Temperature High Pressure Water Research Articles

Exploring heat treatment on the corrosion resistance of SA106B tubes in high temperature pressurized water with different flow velocities

The SA106B carbon steel was widely used for the pipeline in pressurized water reactor and suffered from severe high temperature corrosion. In this work, we expected to improve its corrosion resistance through simple heat treatment. The results showed that the tubes after the treatment normalized at 920 ℃ for 20 min and subsequently cooled in air displayed the best corrosion resistance due to the elimination of banded ferrite/pearlite structure, the reduction in the area ratio of anode/cathode and the decrease in grain size. In addition, the oxidation process and the effect of flow velocity were also discussed in detail.

Effect of fretting wear regimes on stress corrosion cracking of Alloy 690TT in high-temperature pressurized water

Stress corrosion cracks initiation and propagation of Alloy 690TT under different fretting regimes were investigated. The results indicated that mixed regime had the highest susceptibility to stress corrosion cracking, followed by gross slip regime, and then partial slip regime. Crack initiation depended on the distribution of residual strain induced by fretting regimes. In partial slip and mixed regimes, cracks were mainly initiated at the edge of the wear scar, while in gross slip regime, cracks were randomly distributed on the wear scar. Crack propagation was related to the type of grain boundaries and geometrically necessary dislocation density induced by fretting loading. In partial slip and gross slip regimes, cracks usually tended to propagate intergranularly. While in MR, cracks mainly propagated in a transgranular manner.

Blanket test facility for mockup testing on water cooled ceramic breeder blanket system

Intensive research and development activities have been conducted for designing a water-cooled ceramic breeder (WCCB) blanket system. In this system 325 °C/15.5 MPa of pressurized water removes heat injected and accumulated in blanket containers made of a reduced activation ferritic/martensitic steel, F82H. The container has lithium ceramics and beryllium pebbles as tritium breeder and neutron multiplier, respectively. In order to demonstrate performance of the system, especially for high-temperature pressurized water coolant, experimental apparatus have been installed in Rokkasho Fusion Institute, National Institutes for Quantum Science and Technology, Japan. These apparatuses enable to conduct the following experiment on full-scale mockups: 1) high heat flux (HHF) test to demonstrate heat removal of surface heat flux by electron beam gun simulating plasma, 2) flow assisted corrosion, 3) coolant ingress into dummy pebble beds, and 4) beryllium-water reaction between the coolant and the pebbles. In this paper, overviews, specifications, early results of these apparatus are reported.

Thermal corrosion fatigue crack growth behavior and life prediction of 304SS pipeline structures in high temperature pressurized water

The influence of transient water temperature changes on the fatigue crack growth behavior of 304SS pipeline structures was studied based on high-throughput testing method through the modification of dual loop circulating water equipment. Results demonstrated that the fatigue crack growth rate gradually decreased with the decrease of cooling rate, and the crack growth rate was exponentially related to the cooling rate. Both the base material and weld of the stepped pipe showed a transgranular cracking mode, and propagated continuously by slip-oxidation mechanism. Compared with the fine equiaxed grain of the base material, the grain in the weld was coarse and the residual strain was large, and the crack growth rate of the weld was obviously higher. Then, the thermal fatigue crack growth rate model for stepped pipes was established by combining finite element thermo-mechanical coupling simulation and three-dimensional crack propagation analysis software, and the model was modified based on the experimental results.

Effects of pressurized water reactor environment and cyclic loading parameters on the low cycle fatigue behavior of 304L stainless steel

Austenitic stainless steels used in light water reactor coolant environments are susceptible to environmentally assisted fatigue due to non-monotonic loading conditions, primarily associated with load-follow, thermal transients, or intermittent plant shutdowns and start-ups. This study investigates the effects of a high-temperature pressurized water reactor (PWR) water environment and cyclic loading parameters on the low cycle fatigue behavior of austenitic 304L stainless steel. Prolonged exposure to a PWR environment and cyclic loading conditions such as a lower strain rate or a higher fraction of slow strain rate enhances the initiation and accelerates the crack growth rate of fatigue cracks, resulting in decreased fatigue life. The deformation-induced α'-martensite is observed in proximity to fatigue crack tips primarily in specimens tested in simulated PWR primary water, while cellular dislocation structures are more frequently observed near crack tips in specimens tested in high-temperature air. The deformation-induced martensitic transformation from γ-austenite to α'-martensite, occurring via the precursor ε-martensite phase, contributes to the accelerated fatigue crack growth rate in a PWR environment with hydrogen.

Effect of thermal aging on the low cycle fatigue behavior of Z3CN20.09M stainless steel in high-temperature pressurized water

The effect of thermal aging (0 h- 15,000 h at 400 °C) on the low cycle fatigue properties of Z3CN20.09M stainless steel was investigated. The micro-hardness of the ferrite increases with thermal aging time, while that of the austenite is almost unchanged. The fatigue life of Z3CN20.09M stainless steel in high-temperature pressurized water decreases with thermal aging time. The fatigue cracks formed everywhere, mainly including at slip bands in austenite, at the δ/γ phase boundary and in ferrite. Thermal aging promotes crack initiation and propagation in ferrite. The effect of thermal aging on the fatigue damage process is discussed.

Microstructurally and mechanically small fatigue crack growth behaviors of 316LN stainless steel in high-temperature pressurized water

Corrosion fatigue behaviors at different stages of microstructurally small crack (MSC) and mechanically small crack (MeSC) for 316LN stainless steel were investigated in high-temperature pressurized water by interrupted tests. An improved model about the proportion in total fatigue life and growth rate for the MSC and MeSC has been proposed. It is found that the proportion in total fatigue life for the MSC is lower and the crack growth rate is higher at a lower strain rate due to the high plastic deformation and dislocation density at grain boundary. Mechanism of crack growth in high-temperature pressurized water is discussed.

Sequence and mechanism of early microstructure evolution in alloy 690TT subjected to fretting corrosion in high temperature pressurized water

The fretting corrosion-induced early microstructure evolution of Alloy 690TT was investigated. The results indicated that multiple material transfers of 405 SS caused nano-cavities formed, which provided nucleation sites for internal oxidation of the material transfer layer (MTL), and fretting corrosion-induced nano-grains boundaries offered massively high pathways for oxygen diffusion and accelerated oxidation process. An oxide layer developed on MTL by sufficient oxidation and persistent mechanical effect. Under fretting loading, high-density geometrically necessary boundaries (GNBs) appeared inside matrix and developed into deformation layer. With GNBs orientation increased, tribologically transformed structure (TTS) formed. The formation mechanism of TTS was continuous dynamic recrystallization.

Effect of temperature on the fretting wear behavior of Cr-coated Zircaloy cladding in high-temperature pressurized water

Cr-based coatings are promising candidates to protect the claddings on accident-tolerant fuel (ATF) rods in pressurized water reactors (PWRs). In this study, the effect of water temperature on the fretting wear behavior of an N36 Zirconium alloy cladding was investigated. In addition, the effect of applying a protective Cr coating to the cladding was also analyzed. Fretting wear tests were carried out using a unique apparatus that simulated the high-temperature and high-pressure (HTHP) water environment in a real PWR. Results show that changes in temperature alter the wear mechanism of cladding tubes. Furthermore, a Cr-coating improves the wear resistance of an N36 cladding significantly. The main wear mechanisms of Cr-coated cladding in HTHP water were observed to be abrasive and adhesive wear. The protective effect of a Cr coating on the cladding in a low-temperature water environment (25 °C, 90 °C) was less than it was in a high-temperature water environment (260 °C, 315 °C), indicating that Cr coatings can improve wear resistance in HTHP water.

Fretting wear behavior of Zr alloy cladding tube mated with Zr alloy dimple under mixed fretting regime in simulated primary water of PWR

The fretting wear behavior of Zr alloy cladding tube under mixed fretting regime in a high-temperature pressurized water was investigated. The main wear mechanism is adhesive wear, with characters of small-scale delamination at the center of worn area and serious delamination on the worn edge. A long crack throughout the worn area and other cracks propagated towards the substrate are observed. The cross-sectional microstructure of worn area can be divided into a thick third-body layer, thin inner oxide layer and thick tribologically transformed structure layer, and their formation mechanisms are analyzed in detail. Finally, the mixed fretting regime process and the microstructural evolution during fretting wear are discussed.

Effects of Zn injection into boric acid and lithium hydroxide solutions on the corrosion behaviors of 316LN stainless steel in simulated hot functional test high-temperature pressurized water

The effects of Zn injection into boric acid and lithium hydroxide solutions on the corrosion behaviors of 316LN stainless steel (SS) in simulated hot functional test (HFT) high-temperature pressurized water at 573 K were investigated. Low concentration of lithium hydroxide solutions with 20–100 ppb Zn injection are recommended for Zn-injected HFT water chemistry and the beneficial effects of Zn injection into both HFT and primary coolant water chemistry are confirmed in view of the protective properties of the oxide films on 316LN SS. The Zn injection involved corrosion mechanism during HFT is discussed.

Corrosion fatigue damage mechanism and life evaluation of Inconel Alloy 690TT steam generator tube in high temperature pressurized water

Corrosion fatigue behavior of the actual Alloy 690TT steam generator (SG) tubes in high temperature water were systematically studied by using the designed boat-shaped specimen. Results demonstrated that the environmental fatigue correction coefficient of the SG tube in high temperature water was lower than that of round bar specimen in ANL model, which may be related to the internal surface oxide film rupture-persistent slip bands (PSBs) deformation zone preferential dissolution caused by the shape effect of SG tube. Moreover, the corrosion fatigue life of the actual SG tube was evaluated by the method of model correction.

Effects of Zn injection on corrosion behavior and crud deposition of FeCrAl fuel cladding under subcooled nuclear boiling condition in high-temperature pressurized water

The effects of Zn injection on corrosion behavior and crud deposition of FeCrAl fuel cladding in high-temperature pressurized water were investigated under subcooled nuclear boiling condition. The crud deposition and the growth of double-layered oxide films under the crud occurred simultaneously. Zn injection decreased the oxide films thickness and reduced the quantity/size of the outer oxide particles. These effects changed the surface roughness and wettability of the oxide films, resulting in a reduction of deposited crud at the initial stage. Both Zn and released matrix elements could be incorporated into the crud and Zn reduced the size of crud particles.

Establishment of fretting maps of Zr alloy cladding tube mated with Zr alloy dimple in simulated primary water of pressurized water reactor

Fretting maps of Zr alloy tube under grid-to-rod configuration in high temperature pressurised water were established. Running condition fretting map shows three fretting regimes, namely, partial slip regime, mixed fretting regime and gross slip regime. According to material response fretting map, the wear mechanism under partial slip regime is adhesive wear with the character of delamination of local regions, both adhesive wear and cracking are found for mixed fretting regime, while abrasive wear and severe delamination for gross slip regime. Compared with the results at room temperature, the mixed fretting regime range increases obviously at high temperature, while friction coefficient at high temperature is lower. In addition, fretting wear behaviour of Zr alloy tube under different fretting regimes is discussed.

Effect of surface roughness on low-cycle fatigue behaviors of 316LN stainless steel in borated and lithiated high-temperature pressurized water

Low-cycle fatigue behaviors of 316LN stainless steel with three surface roughness were investigated in high-temperature pressurized water at different strain rates (0.001−0.04%/s) under strain amplitude of 0.3%. More significant reduction of fatigue life was found for samples with higher roughness. The environmental fatigue effects with different surface roughness were strain rate dependent and the weakened effect at low strain rates was related to the plastic deformation layers which enhanced the diffusion of Cr and played an inhibiting role on fatigue crack growth. Besides, the fatigue damage mechanisms for polished and rough samples are discussed.

Fretting corrosion-induced microstructural evolution of Alloy 690TT tube in high temperature pressurised water

The friction-induced microstructural evolution of Alloy 690TT tubes submerged in a high temperature pressurised water was investigated. Two typical local regions characterised by significantly different worn morphologies (resulting from the stress field and material couple) were investigated in detail. A thin third-body layer and a thick Fe-rich layer were observed and their oxidation behaviour was analysed. Moreover, the main oxide was spinel, whereas the amorphous band was only observed in the Fe-rich layer. The tribologically transformed structure is formed by the mechanism of discontinuous dynamic recrystallisation. Finally, the microstructural evolution of the two areas during fretting corrosion is discussed.

Fretting wear behaviour of Zr alloy cladding tube under partial slip regime with different duration in simulated primary water of PWR

The fretting wear behaviour of Zr alloy cladding tubes under partial slip regime in a high temperature pressurised water was investigated. The fretting regime remained unchanged with the increasing fretting time and hence both the wear volume and depth of the worn scars formed on Zr cladding tubes changed slightly. The wear mechanism was delamination at some local regions, resulting in a slight damage. Third-body layer, oxide layer, tribologically transformed structure layer, and general deformation layer were observed form the cross-section of the worn scar and their formation mechanisms were analysed in detail. Moreover, from the metal/oxide interface to surface, the main oxide transitioned from tetragonal-ZrO2 to monoclinic-ZrO2. Finally, the partial slip regime process and the microstructural evolution during fretting wear were discussed.

Effects of cutting parameter on microstructure and corrosion behavior of 304 stainless steel in simulated primary water

• Cutting can induce a gradient surface microstructure with a several microns deep fine-grain layer on top, followed by several tens or hundreds of micrometers deep plastic deformation region. • Even with the similar surface roughness, the deformation microstructure can be very different due to the different cutting parameters. • The effect degree on the depth of machining-affected zone (MAZ) is feed rate > cutting depth > cutting speed. • At the same depth of MAZ, the localized corrosion rate along the deformation bands is higher than that along the grain boundaries. The influence of surface conditions on the corrosion behavior of engineering structures has been paid more attention. However, there is still a lack of systematic research on the effect of cutting parameters on material's microstructure and performance in service. In this paper, the effect of cutting parameters on microstructure and corrosion behaviors of 304 stainless steel in simulated primary water is well investigated. The results show that different cutting parameters can cause the superficial layer a gradient microstructure with nanocrystalized layer on top and deformation band structures underneath. With the similar surface roughness, the deformation microstructure can be very different due to the different cutting parameters. The effect degree on the depth of deformation zone is feed rate > cutting depth > cutting speed. The larger feed rate, lower cutting depth, lower cutting rate may induce a deeper deformation zone. With the increasing depth away from the machined surface, the localized corrosion rate is decreased, and at the same depth the localized corrosion rate along the deformation bands is higher than that along the grain boundaries (GBs). The nanocrystalized surface has a smallest general corrosion rate due to the quick formation of Cr rich oxide film. However, once the corrosion penetrates through this nanocrystalized layer, subsequent preferential corrosion at deformation bands and GBs will dominate and may lead to the significant increase of corrosion rate of the component in high temperature pressurized water.

Crud deposition behavior on zirconium alloy fuel cladding in high-temperature pressurized water environments

Crud deposition behavior on zirconium alloy fuel cladding in high-temperature pressurized oxygenated water environments was investigated. Porous crud with typical boiling chimney was found on the cladding surface which is similar to the crud observed in nuclear power plants. Crud particles were identified as Fe2O3 and NiFe2O4 when Fe3+ was added individually and Fe3+ and Ni2+ were injected simultaneously, respectively. Boron enrichment was detected on the whole cross section of the porous crud layer. The mechanisms of crud deposition on the fuel cladding and the boron enrichment within the crud are discussed.

Some fundamental understandings of Zn-injection water chemistry on material corrosion in pressurized water reactor primary circuit

The optimization of water chemistry in pressurized water reactor (PWR) primary circuit is one of the most effective ways to achieve both safety and economy for operating PWR nuclear power plants (NPPs). Special attention has been paid to fundamental research and engineering application of Zn-injection water chemistry (ZWC) in PWR primary circuit in recent years in China due to the rapid development of nuclear power. The present paper mainly reports the status of PWR NPPs in China and some fundamental understandings of ZWC on material corrosion. Effects of temperature (T), pH at T value, Zn concentration, Zn-injection sequence and lasting time on electrochemical corrosion behavior, oxide film characteristic and stress corrosion cracking (SCC) susceptibility of nuclear-grade austenitic alloys were investigated. A modified point defect model was used to discuss the effects of ZWC on the oxide films in high-temperature pressurized water. Some water chemistry parameters in PWR primary coolant system are proposed for mitigating corrosion and SCC of nuclear-grade austenitic alloys.