Uncertainty and sensitivity analyses as a validation tool for BWR bundle thermal-hydraulic predictions

In recent years, more realistic safety analyses of nuclear reactors have been based on best estimate (BE) computer codes. The need to validate and refine BE codes that are used in the predictions of relevant reactor safety parameters, led to the organization of international benchmarks based on high quality experimental data. The OECD/NRC BWR full-size fine-mesh bundle test (BFBT) benchmark offers a good opportunity to assess the accuracy of thermal-hydraulic codes in predicting, among other parameters, single and two phase bundle pressure drop, cross-sectional averaged void fraction distributions and critical powers under a wide range of system conditions. The BFBT is based on a multi-rod assembly integral test facility which is able to simulate the high pressure, high temperature fluid conditions found in BWRs through electrically heated rod bundles. Since code accuracy is unavoidably affected by models and experimental uncertainties, an uncertainty analysis is fundamental in order to have a complete validation study. In this paper, statistical uncertainty and sensitivity analyses are used to validate the thermal-hydraulic features of the POLCA-T code, based on a one dimensional model of the following macroscopic BFBT exercises: (1) single and two phase bundle pressure drop, (2) steady-state cross-sectional averaged void fraction, (3) transient cross-sectional averaged void fraction and (4) steady-state critical power tests. The Latin hypercube sampling (LHS) strategy was chosen since it densely stratifies across the range of each uncertain input probability distribution, allowing a much better coverage of the input uncertainties than simple random sampling (SRS). The results show that POLCA-T predictions on pressure drop and void fractions under a wide range of conditions are within the validation limits imposed by the uncertainty analysis, while the accuracy of critical power predictions depends much on the boundary and input conditions.     

Dynamic analysis of a nuclear reactor with fluid–structure interaction: Part II: Shock loading, influence of fluid compressibility

The present paper is related to the dynamic (shock) analysis of a naval propulsion (on-board) reactor with fluid–structure interaction modelling. In a previous study, low frequency analysis has been performed; the present study deals with high frequency analysis, i.e. taking into account compressibility effects in the fluid medium. Elasto-acoustic coupling effects are studied and described in the industrial case. The coupled problem is formulated using the so-called (u, p, φ) formulation which yields symmetric matrices. A modal analysis is first performed on the fluid problem alone, then for the coupled fluid–structure problem in the following cases: (i) with incompressible fluid; (ii) with compressible fluid at standard pressure and temperature conditions; (iii) with compressible fluid at the operating pressure and temperature conditions. Elasto-coupling effects are then highlighted, in particular through the calculation of an elastic energy ratio. As a general conclusion, compressibility effects are proved significant in the dynamic response of the reactor in the high frequency range.     

Conception assistée par ordinateur des circuits intégrés monolithiques hyperfréquences

Computer aided design of microwave monolithic integrated circuits must combine two different fields. The first domain is the simulation of microwave circuits taking into account non linear aspects development of time domain and harmonic balance simulation algorithms specialized for microwave circuits. In the second place are found, the layout algorithms which were developed for logic circuits (on Si or GaAs). The association of these two types of algorithms leads to the constitution of aCad workstation for microwave monolithic integrated circuits. Two examples of design and realization of integrated circuits with these tools are presented.     

Acquisition of understanding and skill in relation to subjects' preparation and meaningfulness of instruction.

4 experiments examined effects of a total of 224 college students' aptitudes, preinstructional experience, method of instruction, and differences among posttest items. Instruction that emphasized meanings of concepts led to better performance on posttest items requiring understanding, but Ss with emphasis on computation performed better on simple problems. Ss with higher measured aptitudes directly relevant to instruction or given relevant preinstructional experience had more success in meaningful instruction than did Ss with lower aptitude scores, but little or no aptitude difference was found for instruction emphasizing algorithms. 2 kinds of operations were distinguished-identifying relevant information in the problem situation and carrying out computations. The former appears more closely related to conceptual understanding, the latter to computational skill. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

New methods for the determination of hydrogen content of aluminum and its alloys: Part II. Rapid determination by the nitrogen carrier fusion method

A method for determining hydrogen in steel by melting with nitrogen as a carrier gas was adapted for aluminum and its alloys. Dehydrogenationvs temperature was investigated in order to define an optimal sequence of operating conditions. The results obtained by the method were systematically compared to those given by the reference vacuum hot extraction method. The essential characteristics of this new method can be summarized as follows: 1) The detection limit is 0.02 ml/100 g (0.02 ppm H₂). 2) The method is valid for any alloy, even for those with high volatile constituent content such as Zn or Mg. 3) The bulk hydrogen content is not significantly different from that given by the vacuum hot extraction method. 4) “Surface” hydrogen could be eliminated by a thermal treatment at 400°C prior to melting. 5) Correlations appeared between changes in thermal and dehydrogenation curves, the last one representing a characteristic spectrum of the alloy studied. 6) A complete analysis requires 15 min instead of several hours for the hot extraction method. It is thus applicable in routine industrial work.     

Rohrfertigung für den Reparaturbereich

Pipe fabrication for the repair sector. The paper discusses the changes in pipe fabrication that have taken place in recent years. These enable repair work to be carried out more efficiently, without thereby impairing the flexibility and speed of operation that are essential to maintenance work. A prerequisite for this is that work on the pipes be transferred to workshops. Only here is it possible for manual operations, such as manual welding, to be reduced to a minimum and be replaced by mechanized or semi-mechanized welding methods. The use of modern machines for bending the pipes is more economic than the welding in of pipe bends. Necking out of the pipes by mechanical means or the use of mechanically pre-fabricated connections permit optimum preparation of the weld seam for branch fittings. Any additional work on the pipes, where this is necessary, is carried out at workplaces specially designed for the purpose.     

The ITER divertor pumping system,design evolution,simplification and performance

The ITER tokamak will be fuelled at a time averaged rate of up to 200 Pam³ s^?1 requiring neutralised gas in the divertor to be pumped to balance the fuelling and remove the fusion helium and other impurities in the exhaust. This is achieved on ITER using large bespoke cryo-sorption pumps. In this paper design evolution of the ITER divertor pumping system is outlined from the 1998 configuration to the current design. Details of the new, 6 direct pump, system design which will be used in the build of ITER are given. The operating modes of the new system configuration for different plasma scenarios are described and the performance of the new system is analysed and compared with previous baselines.     

Progress in the design of ITER front-end vacuum instrumentation and controls

The ITER vacuum system will be one of the largest and most complex vacuum systems ever to be built. Extensive instrumentation and controls are being developed to satisfy the stringent vacuum processes necessary for the successful and safe operation of the ITER Tokamak. The complexity and deep integration of the vacuum systems within the ITER machine presents a challenge to implement all of the controls necessary for reliable operation. Several thousand valves and sensors have to be implemented within the harsh environmental conditions of the Tokamak vicinity, and require engineering of instrumentation and controls with remote electronics solutions.In this paper the status of the design of field end vacuum controls and instrumentation for the ITER vacuum systems is described. Details of the progress on selection of sensors and actuator technologies are given herein and solutions for remote device operation, including those for cryogenic devices, are described together with necessary local shielding.     

Rasterkraftmikroskopie im Vakuum an plasmabehandeltem und metallisiertem Polycarbonat

Atomic force microscopy under UHV conditions on plasma etched and metallised polycarbonate The paper describes different AFM modes of operations (static ?contact”? mode and dynamic mode). The influence of ECR plasma treatment and Almetallisation is shown on polycarbonate. The plasma etching changes the surface morphology in the nm scale. Aluminum that exhibits low adhesion to the polycarbonate could be resolved only by AFM in the dynamic mode of operation.     

Heat-induced gelation of whey protein at high pH studied by combined UV spectroscopy and refractive index measurement after size exclusion chromatography and by in-situ dynamic light scattering

Summary The interactions between β-lactoglobulin and α-lactalbumin involved in gelation at 67.5 °C at high pH and low salt concentration were studied by size exclusion chromatography, followed by UV and refractive index measurements, and by in-situ dynamic light scattering. This was achieved by choosing whey protein samples with different proportions of the two proteins. The ratio of absorbance at 280 nm to the refractive index was used to demonstrate that α-lactalbumin was incorporated in aggregates and gels and drastically changed the properties of the gel, making them much more turbid than the transparent gels formed by β-lactoglobulin alone at the same pH and ionic strength. At a ratio of 1:2 for α-lactalbumin relative to β-lactoglobulin in the samples, the gel consisted of a 1:1 mixture of the two proteins. The aggregates present after 10 min of heating at 67.5 °C had molar mass of about 6.10⁶ g/mol and a radius of gyration of about 40 nm. After gel formation the field autocorrelation function could be described as a power law over many decades of lag time for all samples, demonstrating selfsimilarity of the gel structure. The only exception to this was for the gel with high content of α-lactalbumin which showed an oscillatory behaviour of the autocorrelation function. Significant amounts of glycosylated caseino-macro-peptide were observed in many of the samples at the position of β-lactoglobulin. However it did not affect gelation as it remains in solution.