JPS5847676B2 - Genshiroyounenriyoyouso - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a fuel element assembly for a nuclear reactor in which light water or heavy water is used as a coolant.

In a common configuration of fuel element assemblies, nuclear fuel rods are supported in clusters and spaced apart by transverse grids, so that the spaces between the fuel rods form secondary flow passages and carry the reactor's main coolant. passes through this secondary channel in a direction parallel to the longitudinal axis of the fuel rod.

It has previously been proposed to place auxiliary cooling conduits within clusters of fuel rods for auxiliary cooling.

These conduits are sparge tubes, having perforated side walls and one plugged end, so that in connection with the coolant source,
A spray of auxiliary coolant is injected into the cluster of fuel rods perpendicular to the flow direction of the main coolant.

In accordance with the present invention, a fuel element assembly for a nuclear reactor has a cluster of fuel rods supported in an annular array at a number of symmetrical grid positions about a longitudinal axis and having open ends. The fuel rods have a peripheral wall coaxial with the longitudinal axis, and the spacing between the fuel rods is such that secondary channels are created between the fuel rods that act as flow paths for the main coolant.

The sub-channels interconnect to form a number of annular passages between the annular rows of fuel rods and a number of radial passages intersecting the annular passages.

A nuclear reactor fuel assembly has a number of sparge tubes for injecting auxiliary coolant into the cluster, one of the sparge tubes being one of the sparge tubes.
One of the sparge tubes coincides with the longitudinal axis (this sparger tube will be referred to as the central sparger tube), and the remaining sparger tubes are arranged at peripheral positions on a common annular passage for effective auxiliary cooling. (This porous dispersion tube will be referred to as the peripheral dispersion tube).

At least some of the remaining annular passages have auxiliary coolant orifices oriented to direct coolant toward the surrounding wall, thereby effectively cooling the surrounding wall.

The auxiliary coolant orifices of the peripheral distribution tubes are spaced at a number of axial positions common to all distribution tubes, with the holes of adjacent distribution tubes at any level alternating toward the peripheral wall. It is also oriented obliquely to the radial direction through the distribution tube, thereby ensuring uniform jetting of the auxiliary coolant.

The surrounding wall may be in the form of a metal tube acting as a heat sink, which tube is cooled by coolant jetted towards it from several surrounding distribution tubes.

As is well known, it is common practice to position clusters of nuclear fuel rods using a grid having a number of cells through which they pass.

In the present invention, it is advantageous to determine the axial spacing of the holes in the dispersion tube with respect to the spacing of the grid, positioning the orifices adjacent to the grid, thereby reducing the possibility of hard-to-cool hot spots on the fuel rods. let

The open-ended tubular wall may be circular or polygonal in cross-section perpendicular to its longitudinal axis and has an annular array of nuclear fuel rods, a central distribution tube for auxiliary coolant and a number of Surround the cluster containing the peripheral dispersion tube.

The peripheral distribution tube is installed in an annular passage between the two annular rows of fuel rods closest to the tubular wall.

The orifices of these dispersion tubes are alternately oriented outwardly away from the longitudinal axis passing through the center of the cluster and inwardly oriented toward the axis.

The centrally located dispersion tube has three orifices equidistantly spaced around the dispersion tube, the relative positions of which are offset by 60° from one position to the next.

The orifices of both the central distribution tube and the peripheral distribution tube for the auxiliary coolant are preferably located at a number of common axial locations or levels.

For a more complete understanding of embodiments of the invention, the invention will now be described with reference to the accompanying drawings.

Referring first to FIGS. 1 and 2, a nuclear fuel element assembly includes a cluster 1 of nuclear fuel rods 2 supported in spaced apart parallel configurations at a first set of grid positions by a transverse grid.
Consisting of

The top grid is marked 3 and the bottom grid is marked 4.

Between grids 3 and 4 there are a number of intermediate grids,
One of them is marked 5.

All these grids have a first grid occupied by fuel rods 2.
There are a set of 60 grid positions and the mutual spaces between the fuel rods define sub-channels 6 (FIG. 2) in the form of concentric annular passages and radial passages with respect to the axis of the cluster.

A second set of grid positions (seven in this example) coincides with some of the secondary channels where the radial passages intersect with the annular passages, with peripheral distribution conduits (conduits) 7 and central distribution for the auxiliary coolant. occupied by tube 8.

The distribution tubes 7, 8 are closed at their lower ends and communicate at their upper ends with a coolant manifold 9 which is connected to an auxiliary coolant source S during operation.

The distribution tubes 7, 8 have a series of holes 7a, 8a in their side walls so that the supplied coolant is ejected laterally.

The extension of the closed end of the dispersion tube 8 carries a spider 10 to which the lower end fitting 11 of the clasp is attached.

The cluster is suspended in pressure tube 14.

This pressure tube is one of many that run through a bulk moderator (eg graphite or heavy water) in a pressure tube reactor.

As will be appreciated, the primary coolant for the fuel rods passes axially through the cluster from one end of the pressure tube 14 to the other.

In this example, the pressure tubes are vertical and the main coolant flow direction is upward in the direction of arrow A.

To replenish this main coolant, the auxiliary coolant starts at a coolant source S and leads to a manifold 9 from where it flows into distribution tubes 7, 8.
flows into the.

In order to ensure effective use of this auxiliary coolant, a special arrangement of the auxiliary coolant orifices 7a, 8a is made.

That is, the arrangement pattern is determined in advance by the position of the dispersion tube within the cluster.

First, the orifices are located axially at a number of common levels along the cluster, these levels being designated I■ in Figures 1 and 8a.

Second, the orientation of the orifices in the wall of any one distribution tube at any level is determined by the distribution tube's position within the cluster.

Third, at least some of the orifices of the surrounding dispersion tubes are directed to direct the supplemental coolant along a trajectory directly against the wall of the pressure tube.

Fourth, the axial position of level I-[ is determined by the temperature profile along the cluster.
file), but is usually related to the position of grid 5.

Correct orientation of the orifices in the peripheral distribution tubes for the auxiliary coolant is achieved by having two types of tubes (FIG. 5).

In both types, the orifices are drilled alternately at level I, as shown in Figures 6a and 6b.

That is, one hole 16 in the radial direction (FIG. 6a) is opened at the center of the pair of holes 17 (FIG. 6b) on the opposite side to the bending direction.

The radius passing through the hole 16 is 180 degrees from the direction of the bend 20 of the distribution tube.
Makes an angle of 0.

The radius passing through the center of the pair of holes 17 is 70~
make an angle β between 85°.

These dispersion tubes have orifice patterns of levels i, i, ■
, ■, ■ are arranged as shown in FIG.

The pattern of the nozzle holes is as shown in FIG. 4 at levels I, IV, ■ and ■.

The direction of the ejection holes 8a of the central dispersion tube 8 is as shown in Fig. 7a, and since they are alternately displaced by 600 degrees when viewed from the plane, the effects at the respective levels shown in Figs. 3 and 4 are obtained. is achieved.

In addition to the injection of auxiliary coolant through the holes at levels I to II, it is advantageous to provide a set of holes at the top of the clasp, designated at level X.

At level X, the surrounding dispersion pipes 7 are 1 as shown in FIG.
At level
It has a number of nozzle holes 19.

The hole in the central tube 8 is 120° at all other levels I-N.
(Figure 7a), but Figures 3 and 4
As shown in the figure, the phase is shifted with respect to the holes in the surrounding dispersion tubes.

The axial position of level I-■ is preferably influenced by the position of the intermediate grid and the temperature distribution along the cluster.

FIG. 8a shows the relative position of the levels in which the orifices for the auxiliary coolant are located along the cluster and are exactly out of phase with respect to the position of the grid and the temperature distribution in FIG. 8b.

In general, it can be seen that most grids have coolant jets just above the grid.

Generally, there is also a level between each pair of adjacent grids, except where the temperature approaches the maximum, erupting at two levels located between a pair of adjacent grids, ■ and ■. It has an auxiliary coolant jet.

[Brief explanation of the drawing]

FIG. 1 is a partial cross-sectional view showing a general arrangement of a nuclear fuel assembly; FIG. 2 is a partially schematic plan view of a fuel assembly with a circular lattice pattern of fuel rods; FIG. Figure 4 shows the relative jetting direction of the auxiliary coolant; Figure 5 is a side view of one circumferential distribution tube for the auxiliary coolant; Figures 6a, 6b and 60; line Via-VIa
, VIb-Vlb and VIc-VIc", FIGS. 7a and 7b are cross-sectional views of the central distribution tube for auxiliary coolant at levels I to II and level X, FIGS. 8a and 8b, respectively. The figure shows the level at which the auxiliary coolant orifices are placed relative to the intermediate grid that positions the fuel rods in clusters: 1...cluster, 2...nuclear fuel rods. ,6
... Sub-channel, 7 ... Surrounding dispersion pipe, 8.
...Central dispersion tube, 7a, 8a...Blowout hole.

Claims (1)

Claims: 1. A nuclear fuel rod comprising a cluster of nuclear fuel rods supported in an annular row at a plurality of lattice locations symmetrical about a longitudinal axis;
The fuel rods are open ended and have a peripheral wall coaxial with the longitudinal axis, the spacing between the fuel rods is determined to define a secondary flow path between the fuel rods that acts as a flow path for the main coolant, and The secondary channels interlock to form concentric annular passages between the annular rows of fuel rods and radial passages intersecting the annular passages, and a number of porous sparge tubes for injecting auxiliary coolant into the clusters. has
One of the sparge tubes is aligned with the longitudinal axis, the remaining sparge tubes are arranged in circumferential positions on a common annular passage, and some of the remaining sparge tubes direct the coolant to the surrounding wall. A nuclear fuel assembly having an auxiliary coolant orifice oriented such that it points toward. 2. The remaining sparge tubes arranged at peripheral locations have auxiliary coolant orifices, the orifices being oriented such that every other sparge tube directs the coolant toward the surrounding wall. A nuclear fuel assembly according to claim 1.