Preparation of the multidimensional two-phase flow analysis code for nuclear reactor safety regulation in Japan nuclear energy safety organization (JNES)

Full text of publication follows: It is desirable that many nuclear reactor safety problems, such as DNB, CHF, ECCS bypass, and SG tube vibration, are resolved by using the two-phase CFD tools, which simulate the complex two-phase flows with a finer space and time resolution than that used in the present system codes such as RELAP, TRAC, CATHARE, and ATHLET. Using such tools as part of a safety demonstration may bring better understanding of physical situations, more confidence in calculated results, and an estimation of safety margins. Japan Nuclear Energy Safety Organization (JNES) have started the project to prepare the two-phase CFD tool in 2004. The project includes the following three steps. (1) Compare the CFD codes available in JNES and select the optimum one, (2) Execute verification and validation studies for the selected code, (3) Apply the selected code to nuclear reactor safety problems. The VESUVIUS, ACE-3D, CHAMPAGNE, and FLUENT code having ability to simulate 3D two-phase flows are available in JNES so far. The 3D shape and temperature profile of a vapor jet injected in almost saturated water pool have been calculated by using those four codes and calculated results have been compared one another in order to select the optimum one. Since a 3D two-phase CFD calculation needs to solve many equations and treat strong interactions among those equations suitably in a lot of grids, fast running and high stability in numerical algorithm are the most important target for selection of the codes. Simple procedure for modification of the code to apply a wide variety of two-phase flows appeared in nuclear reactor safety is another important target. Of course small discrepancy between calculated results and test data is important factor for selection. (authors)