JP2019502106A - Steam generator and corresponding manufacturing and use method - Google Patents

Abstract

The steam generator comprises at least one element (1) made from a nickel alloy, which alloy has the following weight content: Ni greater than 50%, 14% -45% Cr. According to the invention, the element (1) has a weight content of chromium wCr (p), a weight content of carbon wc (p) and a weight content of effective chromium wCr_dispo (p) at a depth p from the inner surface. Where wCr_dispo (p) = wCr (p) −16.61wc (p). The weight content of effective chromium wCr_dispo (p) averaged over the entire thickness of the metal surface layer from the inner surface is greater than zero.

Description

  The present invention generally relates to nickel-based alloy elements including reactor steam generator tubes.

More particularly, the present invention, in a first aspect, is a steam generator for a pressurized water reactor,
An enclosure in which a water chamber divided into an upstream compartment and a downstream compartment is delimited, wherein the upstream compartment is designed to be in fluid communication with the reactor vessel outlet, the downstream compartment being a reactor vessel An enclosure designed to be in fluid communication with an inlet of the
At least one element, each element being a tube or plate open through the upstream end into the upstream compartment and through the downstream end opposite the upstream end into the downstream compartment Each element is made from a nickel-based alloy and the alloy has the following mass content:
・ Ni exceeding 50%,
14% to 45% Cr
And a steam generator of the type comprising an element.

  The primary liquid circulates inside the tube and transfers its heat to the secondary liquid. The primary liquid then passes inside the reactor core where the temperature rises before being redirected to the steam generator. The plate comes into contact with the primary liquid.

  In some reactors, the inner surface of the tube constitutes about 75% of the inner surface of the primary circuit.

It is known that the main proportion of dose rate around the primary circuit is from cobalt, more specifically from the radioisotopes of Co-60 and Co-58. These isotopes are formed by the activation of nickel in the core according to the following mechanism.
Ni-58 + 1n → Co-58 + p
Co-58 + 1n → Co-60 + γ

  In pressurized water reactors, the majority of nickel comes from the steam generator tubes. It is released into the primary liquid and drawn into the core by the primary liquid.

  In a pressurized water reactor, the primary liquid, also called the primary medium, is a solution whose main components are water, boric acid and lithium in order to obtain a pH close to the temperature neutral range. During the power generation phase, the temperature of the primary medium is close to 300 ° C. (generally 280-345 ° C.). The primary medium contains dissolved hydrogen. The primary liquid is purified at low temperatures in power plant chemical circuits to limit its concentration of metal cations and colloids resulting from corrosion of circuit materials. In the prior art, the metal cation concentration in the primary medium of an operating power plant is not exactly known, but is close to the published minimum solubility limit concentration.

  In the case of a boiling water reactor, the primary medium is as pure water as possible containing trace amounts of hydrogen and dissolved oxygen, and the temperature is about 290 ° C.

  Subsequently, primary medium is understood to mean any primary water reactor medium during the energy production phase, in keeping with the specifications of the main reactor operator or many research and safety organizations in the field. The solubility of most compounds in primary media has been studied and published in the form of commercial databases, particularly those proposed by OLI Systems.

  In this regard, the present invention aims to provide a steam generator that limits radioactive contamination of the primary circuit.

For this purpose, the present invention provides a steam generator of the type described above,
The element has a surface metal layer with an inner surface covered with an oxide layer on the inside that is intended to be exposed to a liquid, the surface metal layer containing a mass of chromium at a depth p from the inner surface. Rate w _Cr (p), carbon mass content w _c (p) and effective chromium content w _{Cr_dispo} (p), where w _{Cr_dispo} (p) = w _Cr (p) −16.61 w _c (P),
The effective chromium mass content, _{wCr_dispo} (p), averaged over the entire thickness of the surface metal layer from the inner surface relates to a steam generator characterized in that it exceeds zero.

_Prior art tubes have an effective chromium mass content W _{Cr_dispo} (p) of less than 0, especially over the first 200 nanometers of the surface metal layer.

The steam generator may also have one or more of the following features that are considered individually or in any technically feasible combination.
The effective chromium content w _{Cr_dispo} (p) averaged from the inner surface to a thickness of 200 nm is greater than 0,
The effective chromium content w _{Cr_dispo} (p) averaged over a thickness of 10 nm from the inner surface, preferably over a thickness of 1 nm, is greater than 0;
The effective chromium content w _{Cr_dispo} (p) is constantly over 0 from the inner surface through the thickness of the surface metal layer,
The alloy is alloy 690 according to standard UNS N06690 / W No 2.4642,
The chromium content w _Cr (p) averaged over the entire thickness of the surface metal layer from the inner surface is less than 45%,
The chromium content w _Cr (p) increases from the inner surface over the entire thickness of the surface metal layer,
The surface metal layer does not contain particles whose solubility exceeds the solubility of the nickel oxide compound in the primary medium, in particular when it is covered with an oxide layer that does not contain any aluminum-rich oxide particles, and if the element is new, The oxide layer has a thickness of less than 10 nm.

According to a second aspect, the present invention is a method for producing a steam generator having the above characteristics, comprising the following steps:
Producing an untreated element having an inner surface;
Applying a surface treatment to the inner surface of the untreated element, the surface treatment being selected from electropolishing, mechanical or chemical mechanical polishing, chemical cleaning, the untreated element comprising said element after the surface treatment And a method including the steps.

In addition, the method has the following features:
Assembly of the raw elements in the steam generator;
A steam generator upstream and downstream compartments connected to the reactor primary circuit,
The surface treatment is performed by circulating a solution of a predetermined chemical composition in the primary circuit so that the inner surface of the untreated element is in contact with the solution.

  According to a third aspect, the present invention is another method of manufacturing a steam generator having the above characteristics, which is an alternative to the above method, and rolling an ingot using a non-carbonaceous lubricant. Or by continuous casting and then rolling with a non-carbonaceous lubricant.

According to a fourth aspect, the present invention is the use of a surface treatment on an element of a steam generator having the above characteristics,
The surface treatment _{strips the} inner surface until the mass content w _{Cr_dispo of} effective chromium averaged over the entire thickness of the surface metal layer from the inner surface exceeds zero,
Its use is the oxidation when the inner surface is exposed to the primary liquid during normal operation of a pressurized water reactor, and its mass composition tends to lead to the formation of nickel rich filaments and / or It relates to the use, which is intended to limit the direct release of ions or colloids from the region where the filament is liable to be formed into the primary liquid.

  According to a fifth aspect, the present invention is the use of a steam generator having the above characteristics in a pressurized water reactor, wherein the inner surface is exposed to a primary liquid during normal operation of the pressurized water reactor. Limit oxidation of nickel-rich filament elements that tend to lead to formation on the inner surface and / or direct release of ions or colloids directly into the primary liquid from areas where these filaments may form Concerning use intended to do.

  Other features and advantages of the present invention will become apparent from the following detailed description, with reference to the accompanying drawings, not merely for the purpose of information and in any way limiting.

Figure 2 shows a schematic cross-sectional view of the inside of a steam generator tube according to the invention. Figure 2 shows a graph showing the mass content of chromium and the normalized effective chromium content as a function of depth measured on a tube sample. Figure 3 shows a graph showing the normalized mass content of available chromium as a function of depth, measured on other samples. Figure 2 shows a simplified schematic diagram of a reactor primary circuit including a steam generator according to the present invention.

  The present invention will be described in the following by detailing the structure of element 1 which is the tube of the steam generator. Alternatively, the element may be a steam generator plate, one of which has an inner surface exposed to contact the primary liquid.

Element 1 partially shown in FIG. 1 is made from a nickel-based alloy. The alloy has the following mass content on a macroscopic scale:
Ni exceeding 50%,
14% -45% Cr
Have

The alloy preferably has the following mass content on a macroscopic scale:
Ni exceeding 50%,
14% to 45% Cr,
0% to 16% Fe,
It has a balance of impurities resulting from manufacturing.

The alloy preferably has the following mass content:
50% to 75% Ni,
14% to 35% Cr,
0% to 16% Fe,
It further has a balance consisting of impurities resulting from manufacturing.

Typically, the alloy is a 690 alloy according to standard UNS N06690 / W No 2.4642, also known as the INCONEL® alloy 690. On a macroscopic scale, the mass content of the chemical elements that make up this alloy is as follows:
Ni exceeding 58.0%,
27% to 31% Cr,
7% to 11% Fe,
Less than 0.05% carbon,
Less than 0.50% silicon,
Less than 0.50% manganese,
Less than 0.015% sulfur,
Less than 0.50% copper.

  On a microscopic scale, these contents can be varied.

  Such elements are used in pressurized water reactor steam generators. Primary liquid from the core flows inside the tube or in contact with the plate.

  Element 1 has a surface metal layer 7 having an inner surface 5 covered by an oxide layer 3 on the inside intended to be exposed to the primary liquid.

  When element 1 is new, oxide layer 3 typically has a thickness of less than 10 mm, due to the manufacturing method of element 1 described below. This oxide layer typically includes an oxide layer called an outer layer of spinel oxides of iron, chromium and nickel that covers another oxide layer, commonly referred to as a chromium-rich inner oxide layer.

  The thickness of the oxide layer 3 is measured by glow discharge spectroscopic analysis (calibrated by the prior art) from the free outer surface 4 until the oxygen mass content is less than 50% of the oxygen mass content in the free outer surface 4. Defined as the thickness.

  In tubes that have been exposed to the primary environment of the reactor for several years, the oxide layer can have a total thickness of up to several micrometers.

  The surface metal layer 7 has a composition different from the composition of the nickel-based alloy but still close. Below the surface metal layer 7 is the base metal 9 of the tube. Typically, layer 7 has a thickness of about 1 μm (see FIG. 2).

  Accordingly, in the following description, the inner surface 5 of the element 1 is understood to mean the surface formed by the metal interface / inner oxide layer that delimits the internal passage through which the primary liquid flows in the case of a tube.

  The base metal 9 has substantially the mass content of the alloy used to make the tube. The surface metal layer 7 is made primarily of metal rather than metal oxide, but contains non-metal inclusions, ie inclusions that can be up to several hundred nanometers for larger dimensions. It has a mass content slightly different from the mass content of the base metal resulting from the treatment applied during the manufacture of the tube.

  Under some conditions, especially when the liquid medium representing the primary medium of the power plant has a low flow rate and the primary medium is slightly unsaturated (several tens of hours of contact between the material and the primary temperature medium) On the other hand, if the nickel concentration is low, less than one tenth of the lowest solubility limit published in the literature), in the state of the art steam generator tube, in the form of a metal oxide on the oxide layer 3 A filament 11 is formed. Generally, these filaments 11 are mainly composed of nickel. Under the influence of shear resulting from the circulation of the primary liquid in the tube and the heat shrink / expansion cycle, or under the impact of moving objects or, for example, as a result of a decrease in the solubility of nickel as a result of a decrease in pH, The filament 11 is either peeled off from the oxide layer or dissolves during their growth and enters the primary circuit. They therefore constitute one of the Co-58 and Co-60 sources. On the other hand, the mechanism explaining the formation of these filaments has not been published.

  The Applicant has surprisingly determined that the oxidation of the tube material depends on the rate of formation of the filament 11, which is formed especially when the velocity of the primary medium is low and when the primary medium tends to saturate with nickel in ionic form. It has been discovered that a significant percentage of speed can be characterized.

  The Applicant has surprisingly restricted or further prevented the formation of filaments 11 in the primary medium while maintaining a significant effective chromium mass content in the surface metal layer 7, and thus one of the oxidized forms of the metallic material. Has been found to be possible to slow down or eliminate. Maintaining a low carbon content also helps to prevent the formation of the filament 11 under conditions where it can occur. Finally, oxide or carbide particles whose solubility exceeds that of the primary medium nickel oxide (especially aluminum oxide particles when used in place of the native oxide layer) are also subject to the conditions under which this may occur. This contributes to the formation of the filament 11 in the primary environment.

  In the present invention, particularly due to the manufacturing method of element 1, the oxide layer 3 does not contain particles whose solubility exceeds the solubility of the nickel oxide compound in the primary medium, and especially does not contain particles rich in aluminum.

  It is important to emphasize that filaments are not always observable. To obtain filaments, it is preferred to use certain conditions with low convection and low levels of nickel iron, oxygen and dissolved chromium in the primary environment. In a hydrogenated primary medium with a dissolved iron content of less than 1 μg / kg, the oxidation of the alloy is always the origin of filament formation. The rate of oxidation in the filament formation region controls the rate of formation when the filament is formed.

  If there is strong convection, the filaments may dissolve faster than they are formed and / or are pulled away.

  Without being bound by this theory, Applicants have in fact confirmed that the formation of the filament 11 is due to the carbon content present inside or outside the carbide in the surface layer 7 contributing to the formation of the filament. I found out that Furthermore, in this layer, most of the chromium is present in the form of carbides. Chromium incorporated in the carbide does not contribute to the formation of the filament 11 or hardly contributes. Conversely, effective chromium, ie chromium that is not integrated into the carbide, helps to prevent filament formation.

  Thus, the region where the filament is formed is the most convenient region for oxidation and release of the alloy, regardless of its morphology (ion or colloid). These regions are characterized by the presence of low levels of available chromium and / or soluble oxides in the oxide layer.

  The mass content of effective chromium is evaluated by the following method.

In the following, w _Cr (p) is the chromium mass content of the surface metal layer at depth p from the inner surface of the tube, and w _C (p) is the carbon mass content of the surface metal layer at depth p. , W _{Cr_carbure} (p) is the chromium content that may have been integrated into the carbide based on the assumption that the carbide has Cr ₂₃ C ₆ with respect to the stoichiometry of the surface metal layer at depth p, w _{Cr_dispo} (p) is the effective chromium content of the layer surface metal at depth p.

  As shown in FIG. 1, the depth p is taken in the radial direction from the inner surface 5 toward the base metal 9.

  Here, the mass content is defined as the value obtained by dividing the mass of chromium or carbon atoms by the mass of the surface metal layer with respect to the unit volume of a given surface metal layer.

In this case, chromium carbide is considered thermodynamically stable in the type of alloy considered for element 1 having the chemical formula C ₆ Cr ₂₃ . It should be noted that this is the most important hypothesis. There are other forms of carbide that consume less chromium.

The molar masses of carbon and chromium are 12 and 52, respectively. Therefore, the mass content w _{Cr_dispo} (p) of effective chromium at the depth p can be evaluated as follows.
w _{Cr_dispo} (p) = w _Cr (p) −w _{Cr_carbure} (p) = w _Cr (p) −23 / 6 × _52/12 × w _c (p), or w _{Cr_dispo} (p) = w _Cr (p) −16.61w _c (p) Equation 1

The mass content w _{Cr_dispo} (p) of the effective chromium at the depth p may have a negative value. Negative values have no physical meaning but represent non-carbonizable chromium deficiency magnitude or excess carbon magnitude.

  According to the invention, the mass content of effective chromium averaged over the entire thickness of the surface metal layer 7 from the inner surface 5 is greater than zero.

  In other words, the element 1 should on average be free of effective chromium in the surface metal layer 7 located directly below the inner surface 5.

  The free chromium content through the thickness of this surface metal layer forms a chromium-rich oxide layer during its oxidation, so it is nickel-rich when element 1 is used in a pressurized water reactor. It constitutes a barrier that effectively prevents the formation of the filament 11 and the release of a nickel-rich colloid or ionic compound.

In the following cases, the effective chromium content is less than zero.
The carbon and carbide content on the inner surface of element 1 and in the surface metal layer 7 is high.
Chromium is reduced in the surface metal layer 7.

  In general, the carbon or high carbide content results from the high temperature conversion of impurities during manufacture of the element 1, in particular the lubricant. It may also be due to the fact that the alloy casting used for the production of the tube itself had a high carbon content.

  The surface metal layer 7 reduces the chromium by dilution when the content of the elements forming the alloy other than chromium and the content of the minority compounds are concentrated toward the surface of the metal during the production, handling or oxidation of the material. To do.

The effective chromium content averaged over the thickness e from the inner surface 5 is hereinafter referred to as the average effective chromium content in e. This thickness e is typically less than or equal to the thickness E of the surface metal layer 7. The effective average chromium content in ^e , denoted as _{wCr_dispoe,} is evaluated as follows.

The chromium mass content w _Cr (p) and / or the carbon mass content w _c (p) is measured at various depths p of the surface metal layer 7 in the element 1 sample. This sample has, for example, a diameter of 20 ± 1 mm and a thickness of 1 mm on the inner surface.

  Typically, the surface metal layer is analyzed at 100 different depths dispersed in 0-e.

For each depth p, several measurements are taken at different locations. The retained mass content w _Cr (p) and / or w _c (p) corresponds, for example, to the average of the measurement results.

  The mass content of chromium and / or carbon is measured by glow discharge spectroscopy (SDL, GDOES). This technique is known and will not be described in detail here.

  Alternatively, the mass content of chromium and / or carbon is measured by Auger spectroscopy or X-ray photoelectron spectroscopy combined with a polishing method (eg, ion polishing) of the inner surface of the tube. Alternatively, the mass content of chromium and / or carbon can be determined by scanning electron microscopy (SEM) or transmission electron microscopy (TEM) cross section of the tube of interest (or microscopic plate obtained by a focused ion probe). Measured by energy dispersive X-ray spectroscopy (EDS). These techniques are known and will not be described in detail here. These techniques allow the oxide layer composition to be measured, and in particular to visualize the presence or absence of particles, which may have a solubility in excess of that of nickel or nickel oxide, especially in the primary medium. Become.

Next, using Equation 1 above, the effective chromium mass content w _{Cr_dispo} (p) is calculated for various depths p.

Next, the normalized effective chromium mass content w _{N —} Cr — _dispo (p) is calculated to discard the measured value due to errors in the oxide and impurity layer 3 rather than the surface metal layer 7. The content w _{N_Cr_dispo} (p) is calculated for each of the various depths as follows.
_{w N_Cr_dispo (p) = w Cr_dispo} (p) × (w Cr (p) + w Fe (p) + w Ni (p)) / 100 Equation 2
In the formula, w _Fe (p) and w _Ni (p) are mass contents of iron and nickel at the depth p of the surface metal layer 7 from the inner surface 5.

w _Fe (p) and w _Ni (p) are measured using the same technique as w _Cr (p) and w _c (p) at the same location.

The term (w _Cr (p) + w _Fe (p) + w _Ni (p)) / 100 in Equation 2 is close to zero when the measurement is performed on the oxide and impurity layer 3 rather than the surface metal layer.

  Accordingly, weights generally equal to 0 are assigned to measurements made on carbonaceous impurities present in the metallographic specimen, and weights substantially equal to 1 are assigned to measurements made on the surface metal layer.

Next, the effective average chromium content _{wCr_dispoe} over the thickness ^e is calculated as follows.
^{_{w Cr_dispo e = 1 / e ×}} ∫ 0 e w N_Cr_dispo (p). dp equation 3

  As described above, element 1 of the present invention is such that the effective chromium mass content averaged over the entire thickness E of the surface metal layer 7 from the inner surface 5 is greater than zero.

With Equation 3, this becomes the following criterion:
w _{Cr_dispo} ^E > 0
In the ^{_{formula, w Cr_dispo E = 1 / E}} × ∫ 0 E w N_Cr_dispo (p). dp.

  Alternatively or additionally, element 1 of the invention is such that the effective chromium content in the surface metal layer 7 averaged over 200 nm of the thickness of the surface metal layer 7 from the inner surface 5 is greater than zero.

With Equation 3, this becomes the following criterion:
w _{Cr_dispo} ^{200 nm} > 0
In the formula, w _{Cr_dispo} ^{200 nm} = _1/200 ^nm × ∫ ₀ ^{200 nm} w _{N_Cr_dispo} (p). dp.

  As described above, the element 1 of the present invention has an effective chromium mass content averaged at the thickness E of the surface layer 7 from the inner surface 5 and / or at the thickness of 200 nm of the surface metal layer 7. It is to exceed. Alternatively or additionally, element 1 of the invention is such that the effective chromium content in the surface metal layer 7 averaged over a 10 nm thickness of the surface metal layer 7 from the inner surface 5 is greater than zero.

With Equation 3, this becomes the following criterion:
w _{Cr_dispo} ^{10 nm} > 0
In the formula, w _{Cr_dispo} ^{10 nm} = _1/10 ^nm × ∫ ₀ ^{10 nm} w _{N_Cr_dispo} (p). dp.

  As mentioned above, the element 1 of the present invention is effective at the thickness E of the surface 7 from the inner surface 5 and / or at the thickness of 200 nm of the surface metal layer 7 and / or at the thickness of 10 nm. The chromium mass content exceeds 0. Alternatively or additionally, element 1 of the present invention is such that the effective chromium content in surface metal layer 7 averaged over a 1 nm thickness of surface metal layer 7 from inner surface 5 is greater than zero.

With Equation 3, this becomes the following criterion:
w _{Cr_dispo} ^{1 nm} > 0
In the formula, w _{Cr_dispo} ^{1 nm} = _1/1 ^nm × ∫ ₀ ^{1 nm} w _{N_Cr_dispo} (p). dp.

  As described above, the effective average chromium content at thickness E and / or 200 nm and / or 10 nm and / or 1 nm is greater than zero. Preferably, the effective average chromium content at E and / or 200 nm and / or 10 nm and / or 1 nm is greater than 5%, more preferably greater than 15%.

Alternatively, the effective average chromium content at E, and / or 200 nm, and / or 10 nm, and / or 1 nm is not the normalized effective chromium mass content w _{N_Cr_dispo} (p), but the effective chromium mass content Calculated by averaging w _{Cr_dispo} (p).

Furthermore, the element 1 according to the invention preferably has an effective chromium content w _{Cr_dispo} (p) which is constantly greater than 0 throughout the thickness of the surface metal layer 7.

In other words, whatever the depth p is taken into account, the surface metal layer 7 always has an effective chromium content w _{Cr_dispo} (p) greater than zero. This effective chromium content w _{Cr — dispo} (p) is preferably greater than 5%, more preferably greater than 15% at any depth p.

Alternatively, the effective chromium content w _{Cr — dispo} (p) in the surface metal layer 7 is at a thickness of 5 to 200 nm from the inner surface 5 and / or at a thickness of 5 to 10 nm from the inner surface 5 and / or 1 nm from the inner surface 5. In this case, it is constantly over zero.

  Preferably, the effective chromium content is constantly greater than 5% at a thickness of inner surface 5 to 200 nm and / or at a thickness of inner surface 5 to 10 nm and / or at a thickness of inner surface 5 to 1 nm, and more Preferably it exceeds 15%.

  The criteria defined above can ensure that only a small amount of filament 11 is formed or released into the fluid from the oxide layer 3 inside the element 1.

  These criteria have not been demonstrated in a number of existing steam generator tubes as provided by some existing manufacturers, as shown in FIGS.

FIG. 2 shows, for a part of a new steam generator tube, the chromium mass content w _Cr (p) (curve 1) and the normalized effective chromium mass content w _{N_Cr_dispo} as a function of depth from the inner surface. (P) (Curve 2) is shown. It can be seen that there is a high effective chromium deficiency of 0-10 nm in this tube. The effective chromium mass content is negative up to 10 nm and remains below 15% up to a depth of about 50 nm. Negative values of effective chromium mass content have no physical meaning, and negative values simply represent the amount of non-carbonizable chromium deficiency or excess carbon.

FIG. 3 shows the normalized effective chromium mass content w _{N —} Cr — _dispo (p) as a function of depth from the inner surface for parts from various steam generator tubes. These tubes are new and manufactured by different suppliers. They are intended to be installed in new reactor steam generators or new steam generators installed in replacement in old reactors.

  As can be seen in FIG. 2, these samples have a high effective chromium deficiency of 0-10 nm. The effective chromium mass content is negative up to at least 10 nm for most samples.

  As indicated above, the surface metal layer 7 has a composition that deviates from the composition of the nickel-based alloy but is still close. It has a mass content slightly different from the mass content of the base metal, ie the nickel-based alloy, resulting from the treatment applied during the manufacture of element 1.

Typically, the chromium content w _Cr (p) averaged over the entire thickness of the surface metal layer 7 from the inner surface 5 is less than 45%. It is typically 20% to 32% over the first 200 nanometers.

This chromium content w _Cr (p) increases from the inner surface 5 over the entire thickness of the surface metal layer 7. It is typically between 0.1% and 20% at the inner surface 5. It increases constantly as the depth p increases. It is close to the content of nickel-based alloy at a depth of 100 nm. Typically, the difference between the chromium content of the nickel-based alloy and the chromium content of the surface layer is less than 30%, preferably less than 5% at 100 nm.

  The nickel content averaged over the entire thickness of the surface metal layer 7 from the inner surface 5 exceeds 1%. It is typically over 40%. The nickel content averaged over 100 nm from the inner surface 5 is over 40%, typically over 45%.

  The steam generator of the present invention can be manufactured according to various methods.

According to the first aspect, the manufacturing method comprises the following steps:
Producing an untreated element having an inner surface;
Applying one or more surface treatments to the inner surface of the untreated element, the surface treatment comprising a step selected from electropolishing, mechanical or chemical mechanical polishing, chemical cleaning.

  The untreated element is a nickel-based alloy as defined above. It is manufactured by any suitable method. For example, extrusion molding, rolling from an ingot, welding, and the like.

  In the case of a tube, the inner surface 5 delimits the inside of the tube, ie the internal passage of the tube.

  The surface treatment is intended to remove or replace a thin layer on the inner surface of the untreated element that is deficient in effective chromium. In other words, the purpose of the surface treatment is to remove or replace the portion of the surface metal layer 7 having a low effective chromium content.

  For example, the surface treatment is intended to remove or replace the entire surface metal layer 7.

In another example, the surface treatment has a thickness of the surface metal layer 7 selected such that the average effective chromium content _{wCr_dispo} ^E over the thickness E of the surface metal layer 7 is less than a predetermined limit after application of the surface treatment. Are intended to be removed or replaced. The predetermined limit is, for example, 0%, 5%, or 15%. Instead of the average effective chromium content over the entire thickness of the surface metal layer 7, it is also possible to take into account the average effective chromium content at 200 nm, or at 10 nm, or at 1 nm.

  The surface treatment is also aimed at removing unwanted compounds in the oxide layer, including alumina. Such a treatment can be obtained, for example, by chemical cleaning in a heated alkaline solution.

  In general, the thickness of the surface treatment layer is individually selected after analysis of the effective chromium mass content profile as a function of depth from the inner surface of the untreated element. This profile depends on the alloy and manufacturing method used to manufacture the green element. For example, the thickness can be less than 1 μm, preferably less than 200 nm, more preferably less than 100 nm.

  Electropolishing is an electrochemical surface treatment process that removes surface layer metal by anodic dissolution. Some elements of the alloy that are partially insoluble in the electropolishing bath, especially chromium oxide, remain on the surface of the part and form a protective barrier.

  Mechanical polishing involves stripping the part by polishing means. Many means can be used, such as circulation of liquid loaded with abrasive particles in contact with the surface, displacement brought into contact with the surface by an abrasive member such as a disk, brush or the like.

  Chemical cleaning is a technique that contacts a surface to be treated with a chemical solution of a selected composition to dissolve the surface layer of the surface. The chemical solution contains, for example, concentrated acids and complexing agents, making it possible to improve the solubility of some oxides.

  Chemical mechanical polishing combines mechanical polishing and chemical cleaning. Typically, a chemical solution with abrasive particles added circulates in contact with the surface to be treated. Struer sells polishing suspensions suitable for such operations, such as those sold under the names OP-AA and OP-S. They are solutions of colloidal suspensions of acids or bases, complexing agents, and abrasive silicones or alumina oxides.

  These various types of processing are known and will not be described in detail here.

  After surface treatment, the untreated element becomes the element described above having the effective chromium content required by the present invention.

  According to a first variant embodiment, the surface treatment is performed on the untreated elements before final assembly in the steam generator.

According to a second variant embodiment, the method comprises the following steps:
Assembling the raw elements in the steam generator;
Connecting the upstream and downstream compartments of the steam generator with the reactor primary circuit;
A surface treatment step performed by circulating a solution of a predetermined chemical composition in the primary circuit, wherein the inner surface of the untreated element is thus in contact with the solution.

  The chemical composition used is in this case compatible with all the requirements relating to the chemistry of the primary circuit. For example, the solution can include boric acid and / or peroxide.

  Therefore, the surface treatment is performed when the steam generator is permanently connected to the primary circuit in a nuclear power plant.

According to a third variant embodiment, the method comprises the following steps:
Assembling the raw elements in the steam generator;
Connecting the upstream and downstream compartments of the steam generator to the circulation processor;
In a steam generator, a surface treatment step performed by circulating the treatment solution so that the inner surface of the untreated element is in contact with the treatment solution.

  In this case, the treatment is mechanical or chemical mechanical polishing or chemical cleaning.

  The steam generator is still not connected to the primary circuit of the reactor in this case. The treatment is performed, for example, at a steam generator manufacturing work site that is not present at the site of the nuclear power plant.

  According to a second embodiment, the method comprises rolling the ingot with a non-carbonaceous lubricant or by continuously casting and then rolling with a non-carbonaceous lubricant. The manufacturing process is included.

  The ingot is the nickel-based alloy described above. Before rolling, it has the shape of a hollow cylinder when the element is a tube.

  Many non-carbonaceous liquids can be used as lubricants including some molten salts, low melting point metals or many aqueous solutions.

  Since the lubricant used is non-carbonaceous, the amount of carbon on the inner surface of the tube is reduced and the amount of chromium carbide on the inner surface of the tube is likewise reduced. As a result, the amount of effective chromium increases.

  If the element having the effective chromium content required by the present invention is a tube, it is attached to a steam generator as shown in FIG.

  The steam generator 13 includes an outer casing 15 and a tubular plate 17 that divides the inner space of the outer casing into a water chamber 19 and an upper space 21.

  The water chamber 17 is divided into an upstream compartment 23 and a downstream compartment 25 by an internal partition 22.

  The steam generator includes a secondary liquid inlet 27 and a steam outlet 29, both of which are open into the upper space 21. They are connected to a secondary pump and a steam turbine, respectively.

  The pipes 1 open into the upstream compartment 23 through the upstream end of the water chamber and into the downstream compartment 25 through the downstream end opposite to the upstream end, respectively.

  The tubes each have a U-shape and their ends are rigidly fixed to the tube plate 17.

  The upstream compartment 23 is fluidly connected to the outlet 31 of the reactor vessel 33. The downstream compartment 25 is fluidly connected to the inlet 35 of the reactor vessel 33.

  When the reactor is in operation, the primary liquid is heated in the reactor vessel and then flows into the upstream compartment of the water chamber. It then flows from the upstream compartment to the downstream compartment inside the tube 1. It passes some of its thermal energy to the secondary liquid as it passes. It then flows from the downstream compartment to the container inlet.

  Alternatively, the element containing the effective chromium content required by the present invention is a plate attached to the steam generator, the inner surface of which contacts the primary liquid. This plate is, for example, a plate 22 that separates the upstream and downstream compartments from each other.

The invention is therefore also aimed at the use of a surface treatment for element 1 of the steam generator, where element 1 is as described above. Element 1 is made from a nickel-based alloy, which has the following mass content:
Ni exceeding 50%,
14% -45% Cr
Have

Element 1 has an inner side intended to be exposed to a liquid, the surface metal layer 7 has an inner surface 5 covered by an oxide layer 3, and the surface metal layer 7 is deep from the inner surface 5. p has a chromium mass content w _Cr (p), a carbon mass content w _c (p) and an effective chromium content w _{Cr_dispo} (p), where w _{Cr_dispo} (p) = w _Cr ( p) -16.61w _c (p).

The surface treatment is an oxidation that tends to result in the formation of nickel 11 rich filaments when the inner surface 5 is exposed to the primary liquid of the pressurized water reactor during the energy production phase, ie during normal operation of the pressurized water reactor, and Over the entire thickness of the surface metal layer 7 from the inner surface 5 in order to limit the direct release of ions or colloids originating from areas where these filaments can be formed into the primary liquid of the reactor. It is intended to _{strip the} inner surface until the average mass content of effective chromium w _{Cr_dispo} (p) exceeds zero.

  The primary liquid considered here meets the specifications of the main reactor operator or many research and safety organizations in the field. In particular, it has a nickel (ion) content below the published minimum solubility limit, and the flow is characterized by a Reynolds number between 0 and 106.

  By nickel rich filament is meant a filament containing more than 50 wt% nickel.

  The alloy is typically one of the alloys defined above. Surface treatment is one of the surface treatments defined above.

Alternatively, the surface treatment is effective chromium averaged over a thickness of 200 nm from the inner surface 5 and / or averaged over a thickness of 10 nm from the inner surface 5 and / or averaged over a thickness of 1 nm from the inner surface 5. _Until the mass content of _{wCr_dispo} (p) exceeds 0, it is always used for the same purpose.

Preferably, the surface treatment has an effective chromium mass content w _{Cr_dispo} (p) averaged over the entire thickness of the surface metal layer and / or from the inner surface to 200 nm and / or 10 nm and / or 1 nm. It is used until exceeding, more preferably 15%.

  In the pressurized water reactor, when the inner surface 5 is exposed to the primary liquid during normal operation of the reactor, the formation of filament elements rich in nickel on the inner surface 5 and the atoms from these filaments 11 It also relates to the use of a steam generator as described above to avoid direct release in the primary liquid of the furnace colloid.

  Element 1 is a tube 1 that serves for the circulation of the primary liquid of the reactor during normal operation of the reactor, for example from the upstream compartment 23 of the water chamber 19 to the downstream compartment 25 or plate. The primary liquid considered here is as described above.

  The production method of the invention is particularly advantageous because it does not result in heating of the material constituting the green element. It retains its initial microstructure. This is particularly important for steam generator tubes made of, for example, 690TT alloy. This alloy is subjected to a defined heat treatment, particularly for the purpose of forming intergranular chromium carbide, while maintaining the metal grain size within an accurate range prior to the surface treatment step described herein. . By allowing the alloy to exceed, for example, 800 ° C., excessive heating of the tube during the surface treatment results in at least some loss of heat treatment benefits or changes in the metal particle size.

  Furthermore, most of the surface treatments considered herein are performed by circulating fluid in contact with the inner surface of the element being treated. The fluid is driven, for example, by a pump or a mop or felt floss that is pushed by compressed gas. The implementation of these circulation processes is much simpler than the plasma deposition process or another similar process for the steam generator tube. These tubes are significantly longer than 20 m and have a small outer diameter of less than 20 mm. Currently, there is no enclosure to provide PVD (physical vapor deposition) deposits on the inner surface of this type of part.

  A treatment that removes part of the surface metal layer is particularly advantageous. Such a process is simpler to implement than a process involving deposits on the surface metal layer. There is no risk that the deposited material will have cracks or that there is a separation at the interface between the surface metal layer and the deposited material.

Claims (14)

A steam generator for a pressurized water reactor, the steam generator (13) comprising:
An enclosure (15) in which a water chamber (19) divided into an upstream compartment (23) and a downstream compartment (25) is delimited, wherein the upstream compartment (23) is a container (33 ) And the downstream compartment (25) is designed to be in fluid communication with the inlet (35) of the vessel (23) of the reactor. Body (15),
At least one element (1), each element (1) passing through an upstream end into the upstream compartment (23) and through the downstream end opposite the upstream end. A tube or plate open in the compartment (25), each element (1) being made from a nickel-based alloy, said alloy having the following mass content:
Ni exceeding 50%,
14% -45% Cr
Comprising the element (1)
Said element (1) has a surface metal layer (7) having an inner surface (5) covered with an oxide layer (3) on the inside intended to be exposed to a liquid, said surface metal layer (7) has a mass content w _Cr (p) of chromium, a mass content w _c (p) of carbon, and an effective chromium content w _{Cr_dispo} (p) at a depth p from the inner surface (5). Where w _{Cr_dispo} (p) = w _Cr (p) −16.61w _c (p),
Steam generator, characterized in that the effective chromium content w _{Cr_dispo} (p) averaged over the entire thickness of the surface metal layer (7) from the inner surface (5) is greater than zero. Steam generator according to claim 1, characterized in that the effective chromium content _{wCr_dispo} (p) averaged from the inner surface (5) to a thickness of 200 nm is greater than zero. _{3. The} effective chromium content w _{Cr_dispo} (p) averaged over a thickness of 20 nm from the inner surface (5), preferably over a thickness of 5 nm, is greater than zero, according to claim 1 or 2. Steam generator. 4. The effective chromium content _{wCr_dispo} (p), which constantly exceeds 0 from the inner surface (5) through the thickness of the surface metal layer (7), Steam generator according to item.   Steam generator according to any one of the preceding claims, characterized in that the alloy is an alloy 690 according to standard UNS N06690 / W No 2.4642. Any of claims 1 to 5, characterized in that the chromium content _wCr (p) averaged over the entire thickness of the surface metal layer (7) from the inner surface (5) is less than 45%. The steam generator according to claim 1. 7. The chromium content _wCr (p) increases from the inner surface (5) over the entire thickness of the surface metal layer (7), according to any one of claims 1-6. Steam generator.   8. The oxide layer (3) according to any one of claims 1 to 7, characterized in that it does not contain particles whose solubility exceeds that of the nickel oxide compound in the primary medium, in particular or any oxide particles rich in aluminum. The steam generator according to one item.   Steam generator according to any one of the preceding claims, characterized in that, when the element (1) is new, the oxide layer (3) has a thickness of less than 10 mm. It is a method of manufacturing the steam generator as described in any one of Claims 1-9, Comprising: The following processes:
Producing an untreated element having an inner surface (5);
Applying a surface treatment to the inner surface (5) of the untreated element, the surface treatment being selected from electropolishing, mechanical or chemical mechanical polishing, chemical cleaning, the untreated element being a surface Comprising the element (1) after processing. The following steps:
Assembling the raw elements in the steam generator (13);
Connecting the upstream compartment (23) and the downstream compartment (25) of the steam generator (13) with a primary reactor circuit;
The surface treatment is carried out in the primary circuit by circulating a solution of a given chemical composition so that the inner surface (5) of the untreated element is in contact with the solution. Item 11. The method according to Item 10.   A method for producing a steam generator according to any one of claims 1 to 9, wherein the ingot is rolled or continuously cast with a non-carbonaceous lubricant and then non-carbonaceous. A method comprising the step of producing said element (1) by rolling with a lubricant. Use of a surface treatment for the element (1) of the steam generator (13) according to any one of claims 1-9,
The surface treatment is performed on the inner surface (5) until the mass content w _{Cr_dispo} (p) of the effective chromium averaged over the entire thickness of the surface metal layer (7) from the inner surface (5) exceeds zero. Stripping,
The use may include oxidation that tends to result in the formation of a nickel-rich filament when the inner surface (5) is exposed to the primary liquid during normal operation of the pressurized water reactor, and / or the filament. (11) Use for the purpose of restricting the direct release of ions or colloids generated from regions where they may be formed into the primary liquid.   Use of a steam generator according to any one of claims 1 to 9 in a pressurized water reactor, wherein the inner surface (5) is exposed to the primary liquid during normal operation of the pressurized water reactor. From oxidation, which tends to cause formation of filaments rich in nickel in the inner surface (5) of the element (1) and / or where the filament (11) may be formed. Use to limit the direct release of ions or colloids into the primary liquid.

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