Search

• Heat transfer in reactor core in LBLOCA scenario is analyzed with FSA method. • Scaling criteria and their importance are evaluated. • The priority of the criterion for convection heat transfer and heat accumulation is high. • The contribution of some initial and boundary conditions is too slight. In integral test facilities, some phenomena relevant in the separate effect test are usually neglected due to scaling limitations and design compromises. The typical heat transfer phenomenon in reactor core in large break loss of coolant accident (LBLOCA) scenario is analyzed with fractional scaling analysis (FSA) method in this work. A conservation form of cladding temperature is derived on the basis of energy conservation. Then the scaling criteria and their importance are evaluated. It is found that the similarities of the criteria for convection heat transfer and heat accumulation should be guaranteed since their priorities are high. The contribution of initial pressure and distribution of coolant inventory to cladding temperature in LBLOCA scenario is too slight. This work is encouraging and may shed a light on the coupling application of hierarchical two-tiered scaling (H2TS) and FSA method in engineering application. [ABSTRACT FROM AUTHOR]

Two phase flow instability is of vital importance to the safety of nuclear reactors and other boiling systems. In this work, a theoretical model for the two phase flow instability in parallel channels in ocean motions is developed based on drift flux model. The effect of phasic slip effect is considered. The variation of density against temperature and enthalpy is included. The theoretical results are validated with experimental data and pioneer research results with a satisfactory agreement obtained. The effects of several important parameters on the stability boundary are also analyzed. It is found that the effect of rolling motion on the stability boundary in parallel channels is limited in motions with small accelerations. The effect of heeling motion on the stability boundary of parallel channels is slight. In rolling motion, the stable region in parallel channels decreases as the channel distance increasing, which is caused by the increasing of rolling radius and additional forces. This work is valuable for the subsequent research of small modular reactors. [ABSTRACT FROM AUTHOR]

The research and development of small modular reactor in floating platform has been strongly supported by Chinese government and enterprises. Due to the effect of ocean waves, the thermal hydraulic behavior and safety characteristics of floating reactor are different from that of land-based reactor. Many scholars including the author have published their research and results in open literatures. Much of these literatures are valuable but there are also some contradictory conclusions. In this wok, the nuclear reactor thermal hydraulic research in ocean motions was systematically summarized. Valuable results and experimental data were analyzed and classified. Inherent mechanism for controversial issues in different experiments was explained. Necessary work needed in the future was suggested. Through this work, we attempt to find as many valuable results as possible for the designing and subsequent research. [ABSTRACT FROM AUTHOR]

Highlights: [•] An advanced lattice with excellent heat transfer was introduced. [•] The maximum heat transfer coefficient is increased by about 40%. [•] The flow pulsation and vortex structure was analyzed with URANS approach. [Copyright &y& Elsevier]

Abstract: The fluid mixing at the reactor core in rolling motion and steady state is investigated numerically with CFX12.0. The CFD results are validated with experimental data in steady state. In rolling motion, the fluid mixing factor at the center of the core oscillates in a cosine function, but the variation of the fluid mixing factor surrounding the core is not regular. The variation amplitude of the fluid mixing factor next to the boundary line of fluid mixing is the most significant. The variation of fluid mixing factor increases with the increasing of additional force. The increasing of Reynolds number could depress the effect of rolling motion on the fluid mixing. [Copyright &y& Elsevier]

Abstract: The periodic large scale vortex structure is highly accounted for the local flow and heat transfer and turbulent mixing in rod bundles. In this paper, the mechanism of the periodic large scale structures is studied in terms of the vortex dynamics. The vortex structure in rectangular channels with different inlet velocities is also analyzed. It is found that the periodic large scale vortex structure exists in the rectangular channels with transverse vorticity gradient. The distribution of vorticity is strictly related with that of vortex structure. [Copyright &y& Elsevier]

Abstract: The laminar pulsatile flow in tubes in rolling motion is investigated theoretically. The theoretical model of laminar flow in rolling motion is developed and the velocity correlation is also derived. The effect of rolling motion on velocity and frictional resistance factor is analyzed. The rolling motion mainly affects on the laminar flow by the tangential force. The centrifugal force does not affect on the flow. The tangential force affects on the flow in axial direction, its radial effect is very weak and could be omitted. There are two critical rolling points in rolling motion. After the first critical rolling point, the flowing velocity next to the wall reverses. Moreover, the flow rate at the tube cross-section becomes negative after the second critical rolling point. The buoyancy force is only one part of the effects that affects on the average velocity of a natural circulation system in rolling motion. The effect of Womersley number on the velocity is significant, which can not only affect on the average velocity but also on the oscillating period and velocity amplitude. The rolling motion does not affect on the average frictional resistance of laminar pulsatile flow. If the rolling motion is very serious, the flow is at a transitional or turbulent flow state, in this case the effect of rolling motion on the average frictional resistance is considerable. [ABSTRACT FROM AUTHOR]

• Optimized design and safety analysis of a MTR are carried out. • A hexagonal fuel assembly structure with a central mercury heat pipe is adopted in this work. • Specific power has increased by 10 % compared to the previous MTR design. • This MTR design is equipped with very high inherent safety. Medium temperature heat pipe cooled reactor (MTR) can better address problems faced in tradition heat pipe cooled reactor such as challenges in high-temperature corrosion-resistant material, possible startup failure accidents and high steel monolithic thermal stress. The unique advantages of MTR include excellent startup performance, high transient negative temperature coefficient, low monolithic thermal stress, etc. This study works on MTR by adopting a hexagonal uranium zirconium hydride fuel assembly structure with a central mercury heat pipe in replace of the previous fuel pin assembly. A coupled neutronic-thermal–mechanical strategy is discussed with an emphasis on iteration schemes and geometry reconstruction. This method is then applied for core physics analysis, shield design, thermal-mechanics analysis of fuel assemblies, and heat pipe failure analysis. A systematic comparison between the previous design and this work is also discussed. According to the results, the total mass of the core decreased significantly, and specific power increased by 10 % compared to the previous design (Li et al., 2022). A high transient negative temperature coefficient ensures excellent self-regulation ability in the face of accidents. The possibility of fracture is almost eliminated during normal operating conditions, and fuel assembly can be maintained at the normal operating temperature under one heat pipe failure accident. This MTR design is equipped with very high inherent safety. This work provides references to the future design of MTR. [ABSTRACT FROM AUTHOR]

• Core design of medium temperature heat pipe cooled reactor is conducted in detail. • Specific power of the core is further improved. • Neutronics analysis and shielding analysis are carried out by MCNP5 and ORIGEN coupling method. • Simplified control mechanism and high inherent safety of the core are ensured. Medium Temperature heat pipe cooled Reactor (MTR) is a new reactor concept proposed by Li et al. in (2022). Low enriched uranium zirconium hydride fuel and mercury heat pipe are introduced in MTR. The unique advantages of MTR have been verified (Li et al., 2022) and it is considered as a potential candidate for energy supply in decentralized markets. In this work, an optimized MTR core design is proposed with detailed neutronic analysis and evaluation on mercury heat pipe, reflector and control rod arrangement, further increasing the economic efficiency and mobility of MTR. Heat transfer limit of the improved heat pipe model is further increased, contributing to a great reduction on core volume. Reflector material and thickness are analyzed in detail for mass minimization. Core physics characteristics are analyzed for four control rod arrangement schemes. The control mechanism is further simplified with only 9 control rods involved in the normal regulation of the core. Core lifetime is far more than 10 years. High inherent safety of the core is ensured. Besides, preliminary design of the shielding system is also carried out. A shieling layer of 60 cm LiH and 20 cm Pb can reduce the total dose to less than 40 % of the design limits. The total mass of the optimized core is greatly reduced and its specific power is increased by 60 % compared with that of the previous design. [ABSTRACT FROM AUTHOR]