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Stratification and Mixing of Boron

Stratification and Mixing of Boron

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Stratification and Mixing of Boron

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  1. Stratification and Mixing of Boron E. Krepper 4th NC IAEA Research Coordination Meeting Vienna, Sept. 10th-13th 2007

  2. Relevance of the problem • Tanks filled with borated water designed to flood the core under emergency situations • accumulators with pressurized gas • elevated tanks • Precondition for the function: Well mixed water/boron acid • During the filling procedure stratification might occur caused by density difference • This stratification cannot be disturbed by passive phenomena • Only few experiments and theoretical investigations directed on this particular application • In FZD lots of experience exists concerning boron mixing and stratification phenomena in the primary circuit

  3. Boron mixing and stratification phenomena in the primary circuit • Formation of boron diluted slugs • Onset of slug motion • Slug mixing and transport

  4. Formation of boron diluted slugs Main relevant issues: • turbulent mixing in forced flow • buoyancy induced turbulent mixing and stratification • significance of large-scale swirls • turbulence under accelerating and Low-Re flow conditions • flow distribution to the idle loops • influence of the geometry and of internal structures (sieve plates etc.)

  5. Buoyancy induced turbulent mixing • natural circulation conditions • density differences • stratification of the boron concentration • relation of momentum and density controlled forces described by the Froude Number: • Momentum driven flow: Fr >> 1 • Buoyancy driven flow: Fr << 1 Vin – inlet velocity g – gravity acceleration H – height extension ra, rin – fluid densities

  6. Test facilities • Vattenfall mixing test facility • VVER-1000 mixing test facility at EDO Gidropress • FORTUM test facility • ROCOM facility at FZ-Dresden

  7. Code capabilities • Adequate simulation requires the application of CFD models • CFD successful calculating momentum driven flows • Deficiencies at buoyancy driven flow situations • Similarities to simulation of natural circulation and temperature stratification phenomena in large pools