GB2030756A - Core column articulating unit - Google Patents

Abstract

For providing between the ends of two bored blocks, stacked in a column of a nuclear reactor core, a connection which is substantially sealed while yet permitting limited articulation, a pair of tiles 16, 17 are interposed between the blocks. Each tile, apertured in register with the block bores, engages the end of one of the blocks sealingly and without relative movement, and the required articulation is provided between the tiles, whose mutually engaging faces are made slightly bowed and are shaped to accommodate a sealing ring 25 (split into quadrants) between them. Because relatively small, both tiles of a pair can be made from a single piece of (e.g. graphite) material, with the same tools at the same time; and manufacturing tolerances (and sealing imperfections) may thus be minimised. The tiles of a pair can be factory assembled and temporarily pinned together for handling as a single unit in building the core. <IMAGE>

Description

SPECIFICATION Nj clear reactors This invention relates to nuclear reactors, and in particular to nuclear reactor moderator cores comprising blocks of moderator material stacked upon one another in columns.

In such reactor cores, at least some of the columns are composed of axially bored blocks which, aligned end-to-end, form hollow columns into which are inserted nuclear fuel assemblies and through which coolant gas is blown to remove heat generated in the nuclear reactions which the fuel undergoes. It is necessary to locate relative to one another the mutually adjacent ends of adjacent bricks in a column, so as to maintain the required orientations and alignments, and to provide an effective seal, while yet allowing a limited degree of articulation to accommodate, in particular, the type of block-end distortion which is liable to be induced by irradiation of the blocks during operation of the reactor.

It is known to form the ends of moderator core blocks with co-operating recesses to accommodate sealing rings and locating keys, and with non-flat end-bearing surfaces which permit a degree of rocking of one brick upon another.

It is an object of the present invention to gain the advantages which arise from providing these features not on the two adjacent ends of two adjacent blocks but, rather, on mutually adjacent faces of a pair of tiles to be inserted between such block ends.

An embodiment of the invention is described below with reference to the accompanying drawings, in which: Figure 1 is an isometric view of the upper and of a typical reactor-core moderator block, Figure 2 is an isometric view of a pair of locating, articulating and sealing tiles to be interposed between the block and shown in Fig. 1 and the lower end of another similar block, Figure 3 is a part of a sectional view taken on a diameter of the tiles shown in Fig. 2, and Figure 4 is a section taken on the line 4-4 of Fig. 3.

The graphite moderator block 11 whose upper end is shown in Fig. 1 is of generally cylindrical shape with an axial bore 12, four keyways 1 3 to accommodate keys which also project into corresponding keyways of adjacent similar blocks to provide location of the block 11 relative thereto, and four external flats 14 formed with further keyways 1 5 for further keys to provide location relative to smaller blocks provided in the interstices between the block 11 and those similar to it.

As shown in Figs. 2, 3 and 4, a lower tile 16, of a pair of graphite tiles which also comprises an upper tile 17, is provided to fit on the upper end of the block 11. Apart from an absence of external keyways, the tiles 1 6 and 1 7 are peripherally of the same shape as the block 11, and they have bores 1 8 and 1 9 respectively corresponding to the bore 1 2 of the block. The tile 1 6 has four equally-spaced castellations 20 which, when the tile 1 6 is fitted to the block 11, enter the ends of the keyways 1 5 to locate the tile on the end of the block, of whose end face the inner annular part, surrounding the bore 12, is engaged by a flat annular face 21 of the tile 16.The tile 1 7 is similarly formed with four castellations 20 and a flat annular abutment face 21 for engagement with the lower end of another block like the block 11. Thus each tile is fitted to a respective block end; and any relative movement takes place between tile and tile rather than between block and tile.

The tiles 1 6 and 1 7 have annular faces 22 which abut one another, and both these faces are slightly bowed so that the mutual abutment occurs, nominally, along the diameter on which the section shown in Fig. 4 is taken but that there are then gaps 23 between the faces at the ends of the diameter perpendicular thereto so that some rocking of the tile 1 7 on the tile 1 6 can take place. Each of the faces 22 is formed with a respective annular groove 24, and a sealing ring is provided in four separate quadrants 25, accommodated in the grooves 24, for providing a seal between the tiles and for locating them relative to one another while permitting the above-mentioned limited rocking movement between them.To ensure correct rotational positioning of the tiles relative to another at the time when they and the blocks between which they are to be interposed are assembled together, the upper tile 1 7 is preferably formed with a bore 26 and provided with a dowel 27 which projects into a corresponding stopped bore 28 in the tile 16.

The interposition of a pair of tiles as described above between two blocks, rather than providing the required sealing, locating and articulating features directly on the ends of the blocks themselves, has several advantages.

Firstly, an axially bored block tends under irradiation to manifest differential shrinkage across its wall thickness, and that results not only in a radially-inward shrinkage of the block at its ends but also a "dishing" of the annular end face which, in turn, requires the provision of relatively large clearances between seal faces if a seal is made directly between brick and brick. The relatively thin tiles employed according to the invention do not suffer such rotational or angular displacement, and the clearances between grooves 24 and seal ring quadrants 25 can therefore be correspondingly reduced. Again, with two large components manufactured separately, there can be no guarantee that they will respond equally to equal irradiation.The relatively small tiles, by contrast, may be made in pairs from a single piece of graphite, thereby ensuring that the two tiles of a pair will behave similarly and thus permitting seal clearances to be further reduced. The seal grooves of any one pair of tiles can be cut on successive machine operations, and the grooves may thus be considered identical with no extra tolerance being required for differences between them. The splitting of the seal ring into quadrants (or into some other number of parts if desired) also permits the use of reduced clearances, since the diametral tolerance on the ring is eliminated. It also permits the use of a thicker ring cross-section (in the radial dimension) and thereby the provision of increased shear strength in the joint between tile and tile.

Previously, difficulties have sometimes been encountered in assembling large blocks together with continuous sealing rings between them. With the pairs of interposed tiles as described above, such difficulties are avoided.

Each pair of tiles, with its sealing ring quadrants, can be factory assembled and pinned with the dowel 27, and during assembly of a reactor core on site can be handled as a single unit with the orientation of the two tiles relative to one another preserved by means of the dowel. The fit of each tile to the corresponding block end is relatively uncritical, and tolerances there can be relatively loose, any slight eccentricity of the tile relative to the block being accommodated by making the tile bores 1 8 and 1 9 slightly oversize relative to the block bores 1 2.

Claims (9)

1. A core-column articulating unit for interposition between mutually adjacent upper and lower end faces of, respectively, a first core block and a second core block superposed on the first block in a nuclear-reactor core column, the articulation unit comprising a pair of tiles each having a peripheral shape generally similar to that of the said core blocks and each having an articulating face engaging that of the other and a block-engaging face for face-to-face stationary abutment with the said upper or lower end face respectively, at least one of the articulating faces of the tiles being bowed so that the tiles can rock relative to one another while each remains stationary relative to the respective block whose end face it abuts.

2. A core-column articulating unit as claimed in claim 1, wherein each of the tiles is formed with integral projecting keys for engagement in keyways of the respective core bock.

3. A core-column articulating unit as claimed in claim 1 or claim 2, wherein each of the tiles is formed with a central bore or aperture and the articulating and block-engaging faces of each tile are generally annular surfaces surrounding opposite ends of the bore.

4. A core-column articulating unit as claimed in claim 3, wherein the annular-surface articulating faces of the two tiles are each formed with an annular groove surrounding the bore and in register with the corresponding annular groove of the other tile, and there is provided a sealing ring accommodated partly in one of the grooves and partly in the other.

5. A core-column articulating unit as claimed in claim 4, wherein the sealing ring is divided into a plurality of arcuate parts.

6. A core-column articulating unit as claimed in any of claims 1 to 5 and provided with removable means temporarily holding its tiles together in their assembled relationship prior to use of the unit.

7. A core-column articulating unit substantially as described herein and as illustrated in the accompanying drawings.

8. A nuclear-reactor core comprising columns formed of core-blocks superposed upon one another, wherein articulating units as claimed in any of claims 1 to 7 are provided on upper end faces of at least some of the core blocks and provide articulation between those core blocks and core blocks superposed upon them.

9. A method of making a core-column articulating unit as claimed in any of claims 1 to 7, including machining the two tiles thereof from two closely mutually adjacent volumes of a single piece of the tile material.

1 0. A method of making a core-column articulating unit as claimed in any of claims 1 to 7, including the step of assembling together the parts, including two related tiles made by the method claimed in claim 9, and providing temporary holding means which holds the assembly together for handling as a single unit.