Search

In developing organic semiconductor polymers for photovoltaic applications, chlorine substitution has become an effective strategy in replacing fluorine substitution to overcome the drawbacks of low yield and high cost, commonly associated with fluorination. In general, several molecular positions are available for chlorination. To obtain a clear understanding of the impact of chlorine substitution on the intrinsic polymer properties, an investigation of structure-property relationships is necessary. Herein, four donor-acceptor type polymers with the same conjugated backbone and flexible alkyl chains, but with chlorine atoms in different positions, are employed to systematically investigate the effect of the site of chlorination on the optoelectronic properties and photovoltaic performance. Substitution of fluorine by chlorine in the backbone slightly increases open circuit voltage (Voc) and fill factor (FF) of the solar cells but causes a loss of short-circuit current density (Jsc). The introduction of chlorine in the conjugated side chains, however, significantly improves Voc, FF, and power conversion efficiency, benefiting from a lower HOMO energy level, efficient and well-balanced transport properties, and superior nanoscale morphology. This journal is

The effect of the length of solubilizing alkyl side chains, ranging from hexyl to pentadecyl, on the formation and structure of two distinct semi-crystalline semiconductor phases, ß1and ß2, of a single conjugated polymer is investigated for a low band gap poly(diketopyrrolopyrrole-alt-quaterthiophene). Compared to ß1, the ß2phase exhibits a distinct redshifted absorption and an associated near infrared photoluminescence. The length of the alkyl side chains controls the formation of the ß1and ß2phases. Intermediate length alkyl side chains (nonyl and dodecyl) can selectively provide the ß1or ß2phase in solution and in semi-crystalline thin films, depending on the nature of the solvent used. For short side chains (hexyl) the ß2phase forms more readily while for long side chains (pentadecyl) the ß1phase is predominant. The kinetics of ß2phase formation is investigated and reveals a reduced growth rate when long alkyl side chains are present. X-ray diffraction reveals a closer p-p stacking distance for ß2than for ß1, consistent with its redshifted absorption and its higher mobility in field-effect transistors. The polymer with hexyl side chains adopts an edge-on orientation in thin films, while the longer alkyl chains induce a face-on orientation. Photovoltaic devices exhibit an additional near infrared spectral contribution to the photocurrent for the ß2phase. The study shows that the formation of the two polymorphs ß1and ß2is controlled by the alkyl side chains and the solubility that arises from them. Shorter side chains (lower solubility) favor ß2and longer side chains (higher solubility) ß1, and at intermediate lengths both phases can be formed.

Polymorphism of organic semiconducting materials exerts critical effects on their physical properties such as optical absorption, emission and electrical conductivity, and provides an excellent platform for investigating structure–property relations. It is, however, challenging to efficiently tune the polymorphism of conjugated polymers in aggregated, semi-crystalline phases due to their conformational freedom and anisotropic nature. Here, two distinctly different semi-crystalline polymorphs (β1 and β2) of a low-bandgap diketopyrrolopyrrole polymer are formed through controlling the solvent quality, as evidenced by spectroscopic, structural, thermal and charge transport studies. Compared to β1, the β2 polymorph exhibits a lower optical band gap, an enhanced photoluminescence, a reduced π-stacking distance, a higher hole mobility in field-effect transistors and improved photocurrent generation in polymer solar cells. The β1 and β2 polymorphs provide insights into the control of polymer self-organization for plastic electronics and hold potential for developing programmable ink formulations for next-generation electronic devices., Tuning polymorphism of conjugated polymers, though a promising method for studying and controlling the structure-property relations in these materials remains a challenge. Here, the authors identify two aggregated semi-crystalline polymorphs of a low-bandgap diketopyrrolopyrrole-based polymer.

Few semiconducting polymers are known that possess more than one semi‐crystalline structure. Guidelines for rationalizing or creating polymorphism in these materials do not exist. Two different semi‐crystalline polymorphs, β 1 and β 2, and an amorphous α phase have recently been identified for alternating diketopyrrolopyrrole‐quaterthiophene copolymers (PDPP4T). The polymorphs differ structurally by the π–π stacking distance, and electronically by the optical bandgap and charge carrier mobility. Here we investigate the corresponding terthiophene (PDPP3T) derivatives, to study the effect of the relative orientation of adjacent DPP units on the polymorphism. In PDPP3T, the relative orientation of DPP units alternates along the chain, while in PDPP4T it is constant. We show that the two polymorphs, β 1 and β 2, can also be generated for a PDPP3T polymer in solution and thin film. Interestingly, compared to PDPP4T, more solvents can induce the two distinct semi‐crystalline polymorphs for PDPP3T via a β 1 → α → β 2 polymorphic transition., Two distinct semi‐crystalline polymorphs (β 1 and β 2) of a poly(diketopyrrolopyrrole‐alt‐terthiophene) form when films are cast from different solvents. While chloroform results in the β 1 phase, several chlorinated aromatic solvents provide the β 2 phase in which the polymer exhibits a smaller π–π stacking distance. The enhanced π–π stacking of the β 2 phase compared to the β 1 phase causes a redshifted optical absorption which contributes to the photocurrent in organic solar cells and doubles the mobility in organic field‐effect transistors.

The effect of the nature of the π-conjugated linker that is positioned between electron-deficient 2,5-dihydropyrrolo[3,4-c]pyrrole-1,4-dione (DPP) and electron-rich dithieno[3,2-b:2′,3′-d]pyrrole (DTP) units in alternating DPP-DTP copolymers on the optical and electrochemical band gaps and the effective exciton binding energy is investigated for six different aromatic linkers. The optical band gap is related to the electron-donating properties of DTP and the electron-withdrawing properties of DPP but likewise strongly affected by the nature of the linker and varies between 1.13 and 1.80 eV for the six different linkers. The lowest optical band gaps are found for linkers that either raise the highest occupied molecular orbital or lower the lowest unoccupied molecular orbital most, while the highest optical band gap is found for phenyl linkers that have neither strong donating nor strong accepting properties. Along with the optical band gap, the electrochemical band gap also changes, but to a lesser extent from 1.46 to 1.89 eV. The effective exciton binding energy (Eb), defined as the difference between the electrochemical and optical band gaps, decreases with an increasing band gap and reaches a minimum of 0.09 eV for the copolymer with the highest band gap, that is, with phenyl linkers. The reduction in Eb with an increasing band gap is tentatively explained by a reduced electronic interaction between the DTP and DPP units when the HOMO localizes on DTP and the LUMO localizes on DPP. Support for this explanation is found in the molar absorption coefficient of the copolymers, which shows an overall decreasing trend with decreasing Eb.

The European Mini-Plate Irradiation Experiment (EMPIrE) aims to test the in-pile behavior of various ZrN coated UMo powder batches, produced using different technological processes. UMo(ZrN) particles are typical core-shell systems taking advantages of a dense fissile material, UMo, with a coated ZrN layer acting as a diffusion barrier. The U-7Mo kernels were produced by centrifugal or rotating electrode atomization processes and the ZrN coating was performed by physical vapor deposition or atomic layer deposition processes. A total of ten batches of UMo(ZrN) powders were examined in the as-obtained state, i.e prior to fuel-plate fabrication and before in-pile irradiation. The present investigation gives a characterization of each powder batch mainly in terms of morphological and microstructural features carried out by means of SEM-EDS, LOM, EPMA, AFM and TEM analyses. Digital image processing using ImageJ software was employed to determine several particle size (major axis, minor axis, Feret’s diameters, and equivalent diameter) and shape (aspect ratio, circularity, convexity and concavity) parameters as well as the ZrN deposited layer thickness. The quality of the ZrN layer was examined in terms of surface roughness, grain structure and aggregated habits. Our characterization results draw a detailed portrait of the UMo(ZrN) powders selected for the EMPIrE experiment and allow a classification of the powder batches which is presented as radar chart (Kiviat diagram).

In the framework of the SELENIUM project, ZrN coated U-Mo fuel kernels were irradiated in the Belgium Reactor 2 of SCK•CEN to a plate average burnup of 48% 235U and a local maximum burnup just below 70% 235U. The microstructure and chemical composition of ZrN coating before and after neutron irradiation have been analysed using scanning transmission electron microscopy (STEM) equipped with energy dispersive X-ray spectroscopy (EDS) and electron energy loss spectroscopy (EELS), and atom probe tomography (APT). The atomic ratio of N/Zr and fission product distribution determined by three techniques were compared and the combination of three techniques shows the advantages in characterization of chemical information for nuclear materials.

Image analysis was performed on SEM micrographs of recently irradiated UMo dispersion fuel plates. Detailed information on the fission gas inter-granular bubbles accompanying recrystallization, including average diameter, density and size distribution were extracted and compared with previous results on UMo and UO2. A pore density drop was notice at high fission densities and attributed mainly to a pore coarsening dominated by irradiation induced phenomena. Based on the image analysis data and theoretical considerations, a model was developed to estimate the pressure inside the pores as a function of fission density, temperature and pore radius. The developed pressure can give indications of the mechanical stability of the fuel towards the progressive building-up of fission gases. Finally, the proposed methodology was applied to the nanobubble lattice decorating the fuel grains at low fission densities in order to infer the physical state of the contained fission gases. The estimated values suggest the presence of solid xenon precipitates.

To understand interaction layer behavior in U Mo fuel kernels coated with physical vapor deposition (PVD) ZrN barriers, two cubes of irradiated fuel were serial sectioned and imaged in 50 and 200 nm increments using a focused ion beam (FIB) instrument. Locally, the fuel underwent a burnup of 52% U 235 or a fission density of 4.0 × 10 21 fissions/cm 3 . 3D reconstructions were created from the serial sectioned images. 3D reconstructions revealed the morphology of multiple locations where U Mo/Al interaction layer formed between the Al matrix and the U Mo fuel. These locations are associated with breaches in the ZrN barrier and not from diffusion of Al through the ZrN barrier. When not compromised, the ZrN barrier successfully impedes U Mo fuel interaction with Al cladding. The ZrN barrier has decreased from a nominal pre-irradiated thickness of 1.16 μm to a thickness of 0.69 μm. A ZrN-rich phase adjacent to the ZrN barrier was observed on the Al matrix side of the coating. This phase is likely the original ZrN barrier and Al matrix that decomposed with increasing burnup as a result of fission recoil induced mixing. Nominally, the thickness of the irradiated ZrN barrier and the ZrN-rich Al matrix is 1.36 μm.

Post irradiation examinations of full-size U-Mo/Al dispersion fuel plates fabricated with ZrN- or Si- coated U-Mo particles revealed that the reaction rate of irradiation-induced U-Mo-Al inter-diffusion, an important microstructural change impacting the performance of this type of fuel, transited at a threshold temperature/fission rate. The existing inter-diffusion layer (IL) growth correlation, which does not describe the transition behavior of IL growth, was modified by applying a temperature-dependent multiplication factor that transits around a threshold fission rate. In-pile irradiation data from four tests in the BR2 reactors, including FUTURE, E-FUTURE, SELEMIUM, and SELEMIUM-1a, were utilized to determine and validate the updated IL growth correlation. Irradiation behavior of the plates was simulated with the DART-2D computational code. The general agreement between the calculated and measured fuel meat swelling and constituent volume fractions as a function of fission density demonstrated the plausibility of the updated IL growth correlation. The simulation results also suggested the temperature dependence of the IL growth rate, similar to the temperature dependence of the inter-mixing rate in ion-irradiated bi-layer systems.

Two fuel plates, containing Si and ZrN coated U-Mo fuel particles dispersed in an Al matrix, were irradiated in the BR2 reactor of SCK•CEN to a burn-up of ∼70% 235 U. Five samples were prepared by INL using focused ion beam milling and transported to SCK•CEN for transmission electron microscopy (TEM) investigation. Two samples were taken from the Si coated U-Mo fuel particles at a burn-up of ∼42% and ∼66% 235 U and three samples from the ZrN coated U-Mo at a burn-up of ∼42%, ∼52% and ∼66% 235 U. The evolution of the coating, fuel structure, fission products and the formation of interaction layers are discussed. Both coatings appear to be an effective barrier against fuel matrix interaction and only on the samples having received the highest burn-up and power, the formation of an interaction between Al and U(Mo) can be observed on those locations where breaches in the coatings were formed during plate fabrication.

The control of the interaction between the U(Mo) fuel phase and the Al matrix is one of the challenges of dispersion fuel plate development for research reactors. Given the specific properties of this interaction layer, larger amounts of it in the meat could lead to a reduction of the plate mechanical integrity and thermal conductivity, eventually leading to pillowing. The SELENIUM project showed that by depositing a ZrN coating on the surface of the U(Mo) fuel particles, the amount of formed U(Mo)-Al interaction layer is limited but still present. Microstructural analysis performed on the as fabricated coating and fresh fuel plates containing ZrN coated U(Mo) dispersed in an Al matrix, revealed that the coating gets damaged during plate production. The post irradiation examinations (PIE) of the ZrN coated U(Mo) fuel plates, from the SELENIUM and SEMPER FIDELIS experiments, show how the U(Mo)-Al interaction layer is formed - only at those locations where the coating is missing or damaged - and the evolution of coating microstructure during irradiation. As a remedy, to further reduce the amount of interaction layer formed, the use of an Al-Si matrix was proposed based on the higher affinity of Si for U compared to the affinity of Al for U. PIE of a fuel plate consisting of ZrN coated U(Mo) dispersed in an Al-Si matrix irradiated in the SEMPER FIDELIS experiment, clearly demonstrates the benefit of adding Si to the matrix.

Compared to previous irradiation experiments containing UMo/Al dispersion fuel plates, the SELENIUM irradiation experiment performed at the SCK·CEN BR2 reactor in 2012 showed an improved plate swelling behavior. However, in the high burn-up area of the plates a significant increase in meat thickness was still measured. The origin of this increase is currently not firmly established, but it is clear from the observed microstructure that the swelling rate still is too high for practical purposes and needs to be reduced. It was stipulated that the swelling occurred at the high burnup areas which are also the high power zones at beginning of life. For that reason, an experiment was proposed to investigate the influence of fission rate (i.e. power) on some of the observed phenomena. For this purpose, a sibling plate to a high power (BOL>470 W/cm2) SELENIUM plate was irradiated during four BR2 cycles. The SELENIUM 1a fuel plate was submitted to a local maximum heat flux below 350 W/cm2, throughout the full irradiation. At the end of the last cycle, the SELENIUM 1a fuel plate reached a maximum local burnup value of close to 75%235U compared to 70%235U for the SELENIUM high power plates. When comparing to the results on the SELENIUM plates, the non-destructive tests clearly show a continued linear swelling behavior of the low power irradiated fuel plate SELENIUM 1a in the high burn-up region. The influence of the fission rate is also evidenced in the microstructural examination of the fuel showing that there is no formation of interaction layer at the high burn-up region.

Two asymmetric thiophene (T)/pyridine (Py) flanked diketopyrrolopyrrole (DPP) polymers with a regiorandom and regioregular conjugated backbone are synthesized via a Stille polycondensation to investigate the effect of regioregularity on their optoelectronic properties and photovoltaic performance in fullerene-based polymer solar cells. Surprisingly, both polymers possess very similar optical bandgap, energy levels, and photovoltaic performance. These findings, combined with a factor of 19 reactivity difference between the two end groups of the asymmetric DPP monomer, intuitively suggest the formation of regular chain segments in the random polymer. However, by modeling the random polymerization reaction with a kinetic Monte Carlo (KMC) simulation, evidence is obtained for exclusive formation of a fully random polymer structure. UV-vis-NIR absorption spectra of three extended DPP chromophores, containing the donor segments (T-T-T, Py-T-Py, and Py-T-T) present in the regiorandom polymer, confirm that regioregularity of the backbone has a negligible influence on the optical properties.

Understanding the microstructural and phase changes occurring during irradiation and their impact on metallic fuel behavior is integral to research and development of nuclear fuel programs. This paper reports systematic analysis of as-fabricated and irradiated low-enriched U-Mo (uranium-molybdenum metal alloy) fuel using atom probe tomography (APT). This study is carried out on U-7 wt.% Mo fuel particles coated with a ZrN layer contained within an Al matrix during irradiation. The dispersion fuel plates from which the fuel samples were extracted are irradiated at Belgian Nuclear Research Centre (SCK CEN) with burn-up of 52% and 66% in the framework of the SELENIUM (Surface Engineering of Low ENrIched Uranium-Molybdenum) project. The APT studies on U-Mo particles from as-fabricated fuel plates enriched to 19.8% revealed predominantly γ-phase U-Mo, along with a network of the cell boundary decorated with α-U, γ’-U2Mo, and UC precipitates along the grain boundaries. The corresponding APT characterization of irradiated fuel samples showed formation of fission gas bubbles enriched with solid fission products. The intermediate burnup sample showed a uniform distribution of the typical bubble superlattice with a radius of 2 nm arranged in a regular lattice, while the high burnup sample showed a non-uniform distribution of bubbles in grain-refined regions. There was no evidence of remnant α-U, γ’-U2Mo, and UC phases in the irradiated U-7 wt.% Mo samples.

Grain refinement in U(Mo) has been achieved out-of-pile by irradiating an U(Mo) foil with 80 MeV high-flux 127I ions at 140°C up to a high dose of ~ 2.1 × 1018 ions/cm² or a fission density equivalent of ~ 3.7 × 1021 f/cm³. Several locations in the irradiated area were analysed by scanning electron microscopy (SEM) and electron backscatter diffraction (EBSD) in order to study the dose-dependent evolution of the irradiation induced restructuring. The refined U(Mo) grains formed in proximity of the sample surface, where a strong irradiation induced oxidation was also observed. The spatial concomitance between the irradiation induced grain refinement and sample oxidation points out a possible connection between the two phenomena. The EBSD maps suggest that polygonization was the underlying mechanism driving the grain refinement based on the observation of many low-angle grain boundaries surrounding the newly refined grains. In a later stage, the grain boundaries transformed from low-angle to high-angle under the effect of raising local lattice stresses induced by the ion implantation. The estimated ion irradiation dose triggering the polygonization is approximately one order of magnitude lower than what is observed in-pile. This experiment shows that ion irradiation is capable of simulating the high burnup structure forming in U(Mo) in-pile. Ion irradiation therefore once more proves to be a powerful tool to study the fundamental behaviour of neutron irradiated U(Mo) or other fuel materials.

A high-energy Xe ion irradiation experiment was conducted to investigate the temperature dependence of interdiffusion in bilayer Al-UMo samples under irradiation. The amount of interdiffusion achieved at a fixed dose with the increase of temperature showed a clear transition at 175°C (with an estimated error in the range of ±10°C) from temperature-independent to temperature-dependent behavior. The activation energy derived from the curve of interdiffusion quantity vs. irradiation temperature is 0.77±0.16 eV. This information has been utilized to understand the temperature effect on the interdiffusion process that occurred at the interfaces of U-Mo particles and the Al matrix in U-Mo/Al dispersion fuels, whose magnitude significantly impacts the fuel's performance. Although this temperature effect was deemed important, it cannot be examined directly using in-pile irradiation data, as fuel temperatures cannot be measured in reactor irradiation and are highly correlated with fission rate and thermal conductivity evolution. To connect the knowledge accumulated from ion irradiation with in-pile irradiation data, simulation of a full-sized U-Mo/Al dispersion fuel plate irradiated in the FUTURE test in the BR2 reactor was performed with the Dispersion Analysis Research Tool (DART), a dispersion fuel performance code. DART is equipped with an interaction or interdiffusion layer (IL) growth correlation formulated to describe the temperature dependence of ion mixing results. The agreement between calculated and measured fuel meat constituent volume fractions and swelling data demonstrated that the temperature effect on in-pile Al-UMo interdiffusion is well captured with the correlation. In this case, the fitted activation energy is 0.70 eV. Considering the uncertainties associated with the ion irradiation data, the activation energy obtained from in-pile data fitting is in accord with that from ion irradiation results.

The evolution of the high burn-up structure (HBS) in U(Mo) fuel irradiated up to a burn-up of ∼70% 235U or ∼5 × 1021 f/cm3 or ∼120 GWd/tHM is described and compared to the observation made on LWR fuel. Scanning and transmission electron microscopy was performed on several samples having different burn-ups in order to get a better understanding of the mechanisms leading to the high burn-up structure formation. Even though there are some substantial differences between the irradiation of ceramic and U(Mo) alloy fuels (crystal structure, enrichment, irradiation temperature …), it was found that in both fuels recrystallization initiates at the same threshold and progresses in a similar way with increasing fission density. In case of U(Mo), recrystallization leads to accelerated swelling of the fuel which could result in instability of the fuel plate.

Diketopyrrolopyrrole (DPP) polymers possess narrow optical bandgaps and high charge carrier mobilities which make them attractive for solar cell applications. DPP polymers are generally only soluble in chlorinated solvents, which is a drawback for commercial application. Solubility in non-halogenated solvents can be achieved by reducing the translational symmetry of the chain by employing two different aromatic moieties on either side of the DPP units. Here a series of polymers in which thiophene (T) and pyridine (Py) sandwich the DPP units in the main chain is reported. These asymmetric T-DPP-Py units increase the solubility dramatically. The side chain length, nature of the co-monomer, and regioregularity of the main chain are varied to investigate their effect on the solubility in toluene, the active layer morphology and the performance of organic solar cells. We demonstrate that polymers processed from both chloroform and toluene reach very similar power conversion efficiencies and blend morphologies. In general, a small co-monomer, short side chains, a regioregular main chain, and a high molecular weight give the best performance for solar cells processed from toluene.

The microstructure, growth kinetics, and the high temperature phase equilibria of the U Mn binary system are investigated using differential scanning calorimetry. Alloys with various compositions are prepared in a positive-pressure arc melting furnace in order to examine all possible phase changes within the system. Phase composition and morphology were analyzed using XRD, SEM and EDX. Transformation temperatures and enthalpies have been assessed pertaining to: (i) allotropic phase changes αMn → βMn → γMn →δMn, (ii) two eutectic isotherms UMn2 + βMn → L and U6Mn + UMn2 → L and (iii) melting transitions as a function of composition. The development of the two intermetallic phases U6Mn and UMn2 are observed. A faceted morphology accompanies the formation of UMn2 in a matrix of U6Mn, while grain boundary decomposition is found of UMn2 in αMn. The transformation temperatures are compared to existing phase diagrams and are slightly higher than reported in literature. Experimental observations of the allotropic transformations of αMn to βMn and βMn to γMn are in agreement with a calculated phase diagram. The eutectic composition for UMn2 and αMn is found to be 55 wt%Mn, in agreement with previously reported values, while the enthalpy of fusion associated with this eutectic point is found to be 54 ± 6.5 kJ mol−1. The enthalpies of formation for the two intermetallic phases U6Mn and UMn2 are 71 ± 8.5 kJ mol−1 and 42 ± 5 kJ mol−1 respectively.

Aluminum cladding oxidation of research-reactor fuel elements at high power conditions has a disadvantageous effect on fuel performance due to the lower thermal conductivity of the oxide. The oxide growth prediction models available in the literature were mostly developed for low power conditions. To examine the applicability of the models to high power and high temperature test conditions, the models were studied by coupling with the most frequently employed heat transfer coefficient (HTC) correlations including the Dittus-Boelter correlation, the Colburn correlation, the Sieder-Tate correlation, and KAERI-developed correlation. The Griess model over-predicted the oxide growth while the KAERI-Griess model under-predicted the oxide growth for high power tests. The Kim model, coupled with the Colburn correlation, gave most consistent results with the measured data from two BR2 experiments. However, the Kim model was found to be inapplicable to the EUHFRR conditions at the peak power locations if it was coupled with the Dittus-Boelter correlation. A revision of the prediction models to more closely agree with the measured data was recommended. AG3NE and AlFeNi cladding types were tested in the E-FUTURE experiment, and a noticeable (although small) reduction in oxide thickness on the AlFeNi cladding was observed. However, this difference was believed to be only a secondary effect considering other uncertainties in model predictions, so no attempt was made to model the alloying effect.

All-polymer solar cells (APSCs), composed of semiconducting donor and acceptor polymers, have attracted considerable attention due to their unique advantages compared to polymer-fullerene-based devices in terms of enhanced light absorption and morphological stability. To improve the performance of APSCs, the morphology of the active layer must be optimized. By employing a random copolymerization strategy to control the regularity of the backbone of the donor polymers (PTAZ-TPDx) and acceptor polymers (PNDI-Tx) the morphology can be systematically optimized by tuning the polymer packing and crystallinity. To minimize effects of molecular weight, both donor and acceptor polymers have number-average molecular weights in narrow ranges. Experimental and coarse-grained modeling results disclose that systematic backbone engineering greatly affects the polymer crystallinity and ultimately the phase separation and morphology of the all-polymer blends. Decreasing the backbone regularity of either the donor or the acceptor polymer reduces the local crystallinity of the individual phase in blend films, affording reduced short-circuit current densities and fill factors. This two-dimensional crystallinity optimization strategy locates a PCE maximum at highest crystallinity for both donor and acceptor polymers. Overall, this study demonstrates that proper control of both donor and acceptor polymer crystallinity simultaneously is essential to optimize APSC performance.

Irradiation responses of U–Mo/Al dispersion fuel have been investigated by irradiation with 84 MeV Xe26+ ions. Dispersion fuels fabricated with uncoated and ZrN-coated fuel particles were irradiated to various doses at ∼350 °C. The highest dose achieved was 2.9 × 1017 ions/cm2 (∼1200 displacement per atom (dpa)). Following the irradiation, scanning electron microscopy (SEM) and transmission electron microscopy (TEM) experiments were carried out to characterize the microstructures of the irradiated samples. The post irradiation examinations (PIE) revealed that: (1) crystalline interdiffusion product (UMo)Alx developed at locations where no coating or compromised coating layer is present; (2) intact ZrN coating layers effectively blocked the interdiffusion between U–Mo and Al; (3) SEM-observable Xe bubbles distributed along grain/cell boundaries in U–Mo; and (4) gas bubble interlinkage was observed at a dose of 2.9 × 1017 ions/cm2.

The United States High Performance Research Reactor Fuel Development program is developing low enriched uranium fuels for application in research and test reactors. One concept utilizes U–7 wt.% Mo (U–7Mo) fuel particles dispersed in Al matrix, where the fuel particles are coated with a 1 μm-thick ZrN coating. The ZrN serves as a diffusion barrier to eliminate a deleterious reaction that can occur between U–7Mo and Al when a dispersion fuel is irradiated under aggressive reactor conditions. To investigate the final microstructure of a physically-vapor-deposited ZrN coating in a dispersion fuel plate after it was fabricated using a rolling process, characterization samples were taken from a fuel plate that was fabricated at 500 °C using ZrN-coated U–7Mo particles, Al matrix and AA6061 cladding. Scanning electron and transmission electron microscopy analysis were performed. Data from these analyses will be used to support future microstructural examinations of irradiated fuel plates, in terms of understanding the effects of irradiation on the ZrN microstructure, and to determine the role of diffusion barrier microstructure in eliminating fuel/matrix interactions during irradiation. The as-fabricated coating was determined to be cubic-ZrN (cF8) phase. It exhibited a columnar microstructure comprised of nanometer-sized grains and a region of relatively high porosity, mainly near the Al matrix. Small impurity-containing phases were observed at the U–7Mo/ZrN interface, and no interaction zone was observed at the ZrN/Al interface. The bonding between the U–7Mo and ZrN appeared to be mechanical in nature. A relatively high level of oxygen was observed in the ZrN coating, extending from the Al matrix in the ZrN coating in decreasing concentration. The above microstructural characteristics are discussed in terms of what may be most optimal for a diffusion barrier in a dispersion fuel plate application.

In the framework of the SELENIUM project two full size flat fuel plates were produced with respectively Si and ZrN coated U(Mo) particles and irradiated in the BR2 reactor at SCK•CEN. Non-destructive analysis of the plates showed that the fuel swelling profiles of both SELENIUM plates were very similar to each other and none of the plates showed signs of pillowing or excessive swelling at the end of irradiation at the highest power position (local maximum 70% 235 U). The microstructural analysis showed that the Si coated fuel has less interaction phase formation at low burn-up but at the highest burn-ups, defects start to develop on the IL–matrix interface. The ZrN coated fuel, shows a virtual absence of reaction between the U(Mo) and the Al, up to high fission densities after which the interaction layer formation starts and defects develop in the matrix near the U(Mo) particles. It was found and is confirmed by the SELENIUM (Surface Engineering of Low ENrIched Uranium–Molybdenum) experiment that there are two phenomena at play that need to be controlled: the formation of an interaction layer and swelling of the fuel. As the interaction layer formation occurs at the U(Mo)–matrix interface, applying a diffusion barrier (coating) at that interface should prevent the interaction between U(Mo) and the matrix. The U(Mo) swelling, observed to proceed at an accelerating rate with respect to fission density accumulation, is governed by linear solid state swelling and fission gas bubble swelling due to recrystallization of the fuel. The examination of the SELENIUM fuel plates clearly show that for the U(Mo) dispersion fuel to be qualified, the swelling rate at high burn-up needs to be reduced.

This paper focuses on one of the next directions in the evolution of reversible addition-fragmentation (RAFT) polymerization, namely, progress towards the synthesis of discrete or uniform, sequence-defined (co)polymers. Following a brief review of RAFT-single unit monomer insertion (RAFT-SUMI), we describe recent developments in the field. We point to difficulties in achieving consecutive RAFT-SUMI and report two strategies for overcoming the issue of initiator-derived by-products. We show that the selection of RAFT agent is critical in selective RAFT-SUMI of N,N-dimethylacrylamide (DMAm) into a trithiocarbonate in aqueous solution. Finally we recount on the use of photoRAFT- or PET-RAFT-SUMI in the high yield synthesis of discrete oligomers comprising two or more consecutive SUMI steps.

A novel approach is presented to determine the local burnup in irradiated fuels using isotopic quantification obtained by Atom Probe Tomography (APT). Considering the volume of sample used (

A new type of high density fuel is needed for the conversion of research and test reactors from high to lower enriched uranium. The most promising one is a dispersion of atomized uranium-molybdenum (U–Mo) particles in an Al matrix. However, during in-pile irradiation the growth of an interaction layer between the U–Mo and the Al matrix strongly limits the fuel’s performance. To improve the in-pile behaviour, the U–Mo particles can be coated with protective layers. The SELENIUM (Surface Engineering of Low ENrIched Uranium–Molybdenum) fuel development project consists of the production, irradiation and post-irradiation examination of 2 flat, full-size dispersion fuel plates containing respectively Si and ZrN coated U–Mo atomized powder dispersed in a pure Al matrix. In this paper X-ray diffraction analyses of the Si and ZrN layers after deposition, fuel plate manufacturing and thermal annealing are reported. It was found for the U–Mo particles coated with ZrN (thickness 1 μm), that the layer is crystalline, and exhibits lower density than the theoretical one. Fuel plate manufacturing does not strongly influence these crystallographic features. For the U–Mo particles coated with Si (thickness 0.6 μm), the measurements of the as received material suggest an amorphous state of the deposited layer. Fuel plate manufacturing strongly modifies its composition: Si reacts with the U–Mo particles and the Al matrix to grow U(Al, Si) 3 and U 3 Si 5 phases. Finally both coatings have shown excellent performances under thermal treatment by limiting drastically the U–Mo/Al interdiffusion.

Extensive fuel-matrix interactions leading to plate pillowing have caused a severe impediment on the development of a suitable high density low-enriched uranium dispersion fuel for high power applications in research reactors. Surface engineering of the U(Mo) kernel surfaces, where the interaction occurs, is put forward by SCK⋅CEN as a possible solution in the Surface Engineering of Low ENrIched Uranium Molybdenum fuel (SELENIUM) program. The project involved the construction of a sputter coater, the coating of U(Mo) kernels, the production of fuel plates, the irradiation and post-irradiation examination of 2 plates. The irradiation of 2 distinct (600 nm Si and 1000 nm ZrN coated) full size, flat fuel plates was performed in the BR2 reactor in 2012. The irradiation conditions were: 470 W/cm2 peak Beginning Of Life (BOL) power, with a ∼70% 235U peak burnup. The plates were successfully irradiated and did not show any pillowing at the end of the irradiation. This paper reports the results and interpretation of the non-destructive post-irradiation examinations that were performed on these fuel plates and derives a law for the fuel swelling evolution with burnup for this fuel type. It further reports additional PIE results obtained on fuel plates irradiated in campaigns in the past in order to allow a complete comparison with all results obtained under similar conditions. The fuel swelling is shown to evolve linearly with the fission density, with an increase in swelling rate around 2.5 × 1021 f/cm3, which is associated with the restructuring of the fuel. A further increase in swelling rate is observed at the highest burnups, which is discussed in this article.

Several irradiation experiments have confirmed the positive effect of adding Si to the matrix of an U(Mo) dispersion fuel plate on its in-pile irradiation behavior. E-FUTURE, the first experiment of the LEONIDAS program, was performed to select an optimum Si concentration and fuel plate heat treatment parameters for further qualification. It consisted of the irradiation of 4 distinct (regarding Si content and heat treatments), full size flat fuel plates in the BR2 reactor under bounding conditions (470 W/cm 2 peak BOL power, ∼70% peak burn-up). After the irradiation, the E-FUTURE plates were examined non-destructively and found to have pillowed in the highest burn-up positions. The destructive post-irradiation examination confirmed that the fuel evolves in a stable way up to a burn-up of 60% 235 U. Even in the deformed area (pillow) the U(Mo) fuel itself shows stable behavior and remaining matrix material was present. From the calculation of the volume fractions, the positive effect of a higher Si amount added to the matrix and the higher annealing temperature can be derived.

Several irradiation experiments of U(Mo) dispersion fuel performed with aluminum as matrix resulted in unacceptable swelling of the fuel plate due to the formation of an interaction layer between Al and U(Mo). It was found that an improvement in fuel behavior can be achieved by adding Si to the Al matrix and creating a Si rich preformed layer which delays the formation of the interaction layer. Such Al–Si matrices can be formed either by mixing silicon powder with aluminum or using an AlSi alloy. AlSi alloy powders have very different mechanical properties which complicate fuel plate fabrication. Aging experiments on AlSi alloys reveal that giving the alloy the correct heat treatment results in a homogenous dispersion of fine Si precipitates in a soft and strain free Al matrix. The diffusion of such small precipitates towards the U(Mo) particles will be more effective than the transportation of Si from the larger Si particles used in a mixture matrix. Out of pile experiments are performed to show the difference between using a mixture or an alloy for the interaction with U(Mo). It was found that the U(Mo) particles dispersed in an AlSi alloy matrix have a more uniform Si rich preformed layer after heat treatment.

Excessive U-Al interdiffusion hampers the development of UMo/Al based disperse fuel since several years. As a remedy, addition of diffusion limiting elements to the UMo (Zr) or the Al matrix (Si) has been suggested. First test irradiations showed promising results. However, not the full amount of third element addition to the UMo or the Al contributes to the prevention of interdiffusion layer formation. Therefore, surface engineering of UMo particles, i.e. coating of UMo powder with diffusion limiting elements using DC magnetron sputtering, has been suggested. Thereby the diffusion blockers are applied directly where they are needed: at the interface between the UMo and the Al. For this study, samples from full size plates produced with UMo powder coated with Si (300 nm and 600 nm) and ZrN (1000nm) have been examined before and after irradiation with Iodine at 80 MeV. In case of Si coated UMo particles, a dense Si rich layer developed around the UMo particles during plate fabrication. However, the ZrN layer frequently revealed cracks but no interaction with the Al matrix or the UMo occurred. During heavy ion irradiation, no UMo/Al interdiffusion occurred at spots that are protected by a sufficiently thick Si rich layer or a non-cracked ZrN layer. In contrast, a conventional UMo/Al interdiffusion layer (IDL) occurred at spots where the UMo has not been protected by a Si rich layer or the ZrN layer was broken.

The effects of cold and hot processing on the performance of polymer-fullerene solar cells are investigated for diketopyrrolopyrrole (DPP) based polymers that were specifically designed and synthesized to exhibit a strong temperature-dependent aggregation in solution. The polymers, consisting of alternating DPP and oligothiophene units, are substituted with linear and second position branched alkyl side chains. For the polymer-fullerene blends that can be processed at room temperature, hot processing does not enhance the power conversion efficiencies compared to cold processing because the increased solubility at elevated temperatures results in the formation of wider polymer fibres that reduce charge generation. Instead, hot processing seems to be advantageous when cold processing is not possible due to a limited solubility at room temperature. The resulting morphologies are consistent with a nucleation-growth mechanism for polymer fibres during drying of the films. We thank Hans van Franeker and Fallon Colberts for TEM experiments. G. H. L. Heintges acknowledges the Agency for Innovation by Science and Technology in Flanders (IWT). Part of the work was performed in the framework of the TripleSolar (ERC Adv Grant No. 339031) project, and received funding from the Ministry of Education, Culture and Science (Gravity program 024.001.035).

Significant progresses in the performances under in-pile irradiation of particular U-Mo based fuels have been observed over the last fifteen years. One of the remaining issues has still to be tackled for use as a LEU fuel in the high power research reactors: the U-Mo recrystallization and its associated swelling have to be controlled or delayed. One way to mitigate this problem would be to optimize the initial microstructure of U-Mo atomized particle, by homogenizing Mo concentration and increasing grain size. This paper mainly focuses on U-Mo grain growth. Based on samples prepared in the framework of KOMO-5 and EMPIrE tests, a methodological work based on the use of EBSD is presented. In particular, surface preparation procedures are proposed for powders and rods, this last one being most likely readily applicable for plate analysis. As-atomized microstructures are analyzed in detail and subsequently compared to those obtained on particles annealed at 1000 °C under various conditions. It is found that 1 h annealing under vacuum is a good compromise of temperature and time to meet the development goals, provided that few impurity precipitates are present within U-Mo particles, since these can impact grain growth.

In the framework of the elimination of High-Enriched Uranium (HEU) from the civil circuit, the search for an appropriate fuel to replace the high-enriched research reactor fuel in those reactors that currently still require it for their operation has led to the development of a U–7 wt.%Mo alloy based dispersion fuel with an Al–Si matrix. The European LEONIDAS program, joining SCK•CEN, ILL, CEA and AREVA-CERCA, is aimed at the qualification of such a fuel for the use in high power conditions. The first experiment of the program, designated E-FUTURE, was performed to select the appropriate matrix Si concentration and fuel plate post-production heat treatment parameters for further qualification. It consisted of the irradiation of four distinct (4% and 6% Si, 3 different heat treatments) full size, flat fuel plates in the BR2 reactor. The irradiation conditions were relatively severe: 470 W/cm 2 peak BOL power, with a ∼70% 235 U peak burnup.

This paper reports on the temperature calibration and electrical characterization of the calorimeter chip UFS1 (internal design XI-400) developed for the new commercially available differential scanning calorimeter (DSC), the Flash DSC 1 of Mettler-Toledo. The chip consists of 2 identical membranes both with a p-type polysilicon microheater in the center of the membrane and a p/n-type polysilicon thermopile for measuring the sample temperature. The temperature calibration of the XI-400 is performed in the temperature range from 208 K to 723 K. An isothermal calibration is first performed to calibrate the heater resistance and the obtained curve is used to calibrate the integrated thermopile. The accuracy of the calibration is then determined by measuring the extrapolated onset temperature ( T e ) of primary standards. A detailed electrical characterization of the device is also reported. The calibration method implemented and the good temperature reproducibility of the device allow to use devices with uncalibrated heater resistance in the temperature range from 208 K to 723 K with a typical maximum error of ±5 K.

The performance of the Flash DSC 1, a recently introduced, commercial available chip fast scanning calorimeter (FSC) based on MEMS sensor technology, was studied. Topics included calibration; symmetry; repeatability; scan rate control windows of operation. Scan rates up to 20 000 °C/s for empty cell measurements in cooling and heating have been achieved. By combinations of scan rates up to 1000 °C/s various topics in between −95 to 450 °C were studied on polymers including self nucleation; annealing and thermal fractionation; ‘hot’ and ‘cold’ crystallization; amorphization; and cross-over of crystallization behavior with scan rate variation for two polymers. Sample masses around 1 μg and less gave good results with excellent repeatability and acceptable thermal lags. The Flash DSC 1 enables to mimic realistic conditions of practice and to measure (meta)stability and reorganization phenomena of substances and materials, including polymers, metals, pharmaceuticals etc.

This paper presents a new twin-membrane calorimeter chip for fast differential scanning calorimetry (DSC) with the Flash DSC 1 of Mettler-Toledo. The thin silicon nitride membranes enable scan rates in excess of 10 kK/s in heating and up to 4 kK/s in cooling for sample masses between 100 ng and 10 μg in the temperature range of −100 °C to 450 °C. The time constant for cooling is about 12 ms, the power resolution is typically 0.1–0.5 μW, the temperature accuracy of non-calibrated chips is typically better than ±5 K. The paper also shows measurements for the scan-rate dependent thermal lag of the device, showing an empty sensor thermal lag of about 0.2 ms, and a mass dependent thermal lag of about 0.3 ms/μg for Indium for a good thermal contact between Indium and membrane.

Zirconia–5 mol% yttria has been used successfully for pH sensing in high temperature water (≥300 °C). However, this material, which consists of the cubic phase with 2–8 vol.% intergranular tetragonal precipitates, is not always stable in this environment and some batches were found to be fragmented by cracking within a few days. To study this effect, different samples of the material were structurally characterised and exposed to 300 °C water. It was found that the susceptibility to cracking increased with the volume content of the intergranular precipitates. The cracking mechanism was explained by the stress-induced grain boundary cracking of the cubic phase, the stress being due to the water-induced martensitic transformation of the tetragonal precipitates. A model has been proposed which allows to interpret the dependence of crack formation propensity on the size of the tetragonal precipitates.

In 1975, as a result of a blockage of the coolant inlet flow, two plates of a fuel element of the BR2 reactor of the Belgian Nuclear Research Centre (SCK•CEN) were partially melted. The fuel element consisted of Al-clad plates with 90% 235 U enriched UAl x fuel dispersed in an Al matrix. The element had accumulated a burn up of 21% 235 U before it was removed from the reactor. Recently, the damaged fuel plates were sent to the hot laboratory for detailed PIE. Microstructural changes and associated temperature markers were used to identify several stages in the progression to fuel melting. It was found that the temperature in the center of the fuel plate had increased above 900–950 °C before the reactor was scrammed. In view of the limited availability of such datasets, the results of this microstructural analysis provide valuable input in the analysis of accident scenarios for research reactors.

The core of the BR1 research reactor at SCK•CEN, Mol (Belgium) has a graphite matrix loaded with fuel rods consisting of a natural uranium slug in aluminum cladding. The BR1 reactor has been in operation since 1956 and still contains its original fuel rods. After more than 50 years irradiation at low temperature, some of the fuel rods have been examined. Fabrication reports indicate that a so-called AlSi bonding layer and an U(Al,Si)3 anti-diffusion layer on the natural uranium fuel slug were applied to limit the interaction between the uranium fuel and aluminum cladding. The microstructure of the fuel, bonding and anti-diffusion layer and cladding were analysed using optical microscopy, scanning electron microscopy and electron microprobe analysis. It was found that the AlSi bonding layer does provide a tight bond between fuel and cladding but that it is a thin USi layer that acts as effective anti-diffusion layer and not the intended U(Al,Si)3 layer.

Within the development of reduced activation ferritic martensitic (RAFM) steels as prominent structural materials for future fusion reactors, EUROFER97 has recently emerged in Europe as the reference material for the DEMO design. In order to characterise the in-service performance of EUROFER97 as structural material, it is important to assess the properties of welded joints, particularly under irradiation. In the present paper, three EUROFER97 joints (two diffusion welds and one TIG weld) have been irradiated in the BR2 reactor of SCK-CEN at 300 °C up to 1.8 dpa and subsequently characterised for tensile, impact and fracture toughness properties. Comparisons of the results are provided with base EUROFER97 (both unirradiated and irradiated under similar conditions) and, where available, with properties measured on the joints in the unirradiated condition. The post-irradiation mechanical behaviour of both diffusion joints (“laboratory” and “mock-up”) appears similar to that of the base material; therefore, diffusion joining looks a very promising technique. On the other hand, the properties of the TIG joint are affected by the lack of a post-weld heat treatment, which causes the material from the upper part of the weld to be significantly worse than that of the lower region.

The microstructural evolution of atomised U–7 wt%Mo alloy fuel under irradiation was investigated by transmission electron microscopy on material from the experimental fuel plates used in the FUTURE irradiation. The interaction layer that forms between the U(Mo) particles and the Al matrix is assumed to become amorphous under irradiation and as such cannot retain the fission gas in stable bubbles. As a consequence, gas filled voids are generated between the interaction layer and the matrix, causing the fuel plate to pillow and finally fail. The present analysis confirms the assumption that the U(Mo)–Al interaction layer is completely amorphous after irradiation. The Al matrix and the individual U(Mo) particles, with their cellular substructure, have retained their crystallinity. It was furthermore observed that the fission gas generated in the U(Mo) particles has formed a bubble superlattice, which is coherent with the U(Mo) lattice. Bubbles of roughly 1–2 nm size have formed a 3-dimensional lattice with a lattice spacing of 6–7 nm.

Three full size AlFeNi cladded U3Si2 fuel plates were irradiated in the BR2 reactor of the Belgian Nuclear Research Centre (SCKCEN) under relatively severe, but well defined conditions. The irradiation was part of the qualification campaign for the fuel to be used in the future Jules Horowitz reactor in Cadarache, France. After the irradiation, the fuel plates were submitted to an extensive post-irradiation campaign in the hot cell laboratory of SCKCEN. The PIE shows that the fuel plates withstood the irradiation success- fully, as no detrimental defects have been found. At the cladding surface, a multilayered corrosion oxide film has formed. The U-Al-Si layer resulting from the interaction between the U3Si2 fuel and the Al matrix, has been quantified as U(Al,Si)4.6. It is found that the composition of the fuel particles is not homogenous; zones of USi and U3Si2 are observed and measured. The fission gas-related bubbles generated in both phases show a different morphology. In the USi fuel, the bubbles are small and numerous while in U3Si2 the bubbles are larger but there are fewer. 2008 Elsevier B.V. All rights reserved.

Beryllium, irradiated at around 50 °C for 15 years up to a fast neutron fluence (>1 MeV) of 4.67 × 1022 n cm−2, was annealed at temperatures of 500, 750, 825 and 900 °C. In a previous study, the influence of the annealing temperature and time on the He content and the microstructure was investigated with optical and scanning electron microscopy. To complement the observations made, transmission electron microscopy measurements on the same set of specimens were conducted to determine the helium behaviour at nanometer scale. It was found that the as-irradiated material is heavily stressed and contains many dislocation loops. In the samples annealed at 500 and 750 °C, these dislocation loops disappeared and a large number of small faceted bubbles have formed inside the grains. Close to grain boundaries, a bubble-free area was observed. Annealing at 825 and 900 °C results in the complete removal of all small bubbles, and the local defect structure reverts back to the one of the un-irradiated material.

The dynamic; elastic modulus for directions in the plane of the cladding of a reactor pressure vessel was found to have an unusual low value of 165 GPa. In order to examine this phenomenon further, a cantilever bend test method was developed which allowed measuring the modulus along any desired direction relative to the cladding. It was found that in the as-clad as well as in the clad-and-annealed condition the deviations of the modulus from the bulk modulus depend on the orientation. The modulus values range from 145 GPa perpendicular to the cladding plane to 219 GPa at an angle of 35 degrees to the cladding plane. These deviations from the bulk value are explained by the texture resulting from the directional heat flow during solidification and by the presence of the 6 phase. (C) 2007 Published by Elsevier B.V.

The Material Testing Reactor BR2 of SCK·CEN has a beryllium matrix which has been replaced in 1995. Pieces of this matrix, which were irradiated over a period of 15 yr at about ±50 °C up to a fast neutron fluence ( E > 1 MeV) of 4.67 × 10 22 n/cm 2 , have been retrieved for creep and microstructure studies. An amount of helium resulting from transmutation has accumulated up to approximately 2.2 at.% which is comparable to the expected He content of a fusion reactor blanket at its end of life. Post-irradiation anneals have been performed at 500, 750 and 900 °C, with an annealing time ranging between 50 hours and three months. Microstructural analyses show a clear evolution in bubble growth and He diffusion towards the grain boundaries where the bubbles coalesce. Complete release of 4 He is observed at temperatures >750 °C, resulting in a stagnation of the beryllium swelling. The microstructural changes are mainly temperature driven. Only at high annealing temperature, an influence of the annealing time is observed.

EUROFER97 is a 9Cr–1W–0.2V–0.1Ta reduced activation ferritic/martensitic (RAFM) steel, presently considered within the European Union as the primary candidate structural material in a fusion power plant. Its mechanical strength properties currently prevent its use at temperatures higher than 500–550 °C. In an effort to extend the range of operating temperatures to 600–650 °C and therefore enhance the efficiency of the machine, a different production route, oxide dispersion strengthening (ODS), is being investigated. The characteristics of different versions of EUROFER97 ODS have been assessed in recent years, leading to the improvement of the material by a combination of optimized production process and post-HIPping thermal treatment. Until recently, the mechanical properties of EUROFER97 ODS had only been investigated in the unirradiated condition, and no information was available for the irradiation response of the material. However, mechanical samples have been irradiated during 2004–2005 at 300 °C in the Belgian Reactor 2 (BR2) in Mol up to an accumulated dose of 1.73 ± 0.07 dpa; post-irradiation tensile, Charpy impact and fracture toughness tests have been performed in the hot cell laboratories of the Belgian Nuclear Centre (SCK·CEN). The results obtained allow quantitatively assessing the degradation of mechanical properties induced by neutron irradiation. Comparisons are also presented with similar results obtained from base (non-ODS) EUROFER97, previously irradiated in BR2 under comparable conditions (temperature and dose).