The FeCrAl-oxide dispersion strengthened (ODS) alloy is the promising cladding material for the accident-tolerant fuel (ATF) of the light water reactors (LWR) to suppress the oxidation reaction with ...hot steam by Al2O3 formation. Ring-creep tests for FeCrAl-ODS alloy cladding were carried out at 973 K and 1273 K to evaluate the deformation mechanism at the sever accident. The temperature-compensated strain rate by Fe-diffusion coefficient versus the normalized stress by shear modulus was constructed. The dislocation detachment stress from the dispersoid was derived by considering the dislocation-dispersoid elastic interaction and the dislocation relaxation effect by climb motion. When the applied stress exceeds the dislocation detachment stress, dislocations overcome the dispersoids with the reduced values of the stress exponent, which is attributed to the dislocation climb motion. When the stress is lower than the dislocation detachment stress, large size of cavities exists at the grain boundaries. Grain boundary sliding (GBS) is dominant factor for the low strain rate creep deformation at 1273 K, where dislocation climb also plays a critical role for release of the stress concentration induced by GBS. Based on those findings, new constitutive equations for creep deformation were constructed, which is applicable to low stress, low strain rate and high temperature conditions encountered at the reactor sever accident.
Materials for future nuclear energy systems must operate under more extreme conditions than those in current Gen II or Gen III systems. These conditions include higher temperature, higher dpa, and ...more corrosive environments. This paper reviews some of the fuels and structural materials used in advanced nuclear energy systems and identifies promising candidates for these systems. Fuel systems includes metallic fuels for the sodium cooled reactor, TRISO-coated particle fuel for the high temperature gas reactor, molten salt reactor fuels, and accident tolerant fuels for light water reactors. Structural materials applications include the sodium fast reactor, lead fast reactor, high temperature gas reactor, molten salt reactor and extended life light water reactors. A final section focuses on plasma-facing and blanket materials for deuterium-tritium fusion reactors.
In this study, the microstructure of a 12Cr ferritic-martensitic oxide-dispersion-strengthened (ODS) alloy is studied before and after Fe ion irradiation up to 200 peak displacements per atom (dpa). ...Irradiation temperature ranges from 325 to 625 °C. Before irradiation, both coherent and incoherent dispersoids exist in the matrix. In response to irradiation, the mean sizes of dispersoids in both the ferrite and tempered martensite phases change to equilibrium values that increase with irradiation temperature. The evolution of dispersoids under irradiation is explained by a competition between athermal-radiation-driven shrinkage and thermal-diffusion-driven growth, with interface coherency affecting the growth mechanism. However, each coherency type exhibits different evolution behavior under irradiation. Coherent dispersoids, regardless of their initial size, change toward an equilibrium size at each temperature tested. On the other hand, incoherent dispersoids are destroyed at lower test temperatures but survive while shrinking in size at higher temperatures. This difference in behavior can be explained by the lower interfacial energy of coherent dispersoids in comparison with incoherent dispersoids. This study sheds light on the roles of interface configurations in maintaining dispersoid integrity under irradiation.
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The reactive elements (Ti, Al and Zr) have been widely used for the improvement of the strength or the oxide resistance of ODS steels. In the present work, we studied the effect of the reactive ...elements on the precipitation of oxide particles, especially focusing upon the appropriate amount of the oxide composing elements, by addition of the large amounts of Y
2
O
3
and reactive elements. The mechanically alloyed powders are annealed in a wide temperature range from 773 to 1423 K and then analysed by various analysis methods (small-angle X-ray scattering and X-ray diffraction by synchrotron radiation X-ray, scanning transmission electron microscope combined with energy dispersion X-ray spectroscopy, high-resolution transmission microscopy and 3D-atom probe). Ti, Al and Zr enhanced the growth of oxide particles, opposite to the many studies of Ti- and Zr-added ODS steels, as a result of the addition of Y
2
O
3
and these elements ten times larger than those for usual use. The nucleation and growth of oxide particles are discussed by simulating the critical radius of nucleation and the growth based on the LSW theory. Y
4
Zr
3
O
12
is stable and easy to precipitate even at lower annealing temperature. All reactive elements enhance the growth of oxide particles because of their big molar volume as compared to that of Y
2
O
3
.
The FeCrAl-oxide dispersion strengthened (ODS) alloy is a promising candidate alloy for the accident tolerant fuel (ATF) cladding of light water reactors (LWRs) and has been recently developed in ...Japan. This paper reports on the progress of the development of accident tolerant FeCrAl-ODS fuel claddings for boiling water reactors (BWRs) in Japan.
Both experimental and analytical studies were conducted to evaluate the influence of implementation of the FeCrAl-ODS fuel cladding to the current BWRs.
In the experimental study, key material properties of FeCrAl-ODS fuel cladding have been obtained and accumulated using bar, sheet and tube-shaped materials to support the evaluations in the analytical study. In the evaluation at normal operating conditions, strength and ductility, corrosion property, tritium permeability, wear property, resistance to iodine stress corrosion cracking (SCC) and weldability were examined. A preliminary assessment of compatibility of the FeCrAl-ODS fuel cladding with the current recycling system in Japan was also conducted. In the evaluation of the design basis accident and the beyond design basis accident, strength, steam oxidation property, resistance to water quenching during a loss-of-coolant accident (LOCA) and the LOCA burst property were examined.
In order to evaluate the influence of implementation of the FeCrAl-ODS cladding to the current BWRs, the core characteristics and the fuel behavior were evaluated in the analysis study at the normal operating condition. The analysis for the 9 × 9-type and the 10 × 10-type fuel assemblies and the reactor type of the Advanced BWR (ABWR) revealed a good applicability of FeCrAl-ODS fuel cladding.
Finally, the challenges and perspectives found in the program are highlighted to enhance international collaborations to promote the development of the FeCrAl-ODS fuel cladding.
Higher chromium containing 17Cr oxide dispersion strengthened (ODS) steel (Fe-16.78Cr-4.46Al-0.5Ti-0.45Y2O3-0.36Y) with the ferritic structure are a prospective applicant fuel cladding materials for ...the high operating temperatures of future advanced nuclear reactors system. In this study, the microstructure, passive oxide composition and corrosion resistance of the Al-containing 17Cr ODS steel in different concentrations of nitric acid were investigated by means of SEM, TEM, XPS and electrochemical methods. The corrosion result shows that with increasing concentration of 3 M–11.5 M HNO3, open circuit potential revealed nobler potential and the potentiodynamic polarization plots exhibited a shift in corrosion potential toward transpassive region. The boiling nitric acid test after 240 h exposed in 3 M–11.5 M HNO3 showed desirable corrosion rate of ∼0.075–0.25 mm/y. As the nitric acid concentration increased, the corrosion morphology varied from smaller pits to enlarged pits with groove-like features. The improved corrosion resistance of the ODS alloy is attributed to the alloy composition, nature of dispersed oxide and passive film nature, where Al2O3 is prominently enriched. The corrosion mechanisms of ODS steel is further discussed.
•The ennoblement of corrosion potential with an increase in nitric acid concentration.•17Cr ODS with 4.5 wt % Al exhibited lower corrosion rate in boiling nitric acid test.•XPS passive film analyses showed enrichment of Al2O3 in the passive layer.•Dispersed particles act as the pit initiation site.•The ODS steel corrosion mechanisms is discussed.
The high-temperature deformation mechanism of the FeCrAl-ODS ferritic steel was investigated at 1000 °C for the creep loading perpendicular to the elongated and aligned grains. The strain rate was ...varied in the range from the order of 10−2 to 10−7s−1. With decreasing strain rate from 10−2 to 10−5s−1, creep mechanism shifts from conventional dislocation creep pinned by oxide particles to grain boundary sliding (GBS) assisted concomitantly by diffusional creep. With further decreasing strain rate to 10−7s−1, deformation mechanism is drastically changed; group of three grains can move cooperatively, and cooperative GBS (CGBS) was originally recognized. The threshold stress for onset of CGBS was designated as σthI(CGBS). Rate limiting process of CGBS is dominated by dislocation movement over the oxide particles so as to relieve the stress accumulation due to CGBS. The σthI(CGBS) for CGBS corresponds to one third of the conventional threshold stress for dislocation creep.
•Creep deformation mechanism was studied for FeCrAl-ODS ferritic steels.•At the strain rate of 10−7s−1, cooperative grain boundary sliding (GCGBS) was discovered.•CGBS is dominated by dislocation movement over the oxide particles.•The threshold stress for CGBS was found to be one third of the conventional threshold stress for dislocation creep.
Currently, advanced ODS copper alloy is under study as a potential fusion material providing good mechanical properties. In this work, in order to develop a high performance ODS copper containing ...0.5 wt% Y2O3 oxide particles, the effect of room temperature rolling and subsequent annealing on the grain structure evolution, texture development and tensile properties are studied using EBSD, TEM and tensile tests. Microstructure evolution studies show the grain structure coarsens by enhancing the Brass texture during increase of rolling reduction and a unique single crystal-like brass-texture deformed structure is achieved after 80% rolling reduction. We found the deformation mechanism of partial slip by a6〈211〉 dislocations facilitated by the pinning of a2〈101〉 perfect dislocations through fine oxide particles is responsible for formation of Brass texture during room temperature rolling. Furthermore, the recrystallization of ODS copper retards to high temperature of ~700 °C and shows a fine-grained microstructure with different orientations of Goss, Brass, S and Copper. Evaluation of microstructure-mechanical properties of the recrystallized samples expresses that the bimodal grain size distribution at 800 °C for 30 min offers a good tensile strength-ductility (UTS: 491 MPa, elt: 19%) at ambient temperature.
•Corrosion resistance of oxide dispersion strengthened (ODS) steels is evaluated.•12% Cr ODS steel exhibited high corrosion rate in boiling 3M to 9M HNO3.•Increasing concentration of nitric acid ...increases corrosion rate in both ODS steels.•Lower corrosion rate of 15% Cr ODS steel in HNO3 was attributed to the role of Al.•The formation of Y–Ti–O and Y–Hf–O oxides may suppress intergranular corrosion.
The passive film compositions and corrosion resistance of 12% Cr and 15% Cr oxide dispersion strengthened (ODS) steels in 3M HNO3 to 9M HNO3 was evaluated. The potentiodynamic polarization plots exhibited a shift in corrosion potential, and higher passive current density with increasing HNO3 concentrations. In 12% Cr ODS steel, high corrosion rate was observed in all HNO3 concentrations. However, low corrosion rate observed in 15% Cr ODS steel was attributed to Al2O3 enrichment. The TEM analysis indicated a complex Y2Hf2O7 formation in 15% Cr ODS steel, and this may have a role in suppressing intergranular corrosion attack.
The growth of oxide particles in FeCrAl- oxide dispersion strengthened steel (ODSS) considering an accident condition of the light-water reactor at above 1500 K was studied by using a ...high-temperature annealing. Oxide particles grew from 9 nm to more than 50 nm as maximum at 1623 K for 27 h, with decreasing their number density in two orders of magnitude. Most of the oxide particles in 15Cr-7Al were identified as YAM or YAP, while the oxide particles in 15Cr-7Al-0.4Zr were identified trigonal Y4Zr3O12. Zr addition to 15Cr-7Al ODSS accelerated the growth of the oxide particles, which is quite contrary to the effect of Zr addition during sintering as suggested in the literature. The kinetics of coarsening was characterized by an equation of Ostwald ripening. The diffusion activation energies obtained in the present materials were quite larger than the conventional diffusion activation energy of Y in alpha-iron. Gibbs free energy of oxides should be considered to discuss the coarsening.
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