NUCLEAR POWER GENERATION SYSTEM

Abstract

The present disclosure provides a lifting device for lifting a closure head assembly from a reactor vessel body in a nuclear power generation system. The lifting device comprises at least one lifting element having an engagement surface configured to engage an underside surface of the closure head assembly. The at least one lifting element is axially adjustable in height between a retracted position in which its axial height is such that the closure head assembly seals against the body of the reactor vessel and an extended position in which its axial height is such that the closure head assembly is raised above the body of the reactor vessel.

Claims

1. A lifting device for lifting a closure head assembly from a reactor vessel body in a nuclear power generation system, the lifting device comprising at least one lifting element having an engagement surface configured to engage an underside surface of the closure head assembly, the at least one lifting element being axially adjustable in height between a retracted position in which its axial height is such that the closure head assembly seals against the body of the reactor vessel and an extended position in which its axial height is such that the closure head assembly is raised above the body of the reactor vessel.

2. The lifting device according to claim 1 wherein the at least one lifting element comprises a lifting jack, a ram/piston, a rack and pinion, a telescoping linear actuator or a rigid chain actuator.

3. A-The lifting device according to claim 1 wherein the at least one lifting element is operably coupled to a control system so that movement of the lifting element(s) between the retracted and extended position may be effected remotely/automatically.

4. The lifting device according to claim 1 comprising a plurality of lifting elements and wherein the lifting device comprise one or more engagement platforms, each engagement platform consolidating and extending between at least two adjacent engagement surfaces.

5. A-The lifting device according to claim 1 further comprising a failure system comprising at least one pneumatic or hydraulic elements for engagement of the closure head assembly in case of failure of the at least one lifting element.

6. The lifting device according to claim 1 comprising a wheeled frame for guiding horizontal movement of the closure head assembly between a deployment location and the storage location, the wheeled frame comprising two parallel spaced rails mounted on frame wheels with a connecting arm extending between to form a U shaped frame.

7. A-The lifting device according to claim 6 wherein the at least one lifting element(s) is/are mounted on the wheeled frame.

8. A nuclear power generation system comprising a lifting device according to claim 1 and a reactor vessel having: a reactor vessel body defining a cavity housing a reactor core; and a closure head assembly having an underside surface for abutment with an engagement surface of the at least one lifting element.

9. A-The nuclear power generation system according to claim 8 comprising a containment structure wherein the working floor of the containment structure surrounds and is substantially vertically aligned with the opening to the reactor vessel body cavity.

10. A-The nuclear power generation system according to claim 9 comprising at least one linear pathway extending between the reactor vessel body and a storage location, the at least one pathway comprising tracks/rails, the frame wheels of the lifting device being mounted on the tracks/rails.

11. A method of exposing a reactor core in a nuclear power generation system according to claim 8 comprising adjusting the axial height of the at least one lifting element from the retracted position in which the closure head assembly is sealed against the body of the reactor vessel to the extended position in which the lower surface of the closure head assembly is raised above the body of the reactor vessel.

12. The method according to claim 11 further comprising pushing the closure head assembly vertically upwards from below the upper axial end of the closure head assembly.

13. The method according to claim 11 further comprising moving the closure head assembly horizontally from a deployment position to a storage position.

14. The method according to claim 13 comprising: moving the lifting device having the at least one lifting element mounted on the wheeled frame to the deployment position with the at least one lifting element in its retracted position; locating the engagement surface(s) vertically below the underside surface of the closure head assembly extending the at least one lifting element so that the engagement surface(s)/engagement platform(s) engage the underside surface of the closure head assembly and push upwards to vertically raise the closure head assembly from the reactor vessel body.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0074] Embodiments will now be described by way of example only with reference to the accompanying drawings in which:

[0075] FIG. 1 shows a simplified schematic of a reactor vessel and lifting elements in their retracted position;

[0076] FIG. 2 shows the reactor vessel and lifing elements in their extended position;

[0077] FIG. 3 shows a perspective bottom view of the closure head assembly; and

[0078] FIG. 4 shows an embodiment of a lifting device on a wheeled frame.

DETAILED DESCRIPTION AND FURTHER OPTIONAL FEATURES

[0079] FIGS. 1 and 2 show a pressurised reactor vessel 1 for use in a nuclear power generation system of the pressurised water reactor (PWR) type. The reactor vessel 1 has a removable closure head assembly 2 which is an integrated head package (IHP) having a closure head 3 for closing an upper opening in the reactor vessel body 4 thereby sealing the fuel assemblies/reactor core (not shown) in a cavity 5 within the reactor vessel body 4. The IHP further comprises a control rod drive mechanism 10 within a shroud 11.

[0080] As shown in FIG. 3, the closure head 3 has a sealing surface 6 at its lower axial end for sealing against the body 4. The closure head assembly has an opposing axially upper end 13 (visible in FIGS. 1 and 2). The sealing surface 6 is annular and is surrounded by an annular flange 7 having holes 14 for receiving studs for sealing the closure head 3 onto the reactor vessel body. The annular flange 7 is inscribed within a square plate 8 such that four corners 8a, 8b, 8c, 8d of the plate 8 extend laterally from proximal the lower surface 6/annular flange 7.

[0081] The lifting device comprises four lifting elements 9 (only two of which are shown in FIGS. 1 and 2) circumferentially-spaced around the reactor vessel body 4. The lifting elements 9 are spaced vertically below the closure head assembly 2 i.e. below the lower surface 6 of the closure head 3 such that each of the four corners 8a, 8b, 8c, 8d are seated upon a respective one of the lifting elements 9.

[0082] FIG. 1 shows the lifting elements 9 in their retracted position where the lower surface 6 of the closure head 3 is sealed against the body 4. When it becomes necessary to open the reactor vessel 1 (e.g. to change spent fuel rods within the fuel assemblies/reactor core), the studs are removed from the annular flange 7 and the axial height of the lifting element 9 is increased i.e. the lifting elements are moved to their extended position. The extension of the lifting elements 9 applies a force vertically upwards against the seated corners 8a, 8b, 8c, 8d of the plate 8 such that the closure head assembly 2 is vertically raised from below (rather than hoisted vertically upward from above) and the seal between the lower surface 6 of the closure head 2 and the reactor vessel body 4 is broken.

[0083] Once raised vertically by the lifting elements, the closure head assembly 2 is moved horizontally along the containment working floor 12 to a storage position. This (horizontal) movement may be effected by insertion of a wheeled frame (not shown) between the reactor vessel body 4 and the closure head assembly 2 such that the lower surface 6 of the closure head 3 rests on the load carrier. The lifting elements 9 are then disengaged from the closure head assembly 2 by retraction to reduce their axial (vertical) height. The wheeled frame can then be wheeled along tracks/rails on the working floor 12 to move the closure head assembly 2 to the storage position.

[0084] Re-sealing of the reactor core can be effected by using the wheeled frame to move the closure head assembly 2 from the storage position to a position vertically over the reactor vessel body 4 and extending the lifting elements 9 so they engage the four corners 8a, 8b, 8c, 8d of the plate 8. The lifting elements 9 are then further extended to take the weight of the closure head assembly 2 so that the wheeled frame can be removed from between the reactor vessel body 4 and the closure head assembly 2. The lifting elements 9 are then retracted to lower the closure head assembly 2 onto the reactor vessel body 4 so that the sealing surface 6 of the closure head 3 seals the cavity within the reactor vessel body 4.

[0085] An alternative lifting device 1′ is show in FIG. 4. Two rows of lifting elements 9a, 9b are mounted on a wheeled frame 15.

[0086] The wheeled frame 15 comprises two parallel spaced rails 16a, 16b with a linear, perpendicular connecting arm 17 extending therebetween such that the frame 15 forms a squared U shape. The spaced rails 16a, 16b are mounted on frame wheels 18 which extend in two rows, one row supporting each of the spaced rails 16a, 16b. The wheeled frame 15 further comprises a motor (not shown) for driving the frame wheels 18. The motor may be automatically actuable by a control system located remotely from the lifting device 1′.

[0087] The lifting device 1′ comprises two engagement platforms 19a, 19b, each engagement platform 19a, 19b consolidating and extending between the adjacent engagement surfaces of the adjacent lifting elements 9a, 9b. The two parallel engagement platforms 19a, 19b extend vertically above and parallel to the spaced rails 16a, 16b.

[0088] Using this device 1′ comprises moving the lifting device 9′ to the deployment position by driving the frame wheels 18 with the lifting elements 9 in their retracted position and positioning the engagement platforms 19a, 19b directly below the underside surface of the closure head assembly 2. The lifting elements 9 are then extended so that the engagement platforms 19a, 19b engage the underside surface of the closure head assembly 2 (e.g. by engaging the underside surfaces of four corners 8a, 8b, 8c, 8d) of a square plate 8 mounted horizontally and being vertically intersected by the shroud 11 vertically spaced between the upper axial end 13 and lower axial end of the closure head assembly 2. Extension of the lifting elements 9 pushes upwards against the underside surface to raise the closure head assembly 2 from the reactor vessel body 4 so that the closure head assembly 2 is seated on the engagement platforms 19a, 19b vertically above the reactor vessel body 4. The frame wheels 18 can then be driven to move the closure head assembly 2 horizontally away from the deployment position. In this case, the working floor may be at or beneath the height of the flange.

[0089] It will be understood that the disclosure is not limited to the embodiments above-described and various modifications and improvements can be made without departing from the concepts described herein. Except where mutually exclusive, any of the features may be employed separately or in combination with any other features and the disclosure extends to and includes all combinations and sub-combinations of one or more features described herein.