[en] Channel-control-blade interference has been a challenging issue over the past eight years for operating boiling water reactors plants where ∼2-year cycles are normal and Zircaloy-2 is the standard channel material. The primary reason for this was the unaccounted channel distortion caused by differential hydrogen across the channel that resulted from shadow corrosion on the blade side (known as shadow corrosion-induced bow). Zircaloy-2 is particularly susceptible to this distortion mechanism because it has a high hydrogen pickup fraction that increases with exposure. GNF developed a two-stage strategy to mitigate channel distortion. The first was to optimize the performance of Zircaloy-2 by developing a cell friction methodology that accounted for all known distortion mechanisms: the fluence-gradient bow, the elastic and creep bulge, and now the shadow corrosion-induced bow. This has allowed GNF to better manage the use of Zircaloy-2, which in some cases has required rechanneling during refueling outages. The second stage is to implement alternative channel materials that are inherently more resistant to channel distortion. The first part of this second stage is the reintroduction of Zircaloy-4, which is effectively resistant to shadow corrosion-induced bow and has similar irradiation growth and creep performance to Zircaloy-2. The one disadvantage of Zircaloy-4 is that it has less corrosion resistance than Zircaloy-2. However, based on the extensive experience with Zircaloy-4 channels both in the U.S. and Japan (and the processing improvements made to specifically enhance corrosion resistance), the corrosion performance of Zircaloy-4 is shown to be adequate for channel applications

[en] Archival data from the Infrared Spectrometer of the Spitzer Space Telescope are used to study the 15 μm absorption feature of solid CO₂ toward 28 young stellar objects (YSOs) of approximately solar mass. Fits to the absorption profile using laboratory spectra enable categorization according to the degree of thermal processing of the ice matrix that contains the CO₂. The majority of YSOs in our sample (20 out of 28) are found to be consistent with a combination of polar (H₂O-rich) and nonpolar (CO-rich) ices at low temperature; the remainder exhibit profile structure consistent with partial crystallization as the result of significant heating. Ice-phase column densities of CO₂ are determined and compared with those of other species. Lines of sight with crystallization signatures in their spectra are found to be systematically deficient in solid-phase CO, as expected if CO is being sublimated in regions where the ices are heated to crystallization temperatures. Significant variation is found in the CO₂ abundance with respect to both H₂O (the dominant ice constituent) and total dust column (quantified by the extinction, A_V). YSOs in our sample display typically higher CO₂ concentrations (independent of evidence for thermal processing) in comparison to quiescent regions of the prototypical cold molecular cloud. This suggests that enhanced CO₂ production is driven by photochemical reactions in proximity to some YSOs, and that photoprocessing and thermal processing may occur independently.