Development of analytical model for evaluating temperature fructuation in coolant(VIII); Development of a Monte Carlo direct simulation code THEMIS

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Thermal striping phenomena are characterized by stationaly random temperature fluctuations and observed in the region immediately above the core exit of LMFBRs due to the interactions of cold and hot sodium. To evaluate the phenomena, it is neccessary to consider a time-dependent heat transfer coefficient to structures from fluid, in the same manner as a evaluation of a stationaly temperature fluctuation in fluid. For this purpose, a computer program THEMIS (Time-dependent Heat transfer Evaluation by Monte Carlo Direct Simulation) has been developed for the thermohydraulic analysis based on the Boltzmann equation. A two-dimensional duct flow problem has been solved to check the fundamental performance of the THEMIS code. The main results are as follows: (1)Axial distribution of molecular velocity U has shown good agreement with the solution of the Navier-Stokes equation under the condition of Kn=0.0002. (2)An acceleration on the VP-2600 vector processor is about 12 times as the VP-2600 scalar processor. Future works of the THEMIS code development are (1)investigation of the applicabilities in a non-isothermal fluid system and in a complex geometry system and (2)verification with detailed experimental results.