[en] A large-scale and refined three-dimensional numerical simulation of the upper plenum flow field of the pressure vessel of the three-loop pressurized water reactor is carried out by using the commercial CFD software STAR-CCM+ code. The coolant flow at the outlet of 157 fuel assemblies is calculated by the component tracking method. A mixing matrix of the upper plenum with 3 × 157 elements is constructed, which can be used to quantitatively and accurately describe the complex flow process of the coolant flowing out from the reactor core and mixing in the upper plenum and redistributing to the hot legs. It is found that the mixing of the coolant flowing from the core is not thorough and complete in the upper plenum of pressure vessel. The coolant flowing from fuel assembly at different positions in the radial direction is with obvious corresponding relationship in the interface area between the upper plenum and the hot legs, and the difference of the radial power distribution of fuel assembly will inevitably lead to the formation of the thermal stratification of the coolant in hot legs. (authors)

[en] Accelerator Driven Sub-critical System (ADS) applies the spallation neutrons as the external neutron source to drive the sub-critical reactors. It has the sub-critical inherent safety feature and the large flux and powerful transmutation ability for long-lived radiation nucleus, and it has been universally regarded as the most promising approach to dispose the long-lived nuclear wastes. In the ADS system, the external neutron source is generated by the proton beam bombarding of the spallation targets. The beam interruption transients will directly cause the power fluctuation of the subcritical reactor core, and then affect the safety of the whole ADS system. In this paper, a new ADS beam interruption transient model is promoted by researching the existed ADS model and methods worldwide. Based on the universal CFD programme FLUENT, the new model FIUENT-ADS is developed by integrating Point Kinetic Model (PKM) and Pin Thermal Model (PTM) with the assistance of User Defined Functions (UDF) tools. Validated by the international benchmark published by OECD/NEA, the key validating parameters could meet the results in this paper with a maximum calculation error of 5.2% which is equivalent to other international calculation programmes with similar functions. The results demonstrate that the new model has certain credibility, and it could meet the preliminary requirements of the research and analysis of ADS beam interruption transient. (authors)

[en] Design transients' specification is an important work for PWR system design, the thermalhydraulic evolution curves which the important components in primary and secondary system experienced should be produced. The PZR and relative components experienced a quite complex evolution in the design transients. Aim to provide simply and suitable interface files for mechanical analysis department, the codes simulation results need a suitable process. This paper gives the temperature transfer method for interface file for PZR in the analysis of DTS for ACPR1700. (authors)

[en] Uncontrolled withdrawal of rod cluster control assembly bank from subcritical or low power startup condition is classified as a RCC-P condition Ⅱ event and always one of the most limiting events in the safety analysis for the nuclear power plant. Based on typical three-loop PWR, the effects of different initial arrangements of the shutdown banks at the hot-shutdown state on the DNBR margin were studied. The results show that the DNBR margin is further increased by optimizing the initial arrangements of the shutdown banks at the hot-shutdown state in order to assure the enough shutdown margins. (authors)

[en] The experimental research of heat transfer to supercritical water in a triangular-lattice configuration has been performed on the supercritical water multipurpose test loop. Circumferential non-uniformed wall temperature distribution and heat transfer enhancement induced by the grids were observed in the bundles. The heat transfer data under conditions of different heat flux, mass flux and pressure were obtained. Finally, an empirical correlation with the prediction deviation of ± 15% was developed to predict the supercritical heat transfer behaviors in the triangular-lattice. (authors)

[en] To effectively monitor the variety of distributions of neutron flux, fuel power or temperatures in the reactor core, usually the ex-core and in-core neutron detectors are employed. The thermocouples for temperature measurement are installed in the coolant inlet or outlet of the respective fuel assemblies. It is necessary to reconstruct the measurement information of the whole reactor position. However, the reading of different types of detector in the core reflects different aspects of the 3D power distribution. The feasibility of reconstruction the core three-dimension power distribution by using different combinations of in-core, ex-core and thermocouples detectors is analyzed in this paper to synthesize the useful information of various detectors. A comparison of multilayer perceptron (MLP) network and radial basis function (RBF) network is performed. RBF results are more extreme precision but also more sensitivity to detector failure and uncertainty, compare to MLP networks. This is because that localized neural network could offer conservative regression in RBF. Adding random disturbance in training dataset is helpful to reduce the influence of detector failure and uncertainty. Some convolution neural networks seem to be helpful to get more accurate results by use more spatial layout information, though relative researches are still under way

[en] Highlights: • KML, RF and CC methods are introduced for detector layout optimization. • Information theory is used to evaluation the specific detector layout. • CC method provided a much better result than KML and RF. - Abstract: The core monitoring system (CMS) is one of the most important systems in safety of an operational reactor. The detectors arrangement has a significant effect on the evaluation of the reactor power distribution and thermal hydraulic parameters. In this paper, three optimization methodologies are explored under a specific number of detectors to achieve the appropriate detector arrangement. These methods consist of the knight moving law (KML) method, the random forest (RF) method and the correlation coefficient (CC) method. The information theory is used to evaluate the performance of these optimization methods. At last, the CC method can obtain the best detector arrangement with smallest mutual information. Meanwhile, with RF method it may be difficult to obtain the best solution, comparing with the other methods. Although the information entropy method provides a glimpse of the detector arrangement, a more comprehensive evaluation needs to be further refined in engineering practice, taking into account issues such as the influent of detector failure and detector random error, and sensitivity analysis under more reactor operating conditions.

[en] New market requirement for nuclear power has emerged, which require to improve nuclear power safety and economic performances simultaneously. It is required to develop advanced nuclear reactor technologies to satisfy the new market requirement for nuclear power. During the past several years, China General Nuclear Power Corporation (CGN) had made an adequate comparative analysis of all alternate potential advanced reactor technologies and selected the Lead-cooled Fast Reactor (LFR) as the preferred technology for the next generation nuclear power development. Besides the selection of the LFR technology, CGN are proposing a new safety concept named Natural-Driven Safety (NDS) to solve conflicting requirements of safety and economy, which will make it possible to improve reactor safety and economics performances simultaneously then to meet the new market requirement. The paper presents the conceptual design of an innovative LFR based on NDS technologies named CLFR-300, including reactor core, primary system and related auxiliary system and safety system. Two specific NDS systems are applied in the design of CLFR-300, including the Natural Driven Shutdown System (NDSS) and the Natural Driven Decay Heat Removal System (NDDHRS). With the NDSS, it can virtually eliminate risks of unprotected accident, and with the NDDHRS, it can virtually eliminate risks of core damage and large release of radioactivity. These excellent safety features can help CLFR-300 to improve nuclear power safety and economic performances simultaneously and rule out the requirement of evacuation of the local population. (author)

[en] Ni-P-SiC nano-composite coatings were successfully fabricated on a P20 plastic die steel surface by combining acid etching and electroless plating process. Electrochemical behavior of coatings and substrate has also been studied by potentiodynamic polarization curves and electrochemical impedance spectroscopy (EIS). Results demonstrated that the SiC-doped Ni-P coating possessed excellent anti-corrosion property with icorr (0.813µAcm⁻²) about 6% that of steel substrate, the Ni-P-SiC nano-composite coating exhibited good corrosion resistance properties in protecting the P20 plastic die steel. (paper)

[en] The supercritical natural circulation experimental facility is limited at present, and relevant studies, both in theory and experiment, are not sufficient. In this paper, a test facility has been designed and built to study the steady-state characteristics of supercritical carbon dioxide natural circulation. The experiment shows that the test loop could maintain a significant mass flow rate of natural circulation with a small temperature difference between hot leg and cold leg, but the natural circulation of supercritical carbon dioxide would become unstable at relatively high power levels. The lower the pressure is, the earlier the mass flow rate starts a fast growth, and the lower the threshold power at which occurs the flow instability. The lower the inlet temperature of test section, the higher the natural circulation flow rate. (authors)