ERMSAR 2012, Cologne March 21 – 23, 2012 MCCI pool temperature and viscosity: a discussion of the impact of scale A. Fargette AREVA NP GmbH, Paul-Gossen Strasse 100 – Erlangen - Germany

ERMSAR 2012, Cologne March 21 – 23, 2012 Structure of the presentation Step 1: Identification of the thermo-hydraulic pool properties which have a large influence of the pool temperature Step 2: Assessment of how these « controlling » thermo- hydraulic pool properties evolve during an MCCI at small and large scale and deduction of trends for both scales Step 3: Checking of these theoretical predictions on existing MCCI test results Step 4: Extrapolation of trends to the reactor scale

ERMSAR 2012, Cologne March 21 – 23, 2012 Step 1: identification of the « controlling » hydraulic pool properties (1/2) Heat flux density to the concrete: Insertion of the BALI correlation to express h: Obtained temperature law:

ERMSAR 2012, Cologne March 21 – 23, 2012 Step 1: identification of the « controlling » hydraulic pool properties (2/2) We are interested in the hydraulic properties which may vary due to concrete ablation and hence induce a temperature variation T η T immobilization refractory corium less refractory corium

ERMSAR 2012, Cologne March 21 – 23, 2012 Step 2: assessment of the evolution of the « controlling » thermo-hydraulic properties at small and large scale (1/3) Same initial corium composition Same initial heat flux density to concrete walls Same initial temperature t0t0 t 1 = t 0 + Δ t t 2 = t Δ t t 3 = t Δ t Small-scale 2D MCCI Large-scale 2D MCCI

ERMSAR 2012, Cologne March 21 – 23, 2012 Step 2: assessment of the evolution of the « controlling »thermo-hydraulic properties at small and large scale (2/3) t0t0 t 0 + Δ t t Δ t t Δ t T0T0 T1T1 T2T2 T3T3 η1η1 η2η2 η3η3 η0η0 small-scale MCCI large-scale MCCI T 0* T 1* T 2* T 3* η 1* η 2* η 3* η 0* time t0t0 t1t1 t2t2 t3t3 T0T0 T1T1 T2T2 T3T3 T 1* T 2* T 3* Temperature large-scale MCCI small-scale MCCI

ERMSAR 2012, Cologne March 21 – 23, 2012 Step 2: assessment of the evolution of the « controlling »thermo-hydraulic properties at small and large scale (3/3) Pool can be characterized by an (η, φ, T) triplet Both MCCIs travel through the same (η, φ, T) states but at different paces – Reason: Scale-independent relative increase in pool volume (which determines the concrete content and hence the η(T) curve) with surface area (which determines φ) – Example: doubling of pool volume due to concrete ablation leads to the same relative increase in wetted concrete surface, regardless of scale (if pool aspect ratio kept constant) Consequences: – Identical temperature asymptote expected for both curves – Possibility to make blue and red curves identical by shrinking the time-scale of the blue curve!

ERMSAR 2012, Cologne March 21 – 23, 2012 Step 3: Verification of the predictions on various MCCI test results Small 2D MCCI (1/3) Small 2D MCCI tests: VBU-7 tests – Semi-cylinder (radius = 15cm) – Corium mass ~ a few dozen kg Temperature drop from 2250°C to 1550°C in 75min ~ 9K/min Long-term stabilization of temperature: in line with our predictions!

ERMSAR 2012, Cologne March 21 – 23, 2012 Large 2D MCCI tests: CCI tests 2 & 3 – Square crucible (50cm*50cm) – Corium mass ~ several hundred kg We expect a smaller T drop rate due to higher concrete initial mass Temperature derease rate during first 75min: – CCI-2: ( )/75~2 K/min – CCI-3: ( )/75~3.3 K/min Comparison with VB-U7: in line with our predictions: – CCI-2: 9 K/min >2 K/min – CCI-3: 9 K/min > 3.3 K/min Step 3: Verification of the predictions on various MCCI test results Large 2D MCCI (2/3)

ERMSAR 2012, Cologne March 21 – 23, 2012 Step 3: Verification of the predictions on various MCCI test results (3/3): Large 1D MCCI Large 1D MCCI tests: MACE tests M-3b and M-4 – Square crucible (up to 120cm*120cm) – Corium mass ~ up to 2 tons We expect a smaller T drop rate due to higher concrete initial mass and 1D configuration (constant wetted surface area) Temperature decrease rate before flooding: – M-3b: ( )/75~1.3 K/min – M4: no significant decrease before flooding (t=24 min) In line with our predictions

ERMSAR 2012, Cologne March 21 – 23, 2012 Step 4: Extrapolation to reactor scale (1/2) Reactor-scale MCCI characterized by : – Very large corium mass (up to >100 tons) – Large 2D cylindrical pool geometry (R ~ several meters) Consequences: – Slow increase of the concrete content (η(T) curve changes slowly) – Very slow increase of the wetted concrete surface area (φ drops very slowly due to surface effects) Conclusion: – Very slow and gradual drop of the temperature expected  MACE results are initially representative  In the long term, temperature plateau as in VBU tests

ERMSAR 2012, Cologne March 21 – 23, 2012 Step 4: Extrapolation to reactor scale (2/2) The case of the EPR™ MCCI characterized by: – Very large corium mass (>150 tons of core oxides) – Limited amount of sacrificial concrete (50cm): hrs of MCCI depending on decay power Expected temperature trend on the basis of previous discussion: – Slow gradual temperature decline – MACE results relevant – Temperature readings of small 2D tests are not appropriate here!

ERMSAR 2012, Cologne March 21 – 23, 2012 Thank you for your attention! Questions?