CHF flow regime map

1
CHF flow regime map

• Establishment of flow regime map at CHF relevant
  to PWR (and BWR) conditions
• Requires meso-scale visualization at high
  pressure
• High heat flux, near CHF conditions
• Whole range of operating conditions must be
  investigated since flow regime may change
• Simultaneous high-speed temperature measurements

2
Micro-scale physics of CHF

• Choice of phenomena to be investigated based on
  results from meso-scale observations
• Individual nucleating bubble
• Nucleation beneath bubbly layer
• Boiling in thin convective film
• Perform well controlled experiments up to CHF
• Observe wall boiling event and/or transient wall
  temperature distribution
• Investigate wall effects
• Numerical simulation interfacial tracking
  coupled with multi-dimensional transient heat
  conduction

3
Objective of CHF modeling 4 levels

• Fundamental understanding of the events
• Resolve (up to) all relevant scales
• Experimental numerical applications to simple
  setup
• Reliable CHF comparison performance
• Help in selecting fuel (mixing vane) design
• One-time (pre-CHF test) numerical analysis
• Reliable CHF prediction performance
• Extrapolation and interpolation capability
• Extend CHF database
• Fast reliable CHF prediction performance
• Execution speed uncertainties similar to
  current empirical approach
• Replacement of CHF correlations

Execution time
Practicality
4
Needed work in this area

• High pressure DNB visualizations are needed
• Simple geometry (tube) is sufficient
• Observe/categorize two-phase flow pattern(s)
• Issue Experimental difficulties
• Identification using Flow regime map (We/x)
• Next step void measurement in full-scale DNB
  facility
• Check consistency w/ previous experiments
• Lower time resolution

5
Hypothetical CHF flow regime map
6
Needed work in this area (contd)

• Identification of relevant two-phase flow regimes
  under PWR conditions is the 1st necessary step
• Provide framework for lower scale experiments and
  computations
• High resolution visualization (and wall
  temperature measurements) may provide useful
  clues
• DNB event still remains hypothetical at this
  level
• Lower scale investigation is the 2nd necessary
  step

7
Past experimental work and needs

• Such investigations has been performed under slug
  flow and pool boiling
• Very insightful results were found
• Much more experimental work is needed
• to cover the whole range of LWR application
• Before making further hypothesis regarding the
  DNB event