1. Bulatom Confernce 06-08 June 2007
Evaluation of the flow mixing in VVER-1000 downcomer under natural circulation.
V. Lefterov, E. Popov
Atoma Consult Ltd
Bulatom Conference May 2008
Atoma Consult Ltd

2. Reasons for fluid mixing evaluation in a reactor downcomer:
Bulatom Confernce June 2007
Reasons for fluid mixing evaluation in a reactor downcomer:
risk of over-criticality in a local volume of the reactor core by low boron concentration
risk of over-criticality in a local volume of the reactor core by low coolant temperature
risk of local pressurized thermal shock (PTS) on the reactor vessel wall
Bulatom Conference May 2008
Atoma Consult Ltd

3. Evaluation of flow mixing – How to?
Bulatom Confernce June 2007
Evaluation of flow mixing – How to?
large scale transparent model experiments
large scale model experiments, using a lot of sensors in the facility
Residence Time Distribution (RTD) method
three dimensional computational fluid dynamics (CFD) calculations.
Bulatom Conference May 2008
Atoma Consult Ltd

4. CFD model – developed by Atoma Consult Ltd
Bulatom Confernce June 2007
CFD model – developed by Atoma Consult Ltd
Two mutually independent components:
Mesh – represents the geometrical characteristics of the investigated volume;
Solver – implements the mathematical apparatus, applied in the analysis.
Bulatom Conference May 2008
Atoma Consult Ltd

5. Investigated scenario
Bulatom Confernce June 2007
Investigated scenario
Boundary conditions – Main Steam Line Break (MSLB) on loop 2
Calculations with RELAP5/mod3.3;
Conservative initial and boundary conditions;
Sensitivity study – failure of EFW and FAIV;
Results: FAIV failure creates larger temperature difference (80 oC).
Bulatom Conference May 2008
Atoma Consult Ltd

6. Initial and boundary conditions
Bulatom Confernce June 2007
Initial and boundary conditions
Table I – Initial and boundary conditions for the CFD calculations
Bulatom Conference May 2008
Atoma Consult Ltd

7. Bulatom Confernce 06-08 June 2007
Calculation results I
Figure I – Velocity distribution
Bulatom Conference May 2008
Atoma Consult Ltd

8. Calculation results II
Bulatom Confernce June 2007
Calculation results II
Figure II – Velocity stream lines
Bulatom Conference May 2008
Atoma Consult Ltd

9. Calculation results III
Bulatom Confernce June 2007
Calculation results III
Figure III – Temperature distribution in the downcomer and the core inlet
Bulatom Conference May 2008
Atoma Consult Ltd

10. Calculation results IV
Figure IV– Loop 2 flow mixing in the downcomer and the core inlet
Bulatom Conference May 2008
Atoma Consult Ltd

11. Calculation results IV
Bulatom Confernce June 2007
Calculation results IV
Figure V – “Cold spot” rotation in the core inlet
Bulatom Conference May 2008
Atoma Consult Ltd

12. Bulatom Confernce 06-08 June 2007
Sensitivity study
Table II – Loop inlet velocities for the sensitivity study
Bulatom Conference May 2008
Atoma Consult Ltd

13. Sensitivity study – results I
Bulatom Confernce June 2007
Sensitivity study – results I
Figure VI – “Cold spot” rotation in the core inlet for the high velocity case
Bulatom Conference May 2008
Atoma Consult Ltd

14. Sensitivity study – results II
Bulatom Confernce June 2007
Sensitivity study – results II
Figure VII – “Cold spot” rotation in the core inlet for the medium velocity case
Bulatom Conference May 2008
Atoma Consult Ltd

15. Sensitivity study – results III
Bulatom Confernce June 2007
Sensitivity study – results III
Figure VIII – “Cold spot” rotation in the core inlet for the forced circulation case
Bulatom Conference May 2008
Atoma Consult Ltd

16. Sensitivity study – summary
Bulatom Confernce June 2007
Sensitivity study – summary
Table III – Summary on the sensitivity study results
Bulatom Conference May 2008
Atoma Consult Ltd

17. Bulatom Confernce 06-08 June 2007
Conclusions
Selected scenario – MSLB on VVER-1000
Boundary conditions – RELAP5/mod3.3;
Flow mixing and rotation – CFD calculations;
Applied software and models are adequately verified and validated;
Results:
Relatively small core inlet area (~5%) from the quarter fed by the broken loop inlet is with very low ( %) mixing coefficient;
The flow rotation is independent of the velocities magnitudes at constant “intact/damaged” loops velocity ratio;
The flow rotation depends strongly on the “intact/damaged” loops velocity ratio;
Results can be finally validated against large scale model experiments.
Bulatom Conference May 2008
Atoma Consult Ltd