Tubular component of a pressurized water nuclear reactor and method for manufacturing said component

Abstract

The invention provides a tubular component of a pressurized water nuclear reactor having the following composition by weight: 0.8% ≤ Nb ≤ 2.8%; traces ≤ Sn ≤ 0.65%; 0.015% ≤ Fe ≤ 0.40%; preferably 0.020% ≤ Fe ≤ 0.35%; traces ≤ C ≤ 100 ppm; 600 ppm ≤ O ≤ 2300 ppm; preferably 900 ppm ≤ O ≤ 1800 ppm; 5 ppm ≤ S ≤ 100 ppm; preferably 8 ppm ≤ S ≤ 35 ppm; traces ≤ Cr + V + Mo + Cu ≤ 0.35%; traces ≤ Hf ≤ 100 ppm; F ≤ 1 ppm; the balance being zirconium and manufacturing impurities, and having an outer surface with a roughness Ra of no more than 0.5 μm after final mechanical polishing, characterized in that it has an outer surface with a roughness Rsk in absolute value of less than or equal to 1 and a roughness Rku of less than or equal to 10; and a method for obtaining said component.

Description

Technical Field

[0001] This invention relates to the field of manufacturing zirconium alloy components for pressurized water nuclear reactors, particularly structural tubes and cladding tubes for fuel rods in nuclear fuel assemblies. Background Technology

[0002] Various zirconium alloys—class III or IV (i.e., possessing two or three main alloying elements in addition to Zr)—have compositions that can be combined with specific thermomechanical treatments and / or finishing methods to create products with enhanced corrosion resistance, providing users with options for manufacturing pressurized water nuclear reactor components. These alloys are particularly used for structural components of fuel pellets in nuclear fuel assemblies (grids, conduits, and applicable instrumentation lines) and cladding tubes, also known as sheaths. These alloys must be able to withstand the various forms of corrosion that may occur during normal reactor operation, as well as good corrosion resistance under accident conditions, particularly in the case of a Loss of Coolant Accident (LOCA), i.e., at very high temperatures (above 900°C) and in a steam atmosphere.

[0003] It is well known that the high surface roughness of nuclear fuel assembly tubes reduces their corrosion resistance in reactors.

[0004] For example, document WO-A-2006 / 027436 describes a final mechanical polishing step for the outer surface of a cladding tube, which, in conjunction with a zirconium alloy composition, achieves a surface roughness Ra less than or equal to 0.5 μm. Besides zirconium and impurities generated during manufacturing, the zirconium alloy composition contains 0.8–2.8% Nb, 0.015–0.40% Fe, 600–2300 ppm O, 5–100 ppm S, and optionally trace amounts of Sn, Cr, or V. The document also describes a method for producing the tube that improves its corrosion resistance at high temperatures, particularly at temperatures where LOCA (Local Oxide Corrosion Acquisition) may occur. The document further requires limiting the Hf and F content of the alloy as much as possible, and the final mechanical polishing step allows for the removal of any trace amounts of F generated during acid pickling in a fluorinated bath, while simultaneously achieving the desired surface roughness Ra.

[0005] For example, the performance of zirconium alloy tubes under LOCA conditions was evaluated by subjecting tube samples to oxidation tests in a water vapor environment at 1000°C. For instance, the article "AREVA NP" presented at the LWR Fuel Conference (TopFuel2016) on Enhancing Safety and Performance in September 2016... This test is described in "Cladding Benefits for Proposed USNRC RIA and LOCA Requirements".

[0006] Corrosion kinetics, measured by the mass gain of the sample resulting from oxidation, is initially parabolic. Accelerated corrosion and / or large amounts of hydrogen uptake (“hydride cracking”) (typically exceeding 200 ppm) lead to a deterioration in kinetics after a certain test duration (often referred to in the art as “detachment”).

[0007] Hydride cracking of zirconium alloy components reduces their mechanical and microstructural properties and can lead to overall or partial deformation or fracture, for example, due to cracking, followed by localized bursting in the case of the cladding tube of nuclear fuel rods.

[0008] In absolute terms, the pipes recommended in document WO-A-2006 / 027436 have good corrosion resistance under accident conditions, with detachment occurring after approximately 5000 seconds, compared to approximately 1800 seconds for more commonly used alloys.

[0009] However, if the decoupling process can be delayed to a greater extent, this represents a fundamental advantage for nuclear reactor safety in the event of an accident. Summary of the Invention

[0010] The object of this invention is to provide a method that allows for the reliable acquisition of tubes for pressurized water reactor nuclear fuel assemblies, particularly under accident conditions exposed to very high temperatures (such as LOCA), which have better corrosion resistance and resistance to hydride cracking compared to known alloys, especially M5 alloy.

[0011] Therefore, the present invention relates to a tubular component for a pressurized water nuclear reactor, comprising the following components by weight:

[0012] 0.8% ≤ Nb ≤ 2.8%;

[0013] Trace amounts ≤ Sn ≤ 0.65%;

[0014] 0.015% ≤ Fe ≤ 0.40%; preferably 0.020% ≤ Fe ≤ 0.35%;

[0015] Trace levels ≤ C ≤ 100 ppm;

[0016] 600ppm≤O≤2300ppm; preferably 900ppm≤O≤1800ppm;

[0017] 5ppm≤S≤100ppm; preferably 8ppm≤S≤35ppm;

[0018] Trace amounts ≤ Cr + V + Mo + Cu ≤ 0.35%;

[0019] Trace levels ≤ Hf ≤ 100 ppm;

[0020] F≤1ppm;

[0021] The balance is zirconium and impurities generated during manufacturing, and the outer surface obtained after final mechanical polishing has a roughness Ra of less than or equal to 0.5 μm, characterized in that its outer surface has a roughness Rsk of less than or equal to 1 in absolute value and a roughness Rku of less than or equal to 10.

[0022] The outer surface of the component obtained after the final mechanical polishing step can have a roughness Ra of less than or equal to 0.3 μm.

[0023] The outer surface of the component may have a roughness Rsk of less than or equal to 0.75 in absolute value and a roughness Rku of less than or equal to 9.

[0024] The present invention also relates to a method for manufacturing fuel cladding tubes for nuclear reactors, characterized in that:

[0025] Prepare zirconium alloy ingots having the following weight composition:

[0026] *0.8% ≤ Nb ≤ 2.8%;

[0027] *Trace amounts ≤ Sn ≤ 0.65%;

[0028] *0.015% ≤ Fe ≤ 0.40%; preferably 0.020% ≤ Fe ≤ 0.35%;

[0029] *Trace levels ≤ C ≤ 100 ppm;

[0030] *600ppm≤O≤2300ppm; preferably 900ppm≤O≤1800ppm;

[0031] *5ppm≤S≤100ppm; preferably 8ppm≤S≤35ppm;

[0032] *Trace amounts ≤ Cr + V + Mo + Cu ≤ 0.35%;

[0033] *Trace levels ≤ Hf ≤ 100ppm;

[0034] *F≤1ppm;

[0035] The balance consists of zirconium and impurities generated during manufacturing;

[0036] The ingot is forged, optionally followed by quenching, then extrusion and thermomechanical treatment, including cold rolling separated by intermediate annealing, wherein all intermediate annealing is carried out at temperatures below the α→α+β transformation temperature of the alloy, and finally stress-relief, semi-recrystallization or recrystallization annealing is performed, and finally a tube is manufactured.

[0037] Optionally, the outer surface of the tube may be chemically pickled and / or electropolished and / or initially mechanically polished; and

[0038] The outer surface is then subjected to final mechanical polishing to achieve a roughness Ra of less than or equal to 0.5 μm, a roughness Rsk of less than or equal to 1 in absolute value, and a roughness Rku of less than or equal to 10.

[0039] Intermediate annealing can be carried out at a temperature not exceeding 600°C.

[0040] The final mechanical polishing step can be performed using precision rollers.

[0041] The final mechanical polishing step can be performed by abrasive polishing paste.

[0042] Final mechanical polishing can be performed by the following methods: honing, applying polishing paste, or grinding with a polishing felt or polishing pad impregnated with polishing paste.

[0043] The final mechanical polishing step can be performed by roller burnishing.

[0044] As already clearly stated, the present invention includes the production of tubular components, particularly structural tubes, i.e., conduits or instrumentation tubes, for pressurized water nuclear reactors, made of a Zr-Nb alloy containing 0.8–2.8% Nb, with small amounts of Fe and S, and Sn, Cr, V, Mo, and / or Cu, and possibly a relatively high O content, prepared by the method described in WO-A-2006 / 027436, with the possible exception of post-forging quenching, which is not absolutely necessary for Zr-Nb alloys. After sufficient heat treatment to impart the desired mechanical properties, preferably a chemical pickling step (usually performed before the final heat treatment), the outer surface of the tube is polished using a method that allows for specific surface polishing, defined not only by its Ra value but also by the Rsk and Rku values ​​obtained as a result of a mechanical polishing operation (“final mechanical polishing”). These requirements are to ensure that, under accident conditions, particularly in the event of LOCA, the outer surface of the tube has a morphology as unaffected as possible by corrosion and / or hydride decomposition.

[0045] Other polishing operations are not necessarily mechanical and can be performed before the final mechanical polishing step, which yields the roughness type according to the invention, thus constituting the main steps of the method according to the invention. In the following text, "initial polishing" refers to a polishing step that constitutes only an intermediate step in obtaining the desired roughness, while "final polishing" refers to the final polishing step that obtains the desired roughness.

[0046] It goes without saying that if a single mechanical polishing operation is performed in the surface treatment of the product according to the present invention, this operation constitutes a "final mechanical polishing" step. Other production steps, such as inspection, degreasing, etc., can be performed after this final mechanical polishing step, but these other steps must not cause surface contamination, especially halogen contamination, or reduce its roughness.

[0047] Based on its composition, especially the alloys produced by Framatome, the brand name is M5 or M5. Framatome This falls within the scope of the present invention. Attached Figure Description

[0048] The invention can be better understood by referring to the following directions and the following figures.

[0049] Figure 1 The Zr-Nb alloy (M5) conforming to the composition and Ra requirements of WO-A-2006 / 027436 is shown. Framatome The mass gain of the reference sample is a function of the square root of the time taken at 1000°C in a water vapor environment;

[0050] Figure 2 The diagram shows the change in hydrogen content of the same reference sample as a function of the square root of the time taken at 1000°C in a water vapor environment;

[0051] Figure 3 The mass gain and hydrogen content of the same reference sample and the sample according to the invention are shown as a function of the square root of the time taken at a temperature of 1000°C in a water vapor environment. Detailed Implementation

[0052] The performance of the tube in the aforementioned LOCA test depends on the roughness of its outer surface, most commonly described solely by the Ra parameter as defined in standard NFEN ISO 4287. Over a given evaluation length (“reference length”), this corresponds to the arithmetic mean difference of the surface roughness profiles, which includes protrusions and cavities at varying heights relative to the mean line of the roughness profile. Ra is an evaluation of the average of the absolute values ​​of these heights. Ra is calculated using the following formula:

[0053]

[0054] Here, lr is the reference length of the roughness curve, and Z(x) is the ordinate (or height) of the roughness curve with respect to the x-coordinate on the average line of the roughness curve. It should be noted that the origin of the height is the average value of the roughness curve; therefore, the integral of Z(x) from 0 to lr is zero.

[0055] However, in fact, the inventors’ experience has shown that the parameter Ra is insufficient to fine-tune the performance of the alloy under conditions that may cause severe oxidation and / or hydride cracking of the tube, and in particular, insufficient to explain the very good performance observed when its outer surface is treated according to the invention.

[0056] The inventors have discovered that two parameters defined in the standard NF EN ISO 4287 are also particularly important for solving the proposed problem. These parameters are Rsk (“skewness”) and Rku (“kurtosis”).

[0057] The parameter Rsk defines the asymmetry of the evaluated roughness profile. It explains the asymmetric height distribution relative to the mean line of the roughness profile and is defined based on the substrate length lr. It provides information about the morphology of the surface state. A zero Rsk value corresponds to a normal (Gaussian) distribution of height around the mean line. A positive Rsk value corresponds to a “hollow” curve, where the height distribution is skewed towards higher values, for example, in the case of a smooth surface dominated by protrusions. A negative Rsk value corresponds to a “complete” curve, where the height distribution decreases towards higher values, for example, in the case of a smooth surface dominated by cavities. Rsk is calculated using the following formula:

[0058]

[0059] Where Rq is the mean quadratic difference of the curves evaluated over the baseline length lr, according to:

[0060]

[0061] Rq corresponds to the quadratic average of the heights along the base length lr.

[0062] The parameter Rku defines the kurtosis of the roughness curve being evaluated, i.e., the width of the height distribution relative to the mean line of the roughness curve, based on the reference length lr. It provides information about the morphology of the surface state. A Rku value equal to 3 corresponds to a normal (Gaussian) height distribution. An Rku value greater than 3 corresponds to a “dense” curve relative to a normal distribution, i.e., mainly having low absolute heights relative to the mean line of the roughness curve. An Rku value less than 3 corresponds to a “staggered” curve relative to a normal distribution, i.e., a large proportion of the height deviates from the mean line, for example, the height is evenly distributed throughout the time span. Rku is calculated using the following formula:

[0063]

[0064] In particular, Rsk and Rku are used in tribology to evaluate the contact, wear resistance and lubrication properties of the tested surface, but they are not used to evaluate the corrosion resistance of the surface.

[0065] The inventors have discovered that, under identical conditions, if the parameters Rsk (skewness) and Rku (kurtosis) of the outer surface of the tube meet certain criteria, then under accident conditions, especially in the case of LOCA (Local Occurrence of Caution), the oxidation kinetics remain parabolic during the test. Otherwise, oxidation accelerates during the test.

[0066] Macroscopic surface confinement caused solely by oxidation cannot explain the performance differences observed in delayed or non-detached tube samples during testing. The inventors hypothesize that confinement may also have a localized effect on oxidation at the level of surface roughness. Surfaces with numerous prominent protrusions may increase the risk of oxide degradation perpendicular to the oxide-metal interface and locally accelerate oxidation at the locations of the protrusions.

[0067] The required surface is a polished surface (Ra≤0.5μm, preferably≤0.3μm) with a substantially symmetrical roughness distribution, i.e., the skewness coefficient Rsk in absolute value is close to zero: |Rsk|≤1, and preferably |Rsk|≤0.75, and there are no obvious protrusions or cavities, which means that the kurtosis coefficient Rku is less than or equal to 10, preferably less than or equal to 9.

[0068] The observed improved performance can be reproduced by performing careful mechanical surface finishing, giving the outer surface of the tube the desired roughness.

[0069] Since this finishing process can be achieved through various methods, it will not be described in detail here.

[0070] One possible way to achieve this finish involves continuous polishing of the tube with increasingly larger SiC carbide rolls (e.g., up to 240 mesh or larger according to ISO 8486-2), which constitute the initial mechanical polishing steps, and finally finished with finishing rolls, such as rolling finishing wheels, radial brushes, or rotating discs with extremely fine grains, such as Scotch Brite. TM The finishing rolls undergo a final polishing step. This finishing process yields tubes with at least delayed detachment, i.e., detachment occurring after more than 10,000 seconds. The composition and preparation method of this alloy prior to the final polishing step are substantially consistent with those described in WO-A-2006 / 027436.

[0071] The initial polishing step may also include the use of non-mechanical polishing (such as chemical or electrolytic polishing) alone or in combination with mechanical polishing. The final mechanical polishing operation is then performed after the initial polishing step.

[0072] If experience shows that a single mechanical polishing step can give the product the desired roughness, then only a single mechanical polishing step can be performed. This is called the "final mechanical polishing" step because it does constitute the last polishing operation performed on the product surface.

[0073] The mechanical polishing steps and the means used for these steps, especially the final mechanical polishing step, can be determined by the supplier of such equipment according to specifications, which typically include the desired final roughness and its evaluation methods. This also specifies that potentially harmful or difficult-to-remove polishing materials should be avoided, particularly those listed in applicable documents such as AFCEN (Association of...). This refers to the materials in RCC-C (Design and Construction Rules for Fuel Assemblies in PWR Nuclear Power Plants) published by the French Association for the Supervision of Design, Construction and Operation of Nuclear Boiler Equipment.

[0074] Those skilled in the art can determine, experimentally, the exact parameters of the mechanical polishing process that allow for the desired roughness type through a standard test series, including initial and final parameters (if applicable). For this purpose, it is necessary to relate the polishing methods used and their operating parameters to the composition of the tube and the thermomechanical treatment it has undergone, as well as any chemical pickling and / or electropolishing prior to the mechanical polishing step. In particular, all other things being equal, these characteristics affect the hardness and condition of the tube's outer surface prior to the mechanical polishing step, and also influence the outcome of the final mechanical polishing step.

[0075] Therefore, the method for obtaining a fuel sheath using a surface-finished tube according to the present invention is applicable to zirconium alloy tubes that may contain impurities generated during manufacturing, based on the reasons described in WO-A-2006 / 027436, and their weight composition and preparation method are as follows:

[0076] Its Nb content ranges from 0.8% to 2.8%.

[0077] Its Sn content ranges from trace amounts (in other words, the content is equal to or slightly above zero, and the relevant element was not intentionally added simply because of the alloy's manufacture) to 0.65%. The normal detection limit for this element is approximately 30 ppm, and it should be understood that the Sn content may decrease to the values ​​corresponding to only trace amounts as defined above (and therefore include values ​​that are strictly zero).

[0078] Its Fe content is at least 0.015%, preferably at least 0.02%, and not more than 0.40%, preferably not more than 0.35%.

[0079] Cr, V, Cu or Mo may be present selectively to supplement or replace some of the Fe, but their total content shall not exceed 0.35%.

[0080] The carbon content of the alloy must not exceed 100 ppm.

[0081] The alloy contains 600–2300 ppm, preferably 900–1800 ppm, of oxygen.

[0082] The sulfur content must be maintained at 5–100 ppm, preferably 8–35 ppm.

[0083] The presence of hydrogen sulfide (Hf) in the alloy should be avoided. The Hf content should be very low, ensuring that the final alloy contains no more than 100 ppm Hf, preferably no more than 75 ppm Hf. Special care should be taken to separate Hf during the preparation of the Zr sponge used to manufacture the alloy.

[0084] Any F in the alloy should be limited to no more than 1 ppm.

[0085] Another very important requirement is that there are no fluorides on the alloy surface.

[0086] As noted in WO-A-2006 / 027436, in order to obtain structural tubes or cladding tubes with improved corrosion resistance and resistance to hydride cracking under LOCA conditions, the use of surface treatment methods that induce free radical elimination of fluorides is absolutely essential. From this perspective, mechanical polishing after chemical pickling is the most suitable method for preparing the tube surface before use.

[0087] Furthermore, there is a risk that the highly precise requirements for the surface roughness characteristics of the final tubular product, not limited to the maximum Ra value, will not be easily met by chemical polishing. Therefore, it is necessary to perform the final preparation step of the tube surface by at least mechanical polishing, for example, through the methods described above, with relevant examples provided below.

[0088] The method for preparing tubes from ingots produced by the manufacture of alloys includes forging, followed optionally by quenching, spinning, and cold rolling steps separated by intermediate annealing steps. All annealing is performed at temperatures below the α→α+β transformation temperature of the alloy, and thus generally below 600°C. These relatively low-temperature heat treatments result in good corrosion resistance under normal operating conditions and include a final stress-relief annealing, semi-recrystallization, or recrystallization step, depending on the desired microstructure of the final product. This may vary for the various categories and applications of tubes falling within the scope of this invention. For example, recrystallization is preferable if good compressive strength is desired.

[0089] Generally, in industrial practice, it is best to perform 3, 4 or 5 cold rolling passes separated by intermediate annealing steps, with each intermediate annealing step being carried out at a temperature of 500 to 580°C, for example, 1 hour at 500°C and 12 hours or 24 hours at 580°C.

[0090] Another necessary condition for solving the problem is that the outer surface of the tube is given a very low roughness Ra, less than or equal to 0.5 μm, preferably less than 0.3 μm.

[0091] WO-A-2006 / 027436 recommends achieving such a low surface roughness Ra. However, according to the present invention, two additional conditions are required to further optimize the LOCA performance of the alloy:

[0092] The Rsk value, in absolute terms, is less than or equal to 1 (therefore, it is -1 to +1), preferably less than or equal to 0.75 (therefore, it is -0.75 to +0.75); and

[0093] The Rku value should be less than or equal to 10, preferably less than 9.

[0094] This invention attempts to obtain unobserved data including M5. Framatome The time required for the Zr-Nb alloy tube to detach from the alloy is significantly extended.

[0095] Therefore, in particular, clad tube samples (9.5 mm in diameter and 0.57 mm in thickness) obtained through various types of final polishing steps discussed in detail below were tested for different compositions and outer surface roughness configurations.

[0096] The Zr used to manufacture the tubes is obtained by conventional methods in the form of sponge or low-Hf electrolytic crystals (less than 100 ppm in the alloy). After thorough smelting to remove any residual fluorine (F < 1 ppm in the finished tube), the ingot is modified using conventional methods to obtain cladding tubes, conduits, or instrumentation tubes for pressurized water nuclear reactors: forging, optional quenching, 3–5 passes of pilgering, with an intermediate annealing step at a temperature below the α→α+β transformation temperature. Except for the absence of a systematic quenching process, the method is identical to that described in WO-A-2006 / 027436, particularly in terms of the optional pickling and internal polishing steps.

[0097] Combination Figure 1 and 2 and / or Figure 3 Table 1 shows these M5s Framatome The composition of eight samples of alloy tubes, the manufacturing variants used, and their mass gain and hydrogen content. All tubes were in a recrystallized state and pickled before the first heat treatment.

[0098] Figure 1 and Figure 2 M5 is shown to meet the composition requirements of WO-A-2006 / 027436. Framatome The performance of the reference sample of the tube, with the following composition in a water vapor environment at 1000°C (oxidation test as described in TopFuel 2016 cited above): Zr; 1.02% Nb; 200–1000 ppm Fe; 1000–1500 ppm O; 5–35 ppm S; and less than 1 ppm F, with a roughness Ra less than 0.5, but inconsistent with the present invention in the following respects: the roughness Rsk value is in the range of [-1.65; -1] or [+1; +1.48] in some cases, and / or the roughness Rku value is in the range of [10; 15.55] in some cases.

[0099] Figure 1 The diagram shows the mass gain (due to oxidation) as a function of the square root of the residence time in the environment, and Figure 2 The graph shows the change in hydrogen content as a function of the square root of the residence time in the relevant environment (Note: Since the square root of the residence time is shown on the horizontal axis, the curve is significantly flatter compared to the case where the horizontal axis represents the residence time).

[0100] According to the standard, the reference sample exhibited good corrosion resistance and resistance to hydride cracking under accident conditions, but detachment occurred after approximately 5000 seconds, leading to oxidation. Figure 1 ) and hydride cracking ( Figure 2The rapid acceleration of ) is shown by the locations of the experimental points, which are always at the mass gain (before the separation occurs). Figure 1 ) and H content ( Figure 2 Above the extension of the regression line (dashed line). Typically, as... Figure 1 and Figure 2 As shown, the fuel jacket is subjected to LOCA for 1800 seconds, but the jacket must be able to withstand longer exposure times.

[0101] For the sake of simplicity, Table 1 shows only the four reference samples in the test: samples 1, 4, 5 and 7.

[0102] For all samples in Table 1, the nominal composition of the major alloying elements is indicated. They all contain 1.0% Nb and 0.02%–0.07% Fe. They all contain less than 100 ppm of C and Hf, and less than 1 ppm of fluorine. All unmentioned elements are present at most in trace amounts.

[0103] The tubes of samples 1 to 8 all underwent four rolling processes and were intermediately annealed at 580°C for 2 hours.

[0104] Table 1 also shows the results of Ra, Rku, and Rsk roughness measurements of these clad tubes using a Mitutoyo SV2000 roughness meter. These roughness values ​​were obtained through various finishing processes. Measurements were performed according to applicable standards. For example, for polishing marks tangential to the clad tube, measurements were performed on a tube generator with a length of 4 mm and a cutoff of 0.8 mm. Three measurements were performed for each tube; the mean and standard deviation of these measurements are shown in Table 1.

[0105] [Table 1]

[0106]

[0107] Table 1: Composition, manufacturing variants, mass gain, hydrogen content, and roughness of tubes 1–8

[0108] Tube 1 is a reference tube (its absolute value of Rsk is too high), and its roughness was measured after polishing with silicon carbide rolls, the particle size of which was increased (initial mechanical polishing) to 240 (final mechanical polishing). Its roughness Ra is essentially equal to that of tube 2 from the same batch (which itself is consistent with the present invention in all respects), which underwent the same polishing steps, with the particle size continuously increased to 240 (initial mechanical polishing) using silicon carbide rolls, followed by final mechanical polishing with finish rolls.

[0109] Tube 3 (consistent with the present invention), from a different batch than tubes 1 and 2, has a higher Fe content and underwent the same polishing steps as tube 2, except that the initial mechanical polishing was performed with SiC strips of increasing particle size (up to a particle size of 240) instead of polishing with silicon carbide rolls of increasing particle size. Tube 4, from the same batch, underwent the same polishing steps as tube 3, using SiC strips of increasing particle size (initial polishing) until the particle size reached 240 (final mechanical polishing). Unlike tube 3, it did not undergo the final polishing step with finishing rolls, and it is inconsistent with the present invention because its Rsk value is too high.

[0110] Tube 5, from another batch with a higher iron content, bypassed the initial mechanical polishing step of rollers or belts, and instead underwent sandblasting with increasingly smaller SiC particles. It then underwent final mechanical polishing, sandblasting with SiC 240 particles. Tube 6, from the same batch, received an additional polishing with a polishing pad impregnated with polishing paste (colloidal silicon in this example). Tube 5 had an excessively high Rku, while tube 6 conformed to the present invention.

[0111] To confirm the effect of the initial polishing step, a batch of tubes 7 and 8 with medium iron content was initially polished using silicon carbide rolls with progressively larger grain sizes, stopping at a grain size of 120. As expected, to obtain the roughness value conforming to the present invention, the final polishing time of tube 8 with finishing rolls must be extended, but this is possible. Therefore, the roughness value conforming to the present invention depends neither entirely on the initial polishing step nor on the characteristics of the instrument used for the final mechanical polishing step. Those skilled in the art can experimentally determine the conditions of the final mechanical polishing step (the characteristics and usage parameters of the polishing tools, plus the polishing time) to obtain the roughness conforming to the present invention.

[0112] The Rsk value of tube 1 is too high, even though its Rku value is consistent with the present invention, and its Ra value is consistent with the present invention and substantially equal to that of tube 2. The Rsk and Rku values ​​of tube 7 are too high, even though its Ra value is consistent with the present invention and equal to that of tube 8. This clearly demonstrates that the three representative values ​​of tube roughness are not strongly correlated, and the final mechanical polishing step is of particular importance for obtaining an accurate roughness configuration conforming to the present invention.

[0113] The performance of tubes 2, 3, 6, and 8 in the LOCA test in Table 1 is as follows: Figure 3 As shown. For ease of comparison, Figure 3 It is also shown in Figure 1 and Figure 2 The results for the sample (shaded).

[0114] For two samples in the same tube as Sample 2, without any detachment, the tests were extended to 30,000 and 35,000 seconds respectively. The corresponding points are as follows: Figure 3 As shown.

[0115] Figure 3 The results also include those obtained from tubes 11-19 in Table 2 below, with their composition and roughness values ​​described. These tubes differ from those in Table 1, having higher alloy element content, but their composition still meets the requirements of this invention. All tested tubes contained less than 100 ppm of C and Hf, and less than 1 ppm of fluorine. All unmentioned elements were present at most in trace amounts.

[0116]

[0117] Table 2: Composition, manufacturing variants, mass gain, hydrogen content, and roughness of tubes 11–19

[0118] Tubes 11, 13, and 17 underwent initial mechanical polishing within the conventional range using SiC rolls with a maximum particle size of 240; tubes 14 and 15 underwent initial mechanical polishing using SiC strips with a maximum particle size of 240; and tubes 12, 16, and 19 underwent initial chemical polishing, while tube 18 did not undergo any initial polishing step. The final polishing steps differed, as shown in Table 2: chemical or mechanical polishing was performed by various means: fine rolling, grinding with polishing paste (colloidal silicon, synthetic diamond, metal oxides of Ti or Zr), and roll polishing. For tube 19, the final mechanical polishing step was polishing with 240-particle SiC rolls, resulting in an Rku value that was too high and inconsistent with the present invention. For tube 17, the final chemical polishing did not involve final mechanical polishing, and an Rku value consistent with the present invention could not be obtained. The tested polishing paste methods included honing tube 13 with polishing paste containing synthetic diamond and grinding tube 16 with a felt impregnated with a mixture of metal oxides (Ti and Zr). Other polishing methods can be used, such as polishing by extrusion of polishing paste, or without polishing paste, as in the case of tube 14 (roll polishing). Tube 8 is polished directly with a finishing roll after final heat treatment. As expected, to obtain the Ra, Rsk, and Rku characteristics required by this invention, the final mechanical polishing time with a finishing roll must be significantly extended; therefore, this method is not suitable for industrial applications. Examples in Table 3 show that the roughness values ​​conforming to this invention do not depend on the presence or nature (mechanical or non-mechanical) of the initial polishing, and the final mechanical polishing step can be performed in various ways.

[0119] Figure 3 It has been shown that, in terms of composition and surface roughness, the tube manufactured according to the present invention does not exhibit delamination before exposure to water vapor at 1000°C for a duration significantly longer than 5000 seconds for similar alloys known in the prior art; see also Figure 3 The gray and black dots located above the regression line correspond to... Figure 1 and 2 The reference samples and samples 17 and 19 in Table 2 are used. In particular, the mass gain (corresponding to corrosion acceleration) and hydride cracking gradient (hydrogen recovery exceeding 200 ppm) are significantly delayed after 10,000 seconds. No very significant differences in results are observed between the various methods of performing the final polishing step.

[0120] Although it is known that high-temperature oxidation resistance depends on the surface condition, especially the absence of fluorine contamination (e.g., contamination from pickling in a fluorinated nitrate bath) and a controlled roughness Ra value, it is unknown that the accelerated kinetics of oxidation and hydride cracking of the tube under LOCA conditions could be further delayed if other roughness parameters, namely Rsk and Rku, which are related to the peak shape and are below the threshold, are wisely chosen.

[0121] The parameters Rsk and Rsku correspond to the analysis of roughness measurements performed using the 2D curve measurement method, i.e., analyzing the geometric difference in surface condition compared to the average line. In the case of 3D curve measurements, equivalent parameters Ssk and Sku can be used, or the analysis can be performed on one or more generators instead of the entire surface.

Claims

1. A tubular component for a pressurized water nuclear reactor, comprising the following components by weight: 0.8% ≤ Nb ≤ 2.8%; Trace amounts ≤ Sn ≤ 0.65%; 0.015% ≤ Fe ≤ 0.40%; Trace levels ≤ C ≤ 100 ppm; 600ppm≤O≤2300ppm; 5ppm≤S≤100ppm; Trace amounts ≤ Cr + V + Mo + Cu ≤ 0.35%; Trace levels ≤ Hf ≤ 100 ppm; F≤1ppm; The balance consists of zirconium and impurities generated during manufacturing, and the outer surface obtained after final mechanical polishing has a roughness Ra of less than or equal to 0.5 μm. It is characterized by having an absolute roughness Rsk of less than or equal to 1 and a roughness Rku of less than or equal to 10. Specifically, when the tubular component is subjected to vapor corrosion at 1000°C and atmospheric pressure, the tubular component will not detach for at least 10,000 seconds.

2. The tubular component for a pressurized water nuclear reactor according to claim 1, characterized in that, The outer surface obtained after the final mechanical polishing step has a roughness Ra of less than or equal to 0.3 μm.

3. The tubular component for a pressurized water nuclear reactor according to claim 1 or 2, characterized in that, Its outer surface has a roughness Rsk of less than or equal to 0.75 in absolute value and a roughness Rku of less than or equal to 9.

4. A method for manufacturing fuel cladding tubes for nuclear reactors, characterized in that: Prepare zirconium alloy ingots having the following composition by weight: *0.8% ≤ Nb ≤ 2.8%; *Trace amounts ≤ Sn ≤ 0.65%; *0.015% ≤ Fe ≤ 0.40%; *Trace levels ≤ C ≤ 100 ppm; *600ppm≤O≤2300ppm; *5ppm≤S≤100ppm; *Trace amounts ≤ Cr + V + Mo + Cu ≤ 0.35%; *Trace levels ≤ Hf ≤ 100ppm; *F≤1ppm; The balance consists of zirconium and impurities generated during manufacturing; The ingot is forged, optionally followed by quenching, and then extruded and thermomechanically treated, including cold rolling separated by intermediate annealing, wherein all intermediate annealing is performed below the α→α of the alloy. + The process is carried out at the β transformation temperature, followed by stress relief, semi-recrystallization or recrystallization annealing, and finally the tube is manufactured. Optionally, the outer surface of the tube may be chemically pickled and / or electropolished and / or initially mechanically polished; and The outer surface is then subjected to final mechanical polishing to achieve a roughness Ra of less than or equal to 0.5 μm, a roughness Rsk of less than or equal to 1 in absolute value, and a roughness Rku of less than or equal to 10. The fuel cladding tube is configured such that when the fuel cladding tube is subjected to vapor corrosion at 1000°C and atmospheric pressure, detachment of the fuel cladding tube will not occur for at least 10,000 seconds.

5. The method according to claim 4, characterized in that, The intermediate annealing is performed at a temperature of 600°C or less.

6. The method according to claim 4 or 5, characterized in that, The final mechanical polishing is performed using precision rollers.

7. The method according to claim 4, characterized in that, The final mechanical polishing is performed by grinding with polishing paste.

8. The method according to claim 7, characterized in that, The final mechanical polishing is performed by the following methods: honing, applying polishing paste, and grinding with a polishing felt or polishing pad impregnated with polishing paste.

9. The method according to claim 4 or 5, characterized in that, The final mechanical polishing is performed by roller polishing.

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