Title: Advanced boiling twophase flow modeling: A major challenge for nuclear industry
1Advanced boiling two-phase flow modeling A
major challenge for nuclear industry
- A. Guelfi, O. Marchand (EDF RD)R. Assedo, L.
Catalani (AREVA-NP)
2Overview
- Two major stakes safety and competitiveness
- Design and safety studies
- RD challenges for boiling flow modeling
- A major challenge DNB prediction
31. Safety and Competitiveness
4Safety of NPPs
- THE HIGHEST PRIORITY
- FOR EVERY POWER PLANT, AT ANY TIME
- Safety criteria are fulfilled
- Safe operation of the plant is guaranteed by
design and monitoring procedures - NUCLEAR SAFETY 2 basic principles
- Successive barriers (fuel cladding is the first
one) - Defence in depth
5Competitiveness of NPPs
- Thermal Efficiency of main components (core,
exchangers) - Optimized power density and distribution
- Optimized heat transfer mechanisms (primary,
secondary, cooling) - Mechanical resistance of main components
- Irradiation, corrosion, vibrations, thermal
fatigue, etc. - Two major challenges
- PLANT AVAILABILITY (Kd)
- plant LIFETIME EXTENSION (40 years and beyond)
- Maintenance costs savings
6Competitiveness of NPPs
- A key issue fuel design and management
- Overall optimization for the complete nuclear
fuel cycle - Reduction of fuel design/construction/supply
costs - A more and more flexible fuel management
different fuel assembly types, different vendors
within one reactor core - High efficiency fuel assemblies
- High local power density plant power uprates
- High burn-up cycle extension, reduction of fuel
reload costs
72. Design and Safety studies
8Design and Safety studies
- Numerous new studies are required
- Existing NPPs
- Fuel management evolution (reloads)
- Lifetime extension
- Evolution of the tools and methodologies
- New NPPs design and construction of new
reactors - Worldwide Nuclear Renaissance (2008 30 reactors
under construction 90 new projects ! 40
non-nuclear countries have declared their
interest to AEIA) - Among them
- EPR Finland first-off reactor, France, US,
China, South Africa, etc - BWRs
9Design and Safety studies
- Advanced simulation tools and methodologies
- Handling normal operation and accidental
conditions - Covering multi-disciplinary coupled physics,
including 3D thermal-hydraulics - In-depth physical and numerical validation a
prerequisite for Industrial qualification with
uncertainty analysis - Improved physics more accurate and predictive
models - Enhanced safety
- Reduction of excessive conservatisms
10Design and Safety studies
113. RD challenges for two-phase flow modeling
12Two-phase flow modeling challenges (see Guelfi et
al., Nuclear Science and Engineering, 2007)
- Nuclear Thermal-Hydraulics
- Industrial simulation tools
- From macroscopic to local modeling scales
- Different levels of maturity/qualification
13Two-phase flow modeling challenges
- Component and system scales
- Improved models and closure terms, validation
against new experiments - Extension of the qualification scope (e.g.
CATHARE 3) - The advent of CMFD
- Improved knowledge of local flow phenomena is a
key issue for numerous design and safety issues
- Fuel design (spacer grids) local wall-to-fluid
heat transfer, flow mixing, etc. - Crud Deposition local flow interaction with
chemical processes - SG Tube vibrations Fluid-Structure Interaction
in high void fraction 2-phase flow - Etc.
- Fuel management evolution (reloads)
- Lifetime extension
- Evolution of the tools and methodologies
- New NPPs (Gen III, III) design and construction
of new reactors - EPR Finland first-off reactor, France, US,
China, South Africa, etc - BWRs
14Two-phase flow modeling challenges
- The need for validated CMFD tools
- Wall-to-fluid and interfacial transfers must be
correctly predicted - In industrial complex geometries
- Under real thermal-hydraulic conditions
(primary/secondary circuits) - High pressure and temperature
- High turbulence level
- From bubbly to churn turbulent flow
( all-flow-regime tools)
15Two-phase flow modeling challenges
- The NEPTUNE initiative a first step !
- Joint development of NEPTUNE_CFD code
- Physical modeling and experiments
- NURESIM-NURESP European Projects international
collaboration - Collaborative research on CFD-scale two-phase
flow modeling in connection with the industrial
needs (including DNB and dry-out) - CMFD are still based on averaged models
- Understanding of local flow phenomena is required
- Closure terms must be developed/validated
- Significant progress is now expected from very
fine experimental investigation and Direct
Numerical Simulation
164. A major challenge DNB prediction
17A major challenge DNB prediction
- DNB-type CHF prediction still a challenge !
- Competition of numerous microscopic and
mesoscopic scale phenomena - Basic physics not fully understood after decades
of RD... - Current methodologies are very expensive
- Numerous representative CHF experimental data
banks are required - CHF predictors are based on empirical
correlations - CHF studies rely on subchannel-type 3D TH codes
- Statistical methodologies are needed to account
for different sources of uncertainties
18A major challenge DNB prediction
- DNB CFD-based Local Predictive Approach (LPA)
- LPA concept (introduced by EDF, late 90s)
- Development of more general CHF predictors based
on the local flow parameters - A 3-step strategy
- Get a reliable and accurate two-phase flow CFD
tool, with respect to PWR core geometrical and TH
configurations. Improved physical models are
still needed ! - Select adequate CHF data banks and CFD-simulate
the associated experiments to create numerical
data bases - Develop a CHF local correlation on a reference
data bank and further assess its validity against
other data banks - STEP 1 is one of the current major challenges of
the nuclear TH community
195. Conclusion
20- Computing Power is (almost) ready
- Movie
- EDF Code_Saturne calculation
- real geometry real PWR TH conditions
- 100 M nodes, 8000 processors
- We need more predictive C(M)FD models !