Metal treatment – Process of modifying or maintaining internal physical... – Producing or treating layered – bonded – welded – or...
Patent
1994-08-11
1997-04-15
Simmons, David A.
Metal treatment
Process of modifying or maintaining internal physical...
Producing or treating layered, bonded, welded, or...
148520, 148672, 376416, 976DIG283, G21C 2102, G21C 320
Patent
active
056205368
DESCRIPTION:
BRIEF SUMMARY
TECHNICAL FIELD
The present invention relates to a method of manufacturing a nuclear fuel element that includes fuel rods, the cladding tubes of which are provided with an internal liner of zirconium or a zirconium alloy.
BACKGROUND ART
A nuclear fuel element comprises fuel rods with cladding tubes filled with fuel pellets. It is known to provide cladding tubes with an internal layer of zirconium or a zirconium alloy to protect the fuel element from destruction caused by pellet-clad interaction, PCI, in case of rapid power increases.
SE 7810262 describes a nuclear fuel element with improved properties regarding resistance to PCI and comprising a composite cladding container comprising an outer part of a zirconium alloy and an inner part bonded to the outer part and consisting of zirconium with an impurity content to about 1000 to 5000 ppm. This composite cladding tube is manufactured by inserting a sleeve of sponge zirconium, which is to be used as an internal part, into a hollow billet of a zirconium alloy, which is to constitute the outer part, whereupon the unit is subjected to explosion bonding of the sleeve to the billet. Thereafter, the composite product is extruded at a temperature of about 538.degree.-750.degree. C. while using conventional extrusion methods. Thereafter, the extruded composite produce is subjected to a conventional tube production until the desired dimension of the cladding has been reached. The bond of the sleeve to the billet can also take place by means of heating to 750.degree. C. for 8 hours to achieve a diffusion bond. The manufacture of the composite cladding can also take place by extruding the unit, consisting of the inner sleeve and the outer shell, while using conventional technique.
EP 194 797 describes a cladding tube with an outer component and an inner component intended to protect the cladding against PCI damage. The inner component has a specific composition, zirconium with 0.4-0.6% tin, 0.5-1.4% iron and 100-700 ppm oxygen, in order to impart to the inner component good corrosion properties in the event that water should penetrate into the rod. The cladding tube is manufactured by processing the ingot of the inner component in a conventional way for the manufacture of Zircaloy, including beta quenching, before the inner component is joined to the outer component. After the joining of the outer and inner components, the cladding tube can be additionally beta-quenched either before the last cold-rolling step by beta-quenching the outer surface, or before the penultimate rolling step by beta-quenching the entire cladding wall comprising both the outer and inner components.
EP 155 603 also describes a nuclear fuel element comprising a composite cladding tube with an internal lining of zirconium to avoid cracking in the cladding upon thermal expansion of the pellets. According to this patent specification, it is known to reduce the sensitivity of the zirconium lining to cracking by limiting the total amount of impurities to a level below 5000 ppm and by maintaining the ratio of the oxygen content to the iron content greater than 1. The manufacture of a zirconium-lined cladding tube is performed by melting zirconium into an ingot which is then forged and shaped into a hollow billet. The hollow billet is inserted into another hollow billet of a zirconium alloy. The composite billets are heat-extruded into a tube blank. The tube blank is then subjected to repeated cold rolling operations and heat treatments according to conventional tube manufacture. A heat-treatment step consisting of a solution treatment at 800.degree. or 860.degree. C., near the phase transformation temperature to cause secondary phases in the material to become dissolved, and thereafter a rapid cooling to room temperature as well as a stress-removing heat treatment at a low temperature, for example 550.degree. C. for 2 hours, are carried out either after the forging or after the heat extrusion or as a last step on the finished tube, whereby it is considered to be especially effective to carry out
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ABB Atom AB
Phipps Margery S.
Simmons David A.
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