PWR secondary circuit
After describing PWR secondary circuit, PWR recirculating steam generators (SG) and the different materials used, this section will be devoted to introduce the water chemistry management in PWR in order to better understand the different parameters involved in corrosion and TSP clogging phenomena.
The two major secondary systems of a pressurized water reactor (PWR) are the main steam system and the condensate/feedwater system. The steam goes from the outlet of the steam generator into the high pressure (HP) main turbine firstly in order to resist to the steam high pressure (Figure 1.1#1). After passing through the high-pressure turbine, the steam is piped to the moisture separator/reheaters (MSR) (Figure 1.1#2). In the MSRs, the steam is dried by means of moisture separators and reheated to avoid turbine blade corrosion. The stream moves then from the MSR to the low-pressure turbines (Figure 1.1#3) to generate electricity. After passing through the low-pressure turbines, the steam goes to the main condenser (Figure 1.1#4). The steam is condensed into water by the flow of circulating water through the condenser tubes. The condensate then passes through some low-pressure feedwater heaters (Figure 1.1#5). The temperature of the condensate is then increased from 40 to 75 °C in the heaters. The condensate flow then enters the suction of the main feedwater pumps (Figure 1.1#6), which permits to increase the water pressure from 11 to 65 bars so that the condensate can be sent into the steam generator. The feedwater is then heated by means of a set of high-pressure heaters (Figure 1.1#7), which are heated by the extraction steam from the high-pressure turbine (heating the feedwater helps to increase the efficiency of the plant).
Figure 1.1: Scheme of PWR secondary circuit (Pressurized Water Reactor Systems, n.d.).
Recirculating steam generator
A recirculating steam generator (SG) is about 20 meters high, its diameter ranges from 3 to 5 meters and it weights between 300 and 430 tonnes (Delaunay, 2010). In SG, the primary system coolant flows through several thousands of U-tubes (Figure 1.2). Primary coolant enters the steam generator at 315-330 °C on the hot-leg side and leaves at about 288 °C on the cold-leg side. The secondary system flow (feedwater) is fed through a feedwater distribution ring into the downcomer, where it mixes with recirculating water draining from the moisture separators. This downcomer water, in contact with hot primary tubes, flows to the bottom of the steam generator, and is then transferred into steam up through the tube bundle. About 25% of the secondary coolant is converted into steam on each pass through the generator while the other 75% recirculates (Bonavigo and Salve, 2011).
The different types of SG are mainly characterized by two parameters: the total outer exchange area represented by the tube bundle and the external diameter of SG tubes (Prusek, 2012). For example, a 51B type SG (Figure 1.2, left) has a total outer exchange area of 4700 m2 and a tube external diameter of 22.22 mm (Girard, 2014). Complete characteristics of the tube bundle of 51B type steam generators are listed in Table 1.1. As the tubes are long and thin, 8 circular plates called Tube Support Plates (TSP) are used for their mechanical maintain (Figure 1.2, left) in 51B type SG. The tubes fit in the circular holes drilled in the TSP. These holes are surrounded by additional quatrefoil holes to let the secondary steam-liquid mixture flow through (Figure 1.2, bottom right). After several decades of operation, deposit formation is observed in the quatrefoil holes between SG tubes and TSP (See TSP clogging phenomenon in Figure 1.2, top right).
Thermohydraulics in PWR steam generator
TSP clogging phenomena are highly dependent on the thermohydraulics. A general knowledge of PWR SG thermohydraulics is necessary for the further discussions in the present work. In this section, basic notions of two-phase flow parameters, as void fraction, are introduced and defined and different two-flow patterns are presented. Most TSP clogging phenomenon has been observed on the 8th TSP in the EDF NPPs. After describing fundamentals of two-phase flow typical values of major thermohydraulic parameter on the 8th TSP of 51B type SG will be identified in section 184.108.40.206 since thermohydraulics will govern TSP clogging phenomena.
Two-phase flow fundamentals
Basic theory and definitions are introduced in this section. Given that there are many two-phase flow models in the literature and the objectives of this section is not to give a thorough description of two-phase flow models, only few of them are presented hereafter and the reader can find more information about these models elsewhere in the literature (Cong et al., 2013, 2015; Rummens, 1999; Vergnault et al., 2008; Zohuri and Fathi, 2015).
Two-phase flow system basic notions
The primary parameters used in two-phase flow modelling are (Royer, 2015):
• Thermal: thermal power, temperature, heat flux, etc.
• Hydraulic: pressure, mass flow rate, fluid temperature, pressure drop, etc.
• Geometric: flow and heated areas, hydraulic and heated equivalent diameters, etc.
Along with these primary parameters, in two-phase flow analysis, the following calculated parameters are commonly used:
• Mass flux
• Dynamic mass quality
• Void fraction
In addition, two-phase flow calculations require information about fluid properties such as density, viscosity, enthalpy, thermal conductivity, and heat capacity, which depends on the above-mentioned primary fluid parameters. Major basic two-phase flow notions will be briefly defined and presented as following:
Void fraction α (dimensionless) is defined as the volumetric fraction of vapour phase or the cross-sectional area occupied by vapour phase (Av) to the total flow area of a pipe (A) in the limit case of a “thin” volume (Royer, 2015), as expressed in Eq. 1-1. The opposite of void fraction is the liquid fraction.
The vapour in a moving two-phase flow system trends to move at a higher velocity than the liquid because of its buoyancy, density and different resistance characteristics. Experimental data or theoretical correlations for Sv/l covering all possible operating and design variables do not exist. Experimental values of Sv/l under conditions defined for a particular design are difficult to obtain experimentally. Such procedures are usually expensive and time-consuming. In calculations and modelling, the usual procedure is to neglect the difference between vapour phase and liquid phase velocities or to assume a constant value of Sv/l throughout the fuel channel.
Other parameters, like static quality (vapour mass fraction Cg) or thermodynamic quality of the two phases are less used because they do not bring relevant information about the flows (velocities). The associated definitions can be found in (Royer, 2015).
Two-phase flow patterns
Multiphase flow is classified according to the internal phase distributions or « flow patterns » or « regimes ». For instance, in the case of a two-phase mixture of a gas or vapour and a liquid flowing together in a channel, different internal flow geometries or structures can occur depending on the size or orientation of the flow channel, the magnitudes of the gas and liquid flow parameters, the relative magnitudes of these flow parameters, and on the fluid properties of the two phases. In particular, two-phase flow patterns are strongly influenced by phase mass flow rates or velocities (K. Popov, 2015). The sequence of flow patterns generally encountered in vertical two-phase flow as a function of the steam quality x is shown in Figure 1.3.
The bubbly pattern means that the vapour phase is distributed in discrete bubbles within a liquid continuum. When the concentration of bubbles becomes higher, bubble coalescence occurs and progressively, the bubble diameter approaches that of the tube. The slug flow (also named plug flow) regime is entered. As the vapour flow is increased with steam quality, the velocity of these bubbles increases and ultimately, a breakdown of these bubbles occurs leading to an unstable regime. In this regime, there is an oscillatory motion of the liquid upwards and downwards in the tube (churn flow). Annular flow represents the pattern where the liquid flows on the wall of the tube as a film and the gas phase flows in the centre. Finally, in the disperse droplet pattern, the liquid phase loses contact with the tube and forms concentrated individual liquid droplets more or less homogenously in the flow.
Two-phase flow parameters change significantly from one flow pattern to another one. In particular, the interfacial area between the two phases has a significant impact on the exchange of mass, momentum, and heat between phases. Various two-phase flow parameters are affected differently by flow patterns, and hence various correlations and models are needed to capture phenomena for each flow pattern. This implies the need for well-defined and predictable flow patterns in two-phase flow modelling. Many pattern maps are reported in the literature from experiments or calculations (Cheng et al., 2008). They give a good description of the two-phase flow pattern as a function of flow properties such as steam quality, mass flux, etc. However, most of these pattern maps are limited to relatively low temperature systems (from 20 to 80 °C) and they are not relevant for describing water/vapour flow systems like those reported in PWR SG. More experiments are then required under the same thermohydraulic conditions as those reported in SG. Nevertheless, plot of such map patterns is particularly challenging because it needs to develop new sensors, which can operate at high temperature and pressure (Hogsett and Ishii, 1997). Efforts are currently made at CEA Cadarache (France) for the development of such two-phase flow measuring sensors (Dupréet al., 2016).
Thermohydraulics of 51B type steam generators
Numeric simulations based on porous media models and experimental single-phase and steam-water two-phase flow investigations were performed by several groups (Cong et al., 2013, 2015; Tian et al., 2016; Zhang et al., 2017) to investigate the thermohydraulic characteristics of PWR steam generators. Heat transfer from primary to secondary side, pressure drop for a vertical two-phase flow across a horizontal rod bundle and the effects of power level on thermohydraulic characteristics were discussed. However, only few data are available in the literature about basic parameters in a specific localization in SG like at the 8th TSP of 51B type SG (void fraction, secondary temperature, etc.).
An EDF modelling tool (THYC) was used for investigating thermohydraulic parameters at the 8th TSP of 51B type SG (Schindler, 2010, 2016). Schindler’s works summarized the main results of this study and showed the dynamic steam quality varies from about 0.22 to 0.38 on the hot leg side of the 8th TSP. The maximal steam quality is located at the centre of the tube bundle while a steam quality of 0.30 is observed in the intermediate region between the centre and the wall (see definition of the steam quality x in Eq. 1-2). The void fraction ( , Eq. 1-1) reaches 0.85 on the hot leg of 8th TSP with a relatively homogeneous distribution. The pressure is equal to 61.5 bars in the whole 8th TSP section with a temperature of 277.2 °C in the secondary flow. A mean vertical velocity of the two-phase flow of about 3 m/s has been calculated at the intermediate region of the hot leg of the 8th TSP. From these calculated thermohydraulic parameters, the two-phase flow located in the 8th TSP is often supposed to have a disperse droplet regime because of the high void fraction and dynamic steam quality. However, neither experimental nor theoretical works have been performed to confirm such an expectation because of the difficulties mentioned previously.
Most TSP clogging phenomenon is observed on the 8th TSP of PWR 51B type steam generator’s secondary side. A general description of PWR secondary circuit and steam generators has been done. Important thermohydraulic notions have been introduced and associated parameters have been identified specifically for the 8th TSP region in 51 B type SG in order to feed further discussion in the present work. Thereafter, the major source term of TSP clogging phenomenon will be identified, by firstly introducing the different materials used in the secondary circuit and the associated corrosion phenomena under the specific PWR secondary water chemistry. Magnetite is the stable form of iron species under PWR SG conditions and is the main composition of TSP clogging. Its structural and physio-chemical properties will be provided.
Materials used in the secondary circuit
In the secondary circuit, the fluid circulation piping is made of carbon steel. SG tube sheet, turbine rotors, high-pressure heater, condensate and feedwater piping are usually made of carbon steel or low alloy steels (Feron, 2012). The steam generator tubes are made of nickel-based alloys: alloys 600 MA (MillAnnealed: thermal treatment at 980 °C for 15 minutes), alloys 600 TT (Thermally Treated at 700 °C for 16 hours) or alloys 690 TT for the most recent steam generators (Le Calvar and De Curières, 2012). The SG Tube Support Plates (TSP) are nowadays made of stainless steel with about 13%wt of chromium (Delaunay, 2010). Condenser tubes are made of stainless steels, or copper alloys or titanium-based alloys. Chemical compositions (%wt) of alloys usually used in PWR secondary circuit are gathered in Table 1.2.
PWR secondary flow chemistry
Slightly alkaline solution in the secondary circuit is used to limit corrosion phenomena in the PWR secondary circuit (Nordmann and Fiquet, 1996). For this goal, most of the nuclear operators use volatile alkaline reagent (AVT, All Volatile Treatments). Two main reagents are used: morpholine (C4H9NO) and ammonia (NH4OH). Other reagents are less frequently used like ethanolamine (C2H7NO). Hydrazine (N2H4) is used for reducing dissolved oxygen concentration for Stress Corrosion Cracking (SCC) prevention.
Ammonia was largely used thanks to its easy implementation, low cost and its relatively low decomposition. However, its use is limited in the presence of copper alloys in secondary circuit materials because ammonia corrosion leads to the formation copper ions that form stable copper-ammonia complexes (Cu(NO3)62+) when pH is higher than 9.4 at 25 °C (Yang et al., 2017a), which participate actively in the corrosion of copper material and increase the risk of copper reprecipitation elsewhere in the secondary circuit. Therefore, pH25 °C is fixed at between 9.1 and 9.3 in the presence of copper alloys in the secondary circuit. The use of hydrazine in the presence of copper alloys is also limited due to its decomposition inducing the formation of ammonia. Its concentration ranges generally from 5 to 10 µg/kg (ppb) (Delaunay, 2010; Nordmann and Fiquet, 1996; Suat and Francis, n.d.). In the absence of copper alloys, pH25 °C is fixed by ammonia or morpholine around 9.6 to 9.7 to prevent corrosion.
In certain cases, hydrazine concentration can be increased up to 50-100 µg/kg in the absence of copper, especially for enhancing SCC prevention. Morpholine allows providing a homogeneous protection all over the steam-water system since its distribution coefficient (concentration in vapour/concentration in liquid phase) is close to 1. However, more and more operators work on the substitution of morpholine by another reactive because the high concentration of morpholine in secondary circuit and its low thermal stability increase the risk of formation of organic compounds by chemical decomposition such as ethenol and ethenamine (Altarawneh and Dlugogorski, 2012). Ethanolamine (ETA) is a good candidate to replace morpholine. This reactive is for instance largely used in US because it can be used at lower molar concentration than morpholine and thermal decomposition is limited (Suat and Francis, n.d.).
Most chemical elements remain in the liquid phase as their distribution coefficients are generally around 10-4. In order to limit the corrosion phenomena associated with the presence of these pollutants in the liquid phase, periodical purges of secondary water are performed. A purge rate of 1% of the feedwater flow is generally used in France (Suat and Francis, n.d.), which leads to an estimated super-concentration coefficient in SG water of 100 compared to the feedwater.
In restricted zones of SG as in clogged TSP flow holes, primary tubes’ cooling is less efficient due to the reduced secondary water flow, which may induce local overheating, leading to an increase of pollutant concentrations. The super-concentration coefficient in these regions can reach as high as 106 compared to SG water (Nordmann and Fiquet, 1996). The current pollutant concentration is maintained below 0.01 µg/kg in the feedwater. Therefore, the concentration in the SG water can then be estimated to be around 1 µg/kg (1 ppb) with a super-concentration coefficient of 100 and the pollutant concentration can reach between 1 mg/kg (1ppm) and 1 g/kg.
The total iron concentration in the feedwater is measured to be around 30 ppb by EDF (De Bouvier, 2015a). No data is available in the literature for estimating iron concentration in SG water or SG restricted regions by taking into account the super-concentration phenomenon in PWR SG.
Corrosion phenomena in PWR secondary circuit
The PWR secondary water chemistry management, previously presented, aims at protecting the whole secondary circuit towards corrosion phenomena. Flow accelerated corrosion (FAC) of components in carbon steel is found to be the major term source of TSP clogging formation. Effects of different parameters, as material composition and flow thermohydraulics, will be discussed based on previous studies available in the literature. Stress corrosion cracking (SCC) majorly affects SG tubes in alloy 600 and will be briefly presented.
SCC will be firstly introduced, affecting majorly SG tube materials. FAC is believed to be the major source of TSP clogging phenomenon. Effects of major parameters, as pH and oxygen concentration, will be carefully discussed in paragraph 220.127.116.11.
Stress corrosion cracking (SCC)
SCC is responsible for material cracking under both environment and mechanical stresses. The propagation rate of SCC ranges generally from 10-5 to 1 µm/s and increases with stress (Arioka et al., 2006).
Steam generator tubes in the secondary circuit constituted of Alloy 600 MA suffered from SCC. Such SCC induced intergranular stress corrosion cracking (IGSCC) and intergranular attack (IGA). A generic designation for these secondary side degradations is IGA/IGSCC because they are often observed together.
SCC of Alloy 600 MA has been carefully discussed from a mechanistic point of view by Delaunay (Delaunay, 2010). A double-layer deposit composed of a compact inner layer enriched in chromium and a porous outer layer containing nickel oxides was observed onto Alloy 600 surface undergoing SCC.
IGA/IGSCC is mostly found in restricted regions as between the tubes and the TSP. In these locations, the flow of secondary fluid is restricted, which may be further impeded by the presence of corrosion product deposits, like TSP clogging, inducing even more restricted geometries. The restricted flow conditions enable a local super-concentration of any impurities, as previously mentioned in paragraph 1.2.5. Severe chemical conditions can thus be obtained, which are capable to induce IGA/IGSCC of Alloy 600 MA tubes. The main detrimental polluting elements are sodium, sulfur, copper and lead (De Bouvier, 2015b; Feron, 2015).
Alloy 600 TT, Alloy 690 TT and stainless steel suffer much less from IGA/IGSCC than Alloy 600 MA. The older carbon steel TSPs with drilled holes have been more subject to IGA/IGSCC since they undergo more easily concentrated crevice environment than those with current stainless steel quatrefoil tube holes.
General corrosion and Flow accelerated corrosion (FAC)
According to the International Standard ISO 8044, general corrosion of metallic materials is defined as a “general proceeding at almost the same rate over the whole considered surface” (Féron and Richet, 2010). In an aqueous environment, such as water-cooled reactors like PWR, metallic materials corrosion is of electrochemical nature (Feron, 2015), with the metal oxidation as anodic reaction and the reduction of dissolved oxygen or water as cathodic reaction. General corrosion is characterized by these basic electrochemical reactions that take place uniformly over the whole considered surface. If the corrosion products are soluble, general corrosion is evidenced by a decrease in metal mass or thickness over time; if the corrosion products are not soluble, the corrosion is evidenced by the formation of a uniform layer of corrosion products which may be more or less protective against further corrosion. Iron contained in carbon steel is oxidized into magnetite form under typical PWR SG conditions, predicted by various authors using Pourbaix diagrams (Chexal et al., 1998; Chivot, 2004; Delaunay, 2010; Mansour, 2009; Pourbaix, 1963). Figure 1.4 shows that the Pourbaix diagram of iron predicts magnetite as the stable form of iron in deionized and degassed reducing water (Eh = -0.4 V vs. SHE) at 200 °C and pH200 °C > 6 (pH25 °C > 9).
The formed magnetite is constituted of two layers: an inner compact and adherent layer characterized by the presence of small grains (0.05 to 0.2 µm) and an outer porous layer characterized by larger tetrahedral or octahedral particles of 0.5 to 5 µm (Delaunay, 2010). This magnetite layer may play the role of passivation which may limit reactions at the liquid-material interface including electrochemical reactions.
FAC can be considered as a particular case of general corrosion, which is accelerated by turbulent flow. FAC can occur if the flow rate is greater than 1.5 m.s-1 with Reynold number ranging from 105 to 108 (Chexal et al., 1998). FAC is a physico-chemical process that contributes to the increase of general corrosion rate up to a few millimetres per year (Le Calvar and De Curières, 2012). Morrison (J. Morrison, 2014) wrote a review of the magnitude of current corrosion issues affecting NPP primary and secondary coolant systems and stated that FAC represents the largest proportion of various corrosion problems (39.3%). FAC may lead to dramatic consequences in nuclear power plants. For instance severe accidents resulting from FAC were reported in various papers (De Bouvier, 2015a; Le Calvar and De Curières, 2012). The FAC phenomenon is well understood and believed to be largely present in NPP due to the enormous number of geometric singularities, e.g., bends and contractions, inducing flow turbulences. De Bouvier (De Bouvier, 2015a) estimated the presence of more than 1200 geometric singularity elements in French 900 MWe NPPs.
Parameters affecting flow accelerated corrosion – TSP clogging source
FAC is the main source term of corrosion products in the secondary flow and then of TSP clogging phenomenon and other SG degradation phenomena, like the tube fouling. In this section, main parameters affecting FAC rate are identified and discussed. Current efforts for TSP clogging prevention are majorly based on minimization of the source term, without appropriate understanding of its formation mechanisms.
Effects of pH and temperature – magnetite solubility
The magnetite solubility is the key parameter regarding the quality of the passivation layer for limiting carbon steel corrosion. The FAC rate is controlled by reductive dissolution of the magnetite layer on carbon steels (reverse reaction in Eq. 1-10) and the transfer of dissolved iron from the surface to the bulk fluid. According to Eq. 1-10, the proton concentration (and therefore the pH in diluted solution) plays a predominant role on magnetite solubilisation. An increase of proton concentration will promote the magnetite layer dissolution, and thus increase the FAC rate. Numerous studies showed that magnetite solubility decreases with an increase in pH up to 11 at 25 °C (Bignold et al., 1980; Fujiwara et al., 2011; Heitmann and Katsner, 1974; Machiels and Munson, 2005). Similar evolutions were found at higher temperatures up to 150 °C (Chivot, 2004). A recent EPRI report (unpublished results) stated that an increase of pH25 °C from 9.0 to 9.6 induces a decrease of magnetite solubility from about 15 to 5 µg/kg at 250 °C when the solution is conditioned by ammonia. This pH effect explains why the PWR secondary water is maintained to alkaline pH values. More TSP clogging was observed in NPPs functioning with lower pH values (18.104.22.168), as reported by EDF feedbacks.
Temperature also influences the magnetite solubility. In previous studies, some authors investigated the variation of FAC for carbon steel under single-phase flow and found that the maximum FAC rate occurs at temperatures ranging from 130 °C and 150 °C in neutral and alkaline solutions (7 < pH25 °C < 9) (Bignold et al., 1980; Heitmann and Schub, 1994; Rocchini, 1994), while the maximum FAC rate of carbon steel in two-phase flow was observed at about 180 °C (Keller, 1974). De Bouvier (De Bouvier, 2015a) recently reported that the maximum of FAC rate occurs between 150 °C and 180 °C. Therefore, the highest solubility of magnetite is expected to be between 150 °C and 180 °C as the greatest FAC rate temperature matches with the maximum of magnetite solubility (Corredera et al., 2008). It was observed in an unpublished EPRI study that the maximum of solubility is located at about 150 °C whatever the pH values ranging from 8.75 and 9.60 in the presence of ammonia at concentration between 0.1 and 2 ppm, respectively (Figure 1.5). Above 150 °C, magnetite solubility decreases with an increase of temperature (Figure 1.5).
Table of contents :
Chapter 1 State of the art
1.2 PWR secondary circuit
1.2.1 General description
1.2.2 Recirculating steam generator
1.2.3 Thermohydraulics in PWR steam generator
22.214.171.124 Two-phase flow fundamentals
126.96.36.199.1 Two-phase flow system basic notions
188.8.131.52.2 Two-phase flow patterns
184.108.40.206 Thermohydraulics of 51B type steam generators
1.2.4 Materials used in the secondary circuit
1.2.5 PWR secondary flow chemistry
1.2.6 Corrosion phenomena in PWR secondary circuit
220.127.116.11 Stress corrosion cracking (SCC)
18.104.22.168 General corrosion and Flow accelerated corrosion (FAC)
22.214.171.124 Parameters affecting flow accelerated corrosion – TSP clogging source
126.96.36.199.1 Effects of pH and temperature – magnetite solubility
188.8.131.52.2 Effect of oxygen concentration
184.108.40.206.3 Effect of material composition
220.127.116.11.4 Effect of thermohydraulics
1.3 Properties of magnetite particle
1.3.1 Structural property
1.3.2 Magnetite surface charge
18.104.22.168 Electrical double layer (EDL)
22.214.171.124 Zeta potential
126.96.36.199 Surface characterizations of magnetite
1.4 Steam generator degradation phenomena
1.4.1 Tube fouling
1.4.2 Tube Support Plate clogging
188.8.131.52 TSP clogging consequences
184.108.40.206 TSP clogging diagnosis
220.127.116.11.1 Televisual inspections
18.104.22.168.2 Wide Range Level (WRL) monitoring in stationary regime
22.214.171.124.3 Eddy current inspection
126.96.36.199 NPP feedbacks of TSP clogging
188.8.131.52 Current countermeasures
1.5 Phenomenology of TSP clogging formation
1.5.1 Magnetite particle deposition
184.108.40.206 Previous experimental studies
220.127.116.11 Magnetite particle deposition models
18.104.22.168.1 Transport step
22.214.171.124.2 Attachment step
1.5.2 Surface precipitation
126.96.36.199 Attainment of solubility
188.8.131.52 Formation of nuclei
184.108.40.206 Growth of crystals
1.5.3 Specific TSP clogging formation mechanisms at the inlet of TSP
220.127.116.11 Vena contracta mechanism
18.104.22.168 Results of modelling study comprising vena contracta and flashing
1.6 Conclusions of Chapter 1
Chapter 2 Experimental investigation of TSP clogging phenomenon
2.2 Representative experiments
2.2.1 Global deposit build-up tool under representative conditions: COLENTEC facility
2.2.2 COLENTEC – 2015 experimental conditions
2.2.3 Materials used for COLENTEC test
2.2.4 Characterization results of COLENTEC-2015 samples
22.214.171.124 Optical and SEM observations
126.96.36.199 TEM investigations
188.8.131.52.1 Characterization of titanium thin section
184.108.40.206.2 Characterization of stainless steel thin section
2.3 Simulated experiments
2.3.1 Description of autoclave tests
2.3.2 Iron incorporation into stainless steel corrosion layer
2.3.3 Ti/SS galvanic corrosion effects
2.4 Conclusions of Chapter 2
Chapter 3 Specific experimental investigation of deposit build-up by electrokinetic phenomenon
3.1 Introduction and basic notions of electrokinetically induced deposit
3.2 Literature review relative to the effects of water chemistry and thermohydraulics on electrokinetic deposit build-up
3.3 Experimental system
3.4 Experimental conditions
3.5.1 Morphology and characterization of the deposits
3.5.2 Deposit build-up rates
3.6.1 Effect of flow velocity
3.6.2 Comparisons with COLENTEC results and EDF observations
3.7 Conclusions of Chapter 3
Chapter 4 Numerical investigation of TSP clogging phenomenon
4.2 Hypotheses and input data
4.2.2 Input data
4.3.1 Phenomenon prioritization with different particle sizes
4.3.2 Phenomenon prioritization with different total iron concentrations
4.5 Conclusions of Chapter 4
Chapter 5 Overall conclusions and perspectives
Appendix A Scanning Electronic Microscope
Appendix B Transmission Electronic Microscope
Appendix C Synthesis of CeO2-Fe3O4 core-shell particles