CA1250966A

CA1250966A - Short fuel element

Info

Publication number: CA1250966A
Application number: CA000497645A
Authority: CA
Inventors: Douglas E. Teed
Original assignee: Canadian General Electric Co Ltd
Current assignee: General Electric Canada Co
Priority date: 1985-12-13
Filing date: 1985-12-13
Publication date: 1989-03-07
Also published as: KR870006581A; KR940006205B1

Abstract

SHORT FUEL ELEMENT
ABSTRACT OF THE DISCLOSURE

Fuel bundles for use in a pressure tube reactor each comprise a cylindrical assembly of fuel rods extending between a pair of end plates to which the rods are attached. The individual rods have a sheath construction of predetermined length to permit the insertion of a plurality of bundles within existing pressure tube fuel channels, previously containing a lesser number of longer bundles. The adoption of shorter rods militates against rod distortion under thermal and coolant flow forces, to obviate the former necessity of providing spacing appendage means attached to the fuel rod sheaths intermediate the bundle and plates, thereby simplifying manufacture and enhancing the metallurgical dependability of the rod sheath. There is further provided a bundle assembly comprising two or more of the improved fuel bundles secured in end-to-end relation, in predetermined angular relation about the polar axis of the bundle assembly.

Description

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S~IORT FUEL ELEMENT
This invention is directed to nuclear fuel and in particular to a fuel bundle for use in a pressure tube nuclear reactor.
Pressure tube reactors, particularly as exemplified by the Canadian deuterium cooled "natural"
uranium fuelled reactor have evolved a sophisticated fuel bundle arrangement requiring particular manufacturing processes, leading to high costs, and possessing certain disadvantages.
In particular, the individual rods o-f existing fuel bundles are provided with appendages securing as spacers, attached to the outer surfaces of the rod sheaths, and serving to maintain certain prescribed clearances between the sheaths of adjacent rods, and between the sheaths and the adjacent inner surface of the pressure tube in which the fuel bundles repose in axially aligned relation. Some of the problems associated with this prior art fuel include:
the cost and involvement in locating and attaching the appendages to the exterior of the element sheaths, by brazing or welding;
the metallurgical changes produced locally in the sheath material at the zone affected by heat, as a consequence of the attachment process;

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CASE No~964

- 2 the increased likelihood of mechanical failure due to the appendages acting as stress raisers;
the increase in cost of fuel production due to the number of rejects arising in the manufacturiny process.
In order to overcome the existing problems of the present fuel there is provided a much stiffer fuel rod construction, to obviate the need of providing spacer appendages intermediate the rod ends.
In accordance wi.th the present invention there is provided a fuel bundle having a pluxality of plain fuel rods extending in mutual parallel relation between a pair of opposed end plates, the length to diameter ratio of the fuel rods being not greater than about 30 to 1.
It is contemplated that multiple bundles can be assembled, having their end plates in secured relation to provide a single entity for fuel handling ~0 purposes. In particular, such an assembly permits the assembling of the respective fuel bundles in mutual angular orientation about their polar axis, for puxposes of controlling the pressure drop along the bundle, and also influencing the local turbulence effect on the liquid coolant, under operating conditions.
In order to position the fuel bundles in radial spaced relation from the inner support surface of the fuel channel there is provided spacer means extending from the bundle end plates outwardly in radial projecting relation, relative to the radially outer envelope of the fuel rods, to provide lateral support to the bundle for handling and coolant flow purposes.

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CASE ~o.2964 The spacer means may take a number of forms, generally comprising outwardly extending ribs connecting with the end plate and extending in mis-aligned relation with the individual fuel rods.
The radially outer ends of these ribs incorporate bearing means for contacting the surface of the fuel channel, and may comprise an axially elongated bearing pad of streamline form extending in axial overlapping relation with the ends of the fuel rods. Other embodiments comprise bearing bands e~tending arcuately about the bundle. ~ne such embodiment is spaced in radial clearing relation from the fuel rods. Another embodiment provides contact of the bearing band inner surface with the respective rod sheaths.
Certain embodiments of the invention are described, reference being made to tlle accompanying drawings, wherein:
Figure 1 is an end view of a portion of a first embodiment fuel bundle Figure 2 is a side view of the bundle portion of Figure l;
Figure 3 is an end view of a portion of a second embodiment fuel bundle;
Figure 4 is a side view of the bundle portion of Figure 3;
Figure 5 is an end view of a portion of a third embodiment fuel bundle;
Figure 6 is a side view of the bundle portion of Figure 5; and Figure 7 shows two bundles in coupled relation.
In Figure 1 the components of the fuel bundle 10 comprise fuel rod elements 12, the outer rim portion 15 of end plate 14, rod sheath portion 16 and fuel pellet 18, and spacer means 20 comprising spacer rib 22 and spacer pad portion 24.

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CASE No.2~64 -- 4 ~
In the Figure 3 embodiment the spacer ribs 32 connect with spacer band 36 which contacts the sheaths 16 of the outer row of fuel rods 12.
In the Figure 5 embodiment the spacer ribs 52 are attached to spacer band 56 which enshrouds the ends of fuel rods 12, to form a flow passage thereabout.
Figure 7 shows a fuel assembly 70 comprising a pair of fuel bundles 10 welded together at the end plates 14 in back-to-back relation. By welding the end plates 14 so that the spoke portions and other parts thereof are in axial registry, the hydraulic pressure drop thus created will be minimised. By welding the end plates in co-axial but angularly off-set relation, the hydraulic pressure drop can be increased. ~enerally, welding is ~ffected at or adjacent the rim portion 15.

Claims

The embodiments of the invention in which an exclusive property or privilege is claimed are defined as follows:-

1. A fuel bundle for use in a liquid cooled nuclear reactor, having a plurality of plain fuel rods extending in mutual parallel relation between a pair of opposed end plates, the length to diameter ratio of the fuel rods being not greater than about thirty to one (30:1).

2. The fuel bundle as set forth in claim 1, said end plates including spacer means extending outwardly in radial projecting relation, relative to the radially outer envelope of said fuel rods, to afford lateral support to the bundle.

3. The fuel bundle as set forth in claim 1, in combination with at least one other said bundle and means securing adjacent ones of said end plates in mutually attached relation, to provide a unitary fuel assembly.

4. The fuel bundle assembly as set forth in claim 3, said end plates being mutually orientated about the polar axis of the bundle assembly in predetermined angular relation.

5. The fuel bundle assembly as set forth in claim 4 wherein in use said predetermined angular relation promotes a low drop in pressure of liquid coolant flowing past the bundle.
6. The fuel bundle as set forth in claim 2, said spacer means including rib portions extending

Claim 6 continued:
from said end plate axially in overlapping relation with said fuel rods.