Satoshi Ikejiri

Improvements of Feedwater Controller for the Super Fast Reactor

The main steam temperature of SCWRs sensitively changes with the power-to-flow ratio. In this article, the feedwater controller of the Super FR (fast-spectrum SCWR) is modified from that of the Super LWR (thermal-spectrum SCWR) for suppressing the variation of the main steam temperature. A plant system analysis code SPRAT-F is used. One of three feedback terms is added to the original feedwater controller that took only the deviation of the main steam temperature into consideration. In the feedwater controller (A), the deviation of the power-to-flow ratio is considered. In the feedwater controller (B), the deviation of the power is considered. In the feedwater controller (C), the time derivative of the power is considered. All the modified feedwater controllers keep the variation of the main steam temperature within 2°C, which has been achieved in recent supercritical coal-fired power plants, against typical load change. In order to further confirm the performance of the modified feedwater controllers, five typical perturbations are analyzed. All the feedwater controllers including the original one stably control the Super FR against all the perturbations without a significant oscillation or offset. Among them, the feedwater controller (B) gives a smaller or at least not larger variation of the main steam temperature compared with the original one at all the perturbations, while the feedwater controllers (A) and (C) give a larger variation in particular cases. From these results, it is concluded that the original feedwater controller is successfully improved as the feedwater controller (B).

Simulation of a Single Bubble Rising with Hybrid Particle-Mesh Method

A computational study of the dynamics on a gas bubble rising in a viscous liquid by a hybrid particle-mesh method is presented. The hybrid particle-mesh method has been developed for the simulation of a two-phase flow. One phase is represented by moving particles and the other phase is defined on a stationary mesh. The flow field is discretized by conservative finite volume approximation on the stationary mesh, and the interface is automatically captured by the distribution of particles moving through the stationary mesh. The moving particles are calculated by Moving Particle Semi-implicit (MPS) method. The effect of surface tension is evaluated by the continuum surface force model. In this study, we simulate the motion of a gas bubble rising in a viscous liquid. The buoyancy driven motion of the bubble in a wide range of flow regimes is simulated successfully by the present method. The deforming interface of the bubble is captured effectively by the moving particles although significant density and viscosity differences exist. By comparing the simulation results with experimental ones, we approve the possibility of applying the hybrid method to the two-phase flow with particles representing the gas phase and mesh representing the liquid phase.

LOCA Analysis of Super Fast Reactor

This paper describes loss of coolant accident (LOCA) analyses of the Supercritical-pressure Water-Cooled Fast Reactor (Super Fast Reactor). The features of the Super Fast Reactor are high power density and downward flow cooled fuel channels for the improvement of the economic potential of the Super Fast Reactor with high outlet steam temperature. The LOCA induces large pressure and coolant density change in the core. This change influences the flow distribution among the downward flow parallel channels. It will affect the safety of the Super Fast Reactor. LOCA analysis of Super Fast Reactor is important to understand the safety features of the Super Fast Reactor. Keeping the flow rate in the core is important for the safety of the Super Fast Reactor. In LOCA, it is difficult to maintain an adequate flow rate due to the once-through coolant cycle and the downward flow cooled fuel assemblies. Therefore, the early actuation of the Automatic Depressurization System (ADS) and reduction of the maximum linear heat generation rates of the downward flow seed fuel assemblies and Low-Pressure Core Spray (LPCS) system are necessary for the Super Fast Reactor to cool the core under LOCA. Analysis results show that the Super Fast Reactor can satisfy the safety criteria with these systems.

Numerical Simulation on Direct Contact Condensation of Single Bubble in Subcooled Water using MPS method

In present study, single steam bubble condensation in subcooled water have been simulated by using Moving Particle Semi‐implicit(MPS) method. The liquid phase was described using moving particles and the two phase interface was set to be movable boundary which can be easily traced according to the motion of interfacial particles. The transient bubble deformation behaviors have been obtained and the results showed that both initial bubble size and subcooled degree influence bubble deformation behaviors greatly. Larger bubble experiences more severe deformation at lower liquid subcooled degree while bubble keeps near sphericity at higher liquid subcooled degree. All transient shape sequences can be found and explained properly in Grace’s graphic correlation. This work exhibits some fundamental characteristics of bubble condensation using MPS‐MAFL which is expected to be further adopted to evaluate other complicated bubble dynamics problems.

THREE-DIMENSIONAL CORE DESIGN OF A SUPER FAST REACTOR WITH A HIGH POWER DENSITY

The SuperCritical Water-cooled Reactor (SCWR) pursues high power density to reduce its capital cost. The fast spectrum SCWR, called a super fast reactor, can be designed with a higher power density than thermal spectrum SCWR. The mechanism of increasing the average power density of the super fast reactor is studied theoretically and numerically. Some key parameters affecting the average power density, including fuel pin outer diameter, fuel pitch, power peaking factor, and the fraction of seed assemblies, are analyzed and optimized to achieve a more compact core. Based on those sensitivity analyses, a compact super fast reactor is successfully designed with an average power density of 294.8 W/cm3. The core characteristics are analyzed by using three-dimensional neutronics/thermal-hydraulics coupling method. Numerical results show that all of the design criteria and goals are satisfied.

Parallel Computation for Particle-Grid Hybrid Method

In this paper, parallel computational technology is used in the numerical analysis code of particle-grid hybrid method. Particle-grid hybrid method is a rising solution method to analyze two-phase flow problem. It has shown its ability in several two-dimensional simulations. However, when this method was used to predict the droplet entrainment ratio of annulus flow the calculation time was insufferable. When the droplet occurs in the gas core, the density field varying near the droplet is strenuous. The pressure correction equations are very hard to be convergence. Hence, the MPI (Message Passing Interface) library is chosen as the parallel technology to decrease the calculation time. The grid and particle calculation parts are paralleled, separately. Jacobi point iteration method and ADI (alternating direction implicit) combined with divide and flow line programming techniques for grid calculation are discussed. All the particles are divided into several groups depending on the processor number. Then several cases are set for testing the parallel efficiency. Generally, with four processors the efficiency is about 60%. If the processor number is more than four the parallel efficiency will decrease rapidly. This method can accelerate the hybrid method; however, it still needs improving. Finally, some droplet entrainment cases calculated by parallel code are summarized.Copyright

The Study of Hybrid Method in the Onset of Droplet Escaping From the Film

A particle-grid hybrid method for simulating the onset of droplet entrainment is described. The air and liquid phases are expressed by grid and particle separately. The effects of surface tension and wall adhesion are calculated by the continuum surface force model. The fluid film variation and the droplet disengaging procedure are analyzed. The onset of entrainment criterion is obtained and it has a good agreement with Ishii’s correlation. The influences of surface tension and gas phase density on the criterion are also studied. Several simulation flow fields are given for illustrating the efficiency of the method.Copyright