Papers by Keyword: NPP

Abstract: Primary water stress corrosion cracking (PWSCC) has been observed in CRDM nozzles, BMI nozzles and other penetration nozzles. The industry has used the repair method of replacement of nozzles fabricated of Alloy 690. After the replacement of the nozzle, the structural integrity analysis of new nozzle and welds should be performed to ensure the pressure boundary compliance with the original design requirement. In this paper, the pressurizer top head instrument nozzle of PWR nuclear power plant is evaluated as a typical pressure vessel penetration nozzle. The results showed that the repaired nozzle satisfies the ASME Code design requirement and the crack growth of the postulated flaw in 40 years of the nuclear plant life is acceptable.PWSCC degradation mechanism has been observed in CRDM nozzles, BMI nozzles and other penetration nozzles [1]. In some nuclear power plants built in China earlier, such as DAYABAY nuclear power plant and QINSHAN nuclear power plant, PWSCC degradation mechanism has been found in CRDM nozzle welds which manufactured of Alloy 600 and welded of Alloy 82/182[2]. The repair of the degraded nozzles is the popular choice for the nuclear power plant owners. After the replacement of the nozzle, the structural integrity analysis of new nozzle and welds should be performed to ensure the pressure boundary compliance with the original design requirement. In this paper, the pressurizer top head nozzle of PWR nuclear power plant is evaluated as a typical pressure vessel penetration nozzle. Stress intensities were conservatively determined for pressure and applicable thermal transients and compared to the allowable values of the ASME Code, Section III. Thermal stress of the transients was obtained from 3D finite element model (FEM). Residual stress of J-groove weld was obtained from 2D FEM analysis and used for fracture mechanics analysis. All of the analysis showed that the repaired nozzle satisfies the ASME Code design requirement and the crack growth of the postulated flaw in 40 years of the nuclear plant life is acceptable.

Abstract: This paper presents the probabilistic safety assessment of nuclear power plant (NPP) in Slovakia due to earthquake event. The experiences from the deterministic and probabilistic seismic analyses of the structure resistance are mentioned. On the base of the geophysical and seismological monitoring of locality the peak ground acceleration was defined for the return period 10⁴ years using the Monte Carlo simulations. The synthetic spectrum compatible accelerograms generated in program COMPACEL are presented in comparison with requirements of ASCE4/98 standard.

Abstract: Although turbo equalization has superior performance, the data processing delay produced by large iterations has become its major drawback for real-time situations. Based on the MMSE criterion, the normal-probability-plot (NPP) of linear equalizer’s extrinsic information is studied in this paper, with the conclusion of the extrinsic information’s approximate Gaussian distribution obtained. In various conditions, the iterative number can be controlled dynamically based on the extrinsic information statistics. The simulation results approves that the technique is able to make delay dwindle largely with small performance degradation.

Abstract: In recent years, advanced small nuclear power reactors, namely small modular reactors (SMRs), gained widespread attention. In areas where energy can’t be provided by large scale reactors and the nuclear power plants with large scale reactors can’t compete with the non-nuclear power plant technology, SMRs, as a versatile distributed integrated energy source, which result in expanding peaceful applications of nuclear energy, have enormous potential. This article describes the characteristics and analyzes prospects and challenges of SMRs.

Abstract: Nuclear energy is a carbon-free, clean and efficient energy. It is very important in the progress of human civilization and modern development of the world, however, there are still some problems such as nuclear leak and nuclear waste. In this paper, the worlds nuclear energy utilization and nuclear power plant constructions are reviewed and plans are forecasted. The basic reason of previous nuclear power plant accidents in history is summarized. Taking 2011 Tohuku earthquake-fukushima nuclear power station accident as an example,threats to the nuclear power plant by earthquake are investigated and impacts on social, economic and ecological environment caused by nuclear power station accident are analyzed. This paper drew lessons from previous accidents and put forward a variety of countermeasures which are from both the technical and management aspects. We also appeal people all over the world to respect the nature, enjoy the nature, and to create and enjoy the new civilization of human beings.

Abstract: This paper presents a optimal design of a damping devices for the protection of the reinforced concrete structure of a nuclear power plant (NPP) against the impact loads from a container of nuclear fuel of the type TK C30 drop. The finite element idealization of the building structure is used in space. The interaction of the soil-structure, as well as the fluid-structure of the deactivated basin is considered in space. A steel pipe damper system is proposed for the dissipation of the kinetic energy of the container is free fall. The Newmark’s integration method is used for the solution of the dynamic equations.

Abstract: on the basis of the measurement of ecological parameters by using remote sensing technology, combined with ecological method and Landsat–7 ETM +, we made a quantitative measurement of ecological assets of Sanjiang Plain in 2010, got the spatial distribution of ecological assets. The results show that: the value of ecological assets in Sanjiang Plain was 2.35 × 1012 yuan. The value was generally higher in the southern and lower in the northern parts of the study area. Baoqing has the highest sum value and Youyi has the lowest value than other areas. Forestlands have higher value of ecological assets than other land use types. Land use type may be the mainly reason for the spatial difference of ecological assets in Sanjiang Plain.

Abstract: Northern Shaanxi is one of the pilot zones for implementating of Grain for Green Project. Monitoring the net primary production (NPP) change before and after the project would help understand the spatial patterns and the accomplishment of the Grain for Green project, and also be propitious to calibrate the projects benefits. Using the improved Carnegie-Ames-Stanford Approach (CASA) modeling, the terrestrial NPP was estimated. Meanwhile, the carbon (C) stock benefits of Grain for Green Project were analyzed through the different land cover types and slope gradients. The results are as follows: (1) There was an apparently increase of average NPP in Northern Shaanxi from 2000 to 2007. Based on the trend analysis, the areas with high NPP growth rate (more than 20%) account for about 75% area of the whole Northern Shaanxi. (2) The C stock increased significantly from 2000 to 2007 in Northern Shaanxi. The total C stock of vegetation was 7169.4 t and the C stock per unit area was 121.2 t Ckm^-2a^-1. The total C stock of sloping farmland was more than 2000 t, which account for 31.3% of the whole C stock in Northern Shaanxi. (3) The main districts of the Grain for Green Project, such as the sloping farmland, open forest and lands with slope 15° to 35°, gained better C stock benefits than other areas. The results in this study indicated that the Grain for Green project resulted in good C stock benefits.

Abstract: In nuclear power plant (NPP), particulate matter and gaseous pollutant release into the environment in severe accidents. To prevent from this disaster, filtered vented containment system (FVCS) containing venturi scrubber is being installed. The present work herein is the CFD simulation of throat pressure in venturi scrubber. A commercial software ANSYS CFX tool has been selected for this research. Euler-Euler regime is used to get the picture of behavior of fluid dynamics inside the venturi scrubber. Gas and liquid interact with each other in throat section of venturi scrubber. The pressure at the throat is one of the important factors to analyze the performance of venturi scrubber. In order to verify the results, mesh independency is checked. CFX and experimental results show good agreement with each other. The results obtained from CFX simulation are useful to improve the venturi design.

Abstract: Venturi Scrubbers are used in filtered vented containment system (FVCS) for collection of aerosols produced in NPP in severe accidents. Therefore, venturi scrubber (VS) needs an attention to design it properly and improved in all aspects. In this research, CFD simulations of prediction of pressure drop in venturi scrubber has been carried out. ANSYS CFX tool is used to obtain the simulation results. k-ε turbulence model is employed to study the fluid dynamics of the venturi scrubber. Mesh size plays an important role for convergence and accuracy of results. Therefore, the mesh independency is checked for optimized mesh size.