm},D_{\max }=2.Math.\left[\sqrt{2}.Math.\left(n_1-1\right).Math.S_{}+\frac{\sqrt{2}}{2}.Math.B_2-\frac{\sqrt{2}}{4}.Math.\left(n_1+n_2\right).Math.S_{}-R_{}.Math.\mathrm{tg}\left(\frac{}{8}\right)+100\right]=1987\mathrm{mm}.$

(31) If coolant header diameter D is less than 1517 mm, for instance, 1500 mm, horizontal spacing of tubes along the outer header surface will be:

(32) $S=\frac{.Math.D}{2.Math.\left(n_1+n_2\right)}=\frac{.Math.1500}{2.Math.\left(44+44\right)}=26.78\mathrm{mm}$

(33) In case of design pressure values specific to the primary circuit equipment of NPPs with VVER reactors, the header thickness will be 205 mm.

(34) Therefore, the inter-tubular horizontal spacing along the inner header surface will be

(35) $S_{\mathrm{in}}=S.Math.\frac{D}{D+2.Math.205}=21\mathrm{mm},$
and the gap between the tubes within the header will be: =S.sub.ind=2118=3 mm. If the gap between adjacent tubes is 3 mm, it will not be possible to scald them and technically manufacture a steam generator, as leak-tightness and strength of the heat-exchange tube connections with the primary circuit coolant header are not provided.

(36) If the diameter exceeds 1987 mm for the part of heat-exchange bundle tubes it will not be possible to insert them into the holes of the perforate header part as the header side surface will cross over the bent tube section. Bent tube cannot be inserted into the hole. Subsequently, steam generator heat-exchange tube filling level, the area of the steam generator heat-exchange surface, its capacity, techno-economical and performance indices will be reduced.