INTEGRATED HEAD PACKAGE

Abstract

The present disclosure provides an integrated head package for a nuclear power generation system, the integrated head package comprising a closure head, and a control rod drive mechanism housed within a shroud. The control rod drive mechanism comprises at least one drive rod extending through the closure head and having a coupling element for releasably coupling to a control rod assembly within a reactor core. The at least one drive rod is movable to a maintenance/refuelling position in which the at least one drive rod is uncoupled from the control rod assembly and at least partially retracted into the integrated head package. The integrated head package further comprises at least one engagement feature for securing the at least one drive rod in the maintenance/refuelling position.

Claims

1. An integrated head package for a nuclear power generation system, the integrated head package comprising a closure head, and a control rod drive mechanism housed within a shroud, the control rod drive mechanism comprising at least one drive rod extendable through the closure head and having a coupling element for releasably coupling to a control rod assembly within a reactor core, the at least one drive rod being movable to a maintenance/refuelling position in which the at least one drive rod is uncoupled from the control rod assembly and at least partially retracted into the shroud, the integrated head package further comprising at least one engagement features for securing the at least one drive rod in the maintenance/refuelling position.

2. The integrated head package according to claim 1 wherein the at least one drive rod is fully retracted within the shroud in the maintenance/refuelling position.

3. The integrated head package according to claim 1 wherein the coupling element is configured to have a radially expanded rest configuration and is moveable by an actuator to a radially contracted configuration for retraction into the shroud.

4. The integrated head package according to claim 1 wherein the coupling element is actuable by a pneumatic, hydraulic, electro-mechanical or mechanical actuator.

5. The integrated head package according to claim 1 comprising one or more sensors for confirming decoupling of the at least one drive rod.

6. The integrated head package according to claim 5 wherein the one or more sensors comprises a load sensor and/or a velocity sensor.

7. The integrated head package according to claim 1 wherein the engagement feature comprises a recess for engaging the coupling element within the integrated head package to secure the at least one drive rod in its retracted maintenance/refuelling position.

8. A nuclear power generation system comprising a reactor vessel having a reactor vessel body defining a cavity housing a reactor core containing a control rod assembly and an integrated head package according to claim 1, wherein the closure head is configured to seal against the reactor vessel body.

9. The nuclear power generation system according to claim 8 further comprising at least one neutronic sensor to monitor the level of neutron radiation within the reactor core.

10. The nuclear power generation system according to claim 8 further comprising one or both of an optical position sensor and/or an electrical position sensor to monitor control rod assembly position.

11. The nuclear power generation system according to claim 8 comprising a control system for sending control signals and receiving sensor output signals, the control system being remote from the reactor vessel.

12. The nuclear power generation system according to claim 8 comprising a cable manifold with one or more cables extending from the cable manifold to a connection terminal on the IHP, the one or more cables being movable between an elongated configuration when the closure head of the integrated head package is sealed against the reactor vessel body to a retracted configuration when the integrated head package is moved out of vertical alignment with the reactor vessel body.

13. A method of exposing a reactor core within a nuclear power generation system according to claim 8 by decoupling the at least one drive rod from the control rod assembly, at least partly retracting the at least one drive rod into the integrated head package, securing the at least one drive rod in the retracted maintenance/refuelling position and removing the integrated head package from the reactor vessel body.

14. The method according to claim 13 comprising remotely decoupling the or each drive rod from the control rod assembly.

15. The method according to claim 13 comprising fully retracting the or each drive rod within the integrated head package.

16. The method according to claim 13 wherein the control rod drive mechanism comprises a plurality of drive rods, the method comprising non-simultaneous decoupling and retracting of the plurality of drive rods.

17. The method according to claim 16 comprising decoupling and retracting a first batch of non-adjacent drive rods followed by decoupling and retracting a second batch of non-adjacent drive rods.

18. The method according to claim 13 comprising confirming decoupling of the or each drive rod from the associated control rod assembly using one or more of a load sensor, a velocity sensor, a neutronic sensor and/or a position sensor.

19. The method according to claim 13 comprising lifting the integrated head package from below a lifting structure mounted proximal the closure head.

20. The method according to claim 13 comprising lifting the IHP by less than 10 cm and then moving it horizontally out of alignment with the reactor vessel body.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0068] Embodiments will now be described by way of example only with reference to the accompanying drawings in which:

[0069] FIG. 1 shows a schematic cross section through an integrated head package; and

[0070] FIGS. 2a and 2b show an integrated head package with cables.

DETAILED DESCRIPTION AND FURTHER OPTIONAL FEATURES

[0071] FIG. 1 shows a schematic cross section through an integrated head package (IHP) 1 for a nuclear power generation system. The IHP 1 comprises a closure head 2, and a control rod drive mechanism 3 housed within a shroud 4. The shroud 4 is a radiation shielding shroud and comprises at least one access hatch 5 for access to the control rod drive mechanism 3.

[0072] The control rod drive mechanism 3 includes a drive rod 6 which can extend and retract through the closure head 2. For simplicity, only a single drive rod 6 is shown (and displayed larger than to scale) but the control drive mechanism will comprise a plurality of drive rods 6.

[0073] At the axially lower end of the drive rod 6, there is a coupling element 7 for releasably coupling to a control rod assembly within a reactor core (not shown). The coupling element 7 comprises two semi-circular sector plates which are spaced from one another in a radially expanded rest configuration. The radially expanded coupling element 7 is engaged within an annular engagement recess 9 to maintain the drive rod 6 within the IHP.

[0074] The reactor core is contained within a cavity defined by a reactor vessel body. The reactor vessel body has an upper end that is sealed by the closure head 2 of the IHP 1.

[0075] The closure head 2 and the upper end of the reactor vessel body both have complementary fixing flanges (not shown) having aligned though-holes housing tensioned studs that seal the IHP to the reactor vessel body.

[0076] When the IHP 1 is sealed to the reactor vessel body, the radially expanded coupling element 7 is housed within a recess in the control rod drive assembly within the reactor core so that as the drive rod 6 is translated, the extent of the control rod assembly within the reactor core is vertically adjusted so as to adjust the amount of neutron radiation absorption thus controlling the nuclear reactions within the reactor core.

[0077] The IHP 1 further comprises a seismic support 13 to dampen any horizontal movement of the control rod drive mechanism 3/drive rods 6 and a cooling circuit comprising a cooling air duct 14 and a fan 15 for cooling the interior of the IHP 1/shroud 4.

[0078] When it becomes necessary to expose the reactor core (e.g. for maintenance or refuelling), it is first necessary to de-tension the studs in the fixing flanges. This is effected by mounting a stud tensioner device on a monorail 8 which circumscribes the shroud 4. The stud tensioner device is lowered to engage, de-tension and remove the studs.

[0079] Next the drive rod 6 is disengaged from the control rod assembly by applying pneumatic pressure using a pneumatic actuator (not shown) at the coupling element 7 to force the sector plates towards each other so as to move the coupling element 7 to a radially contracted configuration so that it disengages from the recess on the control rod assembly. This decoupling can be effected remotely at a user interface of a remote control system thus eliminating the need for any manual intervention.

[0080] The drive rod 6 is then retracted into a maintenance/refuelling position where it is fully enclosed within the shroud 4 as shown in FIG. 1. The IHP comprises an engagement recess 9 which engages with the radially expanded coupling element 7 once the pneumatic pressure is removed and secures the drive rod 6 in its retracted position.

[0081] The IHP 1 further comprises a load sensor 10 to detect the load on the control rod drive mechanism as the drive rod 6 is moved to its retracted maintenance/refuelling position within the IHP shroud 4. If the load exceeds the expected load (i.e. exceeds the weight of the drive rod 6), this indicates that the decoupling has failed and a signal can be sent from the load sensor 10 to the remote control system to prevent any lifting of the IHP 1. If the load is as expected, the load sensor 10 can provide a signal to indicate that decoupling has occurred successfully and lifting can proceed.

[0082] The IHP 1 further comprises a velocity sensor 11 to measure velocity of the drive rod 6. If velocity is reduced below an expected velocity (for the applied power) as the drive rod 6 is moved to its retracted maintenance/refuelling position within the IHP shroud 4 (because the movement is impeded by a connection to the control rod assembly), the velocity sensor 11 can provide a signal (to the control system) to indicate that decoupling has failed and lifting of the IHP 1 cannot proceed. If the velocity is as expected, the velocity sensor 11 can provide a signal to indicate that decoupling has occurred successfully.

[0083] In addition to the load sensor 10 and the velocity sensor 11, the reactor core may also comprise a neutronic sensor and a control rod position sensor (not shown) to also detect any failure in decoupling.

[0084] The decoupling of the drive rods 6 occurs in batches with a first batch of non-adjacent drive rods being decoupled and retracted prior to a second batch of non-adjacent drive rods 6.

[0085] Once all drive rods 6 are decoupled and retracted into the IHP 1, the IHP 1 can be lifted so that the closure head 2 no longer seals the reactor core.

[0086] The IHP further comprises a lifting structure 12 which, in this embodiment can be attached to a hoist of an overhead crane (not shown) to raise the IHP 1 vertically or from a lifting device positioned below the lifting structure. Because the drive rods 6 are entirely enclosed within the IHP 1 and thus there is no need for a refuelling cavity, the IHP need only be lifted vertically between 100 and 300 mm before being moved horizontally and lowered to the storage stand.

[0087] The IHP further comprises a connection terminal 16 for the connection of cables 17 extending to a cable manifold 18 in connection with the power supply and/or to the control system. The cables 17 are unreleasably connected to the connection terminal. The cables 17 may be movable between an elongated configuration (shown in FIG. 2a) when the closure head 2 of the IHP 1 is sealed against the reactor vessel body to a retracted e.g. a concertinaed configuration (shown in FIG. 2b) when the IHP 1 is moved out of vertical alignment with the reactor vessel body.

[0088] 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.