Summary of the OECD VVER-1000 MSLB benchmark results

Recent coupled code benchmarks have identified coolant mixing in the reactor vessel as an unresolved issue in the analysis of complex plant transients with reactivity insertion. This issue was one of the main topics in Phase 2 of the recently completed OECD VVER-1000 Coolant Transient Benchmark (V1000CT-2). Exercise 1 of this benchmark is a VVER-1000 V320 vessel mixing problem based on a steam generator isolation experiment at Kozloduy-6 in Bulgaria. Plant data are available for code validation. The validated codes can be used to calculate asymmetric MSLB transients involving similar mixing patterns. A variety of mixing models were tested including multi-1D with cross flow, coarse 3D and fine CFD.
This presentation summarizes a comparison of six submitted CFD results for the V1000CT-2 Exercise 1. The results were obtained with a specified CAD model of the real vessel geometry. Five participants used a solution region from vessel inlet to the core inlet. FZK solved the benchmark for the whole pressure vessel. The comparison is code-to-code and code to experiment. The results show good overall agreement with the experiment and between the codes as well as specific features depending on the turbulence model.