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Based on the design parameters of the core decay heat removal through natural circulation of the typical high-power sodium-cooled fast reactor, using the system analysis program ERAC, a detailed analysis of the reactor core decay heat removal process characteristics after emergency shutdown was conducted, and comparative analysis was conducted on the cooling effects in the reactor under two sets of four conditions of decay heat removal system (DHRS). The results indicate that enabling DHRS requires thousands of seconds as it has a significant cooling effect on the core. During this period, the removal of core decay heat relies on the inherent thermal-hydraulic safety characteristics of the reactor. In principle, DHRS only needs to carry out the heat inside the reactor before the temperatures at the critical locations reaches its limit value, and keep the temperatures in a decreasing trend. When the independent heat exchanger (DHX) is arranged in the hot pool, the temperatures of the hot pool and the main vessel are relatively lower, which is beneficial for temperature control of the main vessel as the main circuit pressure boundary, and its effect is better than when arranged in the cold pool. In addition, different locating arrangements of DHXs will have an impact on the mass flow in the assembly wrappers and inter-wrappers, but the impact on the overall cooling effect on the core temperature is not significant. In order to reduce the investment and operating costs of nuclear power plants and then improve economic efficiency, it should be optimized on the natural circulation design of the pool-type sodium-cooled fast reactor. The optimization direction is to fully utilize the inherent thermal-hydraulic safety characteristics of the pool-type sodium-cooled fast reactor, reduce the requirements for the start cooling time and the power of heat discharge of DHRS. It is feasible to consider arranging all DHXs in the heat pool, reduce their volume, and lowering their design value of heat dissipation power. Alternatively, without compromising safety, other more economical and convenient effective methods could be selected. These research results will provide important references for the natural circulation design of pool-type liquid metal reactors such as commercial fast reactor and integrated fast reactor in China.

China is accelerating the development of sodium-cooled fast reactor technology. For nuclear reactors, whether it is a pressurized water reactor or a fast reactor, core flow distribution is a key concern, which directly determines whether the reactor can operate safely and reliably. Sodium-cooled fast reactor core adopts a three-stage flow distribution method consisting of diagrid, distribution headers and assemblies. Distribution headers are installed on diagrid, and various types of assemblies are installed on distribution headers. Pressure drop of the core is composed of distribution header pressure drop and assembly pressure drop. The distribution header pressure drop itself affects the flow distribution of the assemblies, thereby affecting the safety of the core. Therefore, it is of great significance to study the impact of distribution header pressure drop on the flow distribution of assemblies for the sodium-cooled fast reactors. In order to reduce the flow distribution deviation of assemblies caused by the distribution header pressure drop, it is necessary to carry out a reasonable assembly pressure drop design. Based on the mechanism of flow distribution deviation of assemblies caused by distribution header pressure drop, a theoretical calculation model was proposed, and an optimized design of assembly pressure drop was carried out for the China Experimental Fast Reactor (CEFR) core. Based on the actual layout of CEFR core, the maximum deviation of flow distribution of fuel assemblies was obtained, and the optimization direction of nominal assembly pressure drop was determined, indicating that optimization design of nominal assembly pressure drop should be carried out for the first five rings. After adjusting the nominal pressure drop of the first five rings of assemblies from 250 kPa (the original nominal pressure drop) to 249 kPa, 248.5 kPa, and 248 kPa, respectively, the maximum deviation of flow distribution of fuel assemblies firstly decreases from −0.99% to −0.95%, and then increases to −1.02% and −1.08%, which indicates that nominal assembly pressure drop should be elaborately determined to obtain a minimum flow distribution deviation of fuel assemblies. In conclusion, when conducting core thermal hydraulic design for sodium-cooled fast reactors, it is necessary to analyze the optimization direction of nominal assembly pressure drop based on actual core layout, and sensitivity analysis should be conducted to finally determine the nominal assembly pressure drop to reduce the impact of distribution header pressure drop on flow distribution of assemblies to the lowest extent.

Approximately 15% of US adults have circulating levels of uric acid above its solubility limit, which is causally linked to the disease gout. In most mammals, uric acid elimination is facilitated by the enzyme uricase. However, human uricase is a pseudogene, having been inactivated early in hominid evolution. Though it has long been known that uric acid is eliminated in the gut, the role of the gut microbiota in hyperuricemia has not been studied. Here, we identify a widely distributed bacterial gene cluster that encodes a pathway for uric acid degradation. Stable isotope tracing demonstrates that gut bacteria metabolize uric acid to xanthine or short chain fatty acids. Ablation of the microbiota in uricase-deficient mice causes severe hyperuricemia, and anaerobe-targeted antibiotics increase the risk of gout in humans. These data reveal a role for the gut microbiota in uric acid excretion and highlight the potential for microbiome-targeted therapeutics in hyperuricemia.

Traceability is an important tool in the harmonization and standardization of reporting laboratory results, making them comparable across measurement systems. Driven by International Standardization Organization (ISO) 15189 accreditation requirements, medical laboratories have entered the era of metrological traceability. Although calibrators are a key component in the entire metrological traceability system, there is controversy over internal quality control (IQC) materials. It has been proposed that trueness materials supplied by the system's manufacturer with metrological traceability can be used to confirm that the performance of the measuring system is properly unbiased. This article focuses on the implementation challenges and operational hurdles of applying traceability concepts to IQC materials for trueness verification in medical laboratories regarding the most recent 2022 edition of ISO 15189 standard requirements for IQC and metrological traceability. There are practical considerations concerning the acquiring of IQC materials. We must acknowledge the limitations and restrictions that manufacturers and laboratories face before the recommendations can be applied in routine practices.