Kenta Inagaki

Early construction and operation of the highly contaminated water treatment system in Fukushima Daiichi Nuclear Power Station (III) – a unique simulation code to evaluate time-dependent Cs adsorption/desorption behavior in column system

A simulation code was developed to evaluate the performance of the cesium adsorption instrument operating in Fukushima Daiichi Nuclear Power Station. Since contaminated water contains seawater whose salinity is not constant, a new model was introduced to the conventional zeolite column simulation code to deal with the variable salinity of the seawater. Another feature of the cesium adsorption instrument is that it consists of several columns arranged in both series and parallel. The spent columns are replaced in a unique manner using a merry-go-round system. The code is designed by taking those factors into account. Consequently, it enables the evaluation of the performance characteristics of the cesium adsorption instrument, such as the time history of the decontamination factor, the cesium adsorption amount in each column, and the axial distribution of the adsorbed cesium in the spent columns. The simulation is conducted for different operation patterns and its results are given to Tokyo Electric Power Company (TEPCO) to support the optimization of the operation schedule. The code is also used to investigate the cause of some events that actually occurred in the operation of the cesium adsorption instrument.

Improved models of surface tension and air resistance for multiphysics particle method

ABSTRACT A multiphysics particle method is being developed to simulate the dynamic behaviors of fluid and solid involving their freezing and melting which occur in a severe accident at a nuclear reactor. So far, the conventional particle method code for fluid dynamics has been expanded so that thermodynamics, melting, and freezing can be treated. In this study, new models for the surface tension and air resistance were developed. The developed surface tension model is based on the potential model, where the magnitude of the normal force to the surface is corrected to agree with the theoretical value. A simulation of droplet collisions was conducted to verify the developed model. The simulation results were compared with experimental results and their good agreement was confirmed. The developed air resistance model is based on the assumed pressure distribution around a sphere located in an air stream, hence, the direct simulation of the air phase is not necessary, reducing the computational time. The breakup of a droplet in air was simulated for verification and it was confirmed that reasonable results are obtained using the developed model when the parameters of the analysis object are appropriately chosen.