Low Neutron Absorption Cross Section Research Articles

Improving Temperature Sensing in Nuclear Environments

Substantial improvements in high temperature measurement have been made in the last few years at national measurement institutes, which can be of benefit to the nuclear industry. In this article some of these developments are summarised. In addition, the temperature aspects of a major European project, ‘MetroFission’, to build on these improvements and disseminate these developments are described. Novel aspects include new temperature calibration techniques and artifacts, new thermocouple types with much improved stability and low neutron absorption cross-section, self-calibrating thermocouples and practical acoustic thermometry - a driftless technique for measuring absolute temperature.

Research on long-time self-irradiation of alloy δ-Pu 242–Ga

Self-irradiation of Pu–Ga alloy was studied by neutron diffraction, which provided information about the crystalline structure and yielded mean-square atom displacements 〈 u 2〉 from the Debye–Waller factor. The measurements were performed at room temperature using the sample based on the isotope Pu 242 with low neutron absorption cross-section to which the short-living isotope Pu 238 (1.4%) was added to accelerate self-irradiation. This composition of the sample sped up the aging processes by the factor of four and allowed us to obtain the maximum equivalent time of 23.5 years. Fcc structure remains the same throughout this interval. The changes in 〈 u 2〉 due to static displacements occur in two stages, viz. a relatively rapid growth (roughly by 50%) over the first 5–6 equivalent years and slow decline during 6–23 equivalent years making a close approach to the initial values. The latter stage has not been described in the literature. It can be explained by the confluence of point defects into helium bubbles and dislocation loops accumulated over time.

Positron annihilation study of recrystallization behaviour in Zr2.5%Nb alloy

AbstractIn CANDU reactors Zr 2.5%Nb alloy is used as pressure tube material due to low neutron absorption cross section, a high resistance to corrosion in water, high strength and good creep resistance. The two phase alloy consists of α‐fcc and β‐bcc. The recrystallization behavior of Zr2.5Nb strongly depends on morphology and distribution of second phase. In this study, the material was deformed to 60% and then was recrystallized in α + β region for different duration (i.e. 2 minutes to 14 days at 700 °C). The recrystallized microstructure was characterized by Orientation Imaging Microscopy (OIM). The evolution of microstructure was examined by Positron Lifetime Spectroscopy and Doppler Broadening measurement for each heat treated samples. Results from positron annihilation studies and other microstructural examination have been used to rationalize the recrystallization aspects, defects and β‐phase distribution. (© 2009 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)

HALO – the helium and lead observatory for supernova neutrinos

The Helium and Lead Observatory (HALO) is a supernova neutrino detector under development for construction at SNOLAB. It is intended to fulfill a niche as a long term, low cost, high livetime, and low maintenance, dedicated supernova detector. It will be constructed from 80 tonnes of lead, from the decommissioning of the Deep River Cosmic Ray Station, and instrumented with approximately 384 meters of 3He neutron detectors from the final phase of the SNO experiment. Charged- and Neutral-Current neutrino interactions in lead expel neutrons from the lead nuclei making a burst of detected neutrons the signature for the detection of a supernova. Existing neutrino detectors are mostly of the water Cerenkov and liquid scintillator types, which are primarily sensitive to electron anti-neutrinos via charged-current interactions on the hydrogen nuclei in these materials. By contrast, the large neutron excess of a heavy nucleus like Pb acts to Pauli-block p⟩n transitions induced by electron anti-neutrinos, making HALO primarily sensitive to electron neutrinos. While any supernova neutrino data would provide an invaluable window into supernova dynamics, the electron neutrino CC channel has interesting sensitivity to particle physics through flavour-swapping and spectral splitting due to MSW-like collective neutrino-neutrino interactions in the core of the supernova, the only place in the universe where there is a sufficient density of neutrinos for this to occur. Such data could provide a test for θ13 ≠ 0 and an inverted neutrino mass hierarchy. In addition, the ratio of 1-neutron to 2-neutron events would be a measure of the temperature of the cooling neutron star. For the 80 tonne detector, a supernova at 10 kpc is estimated to produce 43 detected neutrons in the absence of collective ν-ν interactions, and many more in their presence. The high neutrino cross-section and low neutron absorption cross-section of lead, along with the modest cost of lead, makes this technology scalable and a future upgrade, to of order 1 kilotonne, is under active consideration.

Thermal equations of state of theα,β, andωphases of zirconium

We have conducted synchrotron x-ray diffraction studies on high purity zirconium metal at pressures $(P)$ up to $17\phantom{\rule{0.3em}{0ex}}\mathrm{GPa}$ and temperatures $(T)$ up to $973\phantom{\rule{0.3em}{0ex}}\mathrm{K}$. Unit cell volumes $(V)$ were derived from the refinements of x-ray diffraction data for the $\ensuremath{\alpha}$, $\ensuremath{\beta}$, and $\ensuremath{\omega}$ phases of zirconium and fitted to a Birch-Murnaghan equation of state with the pressure derivative of the bulk modulus, $K_{0}{}^{\ensuremath{'}}$, fixed at 4.0. The derived thermoelastic parameters for $\ensuremath{\alpha}$ zirconium are isothermal bulk modulus ${K}_{0}=92(3)\phantom{\rule{0.3em}{0ex}}\mathrm{GPa}$, temperature derivative of bulk modulus ${(\ensuremath{\partial}K∕\ensuremath{\partial}T)}_{P}=\ensuremath{-}2.3(8)\ifmmode\times\else\texttimes\fi{}{10}^{\ensuremath{-}2}\phantom{\rule{0.3em}{0ex}}\mathrm{GPa}∕\mathrm{K}$, volumetric thermal expansivity ${\ensuremath{\alpha}}_{T}=a+bT$ with $a=1.5(\ifmmode\pm\else\textpm\fi{}0.8)\ifmmode\times\else\texttimes\fi{}{10}^{\ensuremath{-}5}\phantom{\rule{0.3em}{0ex}}{\mathrm{K}}^{\ensuremath{-}1}$ and $b=1.7(\ifmmode\pm\else\textpm\fi{}1.4)\ifmmode\times\else\texttimes\fi{}{10}^{\ensuremath{-}8}\phantom{\rule{0.3em}{0ex}}{\mathrm{K}}^{\ensuremath{-}2}$, and the pressure derivative of thermal expansion ${(\ensuremath{\partial}\ensuremath{\alpha}∕\ensuremath{\partial}P)}_{T}=\ensuremath{-}2.7(9)\ifmmode\times\else\texttimes\fi{}{10}^{\ensuremath{-}6}\phantom{\rule{0.3em}{0ex}}{\mathrm{GPa}}^{\ensuremath{-}1}\phantom{\rule{0.2em}{0ex}}{\mathrm{K}}^{\ensuremath{-}1}$. For the $\ensuremath{\beta}$ phase we obtained an isothermal bulk modulus of ${K}_{T}=66(3)\phantom{\rule{0.3em}{0ex}}\mathrm{GPa}$ at $973\phantom{\rule{0.3em}{0ex}}\mathrm{K}$ and a unit-cell volume of $V(973\phantom{\rule{0.3em}{0ex}}\mathrm{K})=47.7(3)\phantom{\rule{0.3em}{0ex}}{\mathrm{\AA{}}}^{3}$ at ambient pressure. For the $\ensuremath{\omega}$ zirconium we obtained ${K}_{0}=90(5)\phantom{\rule{0.3em}{0ex}}\mathrm{GPa}$. Within the experimental errors, the ${K}_{0}$ values we determined for the $\ensuremath{\alpha}$ and $\ensuremath{\omega}$ phases and volumetric thermal expansion for the $\ensuremath{\alpha}$ phase are in agreement with previous experimental results, whereas all other thermoelastic parameters represent the first determinations for the three crystalline phases of zirconium metal.

The Use of Molybdenum-Based Ceramic-Metal (CerMet) Fuel for the Actinide Management in LWRs

The technical and economic aspects of the use of molybdenum depleted in the isotope 95Mo (DepMo) for the transmutation of actinides in a light water reactor are discussed. DepMo has a low neutron absorption cross section and good physical and chemical properties. Therefore, DepMo is expected to be a good inert matrix in ceramic-metal fuel. The costs of the use of DepMo have been assessed, and it was concluded that these costs can be justified for the transmutation of the actinides neptunium, americium, and plutonium.

What Happened at Chernobyl?

What Happened at Chernobyl?

What Happened at Chernobyl?

What Happened at Chernobyl?

Beryllium Extraction and Utilisation— Prospects and Constraints

Beryllium and beryllium compounds find wide variety of applications in diverse industries. Low density, high strength, and attractive nuclear properties like low neutron absorption cross section an...

Dynamical neutron diffraction by ideally curved crystals

Neutron diffraction patterns by ideally curved crystals were calculated by extending Taupin’s dynamical theory of X-ray diffraction by deformed crystals. The thickness and the curvature of the crystals were utilized as physical parameters. The results of the neutron diffraction calculations are substantially different from those relative to the X-rays. This is due essentially to the low neutron absorption crosssection. The main part of the neutron results is physically explained with the aid of the concepts of the dynamical theory of diffraction by perfect crystals. This study finds an application in the design of new types of neutron monochromators.

Dynamical neutron diffraction by ideally curved crystals

Neutron diffraction patterns by ideally curved crystals were calculated by extending Taupin’s dynamical theory of X-ray diffraction by deformed crystals. The thickness and the curvature of the crystals were utilized as physical parameters. The results of the neutron diffraction calculations are substantially different from those relative to the X-rays. This is due essentially to the low neutron absorption crosssection. The main part of the neutron results is physically explained with the aid of the concepts of the dynamical theory of diffraction by perfect crystals. This study finds an application in the design of new types of neutron monochromators.

Characterisation of Polycrystalline Silicon Carbide by Scanning and Transmission Electron Microscopy

Silicon carbide is an extremely hard refractory material. Corrosion resistance, which is a general limitation of most carbides, is also good. These features alone make silicon carbide an important engineering material, but in addition, its low neutron absorption cross-section, and its behaviour under irradiation make it a particularly attractive material for use in a nuclear environment.The mechanical strength of self-bonded silicon carbide is primarily dependent on grain size and on the presence of free silicon in the material. Figure 1 shows a scanning electron micrograph of a fracture surface. The morphology is typical of a brittle transgranular fracture, although there is evidence of some ductility in the free silicon phase.

Scattering of Long Wave-length Neutrons by Irradiated Beryllium Oxide

WORK on the scattering of long wave-length neutrons by irradiation-induced defects have been carried out by Antal, Weiss and Dienes for graphite1 and by Antal and Goland for alumina2. The method depends on the fact that in materials of low neutron absorption cross-section, neutrons of wave-length greater than the Bragg cut-off are attenuated principally by inelastic scattering (for which the cross-section is a few hundred millibarns) and by the scattering from defects. Application of Babinet's principle shows that each isolated point defect introduces an amount of scattering equal to the free atom cross-section of the material.

Improvement of magnesium canning alloy for carbon dioxide cooled reactor fuel elements

Improvement of Mg-Al-Be alloy, so-called Magnox series alloys has been contemplated by adding an element of low neutron absorption cross section instead of calcium. Bismuth, zinc, tin, silicon, lead and zirconium are the elements considered. It was found through preliminary experiment that bismuth and zinc are the most effective with a view to enhance strength at the temperature of 400°C or higher. Addition of Al-Zr master alloy into the melt has also been proved to improve the strength of the alloy, but zirconium has not been detected by chemical analysis.Work hardening curves are given and the tensile test data in Table 3. The result of the welding test under argon atmosphere is given in Fig. 2. Less softening was observed in the welded and heat-affected zones of thus improved alloys.Corrosion test has been made in carbon dioxide gas of 8 atmospheric pressure at 400°C (Fig. 3), where, the two improved alloys have shown good corrosion resistnance.From these tests, it was found out that the magnesium alloy, containing less than 2% aluminium, 0.01-0.05% beryllium and 0.1-0.3% bismuth or zinc could be recommended for canning matirials in CO2 around 450°C.