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Recent advances in high-temperature gas-cooled reactor fuel research have captured the global spotlight, as modern operating contexts demand innovative responses to unprecedented challenges. This article offers an overview of contemporary directions in high-temperature gas-cooled reactor fuel design worldwide, pinpointing the shared operational demands and development patterns characteristic of these advanced fuels. It presents an innovative advanced fuel design, which incorporates multi-layer coated particles to boost safety and employs high-temperature-resistant silicon carbide (SiC) ceramics, seamlessly integrated with cutting-edge additive manufacturing (AM) techniques. This design heralds a shift toward modular fuel element solutions that are easily scalable, supporting the diverse array of advanced reactors and marking a significant step forward in the quest for high-temperature gas-cooled reactor fuel technologies.

In fusion reactors, many blanket concepts are designed with water as a coolant to transfer high-density heat from the fusion reaction out of the reactor core. The coolant temperature and pressure are maintained as the validated use in water-cooled fission reactors. However, the flow channel in a water-cooled blanket is independent of each other, and there is no flow mixing between coolant channels. Therefore, flow instability may occur in the independent parallel channels in a water-cooled blanket due to its unique structure and heat distribution, especially under the high heat flux caused by plasma rupture. In this study, the parametric analysis of density wave instability is performed using a thermal-hydraulic code developed for independent parallel channels based on the homogeneous model for the two-phase flow. The parallel-channel system in a water-cooled ceramic breeder (WCCB) blanket of the China Fusion Engineering Experimental Reactor (CFETR) is established for its first wall structure. A small disturbance is introduced into the system to determine if it is stable under different conditions. It is found that the channel number has no obvious influence on the prediction of the flow instability boundary. Therefore, the two-channel system is adopted to investigate the influence of different parameters, such as the pressure, resistance, flow rate, and inclination, on the flow instability boundary of the parallel-channel system in the CFETR WCCB blanket. The results show that flow instability occurs more easily in this study compared to the traditional instability analysis, especially under high-pressure conditions. In general, conditions of high pressure, large flow rate, and no inclination can stabilize the system, while the influence of resistance is quite different under different conditions of resistance and pressure. The research work indicates that more attention should be paid to the joint influence of different parameters for the water-cooled blanket during its design and operation.

Based on the classical Gursone-Tvergaarde-Needleman (GTN) method, a theoretical model was developed and applied to predict the mechanical behavior and fracture characteristics of hydrogenated zirconium cladding. With full consideration of the influence of hydrogen on plastic stain and void volume in materials, the damage parameters in the classical GTN model were modified. Through benchmarking with experimental data, it was proved that the hydrogen embrittlement phenomenon in zirconium materials can be properly simulated by the modified GTN model proposed in this study. By integrating this modified model into ABAQUS software, numerical simulation of a cladding tensile test was further conducted at different temperature, hydrogen concentration and oxidation conditions. Influence of hydrogen embrittlement on the mechanical properties and fracture characteristics of zirconium cladding was analyzed. The results suggest that the effect of hydrogenation on the cladding mechanical performance varies in magnitude at different temperatures, because hydrogen exists in different forms and also varies significantly at different temperatures. At a relatively low temperature, a considerable amount of hydrogen is presented in the form of precipitates, which is more likely to cause hydrogen embrittlement failure. In addition, the numerical simulation of a cladding tube burst test was carried out under a loss of coolant accident. It was concluded that the influence of hydrogen embrittlement on the burst stress and burst strain was still considerable, despite of the rather high temperature at the burst position.

Loss of Coolant Accident (LOCA) is one of the major design-basis accidents in LWRs. Fuel rod may fail due to the rupture of the cladding. By developing a LOCA simulation module, the steady-state fuel rod performance analysis code, FROBA-ROD, is now capable to predict fuel rod behaviors under a LOCA transient. The relevant models and the code was verified and validated by comparing with authoritative commercial codes and with the experimental measurements. Comprehensive calculations and analyses of fuel rod behaviors under different LOCA transients were performed by the new version of FROBA-ROD. Compared the failure conditions to the non-failure conditions through the simulation results, a cladding failure threshold equation was found for a better estimate of the integrity of high burnup fuel rods under LOCA transients.

In this study, based on the modification of the pellet cladding mechanical interaction, gap closure process, and the cladding water corrosion model, Fuel Rod Behavior Analysis-ANNULAR (FROBA-ANNULAR) was uprated. The modified code was verified with FRAPCON-ANNULAR and ABAQUS. The verification calculation was under low power density when both two gaps were open. The calculation results showed good agreement. The modified code was then utilized to evaluate the annular fuel behavior, compared with the original code FROBA-ANNULAR. In this study, the annular fuel exhibits a much lower peak fuel temperature(about 900K). The different results for heat flux fraction(0.55 for the original code, 0.66 for the modified code) indicated that the gap closure process strongly affected the movement of the adiabatic pellet line. The internal pressure results (7.5 MPa for the original code, 6 MPa for the modified code) were also affected by the different assumptions. The results also showed that Zr's oxidation thickness and hydrogen concentration were related to both time and temperature. The higher the temperature was, the larger the oxidation rate was when the transition thickness was reached.

An additional low temperature overpressure protection system which relies on the Pressurizer (PRZ) pressure relief valves has been put forward under the situation in which the Residual Heat Removal System (RHRS) is unavailable or isolated. Taking into account the risk of Reactor Pressure Vessel (RPV) brittle fracture and LOCA under cold overpressurization transients, it is urgent to strengthen the low temperature overpressure protection for in-service Pressurized Water Reactors (PWR) in China. In this paper, the simulation and analysis of two types of overpressure transients at low temperature during the shutdown process are carried out through the detailed Relap5 modeling of CPR1000. The results show that the place where the brittle fracture occurs firstly is the lower plenum. The sensitivities of the system temperature and the opening/closing time of the additional protection system's valve are analyzed. The system set point becomes more restrictive at lower coolant temperature. Additional threshold values of the PRZ pressure relief valve are given under different Effective Full Power Years (EFPY). The set point should be less than 5.5 MPa in the case of 5 EFPY and less than 3.7 MPa at 10 EFPY.The results can be applied to engineering practice, which can effectively improve the safety of CPR1000.

Due to the special structure, helical coil once-through steam generators (HCOTSGs) can withstand greater thermal expansion stress, have a larger heat exchange area, and cause the secondary flow phenomenon to improve the heat transfer capacity. Thus, it is inevitable to further study the thermal-hydraulic characteristics of the HCOTSG, a vital component of reactors. The optimal physical models were selected for different heat transfer areas by detailed investigation and comparison, to adopt in the TACS, a self-developed thermal-hydraulic analysis code that is accurate and widely-used in HCOTSG simulation. After verification with experiments of Santini, taking the IRIS reactor as the object, the TACS was employed to briefly study the thermal-hydraulic performances of the HCOTSG system at first, and then discuss the influences of thermal and geometric parameters on the HCOTSG. The analysis results showed that: the variation of the primary flow rate greatly affects the heat transfer coefficient of the primary side, while the maximum value of the heat transfer coefficient of the secondary side only changes drastically with the secondary flow rate; when the primary side flow drops to 70%, superheated steam is not generated on the secondary side; when the secondary mass flow rate decreases to a certain extent, the steam superheat degree increases by a small amplitude; the primary side inlet temperature has a little influence on the primary temperature difference, but significant influence on the two-phase zone length of the secondary side; the secondary inlet temperature has very little influence on the HCOTSG system; the inner diameter and the outer diameter of helical tubes have obvious influences, while the helical diameter has not.

The supply capacity of water resources, food and meat products is of great importance to the people's livelihood of a country. In recent years, although China has introduced many policies on water resources and grain production, the current situation of China's food self-sufficiency and imbalance between supply and demand of water resources has not been fundamentally changed. Food security and water security are facing a serious situation. This paper takes the water footprint as the connection point, and combines the water food meat system with mutual influence, mutual causation and dynamic feedback into a composite system. At the same time, the simulation model of the composite system is established by using system dynamics, and the dynamic simulation of water grain meat in China from 2000 to 2050 is carried out to explore the current situation and future development trend of China's water, grain and meat supply capacity. It was found that during the simulated period, the agricultural blue-green water footprint on the demand side would continue to dominate, followed by the gray water footprint. The blue water footprint on the supply side remained stable, whereas the green water footprint and the circulating water footprint showed an upward trend. According to the contemporary social and economic development and the model of water resources in China, there will be no meat shortage in the future, but issues have been found in the ability to guarantee water and food supply. The root of China's food support capability problem is excessive grain consumption due to meat production, whereas the cause of the water support capability problem is the slow development of the water conservation. Food support capability issues can be solved by regulating the meat output of livestock farming and fishery operations, reducing excess production capacity, and stabilizing the meat supply and demand. To solve the water support capability issue, China should focus on accelerating the pace of agricultural water-conservation development, improving the sewage treatment system, building rainwater-collection projects, and promoting the research and development of water recycling technology. This study provides support for optimizing the structures of the meat and grain industries and the policy formulation of the efficient use of water resources in China. [ABSTRACT FROM AUTHOR]