Induced nuclear reactions: processes – systems – and elements – Fuel component structure – Nonconventional jacket or can material
Patent
1997-07-29
1999-03-23
Wasil, Daniel D.
Induced nuclear reactions: processes, systems, and elements
Fuel component structure
Nonconventional jacket or can material
420422, 148672, G21C 307
Patent
active
058870458
DESCRIPTION:
BRIEF SUMMARY
The present invention concerns zirconium-based alloy tubes for use in nuclear reactor fuel assemblies. Tubes of that type are usable in particular for constituting fuel rod cladding, for forming the external portion of such cladding, or for forming guide tubes which receive the rods of control clusters.
Cladding of that type is frequently constituted by tubes made from an alloy known as "Zircaloy 4" which contains, in addition to zirconium, 1.2% to 1.7% by weight of tin, 0.18% to 0.24% by weight of iron, 0.07% to 0.13% by weight of chromium and 0.10% to 0.16% by weight of oxygen. A number of alloys which are derived from those previous alloys have also been proposed, in particular alloys in which the chromium is either completely or partially replaced by vanadium and/or in which the oxygen content exceeds that given above, with a corresponding reduction in the contents of some of the other addition elements.
Particular qualities which are required in a tube for use as cladding are good resistance to corrosion by water at high pressure and at high temperature, limited long term creep, long term retention of mechanical properties, limited expansion on irradiation and reduced sensitivity to lithium; in addition, these properties must be reproducibly obtainable, and the alloy must have metallurgical properties at the various production stages (in particular rollability) which keeps the rejection rate down to an acceptable value.
The behavior of Zircaloys on irradiation constitutes a factor which is inhibiting advances in operating conditions for nuclear reactors as regards increasing cycle time. This is mainly due to uniform corrosion.
A particular aim of the invention is to provide a tube with improved characteristics which can be in the recrystallized state when good creep behavior is required above all, or which can be in a metallurgically stress-relieved state, which is more easily manufactured econom-cally to within strict dimensional tolerances (in particular as regards circularity errors) , and which is better as regards generalized corrosion.
For that purpose, there is provided a zirconium-based alloy tube containing, by weight, 1% to 1.7% of tin, 0.55% to 0.8% of iron, 0.20% to 0.60% in total of at least one element selected from chromium and vanadium, and 0.10% to 0.18% of oxygen, the carbon and silicon contents being controlled and being respectively in the range 50 ppm to 200 ppm and in the range of 50 ppm to 120 ppm, the alloy further containing only zirconium and unavoidable impurities. The tube, in its final state, is either stress-relieved or recrystallized depending on the required properties.
Vanadium is essentially present in fine precipitates in the form Zr(Fe,V).sub.2 ; this is also the case for chromium, which is present in precipitates in the form Zr(Fe,Cr).sub.2.
A high Fe/(V+Cr) ratio, which may exceed 3/1, can further improve resistance to corrosion in a lithium-containing medium. As a general rule, this ratio will be close to 2/1. It is generally preferable to use either chromium alone, or vanadium alone rather than a combination of the two.
The precise composition selected from the above range will depend on the properties which are to be prioritized. Usually, an alloy containing 1.3% Sn, 0.60% Fe, 0.25% V or Cr, 0.14% O.sub.2, 140 ppm C and 90 ppm Si will be a good compromise.
The presence of vanadium reduces the fraction of absorbed hydrogen and improves resistance to corrosion in an aqueous medium at high temperature and high pressure, even in the event of localized boiling.
If one requirement is to reduce creep as much as possible during the initial stage of reactor use, it may be advantageous to have a high tin, carbon, and/or oxygen content. A carbon content of more than 100 ppm is favorable as regards creep; but above 200 ppm, expansion on irradiation becomes large. The silicon content is "controlled" to take advantage of its regulatory effect on structures and its favorable influence on corrosion resistance.
A high value for the sum of the beta-producing elements (Fe+V+Cr) c
REFERENCES:
patent: 3150972 (1964-09-01), Rosler
patent: 4735768 (1988-04-01), Stehle et al.
patent: 4938920 (1990-07-01), Garzarolli et al.
patent: 5278882 (1994-01-01), Garde et al.
Charquet Daniel
Mardon Jean-Paul
Senevat Jean
Compagnie General des Matieres Nucleaires
Framatome
Wasil Daniel D.
LandOfFree
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