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• A new model was applied in FROBA-ROD code to conduct transient-state simulations. • The modified models made the updated FROBA-ROD code more accurate and functional. • The results agreed well with commercial codes and experimental benchmark data. To analyze the behavior of PWRs fuel rods under steady operation conditions, some models such as modified Forsberg-Massih model and TUBRNP model were applied to FROBA-ROD code, which was developed by Xi'an Jiaotong University in 2012. Then more significant fuel rod behaviors could be simulated by FROBA-ROD code, which facilitated the safety analysis of fuel elements especially under accident conditions. To conduct transient thermal calculations and to improve the simulation accuracy, existing thermal models in FROBA were modified with the new fuel rod thermal conductivity model and burnup distribution model. The new models were validated by comparing it with the results of authorized commercial codes FRAPCON-4.0 and ABQUS and by comparing it with IFA-432 Rod 1 experimental benchmark data conducted by Oak Ridge National Laboratory. The relative calculation errors of centerline temperature calculated by modified FROBA-ROD, original FROBA-ROD and FRAPCON were 5.44%, 11.68% and 9.47% separately, which indicated that the modification and update of FROBA-ROD were valid. Modified FROBA-ROD code was applied to perform the behavior analysis of the AP1000 fuel rod. The simulation results indicated that there were enough safety margins for fuel rod behavior of AP1000 at rated operation conditions. The maximum oxidation thickness of cladding appeared at the upper part of the cladding tube in AP1000, which indicated that this area suffered a higher risk of cladding failure. Modified FROBA-ROD code is expected to deal with fuel rod scenarios under accident conditions after some additions of transient models. [ABSTRACT FROM AUTHOR]

In view of the high temperature of the single-cell Thermionic Fuel Element (TFE), the fuel mass transfer model was developed and the mechanical model was modified by considering fuel creep and fuel cracks in this paper. Afterwards, implemented models were verified by comparing with the results in the reference or calculated by Matlab or BEEs (a fuel performance analysis code developed upon the open-source MOOSE framework). Further, the thermal–mechanical performance simulation of the single-cell TFE under the normal operation was carried out. The results indicate that the fuel pellet gets in contact with the emitter due to radial mass transfer. Driven by axial mass transfer, the axial distribution of power and temperature are flattened, and the maximum temperature is decreased. Although the single-cell TFE is safe at normal power, once the power is raised due to unfavorable factors, the central channel may be blocked, leading to excessive emitter deformation and increasing the risk of short circuit of the fuel element. [ABSTRACT FROM AUTHOR]

• A RIA simulation module was applied into FROBA-ROD code. • The new version of FROBA-ROD code was verified and validated to be accurate and functional. • A cladding failure threshold equation was found for a better estimation of the integrity of high burnup fuel rods under RIA transients. By developing a reactivity-initiated accident simulation module, the steady-state fuel rod performance analysis code, FROBA-ROD, was updated and was capable of predicting the fuel rod behavior under a reactivity-initiated accident. The RIA simulation module was validated by comparing its results to an authoritative commercial code, FALCON, and to the experimental data of RIA simulation experiments performed on the NSRR in Japan. By using the new version of FROBA-ROD, a series of comprehensive calculations and analyses of fuel rod behavior under different RIA conditions were conducted. It is found that the cladding temperatures are at a low level in all the failure cases and the hydrogen concentration of the cladding is the key factor that effects the integrity of fuel rods under an RIA condition. And a PCMI cladding failure threshold equation was established for a better integrity estimate of fuel rod under RIA conditions in this study. [ABSTRACT FROM AUTHOR]

In this study, a three-dimensional (3D) fluid-solid coupling simulation with the full consideration of irradiation effects for plate-type nuclear fuel assemblies was conducted. Mechanical models of radiation-induced deformations in solid domain and thermo-hydraulic models in fluid domain were established based on ABAQUS and FLUENT, respectively. By use of MpCCI, the capability of fluid-solid coupling simulation was developed through the real-time parameter exchange of different physical fields at fluid-solid boundary interfaces. The accuracy and reliability of fluid-solid coupling methodology by FLUENT-MpCCI-ABAQUS was validated through benchmark with simulation in public reference. The influence of radiation swelling and bending deformation on fluid thermal-hydraulic characteristics was investigated based on the developed coupling analysis method. In addition, the sensitivity study of heterogeneous swelling and flow channel width was carried out. The simulation result shows that radiation swelling and bending deformation exerted substantial influence on flow distribution and outlet temperature. [ABSTRACT FROM AUTHOR]

• The effects of corrugation direction and type on the seismic behavior of corrugated DSCW are analyzed. • The seismic behavior of corrugated DSCW with different connector types is compared. • The corrugated DSCWs with flexural failure achieve a drift ratio exceeding 2%. • The axial compression ratio limitation of corrugated DSCW is considered. • Equations for calculating the flexural strength of corrugated DSCW are provided. This paper presents the seismic behavior of corrugated double-skin composite wall (DSCW) with concrete-filled steel tube boundary elements. Fifteen 1/3-scale DSCW specimens, varying in shear span ratio, axial compression ratio, corrugation direction and shape, connector type and steel faceplate profile, were tested under cyclic loading. All specimens except W15 failed in flexural failure. The cyclic response of vertical corrugated DSCW was much better than that of horizontal corrugated DSCW. Compared to flat DSCW, corrugated DSCW, even with a 20% reduction in the concrete cross-sectional area, had considerably higher peak load, ductility ratio and energy dissipation. The setting of connectors slowed down the damage rate of the corrugated DSCW in the failure stage, and also significantly improved the peak load and ductility of the corrugated DSCW with λ = 1.5. Increasing the shear span ratio significantly reduced the peak load and initial stiffness of the DSCW, but did not affect the ductility and energy dissipation. The corrugated DSCW, failed in flexural-dominated mode, had excellent collapse resistance, achieving a drift ratio exceeding 2% and a ductility ratio greater than 3.3, and it was recommended to take n = 0.3 as the limit value of axial compression ratio of corrugated DSCW. Moreover, the average ratio of P t / P c was 1.082 with a mean absolute error of 0.068 and a root mean square error of 0.084, indicating that the calculated value of proposed formulas for calculating the lateral strength of vertical corrugated DSCW can reflect the measured data well. [ABSTRACT FROM AUTHOR]

• The thermal behavior of a horizontal high-temperature heat pipe under motion conditions are experimentally investigated. • The motion conditions include transitory inclination, vertical heave, and periodic swing. • The impacts of motion types on temperature variation and heat transfer deterioration of heat pipes are summarized. High temperature heat pipe is widely applied to multiple industrial fields, including in small modular reactors to cool the reactor core, or as heat exchangers. The thermal behavior of the high temperature heat pipe has been widely researched by theoretical and experimental approaches, including designing, manufacture, numerical analysis, and experimental test on its thermal characteristics of start-up process and operation. As the heat pipe has a potential application protest on mobile nuclear reactors, this paper carried out experimental study on the thermal behavior of the high temperature heat pipe under various motion conditions. The temperature distributions on the heat pipe surface under transitory inclination, vertical heave, and periodic swing, are measured to evaluate the impact of motion conditions on the heat transfer of heat pipe at horizontal position. The transitory inclination causes an obvious temperature variation at both evaporator and condenser. The vertical heave, of which the motion direction is perpendicular to the heat pipe, has negligible impact on the isothermality of the heat pipe. The periodic swing leads to periodic temperature fluctuation, of which the amplitude increase with the decease of the period time. Besides, the dry out phenomenon is easier to happen at the evaporator when the condenser is longer. This paper summarizes the impact of different motion types on the thermal behavior of a horizontal heat pipe and provides a reference for the design and application of the high temperature heat pipe used in nuclear reactors. [ABSTRACT FROM AUTHOR]

Fully Ceramic Microencapsulated (FCM) fuel is a new type of material in nuclear energy field. It has become a promising accident tolerant fuel (ATF) candidate due to its advantages of high radiation stability, high fission product containment capacity and excellent thermo-mechanical performance. During operation, the temperature, stress, deformation and other key parameters will change significantly, which directly affect the safety of nuclear reactor. Therefore, it is necessary to carry out a multi-physics fully-coupled analysis suitable for the multi-scale, multi-component, multi-phase and nonlinear coupling processes in the reactor, so as to sort out the influences of material properties, radiation behavior, thermo-mechanical performance from numerous influencing factors. In this paper, based on the irradiation-thermo-mechanical coupling method, the performance of TRISO-based FCM fuel under irradiation conditions was analyzed, key thermo-mechanical parameters and other influencing factors of the fuel were obtained, failure behavior of the fuel element was evaluated. On this basis, the theoretical and numerical model of multi-objective optimization method were established, the optimum parameters including material properties, fuel geometry and particle arrangement were found by optimization method. The optimization results showed that the multi-objective optimization results could provide multiple Pareto optimal solutions for the FCM fuel. Specifically, when the TRISO particle spacing is 200 µm and 150 µm, the objective function difference between the optimal heat transfer solutions is only about 1.7%, meanwhile the mechanical properties vary significantly (the difference between the objective functions of the optimal solutions is about 12.4% ∼26.5%), indicating the response of stress is more sensitive than temperature. When the TRISO particles are tightly packed (particle spacing less than 100 µm), the difference of objective function between the optimal solutions is less than 5%, illustrating the optimization has limited improvement on the thermo-mechanical performance of the fuel, namely the optimization space is limited. [ABSTRACT FROM AUTHOR]

• The thermionic conversion model of the single-cell TFE was developed. • With developed and modified models, FROBA-THERMION code was modified and verified. • The thermionic conversion performance simulation of the single-cell TFE was conducted. • The thermionic conversion efficiency will be decreased due to fuel mass transfer. • The influence of key parameters on thermionic conversion efficiency were analyzed. The thermionic conversion performance of the single-cell thermionic fuel element (TFE) is influenced by fuel mass transfer and other parameters. With the consideration of current flow and heat transfer, the thermionic conversion model and the modified heat transfer model were implemented in FROBA-THERMION, a steady-state performance analysis code for the single-cell TFE. Afterward, both implemented models were verified by comparing with experiments or calculation results of KATET (a complex code developed by the Research Inst of SIA 'Lutch' of Russia to simulate single-cell TFE life behavior). Further, a steady-state performance simulation of the single-cell TFE was carried out. The results indicate that the thermionic conversion efficiency will be decreased due to the emitter temperature flattening caused by fuel mass transfer. In addition, the influence of several key parameters on thermionic conversion efficiency and measures to improve the thermionic conversion efficiency were analyzed. [ABSTRACT FROM AUTHOR]

Core Disruptive Accident (CDA) is a critical scenario in the Generation IV sodium-cooled fast reactor development. One of the key issues in the CDA evaluation is the eutectic reaction between Boron carbide (B 4 C) and Stainless Steel (SS). For developing a physical model in the CDA analysis code, it is necessary to investigate the B 4 C-SS eutectic reaction. To assess the reaction, one quantitative and high-resolution method using Joule heating is proposed in this study. Experiments were conducted using B 4 C material and SUS304 tubes. With an originally proposed equation, reaction rate constant data in the 1450 K-1500 K range were obtained, which was scarce in the past. The derived reaction rate constant values are consistent with the reference values. The reaction layer microstructure observation and the associated chemical composition analysis were also conducted. The proposed method is validated by the results. It can be concluded that the new method is credible with high efficiency. [ABSTRACT FROM AUTHOR]

• The SRC columns were tested under combined compression-bending-shear-torsion cyclic load. • The effects of stud on the torsional properties of SRC columns were analyzed. • A certain number of structural studs need to be added for SRC columns with torque under the bending design conditions. • A calculation method of torsional bearing capacity of SRC columns under combined action was proposed. This paper presents the seismic behavior of steel reinforced concrete (SRC) column with welded studs. Nine SRC columns, varying in stud position, stud spacing, stud length and stud layout, were tested under combined compression-bending-shear-torsion cyclic load. All specimens were subjected to bending-torsion failure with the characteristics of concrete crushing and X-shaped cracks. The fullness of hysteretic curves of bending moment and torsion moment showed that the torsional energy dissipation of the SRC columns was poor. The arrangement of studs at the flange could improve the seismic behavior of SRC columns, and decreasing the stud spacing and increasing the stud length could play an enhanced effect, but the effect of setting the studs at the web was not significant. For SRC columns subjected to torsion moment, a certain number of structural studs need to be added to enhance their torsional properties under the condition that the studs can resist bending moment. In addition, the strain distribution illustrated that the web of encased steel played a great role in resisting torsion, so the torsional bearing capacity of SRC columns was mainly controlled by the strength of the web. Based on the unified strength equation established in this paper, a calculation method of torsional bearing capacity of SRC columns, subjected to combined action of compression-bending-hear-torsion, was proposed. [ABSTRACT FROM AUTHOR]