Development of FCI simulation code JASMINE. 1. Premixing

JASMINE is an FCI simulation code developed in the framework of ALPHA Program at JAERI. Two modules, JASMINE-pre and -pro, have been developed separately for the simulation of the premixing and explosion processes, respectively. Whole process of steam explosions will be analyzed using the two modules in tandem. The developmental work of the -pre module started in 1994 and presently the model assessment and improvement is under way. In simulating the experiments using zirconia particles, JASMINE-pre reproduced the behavior of the cold particles relatively well, but badly underestimated the sinking velocity of hot particles. Large scale vapor channel experimentally observed was not seen in the simulation result. This result indicated that present modeling of the water-vapor friction and the flow regime needs further examination and improvement to correctly handle the strong counter current flow which is likely to occur and have a strong influence in the premixing process. The steam generation volume was reproduced well with the initial water temperature set at 372.5K as reported, although the result was very sensitive to the initial water temperature setting. The sensitivity of the sinking velocity and steam generation on the drag coefficient for the particles was not strong. Simulation of the large scale corium jet-water interaction experiment FARO-L14 at JRC Ispra in 1994 was performed to assess the models. The qualitative behavior of the pressure history was significantly improved by using the jet model compared with the case using the originally installed particle breakup model. Also the results became much less sensitive to the empirical constant in the model. However, leading edge progression, energy distribution to water and vapor etc. were not reproduced well due to immaturity of the water-vapor heat transfer model and also due to the present framework of the code, that is the jet column and entrained droplets are handled in a single field. (J.P.N.)