Induced nuclear reactions: processes – systems – and elements – Fuel component structure – Plural fuel segments or elements
Patent
1995-12-18
1997-08-05
Wasil, Daniel D.
Induced nuclear reactions: processes, systems, and elements
Fuel component structure
Plural fuel segments or elements
G21C 332, G21C 306
Patent
active
056549938
DESCRIPTION:
BRIEF SUMMARY
TECHNICAL FIELD
The present invention relates to the field of fuel elements for a pressurized-water reactor (PWR), the fuel element comprising a number of fuel rods arranged in a square lattice and wherein certain positions in the lattice contain guide tubes for receiving control rods.
The invention also comprises a method for manufacturing guide tubes.
BACKGROUND ART, PROBLEMS
A PWR fuel element is composed of a frame consisting of a top nozzle, a bottom nozzle, spacers, and guide tubes (or thimbles) and is filled with fuel rods. The size of a PWR lattice may vary from 14.times.14 to 19.times.19 rods. The primary function of the guide tubes is to provide space for control rods but they also function as supporting rods in the fuel assembly and as spacer holder rods. Usually, the guide tubes are made from a zirconium alloy of the same type as the cladding of the fuel rods.
During operation in a reactor, an extension of cladding and guide tubes takes place because of irradiation-induced growth. The growth is caused by radiation damage in the microstructure arranging itself in certain crystal planes in the hexagonal zirconium lattice and by the fact that the material therefore will grow perpendicular to these planes. The growth means that the fuel element all the time is extended under irradiation and that the element, after a certain irradiation, may become longer than the available space between the upper and lower core plates with an ensuing risk of the element bending or breaking. This means that the burnup of the element, which determines the residence time of the element in the core, must be limited.
The fuel element is designed such that the fuel rods are somewhat shorter than the space between the top and bottom nozzles, to provide a certain space for the fuel rods in which to grow. The guide tubes which serve as supporting rods are longer and must be attached to the top and bottom nozzles to hold the bundle together. In current designs, therefore, the growth of the guide tubes is determining for the burnup for which a fuel element can be designed.
According to EP-B-0 296 972, it is known to heat-treat cladding tubes for PWR fuel to reduce the corrosion and also the growth in the axial direction by heating the cladding tube to a temperature in the interval 950.degree. C. to 1250.degree. C., as a last step in the manufacture, and then rapidly cooling the tube, so-called beta-quenching. According to the patent the cladding shall be of a zirconium alloy, preferably Zircaloy-4 and of a certain composition within the scope of the specification for that alloy.
For fuel elements intended for boiling water reactors, BWR, it is known, according to U.S. Pat. No. 4,770,847, that fuel rods have a faster growth than water rods. To achieve a uniform growth of fuel rods and water rods, it is stated that a cladding tube with less tendency to grow can be manufactured by cold-working in a final step to achieve a suitable dimension, followed by heat treatment at about 538.degree.-705.degree. C. for 1 to 15 hours. A water rod with a somewhat higher tendency to grow is manufactured by heat-treating the tube, after cold working, at 440.degree.-510.degree. C. for 1 to 4 hours.
SUMMARY OF THE INVENTION
According to the present invention, a fuel element for a PWR is obtained which can be utilized for higher burnup than what current technique allows, by making the guide tubes of the element less inclined to grow and at the same time corrosion-resistant.
This can be achieved according to what is stated in the claims.
In the manufacture of guide tubes, at the dimensionally final state of the main part of the tube or after all the desired dimensions of the tube have been attained, the tube is to be beta-quenched by being heated to a temperature in the beta-phase region, 950.degree. to 1200.degree. C., and then be rapidly cooled. The beta-quenching operation can also be carried out in such a way that only part of the tube wall undergoes phase transformation to beta phase. After the beta-quenching operation, at least one add
REFERENCES:
patent: 2924518 (1960-02-01), Raine et al.
patent: 4360389 (1982-11-01), Urquhart
patent: 4649023 (1987-03-01), Sabol et al.
patent: 4770847 (1988-09-01), Plaza-Meyer et al.
patent: 4938921 (1990-07-01), Mardon et al.
patent: 5230758 (1993-07-01), Foster et al.
Dahlback Mats
Vesterlund Gunnar
ABB Atom AB
Wasil Daniel D.
LandOfFree
Fuel element for pressurized--water reactor with guide tubes fin does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Fuel element for pressurized--water reactor with guide tubes fin, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Fuel element for pressurized--water reactor with guide tubes fin will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-1080361