Development of FRACAS-CT module with FRAPCON4.0P01 for simulation of mechanical behaviors for accident-tolerant fuel cladding in a reactor

In order to evaluate the mechanical behaviors of accident-tolerant fuel (ATF) cladding under reactor conditions, a new analytical module, termed FRACAS-CT, was developed. A mechanical model of FRACAS-CT was formulated based on thick-wall theory to consider the multi-layered structure of ATF cladding. Two statuses of a pellet-cladding gap, that is, open and closed, were described by several boundary conditions of pressures, inside radial displacements, and axial strains of the multi-layered ATF cladding. The FRACAS-CT model was verified by comparison with an equivalent finite element (FE) model and was implemented into FRAPCON4.0P1 with consideration of creep and stress relaxation behaviors of the multi-layered ATF cladding. After the implementation, code verification work was performed, and finally, mechanical behaviors and fuel performance of the multi-layered ATF cladding were calculated under normal operating conditions. As a result, the implemented FRACAS-CT can simulate the mechanical response and fuel performance of the multi-layered ATF cladding.     

Multidimensional gap conductance model for thermo-mechanical simulation of LWR fuel behavior using a virtual link element

In light water reactor (LWR) fuel, the modeling of the heat transfer across the gap between the fuel pellets and the protective cladding is essential to understanding the fuel behavior. Based on the Ross and Stoute model, the gap conductance that specifies the temperature gradient within the gap depends on the gap thickness, which is related to the mechanical behavior. A multidimensional gap conductance problem can be challenging in terms of convergence and nonlinearity. In this work, a virtual link gap (VLG) element has been proposed to resolve the convergence issue and nonlinear characteristic of multidimensional gap conductance. The elements that link the node of a pellet surface with the node of the cladding surface are virtually generated so as to transfer heat as a function of gap thickness at every iteration step. To evaluate the proposed methodology for the simulation of the gap conductance, a thermo-mechanical model has been established using ANSYS Parametric Design Language (APDL) for a preliminary study, and a 3D thermo-mechanical module using FORTRAN77 has been implemented. In terms of calculation accuracy and convergence efficiency, the proposed VLG model has been evaluated. As a result, the convergence criterion of the thermo-mechanical calculation considering the iteration characteristics of the VLG element has been proposed. To demonstrate the effect of the VLG model in a 3D simulation with the implemented thermo-mechanical module, the simulation results of a missing pellet surface (MPS) have been compared.     

高温气冷堆新型燃料球传感器的设计

对高温气冷堆中燃料球运行情况的准确监测是保障反应堆安全可靠运行的关键。针对原有探测器的不足,利用穿透式涡流检测原理提出了新型对装式燃料球传感器。运用有限元方法建立了该传感器的电磁场数值计算模型,对传感器结构参数和检测参数进行了分析和优化设计。实验结果表明,该传感器过球信号信噪比高,对连续过球具有很好的分辨率,满足反应堆现场使用要求。     

弥散核燃料等效辐照肿胀计算模拟

本文将弥散核燃料芯体看作一种特殊的颗粒复合材料,利用细观计算力学的方法,假设燃料颗粒在芯体中周期性分布,建立了对芯体等效辐照肿胀进行计算模拟的有限元模型。考虑颗粒的辐照肿胀和基体材料的辐照硬化效应,分别建立了燃料颗粒和基体材料的应力更新算法,编制了用户材料子程序,在Abaqus软件中实现了芯体等效辐照肿胀的有限元模拟。计算分析了颗粒大小和体积含量对芯体等效辐照肿胀的影响,并得到了等效辐照肿胀的拟合公式。研究结果表明,影响芯体等效辐照肿胀的主要因素是颗粒的辐照肿胀和体积含量。     

10MW高温气冷堆球形燃料元件虚拟仪器式探测系统的研制

介绍了一种基于虚拟仪器技术研铜开发的高温堆燃料元件探测系统，该系统有效地解决了10MW高温气冷堆燃料元件装卸过程中现场复杂过球信号的计数判断问题，很大程度地消除了外界干扰，保证了计数的准确性，方便地实现了整个系统的智能管理。     

A method for 3D simulation of internal gas effects on thermal-mechanical behaviors in nuclear fuel elements

A new method for three-dimensional simulation of the interaction between the gas and the solid around is developed.The effects of the gas on the thermal-mechanical behaviors within the surrounded solid are performed by replacing the internal gas with an equivalent solid in the modeling,which can make it convenient to simulate the thermal-mechanical coupling effects in the solid research objects with gases in them.The applied thermal expansion coefficient,Young’s modulus and Poisson’s ratio of the equivalent solid material are derived.A series of tests have been conducted;and the proposed equivalent solid method to simulate the gas effects is validated.     

Atomistic simulations on the interfacial interaction of metallic fuel and structural materials in SFRs - molecular dynamics model for Pu-Fe system

Interaction between metallic fuel and steel structures is one of the predominant phenomena in the progress of core disruptive accidents of Sodium-cooled fast reactor. In this study, the atomic diffusion across the interface between Pu and Fe was investigated by using molecular dynamics. The simulation was performed by using Modified Embedded Atom Method (MEAM). The interactions between plutonium and iron atoms were calculated by using the newly developed potential model determined so as to reproduce the material properties of PuFe₂ and Pu₆Fe. The material properties of the compounds predicted with the developed potential were in good agreement with the referenced data. The dissolution or melting at the interface between solid Fe and solid or liquid Pu were simulated by contacting semi-infinite slabs (or liquid layer) of them. Dissolution was observed for all the tested temperature conditions from 800 K up to 1700 K. The melting at the interface was also observed on the interface between solid Fe and PuFe₂ slabs at the temperature approximately 100 K below the melting temperature of PuFe₂ obtained based on the present model.     

Studies on fluid model for numerical simulation of gas discharges in color plasma displays

The fluid models of gas discharge in alternating current plasma display panel (AC PDP) cell are discussed.From the Boltzmann equation, the hydrodynamic equations are derived, but this model consumes much computational time for simulation. The drift-diffusion approximation model and the local field approximation model are obtained to simplify the numerical computation, and the approximation conditions of these two models are discussed in detail. The drift-diffusion approximation model gives more satisfactory result for PDP simulation, and the expression of energy balance equation is given completely in this model.     

Design of a Prototype EHD Air Pump for Electronic Chip Cooling Applications

This paper presents the design,optimization and fabrication of an EHD air pump intended for high-power electronic chip cooling applications.Suitable high-voltage electrode configurations were selected and studied,in terms of the characteristics of the generated electric field,which play an important role in ionic wind flow.For this purpose,dedicated software is used to implement finite element analysis.Critical design parameters,such as the electric field intensity,wind velocity,current flow and power consumption are investigated.Two different laboratory prototypes are fabricated and their performances experimentally assessed.This procedure leads to the fabrication of a final prototype,which is then tested as a replacement of a typical fan for cooling a high power density electronic chip.To assist towards that end,an experimental thermal testing setup is designed and constructed to simulate the size of a personal computer’s CPU core of variable power.The parametric study leads to the fabrication of experimental single-stage EHD pumps,the optimal design of which is capable of delivering an air flow of 51 CFM with an operating voltage of 10.5 kV.Finally,the theoretical and experimental results are evaluated and potential applications are proposed.     

Development of supercritical water heat-transfer correlation for vertical bare tubes

This paper presents an analysis of heat-transfer to supercritical water in bare vertical tubes. A large set of experimental data, obtained in Russia, was analyzed and a new heat-transfer correlation for supercritical water was developed. This experimental dataset was obtained within conditions similar to those in supercritical water-cooled nuclear reactor (SCWR) concepts.The experimental dataset was obtained in supercritical water flowing upward in a 4-m long vertical bare tube with 10-mm ID. The data were collected at pressures of about 24 MPa, inlet temperatures from 320 to 350 °C, values of mass flux ranged from 200 to 1500 kg/m² s and heat fluxes up to 1250 kW/m² for several combinations of wall and bulk-fluid temperatures that were below, at, or above the pseudocritical temperature.A dimensional analysis was conducted using the Buckingham Π-theorem to derive the general form of an empirical supercritical water heat-transfer correlation for the Nusselt number, which was finalized based on the experimental data obtained at the normal and improved heat-transfer regimes. Also, experimental heat transfer coefficient (HTC) values at the normal and improved heat-transfer regimes were compared with those calculated according to several correlations from the open literature, with CFD code and with those of the proposed correlation.The comparison showed that the Dittus-Boelter correlation significantly overestimates experimental HTC values within the pseudocritical range. The Bishop et al. and Jackson correlations tended also to deviate substantially from the experimental data within the pseudocritical range. The Swenson et al. correlation provided a better fit for the experimental data than the previous three correlations at low mass flux (∼500 kg/m² s), but tends to overpredict the experimental data within the entrance region and does not follow up closely the experimental data at higher mass fluxes. Also, HTC and wall temperature values calculated with the FLUENT CFD code might deviate significantly from the experimental data, for example, the k-? model (wall function). However, the k-? model (low Reynolds numbers) shows better fit within some flow conditions.Nevertheless, the proposed correlation showed the best fit for the experimental data within a wide range of flow conditions. This correlation has an uncertainty of about ±25% for calculated HTC values and about ±15% for calculated wall temperature. A final verification of the proposed correlation was conducted through a comparison with other datasets. It was determined that the proposed correlation closely represents the experimental data and follows trends closely, even within the pseudocritical range. Finally, a recent study determined that in the supercritical region, the proposed correlation showed the best prediction of the data for all three sub-regions investigated.Therefore, the proposed correlation can be used for HTC calculations in SCW heat exchangers, for preliminary HTC calculations in SCWR fuel bundles as a conservative approach, for future comparison with other datasets and for the verification of computer codes and scaling parameters between water and modelling fluids.