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[en] This paper discusses an evaluation of the use of alternate materials as structural components in nuclear spent fuel transportation casks. Principle technical issues are addressed. Focus is on the appropriateness of brittle fracture criteria
[en] Highlights: • The limit for aging time to keep tensile strength is 10,000 h for 550 °C. • No degradation of ductility was detected after all the aging examined. • The strength degradation is described by time-temperature equivalence parameters. - Abstract: The present study conducted tensile tests on F82H steel after aging at 400–650 °C for 1000–30,000 h, and discusses the process for change in tensile properties during the long-term aging, combined with previous study for 100,000 h aging. The limit for aging time to keep tensile strength is more than 100,000 h for 400 and 500 °C aging, 10,000 h for 550 °C, 3000 h for 600 °C, and less than 1000 h for 650 °C. While, no degradation of ductility was detected after all the aging examined. Regression analyses were performed with Hollomon-Jaffe parameter and Lambda parameter on the degradation of tensile strength during aging, and prior tempering in the heat treatment before the aging. Lambda parameter analysis successfully derived a master curve to describe the tensile strength after the long-term aging.
[en] Compliance variations in the threshold regime of a high strength ferritic steel tested under closure-free conditions at room temperature and in air are reported. In contrast to the Paris regime, and irrespective of whether the data during load shedding, at threshold or after postthreshold load increase are considered, it is found that comparatively compliance varies inconsistently in the threshold regime. Therefore, a 1:1 correlation between the averaged optical crack length and that inferred from compliance was not observed. This discrepancy is analyzed. The variations in compliance are utilized to infer the crack front behavior, and the results are discussed in terms of the microstructural impedance. (orig.) With 22 figs., 2 appendices
[de]Compliance-Aenderungen im Schwellwertbereich eines hochfesten Stahls, getestet ohne Rissschliessung bei Raumtemperatur und in Luft, werden berichtet. Im Gegensatz zum Paris-Bereich wurde festgestellt, dass die Aenderungen der Compliance im Schwellwertbereich vergleichsweise inkonsistent waren, und zwar unabhaengig davon, ob die Daten waehrend der Lastabstufung, beim Schwellwert oder nach der anschliessenden Lasterhoehung betrachtet wurden. Demzufolge wurde keine 1:1-Korrelation zwischen der direkt optisch gemessenen und gemittelten Risslaenge und der indirekt aus der Compliance abgeleiteten Risslaenge beobachtet. Die moeglichen Ursachen dieser Diskrepanz werden analysiert. Das Rissfrontverhalten ist aus den Aenderungen der Compliance hergeleitet, und die Ergebnisse werden an Hand des Eigenwiderstandes (microstructural impedance) diskutiert. (orig.) With 22 figs., 2 appendices
[en] Normalized 21/4Cr-1Mo steel has been tempered at 998 K for durations up to 50 h, and then oxidized in air at 773, 873 and 973 K for a maximum duration of 1000 h. The extent of the prior tempering treatment was found to influence the oxidation behaviour of the steel significantly. In general, the oxidation resistance of the steel decreased with increasing duration of prior tempering. However, a pronounced influence has been observed during oxidation at 973 K, when at the end of a 6h exposure the specimens with prior tempering for 50 h were found to have a weight gain 2.5 times more than the specimen without prior tempering. From the results of the pre-and post-oxidation analyses of the oxide-alloy matrix interfaces by SEM/EDAX, the observed oxidation behaviour could be attributed to the degree of depletion of free (effective) chromium from the alloy by the precipitation of secondary phases of chromium compounds during tempering for different durations. The secondary precipitates in the specimen tempered for 50 h at 998 K can become enriched in chromium by one order of magnitude more than that in the specimen with no prior tempering. Such a drastic depletion of chromium from the matrix causes the formation of a less protective inner oxide layer during oxidation. Acoustic emission tests carried out to assess the mechanical stability of the scale showed that the 50 h tempered specimen suffered cracking after about 4 h oxidation at 973 K, which results in subsequent enhanced oxidation. (author)
[en] Highlights: •Aluminum addition to ODS steel improves compatibility between U-Zr fuel and the ODS steels. •It increases the threshold temperature for reaction layer formation by 50 K. •The compatibility improvement mechanism was discussed using general thermodynamic data. -- Abstract: Out-of-pile high-temperature reaction tests are carried out on the diffusion couples between U–Zr fuel and ODS ferritic steels, in which the concentrations of Cr and Al were systematically changed for improvement of corrosion resistance. The results show that the Al addition to ODS ferritic steel considerably improves the compatibility between U–Zr fuel and the ODS steel. The threshold temperature for reaction layer formation is roughly 50 K higher in the Al-containing ODS ferritic steels than in the steels without Al addition for the testing time up to 900 min. The compatibility improvement mechanism by Al addition is discussed from the viewpoint of activity change. The activity calculation results obtained using general thermodynamic data indicate the possibility that stabilization of the intact α-Zr layer by Al addition is the main mechanism and occupation of steel lattice sites by Al that does not easily diffuse into γ-U–Zr also partly contributes to suppression of the inter-diffusion
[en] Corrosion damages of welds occur in spite of the fact that the proper base metal and filler metal have been correctly selected, industry codes and standards have been followed and welds have been realized with full weld penetration and have proper shape and contour. In secondary circuit of a Nuclear Power Station there are some components which have dissimilar welds. The principal criteria for selecting a stainless steel usually is resistance to corrosion, and white most consideration is given to the corrosion resistance of the base metal, additional consideration should be given to the weld metal and to the base metal immediately adjacent to the weld zone. Our experiments were performed in chloride environmental on two types of samples: non-welded (410 or W 1.4006 ferritic-martensitic steel and 304L or W 1.4307 austenitic stainless steel) and dissimilar welds (dissimilar metal welds: joints between 410 ferritic-martensitic and 304L austenitic stainless steel). To evaluate corrosion susceptibility of dissimilar welds was used electrochemical method (potentiodynamic method) and optic microscopy (microstructural analysis). The present paper follows the localized corrosion behaviour of dissimilar welds between austenitic stainless steel and ferritic-martensitic steel in solutions containing chloride ions. It was evaluated the corrosion rates of samples (welded and non-welded) by electrochemical methods. (authors)
[en] Fatigue crack propagation (FCP) behavior of a ferritic steel was investigated under closure free conditions, with particular emphasis on the threshold regime. The post-threshold load level increase was varied in a range between 5% and 45% in one step. Irrespective of the magnitude of load increase, the specimens exhibited hysteresis, such that FCP curves of the same specimen obtained during the K-decreasing and the K-increasing test differed, especially when the crack tended to become non-propagating in the post-threshold regime. While giving due consideration to the possibility of an 'overload' effect, the results are discussed in terms of the microstructural impedance. (orig.)
[en] Near-threshold fatigue crack propagation behavior of a high strength steel was investigated in laboratory air under closure-free testing conditions at R = 0.7 (= Reff), and at two different K-gradients. Depending on the criterion assumed, the threshold value differed; the criterion of non-propagation gave a lower threshold value than that assumed by the propagation criterion. Nevertheless, the subsequent propagation following a load increase was discontinuous in both the cases, and da/dN vs ΔK curves obtained on the same specimen during the K-decreasing and the K-increasing test were not necessarily identical in the threshold regime. This behavior, hysteresis, is analyzed mainly from the experimental viewpoint, and it is shown that hysteresis is not an artifact. (orig.) With 13 figs., 3 appendices
[de]Das Rissausbreitungsverhalten eines hochfesten Stahls wurde in Laborluft untersucht, und zwar bei zwei unterschiedlichen Lastabstufungsraten und einem Lastverhaeltnis von R = 0,7 (= Reff), ohne dass Rissschliessung auftrat. Abhaengig von dem angenommenen Kriterium variierte der Schwellwert. Das Kriterium 'keine Rissausbreitung' (non-propagation) ergab einen niedrigeren Schwellwert als das Kriterium 'Rissausbreitung' (propagation). Dennoch war die an die Lasterhoehung anschliessende Rissausbreitung in den beiden Faellen diskontinuierlich, und demzufolge waren die an derselben Probe waehrend der Lastabstufung und nach der Lasterhoehung erhaltenen da/dN-ΔK-Kurven im Schwellwertbereich nicht unbedingt deckungsgleich. Dieser Effekt, Hysterese, wird hauptsaechlich von experimentellen Gesichtspunkten aus analysiert, und es wird gezeigt, dass der Hysterese-Effekt kein Artifakt ist. (orig.) With 13 figs., 3 appendices
[en] Highlights: • Cavity density increased monotonically and swelling decreased monotonically with helium content. • Low helium levels increased cavity density, but did not influence cavity evolution at high damage levels. • High helium levels lowered the critical cavity radius and produced bimodal distributions. • Cavity evolution was suppressed at high helium levels due to helium trapping, or alteration of cavity and dislocation bias. • Dislocations and precipitates did not significantly influence cavity evolution.
[en] Nucleation of Y-Al-O, Y-Ti-O, and Y-Zr-O enriched nano-clusters (NCs) in nano-structured ferric alloys were comparatively investigated using first-principles calculations. Formation of various possible cluster configurations was energetically evaluated with respect to individually dissolved solute atoms, to explore the preferential precipitation and growth sequence of the NCs. Key results include the following observations. During the earliest nucleation stages, Y-Zr-O NCs are always the most energy favored to form in the supersaturated bcc-Fe based matrix, followed by Y-Ti-O and Y-Al-O NCs. All the three type NCs follow the same nucleation path that begins from the O-O pairs. Y has the strongest thermodynamic driving force to precipitate with the O-O pairs. The most stable six-atomic cluster configuration is predicted as –[2Y-3O-X]–. The (O-Y)-cores may constitute the stable nuclei of larger NCs which grow consistently by attracting extra solutes available nearby.