United Kingdom Atomic Energy Authority

About: United Kingdom Atomic Energy Authority is a government organization based out in Abingdon, United Kingdom. It is known for research contribution in the topics: Creep & Nuclear reactor. The organization has 2020 authors who have published 1515 publications receiving 20782 citations. The organization is also known as: UKAEA & Atomic Energy Authority.

Chapter 1: Overview and summary

Abstract: The 'Progress in the ITER Physics Basis' (PIPB) document is an update of the 'ITER Physics Basis' (IPB), which was published in 1999 [1]. The IPB provided methodologies for projecting the performance of burning plasmas, developed largely through coordinated experimental, modelling and theoretical activities carried out on today's large tokamaks (ITER Physics R&D). In the IPB, projections for ITER (1998 Design) were also presented. The IPB also pointed out some outstanding issues. These issues have been addressed by the Participant Teams of ITER (the European Union, Japan, Russia and the USA), for which International Tokamak Physics Activities (ITPA) provided a forum of scientists, focusing on open issues pointed out in the IPB. The new methodologies of projection and control are applied to ITER, which was redesigned under revised technical objectives. These analyses suggest that the achievement of Q > 10 in the inductive operation is feasible. Further, improved confinement and beta observed with low shear (= high βp = 'hybrid') operation scenarios, if achieved in ITER, could provide attractive scenarios with high Q (> 10), long pulse (>1000 s) operation with beta

Recombination between electrons and atomic ions, II. Optically thick plasmas

Abstract: Consideration is given to the interacting collisional and radiative processes occurring in a plasma. A statistical theory describing the general loss mechanism, for which the name collisional-radiative recombination is proposed, is described. This theory enables the collisional-radiative recombination coefficient a to be determined knowing the relevant spontaneous transition probabilities and the rate coefficients for radiative recombination and collisional excitation and ionization. Detailed calculations are carried out on hydrogen-ion plasm as which are optically thin. It is found that α is an increasing function of the number density of free electron n(c) the increase being especially marked if the electron temperature T is low; for example, if T is 250 °K α becomes almost 20 times as great as the radiative recombination coefficient (which describes the loss in a very tenuous plasma) when n(c) is only about 10 8 /cm 3 , whereas if T is 64 000°K a does not become as great as this until n(c) is about 10 18 /cm 3 . From a similar investigation in which the ground level of the hydrogen atom is made inaccessible (in crude representation of an alkali atom) it is inferred that the value of a is probably not very sensitive to the species of singly charged ion involved. Recombination of electrons with bare nuclei of charge Ze to form hydrogenic ions is similarly treated for an optically thin plasma. It is shown that to a close approximation the reduced coefficient α/ Z is a function of a reduced tem perature T/Z 2 and a reduced number density n(c)/Z 7 only. The values of the reduced coefficients are of com parable m agnitude and have a similar dependence of the reduced temperature and density as the coefficients for hydrogen ion plasmas. The variation of the recombination coefficient α with Z in the same plasma (i.e. same n(c) and T ) is investigated. It may be expressed in the form a α ∝ Z z where the index z depends on n(c) and T . Though z is generally positive as would be expected, it is negative if n(c) and T are very high. A physical explanation of this is presented.

The strength of two-phase ceramic/glass materials

Abstract: The strengths of various glasses, with a range of expansion coefficients, containing 10 vol % thoria spheres, of diameter 50 to 700μm, have been measured. Stresses occur around the spheres, due to differences in the expansion coefficients of the glass and the spheres, on cooling from the fabrication temperature. Stress magnification occurs near the spheres, due to differences in elastic properties, in the presence of an applied stress. When the expansion coefficient of the sphere is greater than that of the glass, circumferential cracks form around the spheres but only when the sphere diameter is greater than a critical value. An approximate value for the critical diameter may be obtained by an energy balance criterion. Cracks may form around spheres smaller than the critical diameter under application of applied stress at stresses below the macroscopic fracture stress. In these cases the strength is governed by a Griffith relationship with the crack size equal to the sphere diameter. When the expansion coefficients of the spheres and glass are similar, the strength of the glass is reduced only when large spheres (⪞300μm diameter) are present. When the expansion coefficient of the spheres is less than that of the glass, linking radial cracks form between the spheres and the material has very low strength.

Outstanding radiation resistance of tungsten-based high-entropy alloys.

Abstract: A body-centered cubic W-based refractory high entropy alloy with outstanding radiation resistance has been developed. The alloy was grown as thin films showing a bimodal grain size distribution in the nanocrystalline and ultrafine regimes and a unique 4-nm lamella-like structure revealed by atom probe tomography (APT). Transmission electron microscopy (TEM) and x-ray diffraction show certain black spots appearing after thermal annealing at elevated temperatures. TEM and APT analysis correlated the black spots with second-phase particles rich in Cr and V. No sign of irradiation-created dislocation loops, even after 8 dpa, was observed. Furthermore, nanomechanical testing shows a large hardness of 14 GPa in the as-deposited samples, with near negligible irradiation hardening. Theoretical modeling combining ab initio and Monte Carlo techniques predicts the formation of Cr- and V-rich second-phase particles and points at equal mobilities of point defects as the origin of the exceptional radiation tolerance.