Patent GB-931676-A (GB)
Title: Improvements in or relating to nuclear reactor core structures
Inventor: BANKS OTHNIEL NEIL
IPC: G21C5/06
Filed: 1960-09-05
Abstract: 931,676. Nuclear reactors. UNITED KING- DOM ATOMIC ENERGY AUTHORITY. Aug. 31, 1961 [Sept. 5, 1960], No. 30515/60. Class 39 (4). A nuclear reactor core structure 1 has fuel assemblies 2 each comprising a tubular, coolantconducting container 5 housing a plurality of individually withdrawable fuel sub-assemblies 3a, first latching means for releasably retaining the sub-assemblies 3a in the containers 5 and second latching means for releasably retaining the containers 5 in the reactor core structure. A reactor cooled and moderated by a terphenylbased organic liquid, described by way of example, has the fuel elements 4 of each assembly 2 divided into four sub-assemblies 3a of twenty-five by longitudinally extending division plates 35, each sub-assembly being supported between grid supports 10 formed by intersecting webs 10a. Lifting heads 37 are attached to the central fuel element 4 of each sub-assembly. The containers 5 have upper and lower end portions 11, 12 located in apertures 13, 14 penetrating upper and lower support plates 15, 16. Coolant enters the containers 5 by way of the lower end portions 12 and, after passing over the fuel elements 4, leaves by way of the upper end portions 11. The upper end portions 11 carry lugs 38 with holes 42 for engagement by projections on a grab (not shown) to allow lifting and lowering of the containers 5. The reactor is controlled by neutron-absorbing control rods 17 of cruciform cross-section disposed between the containers 5. The first latching means referred to above comprises spindles 26 rotatable in tubular supports 27 aligned with the central axes of the fuel assemblies 2 and attached to the lower end portions 12 by webs 28. The upper ends of the spindles 26 carry locking members 33 having four radially-extending arms 34 disposed at right-angles to each other. The second latching means comprises flat strips 20 having parallel sided sections 23 for engagement with circumferential grooves 24 in the lower ends of the end portions 12 and cut-away portions 25 which remain clear of the grooves 24. The spindles 26 which are supported by webs 43 welded to the support plate 16 carry cranks 29 pivotally connected to the strips 20 by links 30 and pivot pins 31, 32. Rack-andpinion type actuators 88 disposed externally of the reactor pressure vessel 52 operate the latching means, and sub-assemblies 3a being removable when the spindles 26 are in such a position that the arms 34 of the locking members 33 can pass between the grid supports 10 at the base of each group (Fig. 2) and the containers 5 being removable when the cutaway portions 25 of the strips 20 are opposite the end portions 12 (Fig. 1). In a modification, the cranks 29 are connected to the links 30 with " lost motion " by providing enlarged holes 87 in the links 30 so that the sections 23 of the strips 20 engage with the grooves 24 before rotation of the spindles 26 is effected. The reactor core can be refuelled en bloc by removal of a dome 72 from the upper end of the pressure vessel 52, after cutting away a weld joint 73, whilst selective refuelling is provided by refuelling apparatus insertable into an aperture 74 in the dome 72 which is normally sealed by a cover 75. Coolant inlets 67 and outlets 68 in the pressure vessel 52 are divided from each other by a mild steel skirt 55 and its support ring 56, the skirt 55 acting as a thermal shield along with tubular mild steel structures 61 and 63. The core structure 1 is supported by the skirt 55. Coolant pumped through the inlets 67 passes downwardly between the structure 63 and skirt 55 and then in counterflow up through the core structure 1 and over the upper end of skirt 55 to leave the pressure vessel 52 by way of the outlets 68.