查看更多>>摘要：Tritium diffusivity in zirconium tritides is key to tritium storage in tritium-producing burnable absorber rods. Experiments struggle with assessing tritium diffusivity in reactor environments because irradiated defects alter diffusion. Here molecular dynamics simulations are used to investigate the irradiation effects on tritium diffusion in 8-ZrT 2-x . We found that for defect-free 8-ZrT 2-x , diffusivity can be described by a single Arrhenius equation for composition range x = 0.01-0.07. The irradiated vacancies slightly increase diffusivity although have no effects on diffusion energy barriers. Interestingly, irradiated self-interstitial atoms substantially increase diffusivity and reduce the energy barriers due to a lattice expansion effect. Published by Elsevier B.V.
Karthik, V.Kumar, Ran VijayAnandaraj, V.Padmaprabu, C....
17页
查看更多>>摘要：Titanium modified austenitic stainless steel 316 (Alloy D9) is the material of clad and wrapper for the 500 MWe Prototype Fast Breeder Reactor (PFBR) at Kalpakkam, India. Towards evaluating the irradiation performance of the mixed oxide (MOX) fuel design and Alloy D9 structural material, a test fuel sub-assembly (FSA) made of Alloy D9 wrapper with 37 MOX fuel pins of Alloy D9 cladding was irradiated in Fast Breeder Test Reactor (FBTR) to a peak burnup of 112 GWd/t. The dimensional changes, swelling and mechanical properties of alloy D9 clad and wrapper at displacement damage levels of 40-62 dpa were evaluated through post-irradiation examinations (PIE) and compared with that of AISI 316 clad/wrapper of FBTR. This study has revealed superior performance of alloy D9 compared to AISI 316 counterparts and suggests that MOX fuel subassembly of PFBR with Alloy D9 cladding and wrapper can safely attain the initial target burnup of 100 GWd/t and corresponding displacement damage of 85 dpa.(c) 2022 Elsevier B.V. All rights reserved.
查看更多>>摘要：Swelling is commonly observed in austenitic stainless steels irradiated at high doses and high tem-peratures, such as fuel claddings in Fast-Breeder Reactors (FBR), as a consequence of the formation of irradiation-induced nanovoids. Macroscopic embrittlement has been reported above a critical swelling level. Several physical explanations have been proposed such as void-related fracture mechanisms and phase transformation associated with local changes of microchemistry. In addition, structural effects can affect the critical swelling level, tentatively explained by local corrosion, swelling gradient and bending effects. In order to address these phenomena, an extended experimental database is first presented, based on fuel pins irradiated in the Phenix fast reactor, showing the evolution of conventional tensile proper-ties with swelling. In the present database, 15-15Ti specimens were irradiated from 30 to 120 dpa, with irradiation temperatures ranging from 400 degrees C to 625 degrees C and a maximum swelling of 11%. Other data pub-lished in scientific literature were also included in the analysis to extend the swelling range up to 30%. SEM and TEM analysis are also summarized to highlight specific embrittlement mechanisms related to the presence of voids. Theoretical analysis and finite element simulations are then performed based on porous materials constitutive equations in order to rationalize the experimental observations. Analytical and numerical results show that swelling-induced embrittlement can be understood from a mechanical perspective as a transition from void growth to void coalescence deformation mode. The effect of the spa-tial heterogeneity of void distribution is quantified and shown to be a key parameter. Structural effects coming from tests performed on ring and axial tensile specimens and from the presence of a swelling gradient in cladding thickness are also quantified. Numerical results are compared to experimental data, and a good agreement is observed. (c) 2022 Elsevier B.V.
Winfrey, A. LeighEchols, John R.Seo, MinsukWang, Ke...
16页
查看更多>>摘要：Tungsten is a candidate divertor material for many tokamak reactors and has potential to be durable to high heat flux conditions. However, plasma-materials interaction and edge localized modes (1-10 GW/m(2)) can cause significant hardening and melting damage. Tungsten in a high heat flux (46.3 GW/m(2)) and helium plasma environment was investigated. We studied possible residual helium and microstructure de-formation in resolidified tungsten. Following this, a 1-30 keV Ga focused ion beam was used for TEM sample milling. In as-received tungsten, dark spots of possible lattice strain and defects were in the grains. After high heat exposure under plasma pressure, intergranular features, dark spots in TEM, diffraction patterns, and elongated FIB induced pore-artifact structures (second phase) formed. Helium appears to be absent from the resolidified tungsten matrix due to erosive melting damage and high temperature conditions. A simple four-step microstructure deformation process from the elastic bulk side to the near-pore environment is proposed. The presence of defects in TEM images, grain size reduction, and microstructure deformation affected hardening. The near-pore environment likely experienced grain refinement, and further disordered nanophases are possible under severe deformation conditions. (C) 2022 Elsevier B.V. All rights reserved.
查看更多>>摘要：Three-point bending tests provide the ability to measure the propagation of axially oriented cracks in thin-walled fuel cladding in a radial outside-in direction. Via three-point bending, unirradiated Zircaloy-2 cladding containing 155 and 305 wppm hydrogen was mechanically loaded at different temperatures, sufficient to initiate delayed hydride cracking (DHC) whereupon the unloading rate was fast enough to arrest further propagation. The crack front dimensions were measured through fractography and implemented with the final load into a finite element model (FEM). Given the average crack length and final load, the FEM was able to back-calculate the stress intensity factor. Over a temperature range of 210-330 degrees C, around 6 MPa root m was calculated as the minimum threshold stress intensity factor for DHC. The trend shows that the ideal temperature for DHC with lowest threshold stress intensity factors may depend on the hydrogen concentration, and that the threshold stress intensity factors quickly increase with higher test temperatures. It has also been shown that creep affects the threshold stress intensity factor for optimal DHC less for lower hydrogen concentrations than for higher hydrogen concentrations. At low hydrogen concentration, the temperature of terminal solid solubility for precipitation (TSSP) is low enough so that creep-induced crack tip rounding plays a less significant role compared to the hydrogen kinetics. (C) 2022 The Authors. Published by Elsevier B.V.
查看更多>>摘要：We investigate here the effects of transient (cyclic) arc-jet plasma and laser heating on fracture behavior of W-foam and solid tungsten. The two key parameters that control the foam thermomechanical response are its density and mean cell size expressed in Pores Per Inch (PPI). Tungsten foam samples were fabricated with Chemical Vapor Deposition (CVD) with variety of PPI and relative density. These were tested under two types of qualitatively different conditions: (1) high-enthalpy arc-jet, and (2) high-power cyclic laser heating. None of the foam samples showed macroscopic through-thickness cracks. However, distributed micro-cracks were observed on ligaments and their triple junctions. Under the same loading conditions, W-foam and solid tungsten showed similar crack network pattern and characteristic length scale. However, Crack Opening Displacement (COD) was twice as large in solid W as compared to W foam. Foam samples that have been previously exposed to a low-pressure helium plasma showed significant changes in their surface forming nano-texture fuzz which was removed by subsequent testing in the arc-jet. Extensive fracture and re-crystallization were observed in the thin solid W disk that was fully constrained from expansion. Thicker and fully-constrained solid W disks did not display recrystallization, grain growth, and extensive cracking. However, thicker disks that were free to expand showed some re crystallization and extensive through-thickness cracks due to less effective cooling and thus higher temperatures. Laser beam testing showed no visible damage formation at 0.19 GW/m(2)& nbsp;and 0.38 GW/m(2)& nbsp;for both low-density (23%) and high-density (43%) foams at low pulses (100-1000). Micro-cracks were observed after 10,0 0 0 pulses at 0.19 GW/m(2)& nbsp;in both foams, and in low-density foam after 10 0,0 0 0 at 0.38 GW/m(2). The nature of thermomechanical damage in W-foam exposed to extreme power (GW/m(2)) short duration laser pulses was found to be qualitatively similar to that of high power (MW/m(2)) long-duration arc-jet. (C)& nbsp;2022 Elsevier B.V. All rights reserved.
Capps, Nathan A.Cheniour, AmaniPastore, GiovanniHarp, Jason M....
12页
查看更多>>摘要：There has been a recent push to accelerate nuclear fuel qualification by combining advanced modeling and simulation with accelerated separate effects irradiation testing. One separate effects irradiation testing capability is the MiniFuel vehicle designed to accelerate burnup accumulation in "mini " fuel samples under isothermal temperature conditions. These steady-state MiniFuel irradiations effectively decouple the fuel temperature from the fission rate (i.e., power) by minimizing the fuel volume and relying on gamma heating in the surrounding components for temperature control. This provides experimenters a flexible means for targeting and evaluating specific fuel microstructures for a wide range of fuel types and operating conditions. However, the accelerated fuel qualification process must be informed by modeling and simulation to properly evaluate the most impactful fuel performance parameters and to identify modeling and data gaps. A test matrix can then be designed to fill those gaps and, ultimately, refine and validate the fuel performance models. This work uses the BISON fuel performance code to conduct an assessment and sensitivity study on calculated fission gas release (FGR) from UO2 MiniFuel disks during isothermal irradiation and temperature transients. Qualitatively, the existing fission gas behavior model in BISON reproduces the effects of temperature and burnup as expected. However, when quantitatively compared with FGR data from irradiated (103 MWd/kgU) UO2 disks under thermal annealing representative of LOCA conditions, the model shows a less satisfactory predictive capability. As a result, development needed to model the specific mechanisms of transient FGR during LOCAs, including fuel fragmentation and the role of the high burnup structure (HBS), are identified. Finally, a UO2 MiniFuel test matrix is proposed to extend the temperature and burnup ranges covered by previous experiments and provide new model validation data for fission gas behavior under high burnup and transient conditions. (C) 2022 Elsevier B.V. All rights reserved.
查看更多>>摘要：& nbsp;Comprehensive molecular dynamics tensile test simulations have been performed to study the delamination processes of seven different grain boundaries / cleavage planes ( sigma 1{111}, sigma 3{111}, sigma 5{10 0}, sigma 7{111}, sigma 9{411},sigma 11{311}, and R{100}/{411}) containing a helium bubble. Combinations of a variety of conditions are explored including different strain rates, system dimensions, bubble density, bubble radius, bubble pressure, and temperature. We found that in general, grain boundaries absorb less energies with decreasing strain rate but increasing bubble areal density, bubble pressure, bubble radius, and temperature. The propensity of grain boundary delamination is sensitive to grain boundary type: The random grain boundary R{100}/{411} is one of the most brittle boundaries whereas the sigma 1{111} cleavage plane and the sigma 3{111} twin boundary are two of the toughest boundaries. The sorted list of grain boundary fracture vulnerability obtained from our dynamic tensile test simulations differs from the one obtained from our decohesion energy calculations, confirming the important role of plastic deformation during fracture. Detailed mechanistic analyses are performed to interpret the simulated results. Published by Elsevier B.V.
Penders, A. G.Konstantinovic, M. J.Yang, T.Bosch, R. -w....
16页
查看更多>>摘要：The microstructural features of intergranular irradiation-assisted stress corrosion crack tips from a redeemed neutron-irradiated flux thimble tube (60 dpa) have been investigated using focused-ion beam analysis and (scanning) transmission electron microscopy. The current work presents a close examination of the deformation field and oxide assembly associated with intergranular cracking, in addition to the analysis of radiation-induced segregation at leading grain boundaries. Evidence of stress induced martensitic transformation extending from the crack tips is presented. Intergranular crack arrest is demonstrated on the account of the external tensile stress orientation, and as a consequence of MnS inclusion particles segregating close to the fractured grain boundary. Exclusive observations of grain boundary oxidation prior to the cracking are presented, which is in full-agreement with the internal oxidation model.(c) 2022 Elsevier B.V. All rights reserved.
Wang, YuzhouHua, ZilongSchley, RobertBeausoleil II, Geoffrey...
7页
查看更多>>摘要：The thermal properties of tristructural isotropic (TRISO) particle coatings have been measured using laser based thermoreflectance methods from room temperature to 900 degrees C. At room temperature the pyrocarbon coatings have comparable thermal conductivities below 10 Wmiddotm(-1).K-1, whereas the SiC coating has a thermal conductivity around 90 W.(-1).K-1. The thermal diffusivities of all coatings display significant reduction with increasing temperature. The thermal conductivity of SiC decreases by more than 25% above 800 degrees C and the thermal conductivities of pyrocarbons increase moderately with the temperature, displaying similar changes to that of amorphous graphite at elevated temperatures. (C) 2022 Elsevier B.V. reseverd.
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