STEADY-STATE THERMAL-HYDRAULIC ANALYSIS OF A PLATE TYPE REACTOR

ABSTRACT In the plate type fuel reactor, all the fuel elements are arranged in parallel in the subassembly and set in the core, which create many isolated parallel rectangular channels. The arrangements of the fuel elements may have significant impact on the thermal-hydraulics of the core. In order to fully understand the geometry impact on the steady-state thermalhydraulic characteristics, based on the mass, momentum and energy conservation equations, a multi-channel code was developed to estimate the steady-state thermal-hydraulic characteristics. Two different types of fuel elements arrangements in the subassembly were proposed and studied, one was uniform distribution with the same gap sizes between each fuel elements, and the other was nonuniform distribution with different clearances among boundary fuel elements. The mass flux distribution, the temperature field and the DNBR were obtained by the developed code. It showed that the mass flux distribution was affected by the flow area of the channel and the given power distribution. The flow area of the channel has bigger influence than the second. In addition, the results of the two different types of fuel elements arrangements were compared, and it could be found that the asymmetrical cooling of the fuel elements occurred when fuel elements were nonuniformly arranged, which leaded to the decrease of the maximum temperature in the asymmetrically cooled fuel elements and the increase of the maximum temperature in the core. Furthermore, the DNBR calculated by the Sudo model indicated that the safety margin of the reactor under the present conditions is sufficient. All the obtained results served some valuable information for the design of the new type research reactor

ICONE18-29172 INVESTIGATION OF PRESSURE DROP FOR FLUID FLOW THROUGH POROUS MEDIA: APPLICATION TO A PEBBLE-BED REACTOR

ABSTRACT The present studied Pebble-Bed Reactor is a light-water cooled reactor that consists of millions of Micro-Fuel Elements, and the TRISO-coated fuel particles(MFE) fill the fuel assembly disorderly and form a porous media with internal heat source. Papers on porous media continue to be published at the rate of about 150 per year and the domain of application is wide spread, ranging from chemical particle beds, mass separator units, debris beds, soil investigations, heat pipes and fluidized beds etc. In this paper, investigation is performed on the press drop under conditions of both single-phase and two-phase flow through porous media. Large number of relations are studied and the relational expressions, which generalize the available data of experiments, are suggested for pressure drop calculation in a pebble bed of spheres at random distribution. Finally, the relational expressions are applied to analyze the flow characteristics of the Pebble-Bed Reactor, such as the influence of pressure on two phase friction factor in the core etc

MicroRNA-22 suppresses NLRP3/CASP1 inflammasome pathway-mediated proinflammatory cytokine production by targeting the HIF-1α and NLRP3 in human dental pulp fibroblasts

Aim To investigate the synergetic regulatory effect of miR-22 on HIF-1α and NLRP3, subsequently regulating the production of the NLRP3/CASP1 inflammasome pathway-mediated proinflammatory cytokines IL-1β and IL-18 in human dental pulp fibroblasts (HDPFs) during the progression of pulpitis. Methodology Fluorescence in situ hybridization (FISH) and immunofluorescence (IF) were performed to determine the localization of miR-22-3p, NLRP3 and HIF-1α in human dental pulp tissues (HDPTs). The miR-22 mimics and inhibitor or plasmid of NLRP3 or HIF-1α were used to upregulate or downregulate miR-22 or NLRP3 or HIF-1α in HDPFs, respectively. Computational prediction via TargetScan 5.1 and a luciferase reporter assay were conducted to confirm target association. The mRNA and protein expression of HIF-1α, NLRP3, caspase-1, IL-1β and IL-18 were determined by qRT-PCR and western blotting, respectively. The release of IL-1β and IL-18 was analysed by ELISA. The significance of the differences between the experimental and control groups was determined by one-way analysis of variance, p < .05 indicated statistical significance. Results A decrease in miR-22 and an increase in HIF-1α and NLRP3 in HDPTs occurred during the transformation of reversible pulpitis into irreversible pulpitis compared with that in the healthy pulp tissues (p < .05). In the normal HDPTs, miR-22-3p was extensively expressed in dental pulp cells. HIF-1α and NLRP3 were mainly expressed in the odontoblasts and vascular endothelial cells. Whereas in the inflamed HDPTs, the odontoblast layers were disrupted. HDPFs were positive for miR-22-3p, HIF-1α and NLRP3. Computational prediction via TargetScan 5.1 and luciferase reporter assays confirmed that both NLRP3 and HIF-1α were direct targets of miR-22 in HDPFs. The miR-22 inhibitor further promoted the activation of NLRP3/CASP1 inflammasome pathway induced by ATP plus LPS and hypoxia (p < .05). In contrast, the miR-22 mimic significantly inhibited the NLRP3/CASP1 inflammasome pathway activation induced by ATP plus LPS and hypoxia (p < .05). Conclusion MiR-22, as a synergetic negative regulator, is involved in controlling the secretion of proinflammatory cytokines mediated by the NLRP3/CASP1 inflammasome pathway by targeting NLRP3 and HIF-1α. These results provide a novel function and mechanism of miR-22-HIF-1α-NLRP3 signalling in the control of proinflammatory cytokine secretion, thus indicating a potential therapeutic strategy for future endodontic treatment

Stability of SARS-CoV-2 in cold-chain transportation environments and the efficacy of disinfection measures

BackgroundLow temperature is conducive to the survival of COVID-19. Some studies suggest that cold-chain environment may prolong the survival of severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) and increase the risk of transmission. However, the effect of cold-chain environmental factors and packaging materials on SARS-CoV-2 stability remains unclear.MethodsThis study aimed to reveal cold-chain environmental factors that preserve the stability of SARS-CoV-2 and further explore effective disinfection measures for SARS-CoV-2 in the cold-chain environment. The decay rate of SARS-CoV-2 pseudovirus in the cold-chain environment, on various types of packaging material surfaces, i.e., polyethylene plastic, stainless steel, Teflon and cardboard, and in frozen seawater was investigated. The influence of visible light (wavelength 450 nm-780 nm) and airflow on the stability of SARS-CoV-2 pseudovirus at -18°C was subsequently assessed.ResultsExperimental data show that SARS-CoV-2 pseudovirus decayed more rapidly on porous cardboard surfaces than on nonporous surfaces, including polyethylene (PE) plastic, stainless steel, and Teflon. Compared with that at 25°C, the decay rate of SARS-CoV-2 pseudovirus was significantly lower at low temperatures. Seawater preserved viral stability both at -18°C and with repeated freeze−thaw cycles compared with that in deionized water. Visible light from light-emitting diode (LED) illumination and airflow at -18°C reduced SARS-CoV-2 pseudovirus stability.ConclusionOur studies indicate that temperature and seawater in the cold chain are risk factors for SARS-CoV-2 transmission, and LED visible light irradiation and increased airflow may be used as disinfection measures for SARS-CoV-2 in the cold-chain environment

Development of Safety Analysis Code TACOS and Application to Fuel Qualification Test Loop

In this study, transient analysis code of SCWRs (TACOS), with the ability of simulating transients or accidents under both supercritical water (SCW) conditions and subcritical water conditions, has been developed with FORTRAN 90 language, and simulation has been performed to the European SCWR fuel qualification test (FQT) system. The semi-implicit finite difference technique was adopted for the solution of coolant dynamic behavior in the loop. Furthermore, an illustration of numerical solution for the heat structure model and other models was presented. The code TACOS is then applied to simulate the Edward-O&apos;Brian blow-down experiment to evaluate its capacity in simulating the fast blow-down progress. Therefore, the design basis accidents (DBAs) with the transcritical transient were investigated for the SCWR-FQT system. The results by TACOS indicate that the SCWR-FQT with the existing safety system can be cooled effectively

WATER HAMMER CHARACTERISTICS FOR PARALLEL PUMPS WATER SUPPLY SYSTEMS

ABSTRACT The water hammer induced by abrupt velocity change of fluid flow is inevitable for nuclear power plant systems because of the sudden opening or closing of valves, the sudden startup or shutdown of the pumps and the rupture of pipes. The water hammer pressure wave can damage the pipes and cause the abnormal shutdown of Nuclear Power Plant(NPP). The object of this study is a Parallel Pumps Water Supply system(PPWS) adopted in a NPP. The PPWS is composed of two parallel mixed-flow pumps connected with a check valve separately, a container, a throttle flap and pipe lines. The Method of Characteristic line(MOC) was adopted to evaluate the water hammer behaviors of the PPWS during the alternate startup and shutoff conditions of two parallel pumps. A code was developed using Fortran language to compute the transient behaviors including he peak pressure, the flow velocity and the movement of the valve plate. The results indicate that the water hammer behaviors under low speed startup condition differ from that of high speed startup condition. The maximum pressure vibration amplitude is up to 5.0MPa occurring under high-high speed startup condition. The computation results are instructive for the optimization design of the PPWS so as to minimize the damage potential induced by water hammer

Reactor Core Design and Analysis for a Micronuclear Power Source

Underwater vehicle is designed to ensure the security of country sea boundary, providing harsh requirements for its power system design. Conventional power sources, such as battery and Stirling engine, are featured with low power and short lifetime. Micronuclear reactor power source featured with higher power density and longer lifetime would strongly meet the demands of unmanned underwater vehicle power system. In this paper, a 2.4 MWt lithium heat pipe cooled reactor core is designed for micronuclear power source, which can be applied for underwater vehicles. The core features with small volume, high power density, long lifetime, and low noise level. Uranium nitride fuel with 70% enrichment and lithium heat pipes are adopted in the core. The reactivity is controlled by six control drums with B4C neutron absorber. Monte Carlo code MCNP is used for calculating the power distribution, characteristics of reactivity feedback, and core criticality safety. A code MCORE coupling MCNP and ORIGEN is used to analyze the burnup characteristics of the designed core. The results show that the core life is 14 years, and the core parameters satisfy the safety requirements. This work provides reference to the design and application of the micronuclear power source

Numerical simulation of natural convection around the dome in the passive containment air-cooling system

The Passive containment Air-cooling System (PAS) can effectively remove the decay heat of the modular small nuclear reactor after an accident. The details of natural convection around the dome, which is a key part of PAS, were investigated numerically in the present study. The thermal dynamics around the dome were studied through the temperature, pressure and velocity contours and the streamlines. Additionally, the formation of the buoyant plume at the top of the dome was investigated. The results show that with the increase of Ra, the lift-off point moves toward the bottom of the dome, and the eddy under the buoyant plume grows larger gradually, which enhances the heat transfer. And the heat transfer along the dome surface with different truncation angles was investigated. As the angle increases, the heat transfer coefficient becomes stronger as well. Consequently, a newly developed heat transfer correlation considering the influence of truncation angle for the dome is proposed based on the simulated results. This study could provide a better understanding of natural convection around the dome of PAS and the proposed correlation could also offer more predictive value in the improvement of nuclear safety