RU2800030C1 - Nuclear reactor fuel assembly bottom nozzle - Google Patents

Abstract

FIELD: nuclear engineering.

SUBSTANCE: invention relates namely to fuel assemblies of nuclear power reactors with pressurized water. The bottom nozzle of the fuel assembly of a nuclear reactor contains a support element, a diffuser, a hexagonal frame with ribs of variable height fixed to non-adjacent corners of the hexagonal frame with an offset from the plane of symmetry of the angles in such a way that the end of one rib is conjugated with the side surface of the other rib. The profile of the ribs is made with a ledge on the lateral surface of the ribs and a thinning of the upper end of the ribs, the ledge serves to install the rim of the anti-debris filter, and the thinning is used to abut against the support grid of the bundle of fuel elements.

EFFECT: invention makes it possible to improve the reliability of the bottom nozzle and the fuel assembly as a whole by reducing the hydraulic resistance of the bottom nozzle and vibration loading of the fuel rods.

2 cl, 5 dwg

Description

FIELD OF TECHNOLOGY

The invention relates to nuclear engineering, namely to fuel assemblies of nuclear power reactors with pressurized water.

PRIOR ART

To increase the reliability of the fuel assembly and protect it during operation from damage by debris particles, an anti-debris filter is installed in the liner of the fuel assembly, placing it between the ribs of the liner in the largest flow area of the liner in order to reduce hydraulic resistance. As a rule, modern anti-debris filters consist of a filter element and a rim, with which the filter is connected to the liner.

A shank of a fuel assembly of a nuclear reactor is known (RF patent No. 2079170, publ. 05/10/1997), equipped with ribs adjacent with their ends to the lower plane of the lower support grid between rows of holes for fuel elements (fuel rods), the disadvantage of which is the partial overlap of the holes for the passage of the coolant through the lower support grid, as well as the inability to equalize the field of coolant flow velocities over the cross section in shank.

The closest in technical essence and the achieved result to the proposed technical solution is the shank of the fuel assembly of a nuclear reactor (RF patent No. 2325714, publ. 10.12.2007), containing coaxially interconnected plinth, support element, diffuser, hexagonal frame with star-shaped ribs fixed on the said frame for installing the support grid of the fuel assembly of the fuel assembly.

The disadvantage of this fuel assembly liner is a decrease in its flow area when anti-debris filters are installed, the presence of a shaded area for the coolant flow at the junction of the fins, the occurrence of turbulence in the coolant flow at the junction of the liner fin with the rim of the anti-debris filter and, as a result, an increase in the hydraulic resistance coefficient, leading to increased vibration loading of the fuel rods.

The proposed design of the shank of the fuel assembly of a nuclear reactor eliminates these disadvantages.

SUMMARY OF THE INVENTION

The technical objective of the invention is to increase the reliability of the shank and, accordingly, the fuel assembly as a whole.

To solve this problem, it is necessary to create a liner design that makes it possible to exclude a decrease in the flow area, minimize the shaded central section that affects the coolant flow, eliminate the turbulence of the coolant flow at the points of contact of the liner fins with the rim of the installed anti-debris filter and preserve the strength properties of the liner.

An increased coefficient of hydraulic resistance of the core leads to a decrease in the coolant flow through the reactor and, as a result, to a deterioration in the cooling of the core in the nominal mode and modes with violation of normal operation. An increase in the pressure drop across the core, caused by an increase in its coefficient of hydraulic resistance, leads to a decrease in the reserve before the fuel assembly floats.

The technical result of the invention is to reduce the hydraulic resistance of the liner and, as a consequence, the vibration loading of the fuel rods.

The technical result is achieved by:

- the shank of the nuclear reactor fuel assembly contains a support element, a diffuser and a hexagonal frame coaxially connected to each other, on which ribs of variable height are fixed;

- the ribs fixed on the hexagonal frame are installed in non-adjacent corners of the frame with an offset from the plane of symmetry of the corners in such a way that the end face of one rib mates with the side surface of the other rib;

- on the side surface of the ribs fixed on the hexagonal frame, a ledge is made, at the upper end of these ribs, a thinning is made, the ledge serves to install the rim of the anti-debris filter, and the thinning - to abut against the support grid of the fuel bundle;

- when performing thinning of the ribs fixed on the hexagonal frame, the upper edges of the ribs are made in the form of teeth with flat tops, interacting with the bridges between the pouring holes of the supporting grid of the fuel bundle.

Fastening the fins in non-adjacent corners of the frame with displacement and mating of the end of one rib with the side surface of the other provides minimal shading for the coolant in the central part of the liner without losing the required structural strength and increasing the flow area of the liner with an installed anti-debris filter. This reduces the hydraulic resistance of the liner and, as a consequence, the vibration loading of the fuel rods.

Making the ribs with a ledge on the side surface of the ribs, thinning the upper end of the ribs and connecting them to each other by mating the end of one rib with the side surface of the other, eliminating the need for a central connecting node, makes it possible to reduce the metal content of the product, as well as the range and number of parts used in the manufacture of the product.

Brief description of the drawings

The essence of the invention is illustrated by drawings, which show:

fig. 1 - fuel assembly, general view;

fig. 2 - shank with ribs, top view;

fig. 3 - liner with installed support grid and anti-debris filter, vertical section;

Fig.4 - edge of the shank, view in two projections;

fig. 5 - shank edge with upper edge in the form of teeth with flat tops, main view.

The shank 1 of the fuel assembly 2 of a nuclear reactor contains coaxially interconnected supporting element 3, a diffuser 4, a hexagonal frame 5. Ribs 6 of variable height are fixed to non-adjacent corners of the hexagonal frame 5 with an offset from the plane of symmetry of the angles of the ribs 6. Ledges 7 and thinnings 8 are made on the ribs 6. The rim of the anti-debris filter 9 is installed in the ledges 7. The thinning 8 is in contact with the bridges between the pouring holes of the support grid 10 of the fuel bundle. The upper thinning of the rib 6 can be made in the form of teeth 11 with flat tops.

The work of the shank is carried out as follows.

The coolant enters the liner 1, equipped with an anti-debris filter 9, installed with its rim in the ledges 7 of the profile of the rib 6, enters the diffuser 4, freely spreads also in radial directions along the ribs 6 and approaches the support grid 10 of the fuel bundle.

Fastening the fins 6 to non-adjacent corners of the hexagonal frame 5 with an offset from the plane of symmetry of the corners in such a way that the end of one rib mates with the side surface of the other fin creates conditions for equalizing the velocity field of the coolant when passing through the diffuser 4.

Relying on the thinning 8 of the profile of the rib 6 of the support grid 10 of the bundle of fuel rods by bridges between the pouring holes eliminates the overlap of some of the pouring holes for the passage of the coolant and creates the possibility for coolant overflows to equalize local flow inhomogeneities between adjacent cavities bounded by common ribs 6.

The velocity-aligned flow in the cross section has lower horizontal velocity components after passing through the support grid 10 of the fuel bundle, therefore, it creates less vibrodynamic loads on the fuel rods and their attachment points in the support grid 10 of the fuel bundle. EFFECT: increased reliability of shank 1 and fuel assembly 2 as a whole.

Industrial Applicability

Thus, the use of the proposed design of the liner of a nuclear reactor fuel assembly allows solving the task of increasing the reliability of the liner by reducing the hydraulic resistance of the liner and vibration loading of fuel elements and is advisable for use in fuel assemblies of nuclear power reactors with pressurized water.

Claims (2)

1. The shank of a fuel assembly of a nuclear reactor, containing a support element coaxially interconnected, a diffuser, a hexagonal frame on which the ribs are fixed, characterized in that the ribs are made of variable height and installed in non-adjacent corners of the hexagonal frame with an offset from the plane of symmetry of the angles in such a way that the end of one rib is associated with the side surface of the other rib, while the profile of the ribs is made with a ledge on the side surface of the ribs and thinning of the upper end of the ribs , the ledge serves to install the rim of the anti-debris filter, and the thinning - to rest against the support grid of the bundle of fuel elements. 2. The shank according to claim 1, characterized in that the thinning of the ribs is made in the form of teeth with flat tops.