Low neutron cross-section FeCrVTiNi based high-entropy alloys: design, additive manufacturing and characterization

The development of high-entropy alloys (HEAs) based on the novel alloying concept of multi-principal components presents opportunities for achieving new materials with desired properties for increasingly demanding applications. In this study, a low neutron cross-section FeCrVTiNi-based HEA was developed for potential nuclear applications. A face-centred cubic (FCC) HEA with the nominal composition of FeCr0.4V0.3Ti0.2Ni1.3 is proposed based on the empirical thermodynamic models and the CALculation of PHAse diagrams (CALPHAD) calculation. Verifications of the predictions were performed, including the additive manufacturing of the proposal material and a range of microstructural characterizations and mechanical property tests. Consistent with the prediction, the as-fabricated HEA consists of a dominant FCC phase and minor Ni3Ti precipitates. Moreover, significant chemical segregation in the alloy, as predicted by the CALPHAD modelling, was observed experimentally in the produced dendritic microstructure showing the enrichment of Ni and Ti elements in the interdendritic regions and the segregation of Cr and V elements in the dendritic cores. Heterogenous mechanical properties, including microhardness and tensile strengths, were observed along the building direction of the additively manufactured HEA. The various solid solution strengthening effects, due to the chemical segregation (in particular Cr and V elements) during solidification, are identified as significant contributing factors to the observed mechanical heterogeneity. Our study provides useful knowledge for the design and additive manufacturing of compositionally complex HEAs and their composition-microstructure-mechanical property correlation.

Migration to Cased Hole Petrophysics: Are We Ready?

In the present Oil & Gas business context, the uncertainties reduction for hydrocarbon production increase in an operational costs and risk reduction scheme, are among the main drivers in several operating companies in the northern region of South America (Colombia & Ecuador). Electrical logging and drilling tools stuck events due to differential pressures, fishing operations, high wellbore tortuosity, difficult geometries and unconsolidated formations affecting wellbore stability, are among the main problems increasing non-productive time and operating costs. Minimizing open hole operations with a full migration to cased hole data acquisition, providing inputs for petrophysical uncertainty reductions without jeopardizing well completion decisions or initial reservoir characterization, would constitute an attractive solution for operators. Following those initiatives, we start by achieving a complete open hole formation evaluation and then migrating to case hole data acquisition and petrophysical assessment while benchmarking against open hole results. Low and variable formation water salinity, complex mineralogy's affecting resistivity and radioactive minerals, are common petrophysical challenges in our reservoirs. We had to implement Archie and salinity-independent formation evaluation solutions with cased hole technologies and in absence of open hole logs. The open hole petrophysics consist on simultaneous assessment of matrix and fluids saturations, while evaluating the oil mobility and water cut with the incorporation of multi-depth of investigation sensors in single logging runs (spectroscopy, dielectric dispersion, and magnetic resonance). We then moved to cased hole formation evaluation, with spectroscopy & nuclear-based petrophysics in gas, light oil, and heavy oil-bearing reservoirs. By implementation of non-archie fluids volumetric computation (that relies on conversion of dry weight total carbon to oil saturation and fast neutron cross section to gas saturation- done through a simultaneous inversion by solving matrix-porosity-fluids volumes into an elemental analysis), we obtained a representative formation saturation range behind casing. We then discussed on the different scenarios were migrating to cased hole is sustainable and its potential limitations.

Optimising Depth Selection on Section Milling Operation to Secure Sustained Casing Pressure During Plug and Abandonment Operation

D-01 was an exploration well requiring a Plug-and-Abandonment (P&A) procedure with sustained casing pressure up to 2,000 psi on the B annulus. The presence of Sustained Casing Pressure (SCP) is one of the major technical challenges to decommission and abandon the well safely. Several attempts to secure the well using the perforation-and-squeeze method were performed – but failed. It was decided to perform section milling operations to create a viable rock-to-rock barrier. In this operation, the key factor in determining success, is selecting the correct depth to mill safely and secure the annular pressure source. A comprehensive approach was taken to determine the optimum depth for the section milling by evaluating existing open-hole and cased-hole data. Additionally, triple-detector Pulsed Neutron Log (PNL) was also performed prior to the section milling operation. The triple-detector PNL tool offered not only behind casing porosity (TPHI) and sigma (SIGM) measurement, but also a relatively new measurement in the oil and gas industry called Fast Neutron Cross Section (FNXS), which were expected to provide more accurate gas detection and gauge the condition near the borehole. By combining all the logs and reservoir data, the milling interval was selected and the section milling and subsequent cement plug operations were performed. Evaluation of existing open-hole and cased-hole logs provided geological and petrophysical insights which were useful in determining the hydrocarbon source charging the B-annulus. Further analysis on PNL data provided indication of possible gas pockets in the B-annulus. This information was used to distinguish between shallower formation sources or gas pockets that were not yet bled off. The operation on D-01 successfully resolved the B-annulus issue and the well was properly abandoned per regulatory requirements. Considering the complexity and high cost of section milling operations, a thorough review of data and pre-job logging increases the probability of selecting the optimum intervals needed to successfully complete P&A operations on SCP wellbores.

Neutron Cross Section Measurement Using the Associated Particle Technique

<p>The associated particle technique is applied to the D(d.n) He3 reaction, in order to produce a tagged neutron beam of accurately known energy, flux, and direction. The incident deuteron beam is obtained from a 400 Kv positive ion Van de Graaff accelerator. A description is given of the design of a uniform field sector magnet and other equipment associated with the stabilization and calibration of the energy of the incident deuteron beam. A versatile n-He3 coincidence system is described. The use of a silicon surface barrier detector with a thin nickel foil window enables complete resolution of the He3 peak with consequent improved neutron flux determination. The tagged neutron beam is used to measure the absolute neutron cross sections of the K39 (n,p) A39 and K39 (n, alpha) Cl36 reactions at a neutron energy of 2.46 Mev. The results obtained, (95 plus-minus 4) mb and (6.2 plus-minus 1) mb respectively, are compared with values obtained by other workers, and with theoretical predictions.</p>

Neutron Cross Section Measurement Using the Associated Particle Technique

<p>The associated particle technique is applied to the D(d.n) He3 reaction, in order to produce a tagged neutron beam of accurately known energy, flux, and direction. The incident deuteron beam is obtained from a 400 Kv positive ion Van de Graaff accelerator. A description is given of the design of a uniform field sector magnet and other equipment associated with the stabilization and calibration of the energy of the incident deuteron beam. A versatile n-He3 coincidence system is described. The use of a silicon surface barrier detector with a thin nickel foil window enables complete resolution of the He3 peak with consequent improved neutron flux determination. The tagged neutron beam is used to measure the absolute neutron cross sections of the K39 (n,p) A39 and K39 (n, alpha) Cl36 reactions at a neutron energy of 2.46 Mev. The results obtained, (95 plus-minus 4) mb and (6.2 plus-minus 1) mb respectively, are compared with values obtained by other workers, and with theoretical predictions.</p>

Weight Gain and Hydrogen Absorption in Supercritical Water At 500°C of Chromium-Coated Zirconium-Based Alloys: Transverse vs Longitudinal Direction

Canadian Nuclear Laboratories (CNL) has an on-going Research & Development programme to support the development of a scaled-down 300 MWe version of the Canadian Super-Critical Water Reactor (SCWR) concept. The 300 MWe and 170-channel reactor core concept uses low enriched uranium fuel and features a maximum cladding temperature of 500°C. Our goal is to test surfacemodified zirconium alloys for use as fuel cladding. Zirconium alloys are attractive as they offer low neutron cross section thereby allowing the use of low enriched fuel. In this paper, we report on the results of general corrosion experiments used to evaluate chromiumcoated zirconium-based alloys in the two chemistries (630 ug/kg O2 in both deaerated and lithiated supercritical water). These experiments were conducted in a refreshed autoclave at 500°C and 23.5 MPa. After exposure, the weight gain and the hydrogen absorption were examined. At adequate coating thickness, longitudinal and transverse coupons show similar corrosion behaviour with improved corrosion resistance compared to uncoated coupons. The measured concentrations of hydrogen absorption are higher for the transverse coupons. Alkaline treatment resulted in higher weight gains than was found in pure oxygenated supercritical water.

Simulating Static and Dynamic Properties of Magnetic Molecules with Prototype Quantum Computers

Magnetic molecules are prototypical systems to investigate peculiar quantum mechanical phenomena. As such, simulating their static and dynamical behavior is intrinsically difficult for a classical computer, due to the exponential increase of required resources with the system size. Quantum computers solve this issue by providing an inherently quantum platform, suited to describe these magnetic systems. Here, we show that both the ground state properties and the spin dynamics of magnetic molecules can be simulated on prototype quantum computers, based on superconducting qubits. In particular, we study small-size anti-ferromagnetic spin chains and rings, which are ideal test-beds for these pioneering devices. We use the variational quantum eigensolver algorithm to determine the ground state wave-function with targeted ansatzes fulfilling the spin symmetries of the investigated models. The coherent spin dynamics are simulated by computing dynamical correlation functions, an essential ingredient to extract many experimentally accessible properties, such as the inelastic neutron cross-section.

Gadolinium contained scintillation glass for neutron detection in a wide energy range.

Inorganic scintillation glasses form a domain of rapidly evolving detector materials used to measure various types of ionizing radiation. The most widespread are lithium-silicate glasses enriched with the 6Li isotope, which are used to register thermal neutrons. At the same time, due to the specificity of the energy dependence of the neutron cross-section of light nuclei, such materials are of little use for the evaluation of epithermal and more highly energetic neutrons. The use of rare earth elements in the composition of glasses makes it possible to increase the sensitivity to neutrons. In the BaO–Gd2O3–SiO2 system, doped with Ce ions, a scintillation glass with a yield of at least 2500 photons / MeV was created for the first time, which permits to create inexpensive detector elements of a significant volume for registering neutrons. It has been shown that a detector based on BaO–Gd2O3–SiO2 glass has satisfactory properties when detecting neutrons in a wide spectrum of their energies.