15 research outputs found
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An evaluation of electrochemical potentiokinetic reactivation techniques for in-service measurements on Type 304 stainless steel
Electrochemical potentiokinetic reactivation (EPR) tests can be used to measure quantitatively the sensitization of Type 304 stainless steel. The single loop (SL) and double loop (DL) EPR techniques were compared as non-destructive methods for determining sensitization under both laboratory and simulated field environments. Measurements were performed on specimens heat-treated to produce levels of sensitization from no sensitization to heavy sensitization. At temperatures of 22/degree/C and 30/degree/C testing with standard laboratory and portable field apparatus, both EPR techniques were capable of distinguishing sensitization levels at the range spanning those characterized as being non-susceptible and susceptible to intergranular stress corrosion cracking (IGSCC). Through correlations developed for the test data, it is possible to translate field results to the standard laboratory test conditions. This was demonstrated for the SL test through measurements performed on a pipe specimen containing IGSCC. 12 refs., 12 figs., 2 tabs
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Metal hydride compacts for hydrogen isotope separation
A column packed with pellets of copper plated LaNi{sub 4.25}Al{sub 0.75} has been evaluated for its separation efficiency using a displacement method. Deuterium breakthrough curves were produced experimentally and compared with those calculated with a stage model. The height equivalent to a theoretical plate was attained and its dependence on temperature and gas flow rate was established. 6 refs., 4 figs
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Fracture assessment of Savannah River Reactor carbon steel piping
The Savannah River Site (SRS) production reactors have been in operation since the mid-1950's. One postulated failure mechanism for the reactor piping is brittle fracture of the original A285 and A53 carbon steel piping. Material testing of archival piping determined (1) the static and dynamic tensile properties; (2) Charpy impact toughness; and (3) the static and dynamic compact tension fracture toughness properties. The nil-ductility transition temperature (NDTT), determined by Charpy impact test, is above the minimum operating temperature for some of the piping materials. A fracture assessment was performed to demonstrate that potential flaws are stable under upset loading conditions and minimum operating temperatures. A review of potential degradation mechanisms and plant operating history identified weld defects as the most likely crack initiation site for brittle fracture. Piping weld defects, as characterized by radiographic and metallographic examination, and low fracture toughness material properties were postulated at high stress locations in the piping. Normal operating loads, upset loads, and residual stresses were assumed to act on the postulated flaws. Calculated allowable flaw lengths exceed the size of observed weld defects, indicating adequate margins of safety against brittle fracture. Thus, a detailed fracture assessment was able to demonstrate that the piping systems will not fail by brittle fracture, even though the NDTT for some of the piping is above the minimum system operating temperature
Extinction vulnerability in marine populations
Human impacts on the world's oceans have been substantial, leading to concerns about the extinction of marine taxa. We have compiled 133 local, regional and global extinctions of marine populations. There is typically a 53-year lag between the last sighting of an organism and the reported date of the extinction at whatever scale this has occurred. Most disappearances (80%) were detected using indirect historical comparative methods, which suggests that marine extinctions may have been underestimated because of low-detection power. Exploitation caused most marine losses at various scales (55%), followed closely by habitat loss (37%), while the remainder were linked to invasive species, climate change, pollution and disease. Several perceptions concerning the vulnerability of marine organisms appear to be too general and insufficiently conservative. Marine species cannot be considered less vulnerable on the basis of biological attributes such as high fecundity or large-scale dispersal characteristics. For commercially exploited species, it is often argued that economic extinction of exploited populations will occur before biological extinction, but this is not the case for non-target species caught in multispecies fisheries or species with high commercial value, especially if this value increases as species become rare. The perceived high potential for recovery, high variability and low extinction vulnerability of fish populations have been invoked to avoid listing commercial species of fishes under international threat criteria. However, we need to learn more about recovery, which may be hampered by negative population growth at small population sizes (Allee effect or depensation) or ecosystem shifts, as well as about spatial dynamics and connectivity of subpopulations before we can truly understand the nature of responses to severe depletions. The evidence suggests that fish populations do not fluctuate more than those of mammals, birds and butterflies, and that fishes may exhibit vulnerability similar to mammals, birds and butterflies. There is an urgent need for improved methods of detecting marine extinctions at various spatial scales, and for predicting the vulnerability of species