US3837694A

US3837694A - Hydraulic head closure mechanism

Info

Publication number: US3837694A
Authority: US
Inventors: H Andrews; E Frisch; D Frisch
Original assignee: Westinghouse Electric Corp
Current assignee: CBS Corp
Priority date: 1970-07-08
Filing date: 1970-07-08
Publication date: 1974-09-24
Anticipated expiration: 1991-09-24
Also published as: NL7109382A; FR2100337A5; CH543693A; BE769665A; CA949467A; JPS52160096U; AT315972B; DE2130590A1; GB1299567A; SE361077B; JPS5315916Y2

Abstract

In order to reduce the time required for removal and replacement of a reactor vessel closure head, previously used studs for securing the closure head are replaced with a reduced member of larger diameter bolts located in radial slots in vessel and head flanges. All bolts are provided with individual hydraulic tensioning and tilting devices mounted on the head flange. The devices are operated simultaneously to preload the bolts and to actuate the bolts and the devices to an inclined position to permit the head to be removed when the tension load on the bolts is released.

Description

United States Patent 1 Frisch, deceased et al.

[ Sept. 24, 1974 1 HYDRAULIC HEAD CLOSURE MECHANISM [73] Assignee: Westinghouse Electric Corporation,

Pittsburgh, Pa.

22 Filed: July 8, 1970 21 Appl. No.: 53,198

[52] US. Cl. 292/256.75, 85/1 T, 176/87,

220/55 D [51] Int. Cl Bd 45/30 [58] Field of Search 292/256.75, 256.73, 256,

292/2565; 176/87; 220/55 D, 55 E, 55 F, 3; 52/223; 85/1 T, 32 T, 58 T; /175 [56] References Cited UNITED STATES PATENTS 2,734,824 2/1956 De Luca 220/55 E 2,844,021 7/1958 Bryant 70/175 3,027,993 4/1962 Sommer 292/256.75 X 3,130,628 4/1964 Blinn /1 T 3,154,006 10/1964 Novak 52/223 R X 3,270,906 9/1966 Christensen 220/3 FOREIGN PATENTS OR APPLICATIONS 135,079 3/1960 U.S.S.R. 220/55 E Primary Examiner-Robert L. Wolfe Attorney, Agent, or Firm-J. R. Campbell [57] ABSTRACT In order to reduce the time required for removal and replacement of a reactor vessel closure head, previously used studs for securing the closure head are replaced with a reduced member of larger diameter bolts located in radial slots in vessel and head flanges. All bolts are provided with individual hydraulic tensioning and tilting devices mounted on the head flange. The devices are operated simultaneously to preload the bolts and to actuate the bolts and the devices to an inclined position to permit the head to be removed when the tension load on the bolts is released.

15 Claims, 5 Drawing Figures PAINTED-89241974 3.831; 694

sow ans 5 1 HYDRAULIC HEAD CLOSURE MECHANISM CROSS REFERENCE TO RELATED APPLICATIONS This application relates to the following applications concurrently filed herewith:

Ser. No. 53,207 entitled Means for Rapidly Exposing the Core of A Nuclear Reactor For Refueling by Erling Frisch and Harry N. Andrews.

Ser. No. 53,203 entitled Cable Support Structure For Enabling A Nuclear Reactor To Be Refueled Rapidly By Erling Frisch and Harry N. Andrews.

Ser. No. 53,201 entitled Rapidly Refuelable Nuclear Reactor by Erling Frisch and Harry N. Andrews.

Ser. No. 53,200 entitled Combination of Nuclear Reactor and Missile Shield by Erling Frisch and Harry N. Andrews.

Ser. No. 53,199 entitled Means for Retaining and Handling Reactor O-Ring Seals by Erling Frisch.

Ser. No. 53,202 entitled Rapidly Refuelable Nuclear Reactor by Harry N. Andrews and Richard S. Orr.

BACKGROUND OF THE INVENTION This invention relates generally, to pressure vessels and, more particularly, to mechanism for securing and releasing the closure heads for nuclear reactor vessels.

Heretofore, the closure heads of large pressurized power reactors have been secured to the pressure vessel by a large number of studs which are threaded into the vessel flange and extend through holes in the head flange. The necessary loading on this flange is obtained by nuts on the upper threaded portion of the studs which are tightened .by hand while the studs are preloaded by hydraulic tensioning devices. Three tensioners are usually provided for each plant. They are applied to the studs in a certain prearranged rotation until all studs carry approximately the same load. To achieve this, each stud must be tensioned at least twice.

To remove the closure head, the studs must be tensioned until the nuts become unloaded and can be backed off. Following this, all nuts and studs must be removed and stored before the closure head can be lifted off and refueling can commence.

In view of the large number of studs, for example 56, utilized in a large reactor vessel, it is easily realized that considerable time, for example 72 hours, is required for removing the closure head after shutdown and replacing it after refueling if there are no complications. Also, the use of threaded studs, which must be completely removed for each refueling, is considered unsatisfactory since galling of the threads, which is a distinct possibility and actually has occurred on several occasions, will seriously affect the refueling schedule. Since the cost of shutdown of a large plant is approximately 55 l00,000 per day, there is a need for reducing the time requirement for refueling and also for avoiding the use of studs.

SUMMARY OF THE INVENTION In accordance with the present invention, the large number of holding studs for securing a closure head on a reactor vessel is replaced with a smaller number of larger diameter bolts, located in radial slots in the flanges of the vessel and the closure head, and all bolts are provided with individual hydraulic tensioning devices which are permanently located on the head flange. The heads of the bolts engage the bottom surface of the vessel flange and each bolt extends continuously through its tensioning device. To permit the bolt heads to clear the vessel flange while lifting the enclosure head, a tilting device is provided for each bolt which actuates the bolt and its tensioning device to an inclined position during this operation. By energizing all tensioning devices simultaneously and all tilting devices simultaneously, the time required for head removal and replacement during re-fueling can be reduced to a few hours.

BRIEF DESCRIPTION OF THE DRAWINGS For a better understanding of the nature of the invention, reference may be had to the following detailed description, taken in conjunction with the accompanying drawings, in which:

FIGS. 1A and 1B, when joined end-to-end, constitute a sectional view through a portion of a reactor vessel and closure head and one of the holding bolts and its tensioning and tilting devices;

FIG. 2 is a view, in section, taken along the line IIII of FIG. 18;

FIG. 3 is a view, in plan, of the tensioning and the tilting devices; and

FIG. 4 is an enlarged detail view of a coupling utilized in the hydraulic system for the devices.

DESCRIPTION OF THE PREFERRED EMBODIMENT Referring to the drawings, particularly to FIGS. 1A and 1B, the structure shown therein comprises a portion of a generally cylindrical reactor vessel 10 having an integral outwardly extending flange 11, and ,agenerally hemispherical closure head 12 having an integral outwardly extending flange 13 which mates with the flange 11 on the vessel 10. The vessel 10 may be of a type, well known in the art, suitable for use .in a nuclear power system.

As shown more clearly in FIG. 2, a plurality of vertically aligned radial slots 15 is provided in the peripheries of the flanges l1 and 13. In order to retain the closure head 12 on the vessel 10, holding bolts 16 are disposed in the radial slots 15. Each bolt 16 has a head 17 engaging the bottom surface 18 of the vessel flange 11.

As shown more clearly in FIG. IA, each bolt 16 extends continuously upwardly through a hydraulic pressure tensioning device 21 which surrounds the upper portion of the bolt 16 and is mounted on the upper or top surface 22 of the closure head flange 13. Each bolt 16 has a threaded portion 23 at its upper end which extends above the top of the tensioning device 21. Each tensioning device 21 is positioned on the flange 13 by means of one or more positioning pins 24 with tapered upper ends which enter holes 25 in a base plate 26 of the device 21, and by an inclined front surface of a bracket 27 which supports a tilting device 28. The bracket 27 may be attached to the top surface of the flange 13 by means of bolts 29.

In order to obtain space for the individual tensioning devices 21, the number of holding bolts 16 has been reduced to 28 which is one-half the number of bolts previously utilized with a reactor vessel of the same size. The diameter of the present bolts is 10 inches, whereas the diameter of the prior bolts is 7 inches. Each bolt 16 is approximately 140 inches long and the preloading will be approximately 2,500,000 lbs. per bolt for a pressure vessel having an inside diameter of 173 inches.

In order to obtain the required bolt loading without exceeding a hydraulic fluid pressure of 10,000 psi, the tensioning device 21 is provided with two

pistons

31 and 32 in tandem. The

pistons

31 and 32 are reciprocably disposed inside cylinders 33 and 34, respectively, supported between the base plate 26 and a top plate 36 of a generally rectangular shape (see FIG. 3) whice are held together by four tie rods 37. The lower cylinder 34 has a base portion 38 which rests on the base plate 26, and the upper cylinder 33 has a base portion 39 which rests on the top of the cylinder 34. A collar 41 is disposed between the top of the upper cylinder 33 and the top plate 36.

The hydraulic fluid is introduced under the piston 31 through relatively small diameter tubing 42 which enters the wall of the cylinder 33 through a bolted flanged coupling 43 having a metal O-ring seal 44 as shown in detail in FIG. 4. The hydraulic flows from the cylinder 33 into the cylinder 34 through a metal tube 45 and couplings 43. Similar couplings 43 are also provided in the hydraulic lines near the top of the tensioning devices to permit ease of disassembly when it becomes necessary to remove the device for inspection or repair. The lines from these couplings to hydraulic manifolds 46, which conveniently may be mounted on an existing structure (not shown) above the tensioning devices, must be flexible to permit tilting of the tensioning devices and the holding bolts, as will be described more fully hereinafter. The flexibility may be achieved by forming this part of the tubing into a loose helical spring 47.

Hydraulic pressure may also be applied above the upper piston 31 to drive both pistons downwardly against any residual pressure under the pistons resulting from a possible stand pipe effect of the pressurizing equipment. In this manner the bolt 16 is permitted to drop downwardly by gravity under certain conditions described hereinafter.

As shown, the tilting device 28 is of the fluid pressure actuated type. It comprises a reciprocating piston 51 disposed inside a cylinder 52 held between a base plate 53 and a top plate 54 by tie rods 55. Hydraulic or other pressure fluid is introduced above the piston 51 through a passageway 56 in the top plate 54 and a coupling 43 of the type previously described. The piston 51 is connected to a bifurcated member 57 by means of a connecting rod 58 which is threaded into the piston 51 and the member 57. The member 57 has arms 59 which straddle a lever 61 secured to or formed integrally with the top plate 36 of the tensioning device 21. A cross pin 62 in the arms 59 engages the lever 61 when the piston 51 is moved downwardly.

In the drawing, the pistons in the tensioning device 21 are shown in a position where hydraulic pressure is being applied under the pistons for tensioning the bolt 16. The developed upward thrust is transmitted through a set of spherical washers 63 to thrust means 64 fixed on the bolt 16. The thrust means 64 may be a nut threaded on the bolt 16 and fixed in positions by means of a screw 65. Other suitable thrust transmitting means affixed to the bolt 16 may be utilized if desired.

When the desired tension is reached, adjustable means, preferably a nut 66 which is free to turn on the threads 23 on the bolt 16 above the tensioning device 21, is lowered by means of handwheel 67 until the nut 66 is in firm contact with the top support plate 36 through another set of spherical washers 68. The handwheel 67 may be attached to the adjustable nut 66 by means of bolts 69.

When the hydraulic pressure is subsequently removed from the tensioning device 21, the bolt tension load will be transferred from the thrust means 64 to the adjustable nut 66, and the tension load is transmitted through the cylinders and other stationary parts of the tensioning device, which are under compression, to the closure head flange 13. In this manner the tension load is transferred from the fixed nut 64, which is inside the tensioning device and not readily accessible, to the adjustable nut 66 which is outside the tensioning device and readily accessible for manual operation.

The actual value of the bolt loading can be estimated by a micrometer 70 on top of the bolt 16 which indirectly measures the elongation or strain of the stressed bolt by comparing its length with that of an unstressed rod 71 of the same material, located in a hole through the center of the bolt and attached to the bolt head 17.

In preparation for removing the closure head 12 for refueling, hydraulic pressure is again applied under the pistons in the tensioning device 21 until the load is completely transferred to the fixed nut 64. This frees the adjustable nut 66 which is subsequently backed off by hand until it reaches its top position as determined by a fixed stop nut 72 on the threaded portion 23 of the bolt 16. The nut 72 may be fixed on the bolt 16 by means of a screw 74.

The pressure under the

pistons

31 and 32 is then removed and pressure is applied above the piston 31 through a passageway 73 in the collar 41 and a coupling 43 attached to the collar. This causes unloading and lowering of the bolt 16 until it assumes its lowest position as indicated by the dot-dash lines of the bolt head 17. With all bolts in this position, pressure is applied above the piston 51 of the tilting device 28. This causes a downward pressure to be applied to the outer end of the lever 61 on each of the tensioning devices, thereby actuating the tensioning device and the bolts 16 from their vertical position to an inclined position as indicated by the dot-dash lines in FIGS. 1A and 1B. The downward force on the lever 61 causes the device 21 to pivot about a pivot line 75 located at the inner corner of the base plate 26 where it abuts the bracket 27 which supports the tilting device 28. The tapered end of the pin 24 and the inclined surface of the bracket 27 permit the tensioning device 21 to tilt about the pivot line 75.

An extension on the bottom of the tilting device piston 51 stops piston movement downwardly when the desired tilting position has been reached. Rotation of the bifurcated member 57 is prevented by an upwardly extending projection 76 on the top plate 54 of the tilting device 28.

With all holding bolts 16 tilted or inclined, the closure head 12 may be lifted vertically without interference of the bolts with the pressure vessel flange 11. Any time after the bolt heads clear the flange, pressure on the tilting devices may be removed causing the bolts to return to the vertical position. A heavy spring 77 in the cylinder 52 of the tilting device returns the piston 51 to its original position after the pressure is removed.

In order that the tilting device 28 can follow the tilting movement of the tensioning device 21, the base plate 53 of the tilting device is mounted on a swivel pin 78 supported on a lower support base 79 attached to the bracket 27 by bolts 81. A spring 82 is provided between the lower support base 79 and the actuator base plate 53 to return the tilting device 28 to the vertical position when the pressure is removed from the piston 51, thereby deenergizing the tilting device.

Each tensioning device 21 may be removed individually for inspection or repair by first disconnecting the hydraulic supply lines and then forcing the tilting device 28 out of the way. The tensioning device 21 may be lifted vertically until clearing the positioning pins 25 and then radially until the bolt heads clear the vessel flange.

From the foregoing description, it is apparent that the invention provides a head closure mechanism which enables the time required for head removal and replacement during refueling of a nuclear reactor to be greatly reduced. The tensioning devices and the tilting devices of the mechanism may be readily mounted on the top flange of the closure head of the reactor vessel. During normal operation of a reactor, the bolt tension load is transmitted to the closure head flange through members of the tensioning devices which are under compression. This increases the effective length of the holding bolts, thereby preventing any appreciable change in bolt loading resulting from differential thermal expansion.

What we claim is:

1. A head closure mechanism for a nuclear reactor comprising: a generally cylindrical reactor vessel and a closure head each having an outwardly extending flange with a plurality of vertically aligned radial slots in the periphery of the flanges, bolts disposed in said slots to retain the closure head on the vessel, each bolt having a head engaging the bottom surface of the vessel flange, a hydraulic pressure bolt tensioning device surrounding each bolt and mounted on the top surface of the closure head flange, said bolt extending continuously through the device with a threaded portion at its upper end, thrust means fixed on the bolt axially outward from the tensioning device, said tensioning device being located between the thrust means and the head flange, said tensioning device applying force in one axial direction against the head flange and in the other axial direction against the thrust means on the bolt for elongating the bolt between the bottom of the vessel flange and said thrust means on the bolt, and adjustable means threaded on the threaded portion axially outward from the tensioning device and the thrust means for maintaining the bolt under tension when the hydraulic pressure is removed from the tensioning device.

2. The mechanism defined in claim 1, wherein the adjustable means is movable into contact with the tensioning device when the bolt is elongated to transfer the tension load on the bolt from the fixed thrust means to the adjustable means when the hydraulic pressure is removed.

3. The mechanism defined in claim 1, wherein the tensioning device includes at least one cylinder containing a reciprocable piston for applying a tension load on the bolt through said fixed thrust means, and the adjustable means is operable movable to a position in which the tension load on the bolt is transmitted to the closure head flange through the adjustable means and the cylinder when the hydraulic pressure is removed from the piston.

4. The mechanism defined in claim 1, wherein the tensioning device includes a base plate mounted on the top surface of the closure head flange, a top plate spaced from the base plate, at least one cylinder disposed between the plates, a reciprocable piston within the cylinder for applying a tension load on the bolt through said thrust means when hydraulic pressure is applied to the piston, and said adjustable means being operable to a position with respect to the top plate to transfer the tension load on the bolt from the thrust means to the adjustable means and transmit the bolt tension load through the top plate and the cylinder and the base plate to the closure head flange when the hydraulic pressure is removed from the piston.

5. The mechanism defined in claim 1, wherein the thrust means includes a nut affixed on the bolt substantially at the top of the tensioning device, and the adjustable means includes a nut having a handwheel attached thereto for manually rotating the nut.

6. The mechanism defined in claim 1, wherein the tensioning device is operable to permit disengagement of the bolt head from the vessel flange, and including a tilting device mounted on the closure head flange for actuating the bolt and its tensioning device to an inclined position to permit the closure head to be lifted vertically without the bolt interferring with the vessel flange.

7. The mechanism defined in claim 6 wherein the tensioning device and the bolt are actuated about a pivot line on the top surface of the closure head flange.

8. The mechanism defined in claim 7, including a lever on the tensioning device engaged by the tilting device to actuate the tensioning device and the bolt about the pivot line.

9. The mechanism defined in claim 8, including a swivel support for the tilting device permitting it to move to an inclined position when the tensioning device and the bolt are actuated to the inclined position.

10. The mechanism defined in claim 9, including spring means for returning the tilting device to a vertical position when the tilting device is deenergized.

11. The mechanism defined in claim 8, wherein the tilting device comprises a fluid pressure actuated piston, a bifurcated member having arms straddling said lever, and a cross pin in the arms engaging the lever when the piston is actuated downwardly.

12. The mechanism defined in claim 11, including a spring for returning the piston to its original position when fluid pressure is released from the piston.

13. A head closure mechanism for a vessel member and a closure head member each having an outwardly extending flange with a plurality of vertically aligned openings therein, comprising bolts disposed in said openings to retain the closure head member on the vessel member, a hydraulic pressure tensioning device surrounding each bolt and mounted on a surface of the flange on one of said members, said bolt extending continuously through the device with a threaded portion at one end, thrust means fixed on the bolt, said tensioning device applying force between the thrust means and tension load on the bolt from the fixed thrust means to the adjustable means when the hydraulic pressure is removed.

15. The mechanism defined in claim 14, wherein the tension load on the bolt is transmitted to the flange on one of said members through the adjustable means and the tensioning device when the hydraulic pressure is re-

Claims

13. A head closure mechanism for a vessel member and a closure head member each having an outwardly extending flange with a plurality of vertically aligned openings therein, comprising bolts disposed in said openings to retain the closure head member on the vessel member, a hydraulic pressure tensioning device surrounding each bolt and mounted on a surface of the flange on one of said members, said bolt extending continuously through the device with a threaded portion at one end, thrust means fixed on the bolt, said tensioning device applying force between the thrust means and said flange for tensioning the bolt, and adjustable means threaded on said threaded portion axially outward of the tensioning device for maintaining the bolt under tension when the hydraulic pressure is removed from the tensioning device.

14. The mechanism defined in claim 13, wherein the thrust means is mounted on the bolt internally of the tensioning device, and the adjustable means is movable into contact with the tensioning device to transfer the tension load on the bolt from the fixed thrust means to the adjustable means when the hydraulic pressure is removed.

15. The mechanism defined in claim 14, wherein the tension load on the bolt is transmitted to the flange on one of said members through the adjustable means and the tensioning device when the hydraulic pressure is removed.