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[en] In order to determine the molecular dipole moment (μ), polarizability (α), and first hyperpolarizability (β) of L-arginine trifluoroacetate (LATF) crystals, a series of basis sets including polarized and diffuse functions have been employed at the framework of Hartree–Fock and second order Möller–Plesset perturbation theory methods. The MP2/6-311++G(d,p) model predicts for the converged value of in-crystal dipole moment, polarizability and first hyperpolarizability are 21.2 D, 20.0 × 10−24 esu and 50.0 × 10−31 esu, respectively. The calculated HOMO and LUMO energies show that charge transfer occur within the molecule. Electronic excitation properties are discussed within the framework of the two-level model on the basis of an orbital analysis. The coupled perturbed Hartree–Fock (CPHF) procedure yields information on the dispersion behavior of first hyperpolarizability terms. The magnitudes of the various hyperpolarizability terms which describe the various second-order nonlinear processes show the following trend: β(−2ω;ω,ω) > β(0;ω,−ω) > β(0,0,0). By using the molecular structures and the molecular first hyperpolarizability, the components of second harmonic tensor coefficient d of the crystals were evaluated by the oriented-gas model. - Highlights: • Optical and electronic properties were investigated. • Dispersion behavior of first hyperpolarizability terms was obtained. • Components of second harmonic tensor coefficient were evaluated
[en] Highlights: • Sensitivity analysis is performed on the reflood model of RELAP5. • The selected influential models are discussed and modified. • The modifications are assessed by FEBA experiment and better predictions are obtained. - Abstract: Reflooding is an important and complex process to the safety of nuclear reactor during loss of coolant accident (LOCA). Accurate prediction of the reflooding behavior is one of the challenge tasks for the current system code development. RELAP5 as a widely used system code has the capability to simulate this process but with limited accuracy, especially for low inlet flow rate reflooding conditions. Through the preliminary assessment with six FEBA (Flooding Experiments with Blocked Arrays) tests, it is observed that the peak cladding temperature (PCT) is generally underestimated and bundle quench is predicted too early compared to the experiment data. In this paper, the improvement of constitutive models related to reflooding is carried out based on single parametric sensitivity analysis. Film boiling heat transfer model and interfacial friction model of dispersed flow are selected as the most influential models to the results of interests. Then studies and discussions are specifically focused on these sensitive models and proper modifications are recommended. These proposed improvements are implemented in RELAP5 code and assessed against FEBA experiment. Better agreement between calculations and measured data for both cladding temperature and quench time is obtained.
[en] Highlights: • Two dimensional module is developed to analyze integrity of lower head. • Verification step has been done to evaluate feasibility of new module. • The new module is applied to simulate large-scale advanced PWR. • Importance of 2-D approach is clearly quantified. • Major parameters affecting vessel temperature distribution are identified. - Abstract: In order to evaluate the safety margin during a postulated severe accident, a module named ASAP-2D (Accident Simulation on Pressure vessel-2 Dimensional), which can be implemented into the severe accident simulation codes (such as ATHLET-CD), is developed in Shanghai Jiao Tong University. Based on two-dimensional spherical coordinates, heat conduction equation for transient state is solved implicitly. Together with solid vessel thickness, heat flux distribution and heat transfer coefficient at outer vessel surface are obtained. Heat transfer regime when critical heat flux has been exceeded (POST-CHF regime) could be simulated in the code, and the transition behavior of boiling crisis (from spatial and temporal points of view) can be predicted. The module is verified against a one-dimensional analytical solution with uniform heat flux distribution, and afterwards this module is applied to the benchmark illustrated in NUREG/CR-6849. Benchmark calculation indicates that maximum heat flux at outer surface of RPV could be around 20% lower than that of at inner surface due to two-dimensional heat conduction. Then a preliminary analysis is performed on the integrity of the reactor vessel for which the geometric parameters and boundary conditions are derived from a large scale advanced pressurized water reactor. Results indicate that heat flux remains lower than critical heat flux. Sensitivity analysis indicates that outer heat flux distribution is more sensitive to input heat flux distribution and the transition boiling correlation than mass flow rate in external reactor vessel cooling (ERVC) channel, and the correlation for molten vessel and ERVC coolant inlet temperature. According to the results achieved, the new developed module shows good applicability to simulate the pressure vessel behavior during melt pool formation. Thus it can be applied for the future study of the severe accidents relating to lower head integrity
[en] Recently, a new supercritical water cooled reactor (SCWR) conceptual design was proposed on the basis of a mixed spectrum core concept consisting of a thermal zone and a fast zone. This new core design was considered to be the hybrid of the existing thermal SCWR and fast SCWR cores. It combines the merits of both thermal and fast SCWR cores, at the same time minimizes their shortcomings. For the thermal zone, the difficulties in the mechanical design and the maximum cladding temperature can be reduced as far as possible by the co-current flow mode; and for the fast zone, a sufficiently large negative coolant void reactivity coefficient and breeding ratio can be achieved by the big value of the ratio p/d and the multi-layer arrangement of fuel rods. The performance, including the burn-up behavior, of the proposed core was investigated with 3-D coupled neutron-physical and thermal-hydraulic calculations. During the coupling procedure,the thermal-hydraulic behavior was analyzed using a sub-channel analysis code and the neutron-physical performance was computed with a 3-D diffusion code. The results obtained so far show that the mixed spectrum SCWR concept (SCWR-M) is feasible and promising. (authors)
[en] Elimination of toxic organic compounds from wastewater is a longstanding challenge in the fields of environmental science, especially, under the visible-light irradiation. Here we present a facile design to fabricate novel porous Ag2S/ZnS composite nanospheres via a hydrothermal procedure followed by a cation exchange method. Field-emission scanning electron microscopy (FESEM), X-ray diffraction (XRD), transmission electron microscopy (TEM), X-ray energy-dispersive spectroscopy (EDS), and UV–vis spectroscopy were used to characterize the crystallinity, morphology, structure and properties of the composite nanospheres. The photocatalytic performance was evaluated by the photocatalytic decolorization of methyl orange in aqueous solution under visible light irradiation. Results show that the composite nanospheres exhibited enhanced visible light photocatalytic activity compared with the initial porous ZnS nanospheres. Among them, sample of Ag0.4Zn0.8S gave the highest degradation rate of about 96% under visible-light irradiation within 15 min. The enhanced photocatalytic activity was presumed to result from the direct photoinduced interfacial charge transfer (IFCT) from the valence band (VB) of ZnS to Ag2S, due to the intimate contact between ZnS and Ag2S, the porous structure, and the appropriate composition ratio of porous Ag2S/ZnS composite. The present method could be extended to fabricate a large number of semiconductor composites for catalysis and solar cells based on the difference of the solubility products. - Highlights: • Porous Ag2S/ZnS composite was fabricated based on different solubility products. • Ag0.4Zn0.8S has the best photocatalytic activity under visible-light irradiation. • Enhanced activity presumably results from the interfacial charge transfer.
[en] Among the six GEN-IV reactor concepts recommended by the Gen-IV International Forum (GIF), supercritical water-cooled reactor (SCWR) is the only reactor type with water as coolant. Due to its high outlet temperature, it achieves a high thermal efficiency and subsequently has economic advantages over the existing reactors. The present paper performs the thermal-hydraulic analysis of the SCWR assembly using the modified COBRA-IV code. Two approaches to reduce the hot channel factor are investigated: decreasing the moderator mass flow or increasing the heat resistant between moderator channel and its adjacent subchannels, and the latter also can get a better moderation. According to this paper, the heat transfer deterioration phenomenon is inevitable in the SCWR design. Thus, it is necessary to calculate the cladding temperature accurately, to preserve the fuel rod cladding integrity under heat transfer deterioration. (authors)
[en] In order to improve the safety and sustainability of a supercritical water-cooled reactor (SCWR) core, both sub-channel and MCNP analysis were carried out to assess thermal-hydraulic and neutronic performances of the fuel assembly, which was proposed for the fast zone of a mixed-spectrum SCWR (SCWR-M). This fast zone assembly had a multilayer structure and was axially divided into several seed and blanket regions. The effects of some design parameters. i. e. axial configuration, fuel rod diameter, pitch to diameter ratio and duct wall clearance on the thermal-hydraulic and neutronic performance of assemblies were investigated and an optimized parameter ranges were obtained. (authors)
[en] For the uncertainty analysis, the Wilks' formula was employed to identify the minimum runs and the upper and lower limits of the calculation. An uncertainty analysis method and program for sub-channel code were developed based on the existing uncertainty analysis method. The void fraction predicted by the sub-channel code was compared with the uncertainty limit. The results show that the uncertainty of the side and the corner sub-channel is smaller, which is about ±5.5%; the uncertainty of the sub-channel around the water rod inside the bundle is bigger, which is about ±9%. The uncertainty of high void fraction sub-channels which are the most important sub-channels is about -5.5%-6%. (authors)
[en] For the safety analysis of Supercritical Water-Cooled Reactor (SCWR), one of the challenge tasks is to predict the trans-critical behavior of the reactor system during some accidents. The current safety codes have some shortcomings when the pressure decreases from the supercritical condition to the subcritical state due to the void fraction discontinuity across the critical point. Another challenge is the validation of the system code, which needs the transient experimental data. To overcome the above-mentioned challenges, this paper validates the modified code ATHLET-SC, which is developed based on the pseudo two-phase method. The trans-critical transient data from SWAMUP test facility in Shanghai Jiao Tong University (SJTU) are adopted to compare with the simulation results. The results obtained so far shows that the ATHLET-SC code has good feasibility to the trans-critical simulation of SCWR, and it can be used for transient analysis of SCWR in the future.
[en] In order to ensure the long-term nuclear power development in China, it is of crucial importance to deploy the innovative nuclear systems of generation IV (GEN-IV). Among the six GEN-IV reactor concepts recommended by the GEN-IV International Forum (GIF), supercritical water-cooled reactor (SCWR) is the only reactor type with water as coolant. Due to its economical advantage, technology and experience continuity, SCWR has attracted significant interests of nuclear industries and research institutions. It is also well recognized as an inevitable extension of the existing nuclear power plants, which mainly utilize water-cooled reactors. This paper presents the main technical features of SCWR and its position in the Chinese long-term nuclear power development. The ongoing research and development activities were summarized and the future needs were clarified. Finally, a roadmap of the development of China SCWR was proposed. (authors)