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Neutron irradiation causes embrittlement of reactor pressure vessel (RPV) steels. Post-irradiation annealing is capable of partly or fully restoring the unembrittled condition. While annealing at high temperatures (e.g. 475 °C) was successfully applied to extend the lifetime of operating VVER-440 reactors, the benefit of annealing at lower temperatures (e.g. 343 °C – the maximum to which the primary cooling water can be heated) is a matter of debate. In this study, neutron-irradiated VVER-440 RPV base metal and weld were exposed to isothermal annealing at 343 °C up to 2000 hours. Given the limited amount of material, the degree of recovery was estimated in terms of Vickers hardness, the ductile-brittle transition temperature derived from small punch tests, and the master curve reference temperature derived from fracture mechanics tests of subsized samples. For the base metal, small-angle neutron scattering was applied to underpin the findings at the nm-scale. We have found significant partial recovery in both materials after annealing for 300 hours or longer. The variations of the degree of recovery are critically discussed and put into the context of wet annealing.

This dataset covers test data related to the WetAnnealing Project, in particular the publication "Recovery of neutron-irradiated VVER-440 RPV base metal and weld exposed to isothermal annealing at 343 °C up to 2000 hours" submitted to Frontiers in Nuclear Engineering. The test data have been derived from Vickers hardness (HV10) testing, Small Punch Tests (SPT), Master Curve (MC) fracture mechanics testing of miniaturized compact tension 0.16-C(T) samples, and Small-Ange Neutron Scattering (SANS) experiments. Plots and figures are also included.

One of the main points of any project implementation is the dissemination of the obtained results among the nuclear community, young researchers, public, stakeholders, etc. Communication and dissemination activities are considered as high-priority elements in European collaborative research projects. The article briefly presents EUROATOM project “STRUctructural MATerials Research for Safe Long-Term Operation of LWR NPPs” (STRUMAT-LTO), that was started in September 2020, describes its goals, main steps, expected outputs, approaches used for dissemination and communication activities and brief status update on interim results after 2 years’ implementation. In general, the deployment of the STRUMAT-LTO project was dedicated to studying synergetic effects of Ni-Mn-Si on RPV embrittlement at high fluences by exploiting unique RPV model steels irradiated in LYRA-10 irradiation experiment and assessing the Embrittlement Trend Curves for LTO and Master curve approach for LTO. All these activities are aimed at finding a solution to justify safe LTO until 80 years of operation.

Post-irradiation annealing of neutron-irradiated reactor pressure vessel steels is a matter of both technical and scientific interest. Small-angle neutron scattering (SANS), while being sensitive to nm-sized irradiation-induced solute-atom clusters, provides macroscopically representative and statistically reliable measures of cluster volume fraction, number density and size. In the present study, SANS was applied to uncover the size distribution of clusters in as-irradiated samples of a VVER-1000 weld and their gradual dissolution as function of the post-irradiation annealing temperature. The same samples were used to measure Vickers hardness. The results are consistent with Mn-Ni-Si-rich clusters of less than 2 nm radius to be the dominant source of both scattering and hardening. Annealing gave rise to small but significant partial recovery at 350 °C and almost complete recovery at 475 °C. The dispersed-barrier hardening model was applied to bridge the gap between the characteristics of nano-features and macro-hardness.

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This dataset covers experimental data obtained for neutron-irradiated reactor pressure vessel (RPV) steels, in detail type and composition of steels, initial microstructure, initial properties, irradiation conditions, irradiation-induced microstructure changes and irradiation-induced property changes. The metadata sections of the data compilation include references to published journal articles and reports, where the data were originally published. A special feature of the data compilation is the availability of the characteristics of irradiation-induced nm-sized solute atom clusters derived from small-angle neutron scattering (SANS) experiments for each of the RPV materials and irradiation conditions considered. These characteristics, including cluster volume fraction and size, are statistically reliable and macroscopically representative. Moreover, results of Vickers hardness tests obtained using the same samples and also probing macroscopic volumes are provided. The data compilation is organized in the format of an Excel workbook called SANS-RPV. There are numerous potential applications of the data compilation such as the comparison of cluster characteristics derived from SANS and APT experiments, the correlation between cluster volume fraction and irradiation-induced hardness increase or brittle-ductile transition temperature shift, microstructure-informed predictions of the initial yield stress or irradiation-induced yield stress increase or the assessment of embrittlement trend curce (ETC) models, to mention a few. As an illustration, selected applications are saved in a separate Excel file called SANS_RPV_Analyses, which is included in the dataset. The background and usage of the data compilation as well as applications and implications are part of a study performed within the European Project ENTENTE. A copy of the project report draft (Deliverable D4.5) is included in the dataset.

Existing knowledge about the effect of neutron irradiation on the mechanical properties of reac-tor pressure vessel steels under reactor service conditions relies to a large extent on accelerated irradiations realized by exposing steel samples to a higher neutron flux. A deep understanding of flux effects is, therefore, vital for gaining service-relevant insight on the mechanical property degradation. Existing studies on flux effects often suffer from incomplete descriptions of the ir-radiation-induced microstructure. Our study aims at giving a detailed picture of irradia-tion-induced nanofeatures by applying complementary methods using atom probe tomography, positron annihilation, small-angle neutron scattering and transmission electron microscopy. The characteristics of the irradiation-induced nanofeatures and the dominant factors responsible for the observed increase of Vickers hardness are identified. The results rationalize why pronounced flux effects on the nanofeatures, in particular on solute atom clusters, only give rise to small or moderate flux effects on hardening.

The objective of this WP is to identify and explain synergetic effects of VVER-1000 typical alloying elements in terms of irradiation-induced microstructures and mechanical property changes. Suitable materials are available in the neutron-irradiated condition from the LYRA-10 irradiation experiment. The approach is based on the application of complementary microstructural characterization techniques such as SEM, (S)TEM, APT, SANS, PAS to study low-Cu base and weld materials of intentionally varied contents of Ni, Mn and Si. In order to identify a synergetic effect of elements X and Y, low-X/low-Y, high-X/low-Y, low-X/high-Y and high-X/high-Y materials are to be compared and statistically evaluated with respect to mechanical property changes as well as type, composition, volume fraction, number density and size of irradiation-induced nano-features. Post-irradiation annealing allows the thermal stability of the defects to be evaluated. An additional objective is to provide a link between irradiated microstructures and mechanical property changes for highly irradiated VVER-1000 type steels.

Origin-files, data for figure 3 and figure 4 of publication in J. Nucl. Mater.

The effect of neutron flux on the irradiation-induced microstructure and mechanical behaviour is one of the still open issues for the scientific community both for RPV steels and internals. In the case of RPV steels, more and statistically more reliable microstructural data are needed, in particular for low-Cu RPV steels irradiated up to high fluence. Within SOTERIA, suitable pairs of low-Cu RPV steels irradiated at different flux up to the same levels of fluence were identified. This deliverable D2.1 reports about the effect of neutron flux on the neutron-irradiation-induced microstructure of RPV base and weld materials. The main methods applied are small-angle neutron scattering (SANS), positron lifetime spectroscopy (PAS), transmission electron microscopy (TEM) and atom probe tomography (APT). Using these methods, a number of different kinds of irradiation-induced nanofeatures were detected. These comprise dislocation loops, vacancies, sub-nm vacancy clusters, solute atom clusters and segregated dislocations. Loops are insufficient in number density and vacancy clusters are too small to contribute significantly to the irradiation-induced changes of the mechanical properties, but play a role in the overall evolution of the irradiated microstructures. Solute atom clusters are decisive for irradiation hardening. SANS and APT indicate a common trend that an increasing flux gives rise to smaller sizes and higher number densities of solute atom clusters. APT additionally shows that the clusters are more dilute at higher flux. The counteracting effects of flux on size and number density of solute atom clusters partly compensate each other and, therefore, rationalize the relative insensitivity of the mechanical properties to the neutron flux.