Results 1 - 10 of 2114
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[en] The stability of a dispersion of particles may be affected by resolution due to radiation recoil. Simple models of the diffusion of solute that recoils into the matrix allow an estimate of when this process will be important, leading either to the complete dissolution of the particles or to inverse coarsening in which small particles grow and large particles shrink. We first find the concentration profile for which solute diffuses back to a particle as a fast as it is expelled by recoils. The transient concentration profiles in the matrix demonstrate the time required to approach steady state. The solution for a single particle is then used to calculate the rate of inverse coarsening by the diffusion of solute from the region near large particles to the region near small particles. The rate of growth or shrinkage depends directly on the recoil rate and the recoil distance cubed. It depends only weakly on the particle spacing and not at all on the diffusion coefficient. (orig.)
[en] Currently there is controversy surrounding the mechanism of fission-gas release from fuel subjected to transient heating. A recent model (SINGAR) suggests that the release mechanism is principally single-atom migration coupled with thermal resolution of atoms from intragranular bubbles. This contrasts markedly with the previous interpretation of the release in terms of biased gas bubble migration in the presence of a temperature gradient. Here we successfully model the extensive release observed during isothermal annealing of irradiated fuel samples. This is major evidence in favour of the SINGAR model since, in the absence of a temperature gradient, the bubble migration model will predict no release, contrary to observation. (orig.)
[en] Some of the rationale for nuclear energy technology development in the US has been lost or forgotten over the past two decades with the lack of a focused reactor development program. But the emergence of new R and D programs points to a need to understand how best to plan for a long-term fuel development program. The rationale for such a program is not easily found in the literature, so the authors have suggested a structure and rationale. The approach is described as four phases, with emphasis on selecting a reference fuel concept, evaluating and improving the fuel to develop a fuel specification for a reference design, obtaining data to support a licensing safety case for the fuel, and final qualification of the fuel for a specific application. Because a fuel program requires long-lead-time irradiation testing, bringing a fuel design from the initial concept through licensing might take over 20 years
[en] This paper collects together the solutions for the diffusion of unstable gas atoms within a semi-infinite solid. Allowance is made for one precursor. These solutions are appropriate to the diffusion of unstable gas atoms from inside the fuel into the pin voidage in situations where the radius of curvature of the surface can be neglected. The solutions are particularly relevant to low-temperature gas atom diffusion and are thus of considerable value to coolant analysis at commercial AGR stations. (orig.)
[en] The specifications of nuclear fuels are defined and discussed in the light of their basic meaning and practical use. They constitute means of exact and complete description of a special class of objects: They characterize this class. An individual object can be characterized only by an individual quality control action. Specifications include in any case quantitative figures with tolerances as well as more qualitative instructions. There are different types of specifications in use, namely specifications for the feed material, for the fabrication routine, for the product itself, for the quality control procedures and also for the overall operation behaviour. Such a network supplemented by commitments concerning e.g. identification and transport help avoid fuel failure. As an example, some typical features of a fuel specification for an irradiation experiment are cited and discussed. Finally it is stated that also the fuel structure needs quantitative characterization. With respect to the necessary effort, specifications are a compromise between fabrication possibilities, quality control methods and operation experience. (Auth.)
[en] Several advanced reactor designs incorporate tristructural isotropic (TRISO) fuel particles to achieve high coolant temperature and high fuel burnup levels and thus require reliable and robust fuel performance models (FPMs) to evaluate reactor performance. This manuscript provides a detailed and concise review of the numerous published TRISO FPMs. The article begins with a brief review of TRISO fuel particles, before describing the important fuel behavior and failure mechanisms of TRISO fuel. Suggested material property correlations for use in TRISO fuel performance modeling are summarized with an emphasis on the limits of validity for those correlations and notes regarding their use and origin. A review of the major historical and current TRISO FPMs assesses each model's capabilities and origin and provides a systematic comparison of the codes to document similarities and differences in their features. Finally, areas of improvement and unsolved problems are discussed that may limit the accuracy of TRISO fuel performance modeling.
[en] Corresponding to the world nuclear security concerns, future nuclear fuel cycle (NFC) should have high proliferation-resistance (PR) and physical protection (PP), while promotion of the peaceful use of the nuclear energy must not be inhibited. In order to accomplish nuclear non-proliferation from NFC, a few models of the well-PR systems should be developed so that international community can recognize them as worldwide norms. To find a good balance of 'safeguard-ability (so-called extrinsic measure or institutional barrier)' and 'impede-ability (intrinsic feature or technical barrier)' will come to be essential for NFC designers to optimize civilian nuclear technology with nuclear non-proliferation, although the advanced safeguards with high detectability can still play a dominant role for PR in the states complying with full institutional controls. Accomplishment of such goal in a good economic efficiency is a future key challenge
[en] There is an increasing desire to integrate thermodynamic computations directly into multi-physics nuclear fuel performance and safety codes. These computations provide, among other matters, boundary conditions in heat and mass transport modules in predicting fuel behaviour. Precision must be maintained in computations involving fission and activation products with very low concentrations, which may nonetheless have significant radiological consequences. Also, there is the concern about the propagation of numerical errors in multi-physics codes. A method to numerically verify equilibrium thermodynamic computations is therefore necessary to satisfy rigorous quality assurance standards of the nuclear industry without significantly impeding computational performance. A technique is presented that can be applied to systems of any number of phases and system components. The technique is reliable and comprehensive in ensuring that all conceivable equilibrium constants have been satisfied without having to formulate each one of a potentially very large number.
[en] The qualification and resolution of questions relating to the cost benefit of quality control are based on the interaction of a broad range of technologies and economics. This paper discusses examples of current areas of interest in quality control, and their relationship to the fuel cycle costs. (orig.)