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McClintock D.A.,Oak Ridge National Laboratory | Hyres J.W.,Babcock and Wilcox Technical Services Group Inc. | Vevera B.J.,Babcock and Wilcox Technical Services Group Inc.
Journal of Nuclear Materials | Year: 2014

The inner surfaces of mercury target vessels at the Spallation Neutron Source (SNS) experience material erosion caused by proton-beam induced cavitation of the liquid mercury. One approach developed and deployed to inhibit erosion of the target vessel material was surface hardening via a proprietary low-temperature carburization treatment, called Kolsterising®, to the target surfaces most susceptible to cavitation-induced erosion. Previous testing has shown that the hardened surface produced by the Kolsterising® treatment can delay the onset of erosion and inhibit erosion once initiated. But the stability of the carbon atmosphere in the treated surface layer after radiation to doses prototypic to the SNS target was unknown. Therefore, as part of the target Post Irradiation Examination program at the SNS, optical microscopy and microhardness testing were performed on material sampled from the first and second operational SNS target vessels. Optical micrographs contained no noticeable precipitation in the super-saturated carbon layer extending into the base material and several micrographs contained evidence of a proposed mechanism for mass wastage from the vessel surface. The hardened layer was characterized using Vickers microhardness testing and results show that the shape of hardness profile of the treated layer corresponded well with known pre-irradiation hardness values, though the microhardness results show some hardening occurred during irradiation. The results suggest that the hardened surface layer produced by the Kolsterising® treatment is stable at the operational temperatures and dose levels experienced by the first and second operational SNS target modules. © 2014 Elsevier B.V. All rights reserved. Source


Vevera B.J.,Babcock and Wilcox Technical Services Group Inc. | McClintock D.A.,Oak Ridge National Laboratory | Hyres J.W.,Babcock and Wilcox Technical Services Group Inc. | Riemer B.W.,Oak Ridge National Laboratory
Journal of Nuclear Materials | Year: 2014

Disk-shaped samples were removed from the first and second operational target modules at the Spallation Neutron Source for post-irradiation examination to assess the extent of radiation-induced changes in mechanical properties and the amount of cavitation-induced erosion to the AISI 316L stainless steel target vessel. Characterization techniques performed include: high-resolution photography of the disk specimens, ultrasonic cleaning to remove mercury residue and surface oxides, surface profile mapping of cavitation pits using high frequency ultrasonic testing, high-resolution surface replication, and scanning electron microscopy accompanied by energy dispersive spectroscopy. The target disk samples were machined using wire electrical discharge machining to produce microstructural and mechanical test specimens for tensile testing, Rockwell Superficial hardness testing, and Vickers microhardness testing. The effectiveness of the cleaning procedure was evident in the pre- and post-cleaning photography, and provided accurate photographs of areas on each disk that facilitated the creation of detailed machining maps. Due to the limited amount of material available and the unique geometry of the disks, test specimen design and development of fixturing for machining operations were critical aspects of this work; multiple designs were considered and refined during mock-up testing on unirradiated disks. The techniques used to successfully machine and test the various specimens will be presented along with a summary of important findings from the laboratory characterizations. © 2014 Elsevier B.V. All rights reserved. Source


McClintock D.A.,Oak Ridge National Laboratory | Vevera B.J.,Babcock and Wilcox Technical Services Group Inc. | Riemer B.W.,Oak Ridge National Laboratory | Gallmeier F.X.,Oak Ridge National Laboratory | And 2 more authors.
Journal of Nuclear Materials | Year: 2014

During neutron production the target module at the Spallation Neutron Source (SNS) is damaged by cavitation-induced erosion and the mechanical properties of the AISI 316L vessel material are altered by high-energy proton and neutron radiation. Recently the first and second operational target modules at the SNS reached the end of their useful lifetime, and disk shaped specimens were sampled from the beam entrance region of both targets. Tensile specimens ranging in dose from 3 to 7 displacements per atom (dpa) were fabricated from the disk specimens using wire electrical discharge machining and tested at room temperature. This paper presents the tensile properties of the irradiated 316L vessel material removed from the first and second operational SNS target modules. Results show an increase in tensile strength and decrease in elongation values similar to previous spallation irradiated 316L results. Abnormally large elongation, 57% total elongation, was observed in a specimen irradiated to 5.4 dpa and considerable scatter was observed in the uniform and total elongation data. One possible explanation for the abnormally large elongations and scatter observed in tensile test results is the so-called deformation wave phase transformation-induced plasticity effect. Microscopy characterization revealed the presence of large nonmetallic inclusions rich in Al, S, Ca, O, and Mg on the fracture surface, which may have also contributed to the scatter in the tensile elongation results. While all specimens exhibited radiation-induced hardening and a decrease in ductility, the predominate topographical morphology on all specimen fracture surfaces examined was ductile microvoid coalescence and all specimens experienced appreciable necking prior to fracture. These findings indicate that 316L retains sufficient ductility (10-20% total elongation) and fractures in a ductile manor after irradiation to approximately 6-7 dpa in the mixed proton/neutron radiation environment at the SNS. © 2014 Elsevier B.V. All rights reserved. Source

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