Nuclear reactor having a modular core

Claim 2

Anuclear reactor comprising a reactor pressure vessel (8), a reactor core (1)surrounded by said pressure vessel, saidpressure vessel having a plurality of fuel assemblies (19) with polygonal cross-section, a plurality of control means located under the core, each control means comprising a finger control rod (20)having a top end, a bottom end and a finger holder (44)at the bottom end, a control rod drive (14), releasable means (51,53) connecting the control rod drive to said finger holder, remote-controlled means (43,57) for releasing said connecting means and a plurality of vertical tubes (13) located under the core, the upper part of each of these tubes forming a guide tube (17) for one of said finger control rods, in which the top end of each finger control rod is shaped with at least one shoulder (82) facing at least partially downwards and arranged to provide a grip for a lifting tool, and the core is built up of a plurality of core units (18)arranged close to each other with substantially no gap laterally between them, each core unit comprising one of said fuel assemblies and one of said finger control rods, means (29,37)for transmitting lifting force from said finger holder to a corresponding fuel assembly after a releasing of said connecting means by said remote-controlled means.

Claim 3

Anuclear reactor comprising a reactor pressure vessel (8), a reactor core (1)surrounded by said pressure vessel, saidpressure vessel having a plurality of fuel assemblies (19) with polygonal cross-section, a plurality of control means located under the core, each control means comprising a finger control rod (20)having a top end, a bottom end and a finger holder (44)at the bottom end, a control rod drive (14), releasable means (51,53) connecting the control rod drive to said finger holder, remotecontrolled means (43,57) for releasing said connecting means and a plurality of vertical tubes (13) located under the core, the upper part of each of these tubes forming a guide tube (17) for one of said finger control rods, in which the top end of each finger control rod is shaped with at least one shoulder (82) facing at least partially downwards and arranged to provide a grip for a lifting tool, and the core is built up of a plurality of core units (18)arranged close to each other with substantially no gap laterally between them, each core unit comprising one of said fuel assemblies and one of said finger control rods, means (29,37)for transmitting lifting force from said finger holder to a corresponding fuel assembly after a releasing of said connecting means by said remote-controlled means.

Claim 4

Anuclear reactor comprising a reactor pressure vessel (8), a reactor core (1)surrounded by said pressure vessel, saidpressure vessel having a plurality of fuel assemblies (19) with polygonal cross-section, a plurality of control means located under the core, each control means comprising a finger control rod (20)having a top end, a bottom end and a finger holder (44)at the bottom end, a control rod drive (14), releasable means (51,53) connecting the control rod drive to said finger holder, remotecontrolled means (43,57) for releasing said connecting means and a plurality of vertical tubes (13) located under the core, the upper part of each of these tubes forming a guide tube (17) for one of said finger control rods, in which the top end of each finger control rod is shaped with at least one shoulder (82) facing at least partially downwards and arranged to provide a grip for a lifting tool, and the core is built up of a plurality of core units (18)arranged close to each other with substantially no gap laterally between them, each core unit comprising one of said fuel assemblies and one of said finger control rods, means (29,37)for transmitting lifting force from said finger holder to a corresponding fuel assembly after a releasing of said connecting means by said remote-controlled means.

Claim 5

The nuclear reactor of claim 1, in which each fuel assembly comprises a shroud having a substantially polygonal cross-section and a fuel rod bundle having a plurality of parallel fuel rods having upper and lower ends, said fuel rods being arranged in a plygonal lattice, said shroud surrounding said fuel rod bundle, said shroud having corrugated sides substantially following the contours of the fuel rods, said corrugated sides of said shroud engaging in the corrugated sides of adjacent shrouds.

Claim 6

The nuclear reactor of claim 2, in which at least amajority of said fuel assemblies each has an elongate neutron flux measuring probe in a corner position of said polygonal fuel rod lattice, all probes being identically orientated in relation to the respective fuel assembly, said probes being distributed evenly over said core and each probe being axially movable into and out of the fuel assembly.

Claim 7

Nuclear reactor according to claim 1, in which each finger control rod comprises a plurality of parallel absorber fingers of equal length, a finger holder at the lower end of the absorber fingers holding the lower ends thereof, said resiliently operated connecting means including a first coupling part carried by said finger holder and a second coupling part carried by the control rod drive, and each fuel assembly comprising a fuel rod bundle having a plurality of parallel fuel rods arranged in a polygonal lattice and guide tubes for said absorber fingers arranged at fuel rod positions in said lattice, in which one of said coupling parts has substantially radially movable coupling elements and the other coupling part has counter elements for engagement with the radially movable coupling elements and the other coupling part has counter elements for engagement with the radially movable coupling elements, and the releasing means comprises a central rd passing through the coupling part of the finger holder, said upper end of the rod, when the absorber fingers are completely inserted into the fuel assembly, projecting axially from the upper end of the fuel rod bundle and the lower end of the rod forming a locking member for said radially movable coupling elements when said elements are in an engagement position, said central rod having a lower locking position from which it is axially movable upwards to disengage said coupling.

Claim 8

Nuclear reactor according to claim 4, comprising a locking head arranged in the lower end of the central rod, a spring arranged to press the locking head down into the locking position, a stop arranged to prevent the locking head from being pressed further down than to the locking position and at least one shoulder facing at least partially downwards arranged in the upper end of the central rod to provide a grip for a lifting tool to lift the rod from the locking position.

Claim 9

The nuclear reactor of claim 4, in which said central rod runs inside said fuel rod bundle in a guide tube, said guide tube being located on a central fuel rod position in said lattice, said guide tube having an inlet throttling means giving a substantially constant flow of coolant through said guide tube irrespective of how far said central rod is withdrawn with respect to said fuel rod bundle.

Claim 10

The nuclear reactor of claim 4, in which at least some of said absorber fingers have upper end parts which, when said absorber fingers are completely inserted into said fuel assembly project axially from the upper end of thefuel rod bundle, each such upper end part carrying a shoulder facing at least partially downwards, said shoulder providing a grip for a lifting tool to lift said core unit.

Claim 11

The nuclear reactor of claim 7, in which said upper end part of each absorber fingeris in axial direction yieldingly attached to an absorbing part of said absorber finger.

Claim 12

The nuclear reactor of claim 7, in which said shoulder on said upper end part of the central rod is located at one level and said shoulders on said upper ends parts of the absorber fingers at another, higher level, the distance between said levels being greater than the distance which said central rod must be lifted to disengage said coupling, but less than the distance available for lifting said central rod between its lower locking position and an upper end position.

Claim 13

The nuclear reactor of claim 4, in which each absorber finger guide tube has an inlet throttlingmeans giving a substantially constant flow of coolant through said guide tube irrespective of how far said absorber finger is withdrawn with respect to said fuel rod bundle.

Claim 14

The nuclear reactor of claim 4, in which each absorber finger has an inner flow channel for coolant.

Claim 15

The nuclear reactor of claim 4, in which each fuel assembly further comprises a plurality of spacers arranged at different levels and firmly attached to said absorber finger guide tubes, said spacers comprising elastically yielding members resiliently abutting each of said fuel rods at at least three contact points on each spacer level, said fuel assembly further comprising a transverse support member rigidly attached to said shroud at a level immediately below said lower ends of the fuel rods and permitting the passage of coolant, said fuel rods being inserted through the sPacers to contact an upper side of said transverse support member, each fuel rod being held in an intended position solely by said spacers and said transverse support member, each fuel rod having an upper end part, each such upper end part carrying at least one shoulder facing at least partially downwards, said shoulder providing a grip for a lifting tool for extracting said fuel rod, thus enabling each individual fuel rod to be exchanged both separately and in a group.

Claim 16

The nuclear reactor of claim 12, in which said transverse support memberis a perforated plate, said absorber finger guide tubes being rigidly attached to said plate.

Claim 17

The nuclear reactor of claim 12, in which each spacer comprises a plurality of spacer elements, each spacer element surrounding one of said fuel rods, each spacer element comprising two identical dodecognal rings surrounding said fuel rod, said rings being spaced from each other and connected to each other by four elongated, strip-shaped, vertical spacer springs evenly distributed around the fuel rod, said strip-shaped springs having varying strip width and having protuberances abutting said fuel rods.

Claim 18

The nuclear reactor of claim 14, in which said fuel rods are arranged in an equilateral triangular lattice and each absorber finger guide tube supports six surrounding spacer elements at each spacer level, said spacer elements being stacked laterally, there being at each spacer level only one spacer spring on a straight line between the center of one of said fuel rod positions in the lattice and the center of an adjacent fuel rod position in said lattice, said spacer springs having parts with a certain freedom of movement along said straight line with respect to a normal position.

Claim 19

The nuclear reactor of claim 4, in which said absorber fingers of each control rod, during insertion into said fuel assembly, are supported laterally by at least one guide member, said guide member being movable in said control rod guide tube between an upper end position and a lower end position.

Claim 20

The nuclear reactor of claim 9, in which said movable guide member runs along at least three guide rods extending along theinnerwall of the control rod guide tube, each guide rod having a stop, said movable guide member in its lower end position resting against said stops.