CASL

Science and Technology

Initial Modeling and Analysis of the Departure from Nucleate Boiling Challenge Problem

Yixing Sung, Jin Yan, Zeses E. Karoutas of Westinghouse Electric Company LLC
Anh V. Bui, Hongbin Zhang of Idaho National Laboratories
Nam Dinh of North Carolina State University

Departure from Nucleate Boiling (DNB) is one of the safety-related Challenge Problems (CP) that CASL is addressing in support of Pressurized Water Reactor (PWR) power uprate, high fuel burnup and plant lifetime extension. A CASL team of researchers and engineers from the national laboratories, universities and the industry has completed initial modeling and assessment of selected PWR rod bundle DNB test data. The work completed as part of the initial assessment included:

  • Two databases of the rod bundle mixing and DNB tests simulating PWR fuel designs with mixing vane (MV) and non-mixing vane (NMV) grid spacers (Figures 1a and 1b) have been identified and selected for CASL use.
  • The initial data review has concluded that the MV grid database is potentially useful and suitable for calibration, validation, and uncertainty quantification (CVUQ) of the modeling and simulation capabilities currently being developed for the DNB Challenge Problem as well as of the VERA one-dimensional and subchannel thermal hydraulics models.
  • Models and solutions of the baseline subchannel code VIPRE-W and Computational Fluid Dynamics (CFD) code STAR-CCM+ have been generated and comparisons with the available mixing test data have been made. These models and solutions represent the current industrial capability for DNB simulation and analysis. The coolant temperature distributions from the CFD simulation are shown in Figures 2a and 2b.
  • Developmental versions of the VERA transient subchannel code COBRA-TF have been applied to the DNB analyses. The COBRA-TF predictions of the local fluid parameters relevant to DNB are in good agreement with both the available test data and the corresponding VIPRE-W predictions as shown in Figures 3a and 3b.

The knowledge gained from this initial work is helping to define a viable roadmap and an implementation plan for the CASL DNB CP.


Figures 1a and 1b – Mixing Vane (MV) and Non-Mixing Vane (NMV) Grid Spacers for DNB Tests


Figure 2a & 2b – CFD Simulation of Subchannel Coolant Temperature Radial and Axial Distributions


Figure 3a & b – Comparison of Subchannel Axial Flow and void fraction between VIPRE-W (VIP) and COBRA-TF (CTF)

Source:  ORNL