Future Reactors Research Articles

Interlocked interface of W–Y2O3/CuCrZr joint obtained by W–Y2O3 surface nanoporosification and Cu magnetron sputtering

The development of a method for bonding W–Y2O3 composites and CuCrZr heat sinks, which can meet the requirements of future magnetic confinement fusion devices, is a key problem that needs to be urgently solved. In this work, CuCrZr was vacuum-diffusion-bonded with W–Y2O3 modified using surface nanoporosification, Cu magnetron sputtering, and annealing. Columnar Cu grains grew perpendicular to the surface nanoporous structure with a preferential Cu [111] orientation during sputtering deposition. A Cu layer was formed on the W–Y2O3 nanoporous surface after Cu sputtering deposition and annealing, resulting in an interlocked and tightly bonded interface. The obtained W–Y2O3/CuCrZr joint exhibited a shear strength of 217 MPa, which was much higher than that of a joint without interface modification (147 MPa). The interface of the W–Y2O3/CuCrZr joint was composed of an interaction layer formed by nano-sized W particles and sputter-deposited Cu. Deposited Cu was embedded in the surface nanopores on W–Y2O3, forming a semi-coherent W/Cu interface, realizing mechanical metallurgical bonding between the W–Y2O3 alloy and Cu, and thus enhancing the interface bonding strength. Improving the strength of W–Y2O3/CuCrZr joints by constructing a well-integrated interface facilitates the development of plasma-facing components for future China Fusion Engineering Test Reactor (CFETR).

Whole core thermal-hydraulic analysis considering inter-wrapper flow phenomena in the liquid metal cooled fast reactor

The inter-wrapper flow (IWF) phenomenon is identified as an integral part of the full core thermal-hydraulic simulation for liquid metal cooled fast reactors. In this work, a whole core thermal-hydraulic simulation code based on the subchannel analysis method, named KMC-FBc, is developed. Both the “two-step” and pin-by-pin level methodologies are investigated together with several inter-wrapper flow and heat transfer models, which are numerically solved simultaneously. To validate the code, it is compared with the experimental data from KALLA-IWF test and the numerical simulation results from computational fluid dynamics (CFD). Both normal conditions and flow blockage scenarios show that the pin-by-pin level method has better accuracy than the two-step method. An in-depth assessment of the influence of different IWF models on the medium-power lead-cooled fast reactor M2LFR-1000 is performed. Current results indicate that IWF heat transfer has little effect on the maximum temperatures and overall thermal-hydraulic characteristics under nominal conditions, while in the internal flow blockage scenario, IWF heat transfer will greatly reduce the maximum temperatures of fuel pellets and cladding, which can improve the accuracy of the whole core thermal-hydraulic analysis and provide margins for future reactor design and optimization.

Radiative pulsed L-mode operation in ARC-class reactors

A new ARC-class, highly-radiative, pulsed, L-mode, burning plasma scenario is developed and evaluated as a candidate for future tokamak reactors. Pulsed inductive operation alleviates the stringent current drive requirements of steady-state reactors, and operation in L-mode affords ELM-free access to core radiation fractions, significantly reducing the divertor power handling requirements. In this configuration the fusion power density can be maximized despite L-mode confinement by utilizing high-field to increase plasma densities and current. This allows us to obtain high gain in robust scenarios in compact devices with P fus > 1000 MW despite low confinement. We demonstrate the feasibility of such scenarios here; first by showing that they avoid violating 0D tokamak limits, and then by performing self-consistent integrated simulations of flattop operation including neoclassical and turbulent transport, magnetic equilibrium, and radiofrequency current drive models. Finally we examine the potential effect of introducing negative triangularity with a 0D model. Our results show high-field radiative pulsed L-mode scenarios are a promising alternative to the typical steady state advanced tokamak scenarios which have dominated tokamak reactor development.

Core localized alpha-channeling via low frequency Alfvén mode generation in reversed shear scenarios

A novel channel for fuel ions heating in tokamak core plasma is proposed and analyzed using nonlinear gyrokinetic theory. The channel is achieved via spontaneous decay of reversed shear Alfvén eigenmode (RSAE) into low frequency Alfvén modes, which then heat fuel ions via collisionless ion Landau damping. The conditions for RSAE spontaneous decay are investigated, and the saturation level and the consequent fuel ion heating rate are also derived. The channel is expected to be crucial for future reactors operating under reversed shear configurations, where fusion alpha particles are generated in the tokamak core with the magnetic shear being, typically, reversed, and there is a dense RSAE spectrum due to the small alpha particle characteristic dimensionless orbits.

Li6BaLa2Ta2O12 solid State Probe for Molten Alloys

Nowadays, most of the energy consumption depends on carbon-based sources such as petroleum, natural gas and coal. If the current trend of CO2 emissions continues, the increment in the global average temperature will exceed 2oC (by 2050). Therefore, there is a need to develop new energy sources to reduce the environmental footprint. In this frame, nuclear fusion appears as a carbon-free alternative that perfectly fits in this sustainable transition. Future fusion reactors are expected to use deuterium and tritium as fuel. On the one hand, deuterium is a stable isotope that can be obtained from water. On the other hand, tritium is a radioactive isotope with a relatively short half-life (12.3 years) and must be generated in the reactor itself. For this purpose, it is suggested that lithium will react with high energy neutrons to produce this hydrogen isotope. 6Li + n → 4He + 3H + 4.8MeVThis nuclear reaction will take place in the tritium breeding modules. Molten Pb-Li alloy, in its eutectic composition, is considered the main breeding candidate. According to reaction (1), lithium will be consumed. Therefore, to maintain the eutectic composition, it is crucial to control both the concentration and the dosage of lithium. As future nuclear reactors will deal with extreme operational conditions, sensors based on solid-state electrolytes are a promising tool to monitor this lithium content.In the present work, potentiometric sensors to measure Li concentration in molten Sn-Li alloys were constructed. These alloys will be used as a first step before Pb-Li assays. For that, Li6BaLa2Ta2O12 (LBLTO) solid-state electrolyte was synthesized and sintered as a pellet. EIS measurements were performed to evaluate the ionic conductivity of the sintered pellets at temperatures from 30 to 300ºC. These pellets were sealed in alumina tubes using a glass binder for sensor construction. On the one hand, Sn-Li alloys with different lithium contents (from 3at%Li up to 10at%Li) were used in the working electrode. On the other hand, a 3at%Li Sn-Li alloy was considered as the reference electrode. Potentiometric measurements were performed at different temperatures. Correlation curves of the recorded potentials versus the Li activity were in good agreement with the Nernst equation.

Studies of aluminum erosion by neutral particles using quartz crystal microbalance and low energy neutral particle analyzer on EAST

The neutral-induced material erosion is still an unsolved issue for ITER and future reactors, which influences the lifetime of the first wall material and tritium retention rate. A low energy neutral particle analyzer (LENPA) and a quartz crystal microbalance (QMB) were recently installed together on the equatorial port of sector H in EAST to study neutral-induced material erosion. The QMB can provide real-time and in-situ measurements on the erosion process of the wall material, while the neutral energy spectrum given by LENPA can help to calculate the material erosion rate for comparison with QMB results. In the 2021 EAST summer campaign, neutral-induced Al erosion was successfully studied with the two available diagnostics for the first time. In a series of long-pulse discharges, the average Al erosion rates measured by the QMB are consistent with the theoretical calculations using the LENPA data. Furthermore, the changes in plasma density, heating power and the real-time lithium powder injection result in different neutral flux and energy, which lead to changes in the neutral-induced material erosion rates.

Experiments and modelling on ASDEX Upgrade and WEST in support of tool development for tokamak reactor armour melting assessments

The risk of metallic armour melting constitutes a major concern for ITER and DEMO. Combined computational and experimental effort has led to a successful understanding of melt dynamics in present-day tokamaks, but there remain unexplored melting regimes of relevance to future reactors. Analysis of recent poor-versus-efficient thermionic emitter sample exposures in ASDEX-Upgrade and ITER-like actively cooled tungsten leading edge exposures in WEST is presented. The coupled thermal response and melt dynamics is modelled with the new MEMENTO code employing the MEMOS-U physics model which has no adjustable parameters. In the weak Lorentz force regime accessed in the exposures, very close agreement between modelling and experiments is achieved not only for the deformation profiles, but also for the additional, unique to these experiments, constraints; simultaneous thermal response of two different materials in ASDEX-Upgrade and in-situ detection of melt build-up in WEST. • Two new melt experiments in ASDEX-Upgrade and WEST have accessed previously unexplored regimes. • The impact of thermionic emission in the energy and momentum balance of tungsten melting events is assessed. • Typically inaccessible in previous experiments secondary thermo-capillary effects are unmasked. • The coupled thermal response and melt dynamics is modelled with the new 5MF code employing the MEMOS-U physics model. • Enhanced value of the model validation effort due to existence of novel, unique to these experiments, constraints.

Development and assessment of a reactor system prognosis model with physics-guided machine learning

Autonomous control systems provide recommendations to help operators in decision-making during plant operations ranging from normal operation to accident management. An important step of autonomous control is prognosis. In nuclear engineering domain, prognosis is the process of predicting future conditions of a system or equipment based on present signs and symptoms of a fault. The prognosis model allows predicting future reactor states for possible candidate control strategies so that the outcomes can be evaluated to determine the best control strategy. The prognosis model requires representing direct relationships between the symptoms and the predictions. In nuclear engineering, computational simulations are approximate representations of the operation of the real system. However, prognosis with computational simulations requires high computation power and time due to possible large number of scenarios. Necessary computation resources can be reduced with machine learning (ML) approach for fast predictions by building a surrogate function using the simulation data. A critical issue is, ML models are ignorant of physical knowledge, and these models approximate statistical relationships between the system variables. This ignorance can produce results that are inconsistent with physical laws, even if an optimal result is achieved from a mathematical point of view. Physics-guided machine learning (PGML) is an approach to tackle this issue. This work formulates and illustrates a framework to guide development and assessment of the ML-based prognosis model for autonomous control systems. The development of the prognosis model considers the training of a ML model which consists of optimizing many aspects of the ML approach. The assessment of the prognosis model considers training data limitations and uncertainties of the ML approach. Prognosis models with standalone ML and PGML are developed and assessed on the loss-of-flow scenario of Experimental Breeder Reactor II. The results indicate that PGML based prognosis model has the best performance compared to other prognosis models.

Damage threshold of CuCrFeTiV high entropy alloys for nuclear fusion reactors

A CuCrFeTiV high entropy alloy was prepared and irradiated with swift heavy ions in order to check its adequacy for use as a thermal barrier in future nuclear fusion reactors. The alloy was prepared from the elemental powders by ball milling, followed by consolidation by spark plasma sintering at 1178 K and 65 MPa. The samples were then irradiated at room temperature with 300 keV Ar+ ions with fluences in the 3 × 1015 to 3 × 1018 Ar+/cm2 range to mimic neutron-induced damage accumulation during a duty cycle of a fusion reactor. Structural changes were investigated by X-ray diffraction, and scanning electron microscopy and scanning transmission electron microscopy, both coupled with X-ray energy dispersive spectroscopy. Surface irradiation damage was detected for high fluences (3 × 1018 Ar+/cm2) with formation of blisters of up to 1 μm in diameter. Cross-sectional scanning transmission electron microscopy showed the presence of intergranular cavities only in the sample irradiated with 3 × 1018 Ar+/cm2, while all irradiation experiments produced intragranular nanometric-sized bubbles with increased density for higher Ar+ fluence. The Williamson-Hall method revealed a decrease in the average crystallite size and an increase in residual strain with increasing fluence, consistent with the formation of Ar+ bubbles at the irradiated surface.

Nonlinear MHD modeling of n = 1 RMP-induced pedestal transport and mode coupling effects on ELM suppression in KSTAR

Fully suppressing edge-localized modes (ELMs), e.g., with resonant magnetic perturbations (RMPs), is essential to reach and sustain high-performance steady-state H-mode plasmas because large ELMs can significantly reduce the lifetime of divertor components in future tokamak reactors. RMP-driven ELM suppression in KSTAR has been modeled by coupling the neoclassical transport code PENTRC to the nonlinear 3D MHD code JOREK. We have found that the radial transport from the combined effects of the kink-peeling, tearing response, and neoclassical toroidal viscosity can explain the pedestal degradation observed in experiments. In addition, it has been found that the RMP response can increase the inter-ELM heat flux on the lower outer divertor by redistributing the heat transport between the divertor plates. In addition to the degraded pedestal, ELM suppression is also attributable to the RMP-induced mode interactions. While the linear stability of peeling-ballooning mode (PBMs) improves owing to the degraded pedestal, the PBM and RMP interaction increases the spectral transfer between edge harmonics, preventing catastrophic growth and the crash of unstable modes. Here, it turns out that the magnetic islands near the pedestal top can play a vital role in mediating the mode interactions.

Updates on CEA Design and Experimental Activities on EU DEMO TF System

In the framework of EU design activities for dimensioning the future fusion DEMOnstration reactor (DEMO), in-depth analyses were conducted in EUROfusion context, aiming to define the design of the DEMO magnets system. For the last DEMO baseline, CEA has proposed for Toroidal Field (TF) coils a concept with radial plates (named WP#4) which is ITER-like, with a round conductor embedded in steel plates. In order to consolidate this design, CEA conducted fine analyses that assess thermal hydraulic and mechanical aspects to allow ensuring compliance with design criteria. The outcomes of theses analyses were used to improve the TF design in order to avoid relying on conservative approaches at pre-design stage, which often end up in material over dimensioning, that penalize cost and space occupation. In this regard, two improving approaches will be exposed, that deal with mechanical consideration and temperature operation, together with future perspectives. On the other hand, CEA designed and manufactured in collaboration with ASIPP a full-size conductor sample derived from a previous TF CEA concept (square-in-square conductor) which is expected to operate at 88 kA and 12T. The two conductor legs of this sample were designed by CEA and manufactured by ASIPP following an extensive quality assurance (QA) preparation process. The sample is presently in course of assembly in CEA Cadarache and is expected to be tested in SULTAN facility (Villigen, CH) to assess its behaviour in both DC and AC regimes. An overview of the status of activities and future perspectives is given in this paper.

Thermal degradation of emerging contaminants in municipal biosolids: The case of pharmaceuticals and personal care products

The presence of emerging contaminants in water and wastewater resources is of ongoing concern for public health and safety. Pharmaceutical compounds are designed to be biologically active and therefore may have effects on nontarget organisms in terrestrial and aquatic environments, even at trace concentrations. The presence of pharmaceutical and personal care products (PPCPs) in wastewater treatment plants is reported in various countries worldwide, mostly in the levels of nanograms to micrograms per litre. The present study investigates the thermal degradation of municipal sewage sludge containing PPCPs at various heating rates. The examined characteristics of the samples include thermal decomposition behavior, volatile release characteristics, and pyrolytic product composition. Thermal characterization of the PPCPs was conducted using differential scanning calorimetry. The gaseous products and typical functional groups of the released volatiles detected by Fourier-transform infrared spectroscopy mainly contained CO2, CO, small-chain hydrocarbons, and oxygen- and nitrogen-containing functional groups together with other species. In addition, the potential of bioenergy production was investigated as a spin-off opportunity during thermal degradation of biosolids. Study results showed that PPCP concentrations can be lowered significantly by thermal treatment of municipal biosolids. Antifungal/antibacterial agents together with opioids, in particular triclosan and tramadol, showed less resistance to thermal degradation while antibiotics could be more recalcitrant to heat treatment. The thermodynamic results provide an important reference for future reactor design and the thermochemical treatment of biosolids as well as their conversion to value-added products.

Evaluation of the impact of experimental fusion-aimed installations on their area of influence: the price of sustainable energy

The need of clean, stable, safe and free of uncertainty energy sources has been increased after the current geopolitical tension. In this framework, nuclear energy is receiving renewed attention which finally led the European Commission to consider it as Green Energy. In spite of the expected "golden age" of nuclear energy, the fission still has some problems that must be solved. For this reason, the research on nuclear fusion is now and more than ever a real must. The path towards the control of fusion is plenty of technical difficulties, mainly related to the extreme temperatures and pressures needed and also to the neutronic radiation. The International Fusion Materials Irradiation Facility – Demo Oriented NEutron Source (IFMIF-DONES) is an experimental facility whose target s the testing of materials with fusion-like neutrons in order to evaluate the damages and decide which material is the most convenient to build the future reactors. The impact of IFMIF-DONES on the people living in the area where it is going to be located (Escúzar, Province of Granada, Spain) has been evaluated through a survey among its inhabitants. The results are presented and discussed in this work.

Strategy for Developing the EU-DEMO Magnet System in the Concept Design Phase

Fusion power plants offer the prospect of a new sustainable source of energy for future generations. The design and R&D of future reactors is expected to largely benefit from the experience gained in the design, construction and operation of ITER. However, deploying reliable fusion power plants, requires to overcome the design challenges and to address the remaining readiness gaps. Europe is starting the Conceptual Design Phase for building a superconducting DEMOnstration Fusion Power Plant (DEMO) and starting operations around the middle of the century. The aim is demonstrating the production of 500 MW of net electricity, with a closed tritium fuel cycle and adequate plant availability. For the design of the Superconducting Magnet System several variants of coils have been investigated in the pre-conceptual design phase, which has concluded in 2020. Some of them are very close to ITER design, therefore have a relatively high technology readiness level. The “alternative” proposed solutions, that are very promising in terms of costs and performances, need a validation to industrial scale in order to be eligible for the down-selection expected in 2024. In particular, the validation regards the design of the layer-wound graded TF winding pack based on React-and-Wind Nb <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sub> Sn conductors, and the hybrid, layer-wound graded CS coil. The challenging aspect is that the CS magnet is made of REBCO conductors in high-field, React-and-Wind Nb <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sub> Sn conductors in medium field and NbTi conductors in low field. Also innovative techniques need to be studied for insulating critical parts of the coils, as penetrations, discontinuities and joints. The main issues of the technological development are illustrated. A R&D work plan is presented for the Conceptual Design phase to validate the technology within 2024 and demonstrate the operational capabilities by testing superconducting insert coils, that is about 50-m long wound conductors, by 2027.

Validating NEUTRO, a deterministic finite element neutron transport solver for fusion applications, with literature tests, experimental benchmarks and other neutronic codes

Neutron reactions on fusion reactor materials are key phenomena to be understood to enable fusion as a feasible energy source for future reactors. We present significant improvements and validations of NEUTRO, a deterministic neutron transport code dedicated to solving the Boltzmann transport equation. The code is integrated as a module in the Alya system developed by the Barcelona Supercomputing Center and uses the discrete ordinates method over an angular portion, multigroup for energy discretization and the finite element method over unstructured meshes to treat special complex domains. Material anisotropy of the scattering medium is introduced into the scattering kernel using real base expressions for spherical harmonics. In order to build the total cross-section and the respective group matrix for the elastic cross-section, we use the NJOY code. We test the solver using different geometries and materials with varying levels of scattering properties. We compare our results on classic tests, benchmarks obtained from a Nuclear Energy Agency database and test cases using other neutron transport codes.

PMT Signal Transmission for Hard X-Ray Diagnostics of Future Tokamaks

A pair of a scintillator and a Photomultiplier Tube (PMT) is often used as a Hard X-Ray (HXR) radiation detector in existing tokamaks such as JET, EAST, COMPASS or ASDEX-U. Future nuclear fusion reactors such as ITER or DEMO will use more powerful magnets and confine a larger volume of hot plasma. Placement of the detectors used for plasma diagnostic will be constrained by high temperatures, magnetic fields and ionizing radiation present near the tokamak vessel. It might be necessary to move detectors away from tokamak to a safer location. This might generate problems with pulse discrimination and transmission of the signal. In the case of the ITER tokamak, sensitive electronics such as digitizers cannot be installed close to the reactor due to harsh environmental conditions. A new approach to component placement is needed to protect those devices. The PMT signal will be transmitted via an over 100 m long coaxial cable to the digitizer located in the adjacent diagnostic building. The long cables will introduce additional signal attenuation. Also, the RF noise from the tokamak environment can couple into the signal. To improve the signal-to-noise ratio a dedicated PMT amplifier with a high output range (from + 1.5 to − 11 V) was proposed.The paper presents issues with signal transmission in HXR diagnostic systems and includes a discussion on the methodology of PMT signal transmission in the conditions of the future tokamaks. A proposal of guidelines for selection of the signal chain components and design of a dedicated PMT amplifier is part of this paper.

Friction factor and Reynolds number correlation for finned tube bundle of the air cooler of Monju reactor

Applicability of the analysis model of the cooling ability under a high temperature and low flowrate condition should be improved to evaluate the plant safety in case of the severe accident due to long-term station blackout.The present study reviews experiments on pressure drop behavior for complicated tube bundle geometry to the flow path and then develops a new correlation equation based on a computational fluid dynamics analysis of the Monju air cooler reflecting the actual geometry and plant data.After a basic simulation model being developed for a typical pressure drop experiment, the simulation is applied to the Monju air cooler that has a finned tube bundle. The obtained relationship between friction factors and Reynolds numbers ranging from 10 to 10,000 are fitted to a power function to derive a correlation equation of the fin tube bundle friction factor. The derived correlation equation can estimate pressure loss in the finned tube bundle more precisely than that used in the Monju design. It is applicable to the future reactor design of the air cooler, especially when the cooling ability in low Reynolds number is requested.

Visible LED photocatalysis combined with ultrafiltration driven by metal-free oxygen-doped graphitic carbon nitride for sulfamethazine degradation

A novel visible light emitting diode (LED) photocatalysis combined ultrafiltration (UF) system driven by metal-free O-doped C3N4 was established for sulfamethazine (SMZ) removal in environmental remediation. Among different O-doping ratios, 8%O-C3N4 exhibited the optimal SMZ degradation efficiency (89.36%) and the flux of 8%O-C3N4/LED/UF system could reach up to 38.92 L/m2/h. Benefitting from the O-doping, the synergetic effect of the expansion of visible-light absorption, enhancement of electron redox capacity, and improvement of e--h+ separation efficiency could produce the intensified photoactivity. Superoxide radical (O2•-) and single oxygen (1O2) were proved to be the primary active species by EPR and quenching tests. Moreover, the influence of several parameters such as photocatalyst dosage, SMZ concentration, raw turbidity and humic acid concentration in 8%O-C3N4/LED/UF system on SMZ removal were systematically studied. Under simulated surface water matrix, 8%O-C3N4/LED/UF system could also remove 96.88% SMZ and stable membrane flux stabilized as high as 33.36 L/m2/h. This study makes a demonstration for applying highly-effective powdery photocatalysts in the actual wastewater treatment and designing future photocatalytic reactors.

Indo-US civilian nuclear deal: challenges and options for Pakistan

The strategic cooperation in terms of the Civilian Nuclear Deal between India and the US has facilitated both the states in terms of supply of nuclear energy, advancement in technology, regional nuclear symmetry, energy crisis, military arsenals and the development in the economic sector. With some mutually agreed terms under the instrument, India agreed to allow the International Atomic Energy Agency (IAEA) to keep a check and have access to India's civilian nuclear program. Moreover, the US will be allowed to build its companies of nuclear reactors in India, whereas India also promised to place all future thermal reactors under the supervision of the IAEA. Furthermore, the deal benefitted both India and the US on one side, while on the other side, it adversely affected Pakistan and disrupted the balance of power in South Asia. This article explores the drastic challenges that Pakistan faces and affects its nuclear status in the region. The method used for the research is qualitative, and data is analysed from secondary sources. Moreover, the study's objective attempts to interpret multiple options that could help the stakeholders overcome the challenges and restore the balance of power in the South Asian region.

Nano oxide particles in 18Cr oxide dispersion strengthened (ODS) steels with high yttria contents

Oxide dispersion strengthened (ODS) steels containing yttria are candidate materials for fuel cladding tubes in future nuclear reactors. Their performance is determined by the size, distribution and volume fraction of the oxide dispersoids. The addition of yttria leads to a significant loss in ductility of steel limiting the yttria content in most ODS steels to 0.35%. This limitation may be overcome by powder forging of ODS steel powders. Two steels having nominal compositions (in wt%) of Fe-18Cr-2W-0.285Ti-0.5Y 2 O 3 and Fe-18Cr-2W-0.571Ti-1Y 2 O 3 were prepared by mechanical alloying of elemental powders with yttria powder in a Simoloyer attritor. The alloy powders were consolidated by powder forging at 1473 K in a flowing hydrogen atmosphere. The microstructure of powder forged ODS steels was characterized by electron microscopy. Both the steels exhibited a fine-grained recrystallized microstructure after forging. Fine (<10 nm) cuboidal oxide particles were found to be present in a ferrite matrix. A few coarse oxide particles were also observed. These coarse (>10 nm) oxide particles were present mainly along the ferrite grain boundaries. The crystal structure of oxide particles was determined by applying fast fourier transformation (FFT) on the fringes observed by high resolution transmission electron microscopy. The extracted FFTs were indexed to identify the crystal structure. The coarse particles were found to be Y 2 O 3 , TiO 2 and Cr 2 O 3 . The fine particles were identified as Y 2 TiO 5 and Y 2 Ti 2 O 7 . The face centre cubic Y 2 Ti 2 O 7 oxide particles were semi coherent whereas the orthorhombic Y 2 TiO 5 oxide particles were found to be incoherent with the ferrite matrix. The number fraction, average size and size distribution of these oxide particles was determined for both the alloys. Cr rich shells were observed around most of the particles which may prevent the coarsening of oxide particles at elevated temperatures. Reasons for this are discussed. • High yttria 18Cr ODS steels were successfully developed through novel hot powder forging route. • Recrystallized equiaxed grains with a uniform distribution of nano oxides particles were observed in the forged alloys. • A majority of oxides present were Y 2 TiO 5 or Y 2 Ti 2 O 7 oxides. Cr-rich shells were associated with these complex oxides. • The cuboidal Y 2 TiO 5 oxides were incoherent while the spherical Y 2 Ti 2 O 7 oxides were semi-coherent with the ferrite matrix. • HR-TEM also confirmed the formation of nano oxide particles such as Y 2 O 3 , TiO 2 and Cr 2 O 3 . These too were analysed.