ermsar 2012, cologne march 21 – 23, 2012 mcci pool temperature and viscosity: a discussion of the...

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 – 91052 Erlangen - Germany


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


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:

)( intTTh bulkconv

22.0

136.03

Pr67.19

g

jNu GM

int364.0408.0636.022.1

408.0408.022.05.0592.0356.0

67.19T

g

hcT

c

Gdecppool


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

int364.0408.0636.022.1

408.0408.022.05.0592.0356.0

67.19T

g

hcT

c

Gdecppool

int636.0592.0356.0)( TTaT cpoolpool

int592.0356.0 ),()( TxTTaT concpoolpoolpool

T

η

Timmobilization Timmobilization

refractory corium

less refractory corium


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

t0

t1 = t0 + Δt

t2 = t0 + 2Δt

t3 = t0 + 3Δt

Small-scale 2D MCCI Large-scale 2D MCCI


Step 2: assessment of the evolution of the « controlling »thermo-hydraulic properties at small and

large scale (2/3)

t0

t0 + Δt

t0 + 2Δt

t0 + 3Δt

T0T1T2T3

η1

η2

η3

η0

small-scale MCCI

large-scale MCCI

T0*T1*T2*T3*

η1*

η2*

η3*

η0*

timet0 t1 t2 t3

T0

T1T2T3

T1*T2*T3*

Temperature

large-scale MCCI

small-scale MCCI

int592.0356.0 ),()( TxTTaT concpoolpoolpool


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!


Step 3: Verification of the predictions on various MCCI test resultsSmall 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!


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: (1900-1750)/75~2 K/min

– CCI-3: (2000-1750)/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 resultsLarge 2D MCCI (2/3)


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: (2200-2100)/75~1.3 K/min

– M4: no significant decrease before flooding (t=24 min)

In line with our predictions


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


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): 1.5-3 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!

Spreading Compartment

Core Catcher Melt PlugMelt Discharge Channel Protective Layer

IRWST

Sacrificial Material

Protective Layer

Sacrificial Material


Thank you for your attention!

Questions?

ermsar 2012, cologne march 21 – 23, 2012 mcci pool temperature and viscosity: a discussion of the...

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