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Chen Y.-D.,China Nuclear Power Engineering Co.
Yuanzineng Kexue Jishu/Atomic Energy Science and Technology

In this paper MELCOR code was applied for modeling of AP1000 NPP primary and secondary circuits, passive safety system and containment compartment. And by applying the code, a severe accident scenario of small loss of coolant accident (LOCA) at hot leg concurrent with failure of internal refueling water storage tank (IRWST) function was selected for simulation and calculation mainly during the invessel phase, the passive mitigation measures were analyzed and evaluated. The analysis results show that the execution of ADS (automatic depressurization system)1-4, will lead to quick and effective injection of cold water from core make-up tank (CMT) and accumulators into the core, before they are exhausted, the core is kept flooded all the time. With broken of ADS4 valve, primary pressure is fast balanced to containment pressure. The passive containment cooling system (PCS) can be adopted as a counter measure to slow pressurization of containment by airborne decay heat and non-condensable gases. The ignition of H2 by igniters before the concentration of H2 are high enough to deflagrate automatically, and can alleviate the risk of containment failure from overpressure due to global deflagration, while continuously ignition may cause temperature in some compartments rise to a value that exceed much more than its design temperature. Under such condition, other system supports to severe accident mitigation are difficult to survival. Source

Xie L.,Shanghai JiaoTong University | Huang X.,Shanghai JiaoTong University | Yang K.,Shanghai JiaoTong University | Li S.,Xian Jiaotong University | And 2 more authors.
Journal of Materials Chemistry A

The introduction of high dielectric constant ceramic nanoparticles into an insulating polymer is an important approach to prepare high dielectric constant nanocomposites for electric energy storage applications. A key to obtaining desirable properties is the homogeneous dispersion of the nanoparticles in the corresponding polymer. Conventional methods used to improve the nanoparticle dispersion enhance the physical interaction between the nanoparticle and the polymer matrix via nanoparticle surface modification. In this work, the covalent bonding between the nanoparticle and the polymer matrix was utilized to simultaneously enhance the nanoparticle dispersion and nanoparticle/polymer interaction by functionalizing both the polymer and the nanoparticles. The poly(vinylidene fluoride-co-hexafluoropropylene) [PVDF-HFP] was functionalized with glycidyl methacrylate (GMA) via atom transfer radical polymerization. The barium titanate (BaTiO3) nanoparticles were modified by amino-terminated silane molecules. Then the nanocomposites were prepared by a "grafting to" method. Namely, grafting GMA functionalized PVDF-HFP to the surfaces of the BaTiO3 nanoparticles. The introduction of GMA into the PVDF-HFP not only increases the dielectric constant, but also changes the dielectric response of PVDF-HFP. More importantly, this "grafting to" approach results in core-shell structured BaTiO3@PVDF-HFP- GMA and thus a homogeneous dispersion of BaTiO3 nanoparticles in the nanocomposites. The dielectric constant, electric energy density and thermal conductivity of the nanocomposites are significantly enhanced with the increase of BaTiO3, while the dielectric loss shows a slight decrease as the nanoparticle loading increases. © 2014 the Partner Organisations. Source

Xie L.,Shanghai JiaoTong University | Huang X.,Shanghai JiaoTong University | Huang Y.,Shanghai JiaoTong University | Yang K.,Shanghai JiaoTong University | And 2 more authors.
Journal of Physical Chemistry C

Polymer nanocomposites with high dielectric constant have extensive applications in the electronic and electrical industry because of ease of processing and low cost. Blending and in situ polymerization are two conventional methods for the preparation of polymer nanocomposites. However, the resulting nanocomposites, particularly highly filled nanocomposites, generally have some disadvantages such as high dielectric loss and low dielectric constant and thus show low energy density and low energy efficiency. Here we developed a core@double-shell strategy to prepare barium titanate (BT)-based high performance polymer nanocomposites, in which the first shell is hyperbranched aromatic polyamide (HBP) and the second shell is poly(methyl methacrylate) (PMMA). This method utilized the advantages of both polymer shells, resulting in superior dielectric property which cannot be achieved in nanocomposites prepared by the conventional blending methods. It is found that, compared with the conventional solution blended BT/PMMA nanocomposites, the core@double-shell structured BT@HBP@PMMA nanocomposites had higher dielectric constant and lower dielectric loss. The energy densities of BT@HBP@PMMA nanocomposites were higher than that of BT/PMMA nanocomposites accordingly. The dielectric response of the nanocomposites was analyzed, and the mechanisms resulting in the higher dielectric constant and lower dielectric loss in BT@HBP@PMMA nanocomposites were proposed. This study suggests that the core@double-shell strategy shows strong potential for preparing polymer nanocomposites with desirable dielectric properties. © 2013 American Chemical Society. Source

Kawahara T.,Waseda University | Kawahara T.,China Nuclear Power Engineering Co. | Oka Y.,Waseda University
Journal of Nuclear Science and Technology

Development of analysis code for predicting the molten core solidification behavior during the severe accident in nuclear power plants is necessary. Although agreeable results have been achieved using existing codes such as CORFLOW and LAVA to analyze some melt spreading experiments, these codes have a common problem of versatility because they all use empirical equations such as mass flux depending on distance from wall to calculate free surface of fluid. Moving particle semi-implicit (MPS) method which calculates free surface without empirical equations is suitable for analyzing the solidification behavior of fluid with large deformation. In this work, the MPS code for incompressible fluid was developed for calculating thermal field, solid-liquid phase transition, and temperature dependence of viscosity. Based on the MPS model, the FARO-L26S core melt solidification experiment was analyzed. For the leading edge position of the melt in this experiment, three-dimensional MPS simulations predicted agreeable multistage curve results with the experiment. © 2012 Atomic Energy Society of Japan. All rights reserved. Source

Zhen L.,Shanghai JiaoTong University | Jiang Z.,Shanghai JiaoTong University | Song H.,China Nuclear Power Engineering Co.
Information Sciences

A novel model of distributed knowledge recommender system is proposed to facilitate knowledge sharing among collaborative team members. Different from traditional recommender systems in the client-server architecture, our model is oriented to the peer-to-peer (P2P) environment without the centralized control. Among the P2P network of collaborative team members, each peer is deployed with one distributed knowledge recommender, which can supply proper knowledge resources to peers who may need them. This paper investigates the key techniques for implementing the distributed knowledge recommender model. Moreover, a series of simulation-based experiments are conducted by using the data from a real-world collaborative team in an enterprise. The experimental results validate the efficiency of the proposed model. This research paves the way for developing platforms that can share and manage large-scale distributed knowledge resources. This study also provides a new framework for simulating and studying individual or organizational behaviors of knowledge sharing in a collaborative team. © 2010 Elsevier Inc. All rights reserved. Source

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