Investigation of rotating mode behavior in BWR out-of-phase limit cycle oscillations – Part 2: TRACE/PARCS model and physical explanation

Journal Article · Thu Sep 13 00:00:00 EDT 2018 · Annals of Nuclear Energy (Oxford)

DOI:https://doi.org/10.1016/j.anucene.2018.08.033· OSTI ID:1481707

Wysocki, Aaron J. ^[1]; Manera, Annalisa ^[2]; Downar, Thomas ^[2]; March-Leuba, Jose ^[3]

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1. Oak Ridge National Lab. (ORNL), Oak Ridge, TN (United States)
2. Univ. of Michigan, Ann Arbor, MI (United States)
3. MRU, Knoxville, TN (United States)

Previous neutronic/thermal-hydraulic (TH) coupled numerical simulations using full-core TRACE/PARCS and SIMULATE-3K boiling water reactor (BWR) models have shown evidence of a specific “rotating mode” behavior (steady rotation of the symmetry line, i.e. constant phase shift of approximately 90° between the first two azimuthal modes) in BWR out-of-phase limit cycle oscillations, regardless of initial conditions and even if the first two azimuthal modes have different natural frequencies. This suggests a nonlinear coupling between these modes; otherwise, the phase shift between these modes would change at a constant rate during the limit cycle. The previous paper (“Part 1”) presented a series of results to examine this rotating behavior with a reduced-order model. The goal of the present study is to provide additional analyses of the predicted rotating mode behavior using higher-fidelity numerical modeling, as well as a physical explanation for why this mode is favored over side-to-side or other oscillatory behaviors from a TH perspective. Results are presented using TRACE and TRACE/PARCS for a small number of parallel channels, which confirmed that the conclusions developed from the reduced-order model remain applicable when applying a full two-fluid, six-equation, finite-volume modeling approach. From these results, a physical explanation has been put forth to explain why the rotating symmetry line behavior is preferred from a TH standpoint, demonstrating that predominantly out-of-phase unstable systems are most unstable when the variation in the total inlet flow rate is minimized (which minimizes the effective single-phase to two-phase pressure drop ratio) and that the rotating mode is the most successful in minimizing this total flow rate variation as compared with the side-to-side case or any other oscillation pattern. The conclusion is that the rotating mode will be favored for any out-of-phase unstable system of parallel channels with no neutronic feedback or relatively weak neutronic feedback. Here, previous analyses have indicated that systems with sufficiently strong neutronic coupling may favor the side-to-side oscillation mode over the rotating mode; this topic is left as a subject of future investigation.

• Research Organization: Oak Ridge National Laboratory (ORNL), Oak Ridge, TN (United States)
• Sponsoring Organization: USDOE
• Grant/Contract Number: AC05-00OR22725
• OSTI ID: 1481707
• Alternate ID(s): OSTI ID: 22834213
• Journal Information: Annals of Nuclear Energy (Oxford), Journal Name: Annals of Nuclear Energy (Oxford) Journal Issue: C Vol. 122; ISSN 0306-4549
• Publisher: Elsevier
• Country of Publication: United States
• Language: English

Related Subjects

22 GENERAL STUDIES OF NUCLEAR REACTORS
BWR stability
Limit cycle
Out-of-phase oscillations
Rotating mode
Time domain analysis