374 research outputs found
Hydrogen solubility in zirconium intermetallic second phase particles
The enthalpies of solution of H in Zr binary intermetallic compounds formed
with Cu, Cr, Fe, Mo, Ni, Nb, Sn and V were calculated by means of density
functional theory simulations and compared to that of H in {\alpha}-Zr. It is
predicted that all Zr-rich phases (formed with Cu, Fe, Ni and Sn), and those
phases formed with Nb and V, offer lower energy, more stable sites for H than
{\alpha}-Zr. Conversely, Mo and Cr containing phases do not provide
preferential solution sites for H. In all cases the most stable site for H are
those that offer the highest coordination fraction of Zr atoms. Often these are
four Zr tetrahedra but not always. Implications with respect to H-trapping
properties of commonly observed ternary phases such as Zr(Cr,Fe)2, Zr2(Fe,Ni)
and Zr(Nb,Fe)2 are also discussed.Comment: manuscript accepted for publication in Journal of Nuclear Materials
(2013
From solid solution to cluster formation of Fe and Cr in -Zr
To understand the mechanisms by which Fe and Cr additions increase the
corrosion rate of irradiated Zr alloys, a combination of experimental (atom
probe tomography, x-ray diffraction and thermoelectric power measurements) and
modelling (density functional theory) techniques are employed to investigate
the non-equilibrium solubility and clustering of Fe and Cr in binary Zr alloys.
Cr occupies both interstitial and substitutional sites in the {\alpha}-Zr
lattice, Fe favours interstitial sites, and a low-symmetry site that was not
previously modelled is found to be the most favourable for Fe. Lattice
expansion as a function of alloying concentration (in the dilute regime) is
strongly anisotropic for Fe additions, expanding the -axis while contracting
the -axis. Defect clusters are observed at higher solution concentrations,
which induce a smaller amount of lattice strain compared to the dilute defects.
In the presence of a Zr vacancy, all two-atom clusters are more soluble than
individual point defects and as many as four Fe or three Cr atoms could be
accommodated in a single Zr vacancy. The Zr vacancy is critical for the
increased solubility of defect clusters, the implications for irradiation
induced microstructure changes in Zr alloys are discussed.Comment: 15 pages including figure, 9 figures, 2 tables. Submitted for
publication in Acta Mater, Journal of Nuclear Materials (2015
Accommodation of tin in tetragonal ZrO2
Atomic scale computer simulations using density functional theory were used to investigate the behaviour of tin in the tetragonal phase oxide layer on Zr-based alloys. The Sn×ZrSnZr× defect was shown to be dominant across most oxygen partial pressures, with Sn′′ZrSnZr″ charge compensated by V∙∙OVO•• occurring at partial pressures below 10−31 atm. Insertion of additional positive charge into the system was shown to significantly increase the critical partial pressure at which Sn′′ZrSnZr″ is stable. Recently developed low-Sn nuclear fuel cladding alloys have demonstrated an improved corrosion resistance and a delayed transition compared to Sn-containing alloys, such as Zircaloy-4. The interaction between the positive charge and the tin defect is discussed in the context of alloying additions, such as niobium and their influence on corrosion of cladding alloys
A side-by-side comparison of Daya Bay antineutrino detectors
The Daya Bay Reactor Neutrino Experiment is designed to determine precisely
the neutrino mixing angle with a sensitivity better than 0.01 in
the parameter sin at the 90% confidence level. To achieve this
goal, the collaboration will build eight functionally identical antineutrino
detectors. The first two detectors have been constructed, installed and
commissioned in Experimental Hall 1, with steady data-taking beginning
September 23, 2011. A comparison of the data collected over the subsequent
three months indicates that the detectors are functionally identical, and that
detector-related systematic uncertainties exceed requirements.Comment: 24 pages, 36 figure
Observation of electron-antineutrino disappearance at Daya Bay
The Daya Bay Reactor Neutrino Experiment has measured a non-zero value for
the neutrino mixing angle with a significance of 5.2 standard
deviations. Antineutrinos from six 2.9 GW reactors were detected in
six antineutrino detectors deployed in two near (flux-weighted baseline 470 m
and 576 m) and one far (1648 m) underground experimental halls. With a 43,000
ton-GW_{\rm th}-day livetime exposure in 55 days, 10416 (80376) electron
antineutrino candidates were detected at the far hall (near halls). The ratio
of the observed to expected number of antineutrinos at the far hall is
. A rate-only analysis
finds in a
three-neutrino framework.Comment: 5 figures. Version to appear in Phys. Rev. Let
Long-Baseline Neutrino Facility (LBNF) and Deep Underground Neutrino Experiment (DUNE) Conceptual Design Report Volume 2: The Physics Program for DUNE at LBNF
The Physics Program for the Deep Underground Neutrino Experiment (DUNE) at
the Fermilab Long-Baseline Neutrino Facility (LBNF) is described
- …