Insight Into Disorder, Stress and Strain of Radiation Damaged Pyrochlores: A Possible Mechanism for the Appearance of Defect Fluorite

We have examined the irradiation response of a titanate and zirconate pyrochlore—both of which are well studied in the literature individually—in an attempt to define the appearance of defect fluorite in zirconate pyrochlores. To our knowledge this study is unique in that it attempts to discover the mechanism of formation by a comparison of the different systems exposed to the same conditions and then examined via a range of techniques that cover a wide length scale. The conditions of approximately 1 displacement per atom via He2+ ions were used to simulate long term waste storage conditions as outlined by previous results from Ewing in a large enough sample volume to allow for neutron diffraction, as not attempted previously. The titanate sample, used as a baseline comparison since it readily becomes amorphous under these conditions behaved as expected. In contrast, the zirconate sample accumulates tensile stress in the absence of detectable strain. We propose this is analogous to the lanthanide zirconate pyrochlores examined by Simeone et al. where they reported the appearance of defect fluorite diffraction patterns due to a reduction in grain size. Radiation damage and stress results in the grains breaking into even smaller crystallites, thus creating even smaller coherent diffraction domains. An (ErNd)2(ZrTi)2O7 pyrochlore was synthesized to examine which mechanism might dominate, amorphization or stress/strain build up. Although strain was detected in the pristine sample via Synchrotron X-ray diffraction it was not of sufficient quality to perform a full analysis on.

Investigation of DPA in the reactor pressure vessel of VVER-1000/V320

The most important ageing effect on the reactor pressure vessel (RPV) is radiationembrittlement, which is mainly caused by fast neutrons during operation lifetime of nuclear reactors. The aim of this study was to investigate the DPA (displacement per atom) rate, an important parameter describing radiation damage to the RPV, and identify the position of the maximum DPA rate in the RPV of the VVER-1000/V320 reactor using the Monte Carlo code MCNP5. To reduce statistical errors in the MCNP5 simulation, the weight window technique was applied to non-repeated structures outside the reactor core. The results showed the distribution of the DPA rate in the RPV and the maximum DPA rate was found to be at the first millimeters of the RPV. Consequently, these calculations could be useful for assessment of radiation damage to the RPV of VVER reactors.

Irradiation Behaviors in BCC Multi-Component Alloys with Different Lattice Distortions

Recently, the irradiation behaviors of multi-component alloys have stimulated an increasing interest due to their ability to suppress the growth of irradiation defects, though the mostly studied alloys are limited to face centered cubic (fcc) structured multi-component alloys. In this work, two single-phase body centered cubic (bcc) structured multi-component alloys (CrFeV, AlCrFeV) with different lattice distortions were prepared by vacuum arc melting, and the reference of α-Fe was also prepared. After 6 MeV Au ions irradiation to over 100 dpa (displacement per atom) at 500 °C, the bcc structured CrFeV and AlCrFeV exhibited significantly improved irradiation swelling resistance compared to α-Fe, especially AlCrFeV. The AlCrFeV alloy possesses superior swelling resistance, showing no voids compared to α-Fe and CrFeV alloy, and scarce irradiation softening appears in AlCrFeV. Owing to their chemical complexity, it is believed that the multi-component alloys under irradiation have more defect recombination and less damage accumulation. Accordingly, we discuss the origin of irradiation resistance and the Al effect in the studied bcc structured multi-component alloys.

Advanced Structural Materials for Gas-Cooled Fast Reactors—A Review

This review summarizes the development of the Gas-Cooled Fast Reactor (GFR) concept from the early 1970s until now, focusing specifically on structural materials and advanced fuel cladding materials. Materials for future nuclear energy systems must operate under more extreme conditions than those in the current Gen II or Gen III systems. These conditions include higher temperatures, a higher displacement per atom, and more corrosive environments. This paper reviews previous GFR concepts in light of several promising candidate materials for the GFR system. It also reviews the recent development of nuclear power and its use in the peaceful exploration of space. The final section focuses on the development and testing of new advanced materials such as SiCf/SiC composites and high entropy alloys (HEA) for the construction and development of GFRs.

Using of Stopping and Range of Ions in Matter Code to Study of Radiation Damage in Materials

The aim of this work to investigate the impact of the radiation damage in the materials by the proton energy irradiation. The damage parameter used in the evaluation is displacement per atom (DPA) in material as a function of proton energy. Stopping and Range of Ions in Matter (SRIM) code was used to calculate the total vacancy and the number of atomic displacements based on the Norgett-Robinson-Torrens model by difference energies for proton irradiation damage. The option of this code was calculated by using Ion Distribution and Quick Calculation of Damage (Kinchin-Pease) for Fe and Cu target and also Full damage cascade (F-C) was chosen for only Fe. The result is that, the prediction of the F-C model are higher than the K-P calculation. Comparisons has been made with an international standard definition of DPA.

Measurement of displacement cross section of structural materials utilized in the proton accelerator facilities with the kinematic energy above 400 MeV

For damage estimation of structural material in the accelerator facility, displacement per atom (DPA) is widely employed as an index of the damage calculated based on the displacement cross section obtained with the calculation model. Although the DPA is employed as the standard, the experimental data of displacement cross section are scarce for a proton in the energy region above 20 MeV. Among the calculation models, the difference exists about 8 times so that experimental data of the displacement cross section is crucial to validate the model. To obtain the displacement cross section, we conducted the experiment in J-PARC. As a preliminary result, the displacement cross section of copper was successfully obtained for 3-GeV proton. The present results showed that the widely utilized the Norgertt-Robinson-Torrens (NRT) model overestimates the cross section as suggested by the previous experiment for protons with lower energy.

Improved model for atomic displacement calculation

Atomic displacement is one of the key factors that influence the behaviors of material properties during and after irradiation. Many models, including the international standard metric Norgett-Robinson-Torrens model (NRT), have been developed to calculate the number of Displacement per Atom (DPA) using the energy of Primary Knocked-on Atom (PKA) as a major parameter. However, extensive experiments and simulations indicate that the NRT-DPA model seriously overestimates (about 3 times) the actual DPA. Nordlund recently developed the Athermal Recombination-Corrected DPA (ARC-DPA) model, which shows that the Molecular Dynamics (MD) simulations can be directly used to compute DPA by fitting the simulated data for each isotope. The present work proposes a simpler expression for the efficiency function to calculate the DPA without requiring fitting parameters as needed in the ARC-DPA model. Our DPA calculation results utilizing the improved efficiency function are validated against the experimental data for the Fe, Ni, Cu, and Ag. The applications in fast breeder nuclear reactors show good agreement with the ARC-DPA metric for 56Fe.