Blind Benchmark Predictions of Nacok Air Ingress Tests Using Computational Fluid Dynamics

MIT has been benchmarking Japanese and German NACOK air ingress tests using the FLUENT code for approximately three years [1]. The first benchmark study was for Japan Atomic Energy Research Institute’s (JAERI) isothermal and non-isothermal experiments [2] which investigate molecular diffusion of N2, and He under isothermal and natural circulation conditions, respectively. Another set of benchmark studies [3] was performed for JAERI’s multi-component experiment which examines the combined effects of natural convection and air ingress, graphite oxidation, diffusion of gas mixture consisting of O2, CO, CO2, N2, and He, and multi-component chemical reactions. This work demonstrated that the three fundamental physical phenomena of diffusion, natural circulation and then chemical reactions can be effectively modeled using computational fluid dynamics. The NACOK test facility at the Julich Research Center has run several experiments over the past three years. The first was a series of natural circulation experiments [4] conducted in air which employed a hot and cold channel with ceramic pebbles. MIT was able to successfully benchmark its FLUENT methodology against these tests with good results. The latest series of tests conducted at the NACOK facility were two graphite corrosion experiments: The first test consisted of an open chimney configuration heated to 650oC with two pebble bed zones of graphite pebbles. The second test is a similar test with cold leg adjacent to the hot channel with an open return duct below the hot channel. Natural circulation, diffusion and graphite corrosion were studied for both tests. Using and adapting previous computational methods, MIT is using the FLUENT code to model these air ingress events in a blind test of the methodology. The objective is to compare these blind test predictions with the actual data and modify the model to improve predictive capability to develop a benchmarked analysis capability and improve understanding of the phenomenon during an air ingress event. Copyright © 2006 by HTR2006 1