Classifications

• • C—CHEMISTRY; METALLURGY
  • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
  • C22C—ALLOYS
  • C22C16/00—Alloys based on zirconium
• • C—CHEMISTRY; METALLURGY
  • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
  • C22F—CHANGING THE PHYSICAL STRUCTURE OF NON-FERROUS METALS AND NON-FERROUS ALLOYS
  • C22F1/00—Changing the physical structure of non-ferrous metals or alloys by heat treatment or by hot or cold working
  • C22F1/16—Changing the physical structure of non-ferrous metals or alloys by heat treatment or by hot or cold working of other metals or alloys based thereon
  • C22F1/18—High-melting or refractory metals or alloys based thereon
  • C22F1/186—High-melting or refractory metals or alloys based thereon of zirconium or alloys based thereon
• • G—PHYSICS
  • G21—NUCLEAR PHYSICS; NUCLEAR ENGINEERING
  • G21C—NUCLEAR REACTORS
  • G21C3/00—Reactor fuel elements and their assemblies; Selection of substances for use as reactor fuel elements
  • G21C3/02—Fuel elements
  • G21C3/04—Constructional details
  • G21C3/06—Casings; Jackets
  • G21C3/07—Casings; Jackets characterised by their material, e.g. alloys
• • Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
  • Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
  • Y02E—REDUCTION OF GREENHOUSE GAS [GHG] EMISSIONS, RELATED TO ENERGY GENERATION, TRANSMISSION OR DISTRIBUTION
  • Y02E30/00—Energy generation of nuclear origin
  • Y02E30/30—Nuclear fission reactors

Definitions

• Zirconium alloy resistant to shadowing corrosion for fuel assembly component for boiling water reactor component made of this alloy, fuel assembly and its use.
• the invention relates to the field of nuclear reactors, and more specifically to the zirconium alloy elements which are used to form fuel assemblies for boiling water type nuclear reactors (BWRs).
• BWRs boiling water type nuclear reactors
• Zr alloys are widely used in fuel assemblies for nuclear reactors to form parts subjected to severe conditions of irradiation, mechanical stress and corrosion.
• these parts may be mentioned the sheaths containing fuel pellets, housings, grids and spacing elements various ...
• shadow corrosion a problem frequently encountered in BWRs is related to the appearance of what is commonly called “shadow corrosion” which can be translated as “shadow shading corrosion”.
• the conducting medium is the boiling water of the reactor.
• This phenomenon is amplified by irradiation which modifies the physicochemical characteristics of the materials and creates oxidizing species at the surfaces of the components by radiolysis of the heat transfer fluid, in addition to those created by dissolved oxygen in the boiling water of the reactor. This amount of dissolved oxygen is clearly greater than that present in the pressurized water of PWR reactors.
• the assemblies REB fuel systems are very sensitive to this type of corrosion, and the solutions developed so far to reduce or eliminate this localized corrosion consist, for example, of coating one of the components in the presence, to make it electrochemically compatible with the other (see US-A-2006/0045232).
• the object of the invention is to provide Zr alloy components for REB fuel assemblies which are as little as possible affected by the phenomenon of shadow corrosion, while having satisfactory properties in use, both in terms of mechanical characteristics and 'in terms of resistance to conventional types of corrosion.
• the subject of the invention is a zirconium alloy resistant to shadowing corrosion for a fuel assembly component for a boiling water nuclear reactor, characterized in that:
• a final heat treatment is carried out at a temperature of between 450 and 610 ° C. for a duration of between 1 minute and 20 hours.
• composition is preferably, in percentages by weight:
• It may undergo during its manufacture one or more cold rolling, located before or between, or before and between the heat treatment or said carried out at a temperature between 450 and 610 0 C of total duration of at least 4 hours.
• He may be in the relaxed state.
• the invention also relates to a fuel assembly component for boiling water nuclear reactor, characterized in that it is made of an alloy of the above type.
• the subject of the invention is also a fuel assembly for a boiling water nuclear reactor, characterized in that it comprises components of the above type, and in that at least some of these components are placed in a galvanic coupling condition with other Ni-based or stainless steel alloy components.
• the invention also relates to a use of a fuel assembly of the above type in a boiling water nuclear reactor whose primary fluid contains up to 400 parts per billion of dissolved oxygen.
• the primary fluid can also contain up to 50 ml / kg of dissolved hydrogen.
• the primary fluid can also contain up to 50 parts per billion of zinc.
• the primary fluid may also contain added chemical species to reduce the corrosion potential of the materials in contact therewith.
• the invention relates to a Zr alloy for a REB fuel assembly component containing significant quantities Nb and Sn and also some Fe. Limited amounts of Cr, Ni, V, S and O may also be present.
• a necessary condition is that these alloys have undergone one or more heat treatments carried out between 450 and 610 ° C., for a total duration of at least 4 hours, in order to be sure of having decomposed the ⁇ Zr phase resulting from the heat treatments. previous, in the ⁇ Nb phase. No thermal treatment after hot deformation should be conducted at more than 610 ° C. In fact, if such a treatment were carried out, a ⁇ Zr phase would be recreated, which would degrade the corrosion behavior of the alloy.
• One or more cold rollings may be performed before, and / or between, and / or after this or these heat treatment (s).
• these heat treatments between 450 and 61O 0 C may be intermediate anneals separating cold rolling passes. At least one of these cold rolling operations must be carried out with a reduction rate of at least 25%.
• This series of heat treatment (s) and rolling (s) must be followed by a final heat treatment whose duration can range from 1 minute to 20 hours, at a minimum temperature of 450 0 C and at a temperature of 610 0 C maximum. Indeed, experience shows that the execution of the heat treatment (s) long (s) previous (s), even a total duration of 10 to 100 hours, does not achieve the l composition balance of the precipitated phases of ⁇ Nb and Zr (Nb 1 Fe) 2 .
• these alloys can be used to also realize REB fuel assembly components that would not be in galvanic coupling conditions, if their properties make them well suited for this purpose.
• FIG. 1 shows the influence of Sn on the oxidation of Zr alloy tubes at 1% Nb and 0.1% Fe in 360 ° lithiated water;
• FIG. 2 shows a micrograph of an alloy according to the invention, with typical precipitates of this alloy.
• the shadow corrosion observed on the components of REB fuel assemblies is due, as we have said, to a galvanic coupling phenomenon assisted by irradiation, occurring in an oxygenated medium.
• the specific effect of irradiation is difficult to reproduce in the laboratory, but it is known that irradiation accelerates the observed phenomena.
• the effects of oxygen and galvanic coupling can more easily be evaluated in laboratory tests, and this is done according to the following protocol.
• Samples of alloys according to the invention and reference samples are introduced into an autoclave under oxidizing conditions. For each alloy, two samples are tested, one coupled to INCONEL® (Ni-based alloy) and the other uncoupled. A dissolved oxygen content of 100 ppm is maintained in the medium, as well as a boron content of 0.12% in the form of boric acid and a lithium content of 2 ppm in the form of lithium hydroxide. The aim is to obtain an aggressive medium with a high oxygen potential, whose effects on samples in a galvanic coupling situation are comparable to those resulting from a residence in BWR.
• the sensitivity of an alloy to shadow corrosion is expressed using the ratio between the oxide thicknesses formed on the coupled sample and the uncoupled sample. The higher this ratio, the more the alloy is sensitive to coupling, and therefore to shadow corrosion. It is considered that a ratio greater than 2.5 reflects a high sensitivity of the alloy to shadow corrosion, which makes it unsuitable for use in the reactor under galvanic coupling conditions.
• Table 1 Composition of the samples showing the influence of Sn
• Figure 1 shows the weight gain of tubes A to F after 112, 168 and 196 days in the medium without galvanic coupling. It can be seen that the 0.039% and 0.19% reference samples A and B have a corrosion resistance in lithiated water which begins to deteriorate between 112 and 168 days, and becomes technically mediocre between 168 and 196 days. In the same periods, the samples according to the invention C to F remain stable in corrosion. It is therefore necessary to impose on the alloys of the invention an Sn content of at least 0.20%, preferably at least 0.25%, so that the areas not subjected to shadow corrosion have a good behavior. corrosion.
• Table 2 Compositions, treatments and performances of recrystallized samples tested in shadow corrosion.
• thermomechanical treatments carried out according to the invention make it possible to obtain equilibrium precipitates containing Nb in a sufficiently reliable number.
• FIG. 2 shows a micrograph taken at high magnification with an electron transmission electron microscope according to the invention, namely the sample L of Table 2. It is noted the presence of precipitates 1 of ⁇ Nb and also Zr (Nb, Fe) 2 (2, 3) intermetallic compounds typical of the invention.
• the presence of Fe is also in the favorable direction, for the alloys at about 3% Nb and 1% Sn, easier recrystallization, thus a better capacity for the alloy to be transformed.
• oxygen at 600 to 1800 ppm
• sulfur at levels of 10 to 400 ppm
• They can be added, in a conventional manner, as disclosed in documents FR-A-2 219 978 for oxygen and EP-AO 802 264 for sulfur, for the purpose of refining the mechanical properties of the alloy, such as than creep resistance.
• Sn apparently has no marked effect on sensitivity to shadow corrosion. Its content must therefore be chosen in order to obtain a compromise between the resistance to uniform corrosion and nodular corrosion that it tends to degrade (but not the corrosion in a lithiated medium), and the mechanical properties that it tends to to improve. This compromise varies depending on the applications. In general, the Sn content is maintained between 0.2 and 1.7%, preferably between 0.25 and 1.7%.
• the Nb content if it is too high (greater than 4.5%), tends to harden the alloy and slow the recrystallization, especially as the Fe content is high and that, therefore, precipitates containing both Fe and Nb are more numerous and tend to anchor dislocations and grain boundaries.
• the Nb content will therefore be chosen between 0.4 and 4.5%, and also satisfying it with the aforementioned Nb ⁇ 9 x [0.5 - (Fe + Cr + V + Ni)] ratio, better Nb ⁇ 9 x [0.4 - (Fe + Cr + V + Ni)].
• Shadow corrosion sensitivity tests were also performed on alloy tubes in the relaxed state. Their composition, the treatments they have undergone and the results of sensitivity to shadow corrosion are shown in Table 3.
• Table 3 compositions, treatments and performances of the relaxed samples tested in shadow corrosion.
• the annealing 2 hours at 575 0 C performed after the last cold rolling is the final annealing within the meaning of the invention.
• the sample W is not in accordance with the invention, in that it does not contain Sn. But it makes it possible to verify that Sn has no marked effect on the shadow corrosion, at least in combination with the other elements present at the recommended contents.
• the excellent performance of the REB fuel assembly components according to the invention makes it possible to use them in conditions where the shadow corrosion is likely to be particularly high, for example when noble metals and / or iron and / or Hydrogen is dissolved in a large amount in the reactor water.

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• Chemical & Material Sciences (AREA)
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• Physics & Mathematics (AREA)
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• Crystallography & Structural Chemistry (AREA)
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• High Energy & Nuclear Physics (AREA)
• General Engineering & Computer Science (AREA)
• Heat Treatment Of Steel (AREA)
• Monitoring And Testing Of Nuclear Reactors (AREA)

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• 2006
  • 2006-12-01 FR FR0610546A patent/FR2909388B1/fr not_active Expired - Fee Related
• 2007
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