ERMSAR 2012, Cologne March 21 – 23, 2012 MOCKA Experiments on Concrete Erosion by a Metal and Oxide Melt J. J. FOIT, T. CRON, B. FLUHRER, A. MIASSOEDOV, T. WENZ Karlsruhe Institute of Technology, Germany (KIT)

ERMSAR 2012, Cologne March 21 – 23, 2012 Behaviour of Concrete under Thermal Load Decomposition of concrete during heat-up starts with evaporation of physically bound water around 100°C. Dehydration of chemically bound water occurs up to 550°C. Decarbonation of CaCO 3 from the cement and carbonate aggregates occurs from 700 to 900°C. Consequently, loss of mechanical and thermal strength. Liquid phases start to form between °C.

ERMSAR 2012, Cologne March 21 – 23, 2012 MOCKA experiments Melt: 39 kg Fe (collapsed melt height: 13 cm) and 70 kg oxide (initially Al 2 O 3, CaO): (MOCKA 1.1, 1.2; 1-dim and MOCKA 1.3; 2-dim), (MOCKA 1.4 with 3 kg Zr at the bottom of the crucible to avoid the outcome of the MOCKA 1.2 test (Fig. 2)!; 2-dim). Initial melt temperature ~ 1900 °C. Siliceous cylindrical crucible with 25 cm inner diameter. Experimental findings: MOCKA 1.1: 3 cm axial erosion. MOCKA 1.2: Compact metal layer embedded in a ~ 0.2 mm thick oxide layer (never seen before)  no detectable concrete erosion.

ERMSAR 2012, Cologne March 21 – 23, 2012 Oxidation behaviour Fig. 1: Time dependent composition of oxide and metal melts in BETA V 5.2.

ERMSAR 2012, Cologne March 21 – 23, 2012 Fig.2: Section of the MOCKA 1.2 crucible.

ERMSAR 2012, Cologne March 21 – 23, 2012 Fig. 3: Section of the MOCKA 1.4 crucible. MOCKA 1.4: Axial erosion: 2,5 cm. Lateral erosion: 1.5 cm: ratio ~ 1.7. Approx. 2.5 cm thick mechanically unstable concrete layer due to long-term thermal load. Remelting of the melt would lead to a fast concrete “erosion”!

ERMSAR 2012, Cologne March 21 – 23, 2012 Fig. 4: MOCKA 1.3 centerline concrete temperatures.

ERMSAR 2012, Cologne March 21 – 23, 2012 MOCKA 1.5: Initial 3 kg Zr not at the bottom. ejection of approx. 49 kg Al 2 O 3 during the thermite reaction leading to low tempe- rature of the oxide melt (crust formation at 4 min after thermite ignition). Rather small fraction of the added 8.3 kg Zr (start at 1 min, end at 4 min after ignition) was oxidized, Fig. 3.b. Axial erosion: 2,5 – 3 cm Lateral erosion: cm, ratio ~ 2-3. Fig. 5: Section of the MOCKA 1.5 crucible with unmelted Zr tubes.

ERMSAR 2012, Cologne March 21 – 23, 2012 Fig. 6: Section of the MOCKA 1.3 crucible (without Zr). Axial erosion ~1 cm. Lateral erosion ~0.5 cm.

ERMSAR 2012, Cologne March 21 – 23, 2012 MOCKA kg thermite (→ 42 kg Fe + 38 kg Al 2 O kg CaO - 17 kg losses from the oxide phase) with 4 kg Zr at the bottom of the crucible; T in ~ 2193 K. After the completion of the thermite reaction alternating additions of thermite and Zr. Total added masses: 63 kg thermite and 24 kg Zr within approx. 11 minutes. MOCKA 1.7 Total added masses: 117,5 kg thermite and 34 kg Zr within approx. 18 min.

ERMSAR 2012, Cologne March 21 – 23, 2012 Fig. 7: Section of the MOCKA1.6 crucible. Max. concrete erosion: Metal: axial 10 cm, lateral 5 cm; Oxide: lateral 4,5 cm. Significant concrete erosion by the oxide melt: approx. 9 l (E dec = 41 MJ). V er (met.)~ 9 l (E dec = 41 MJ). Oxidation of 1 kg Zr with SiO 2 + H 2 O + CO 2, released from approx. 0.8 kg eroded concrete; ~0.74 cm axial erosion, generates ~3.07*10 6 J mainly in the oxide phase. The Zr+SiO 2 gives 0,26 kg Si. The subsequent oxidation of that Si amount delivers 7.9*10 6 J. The thermite reaction of 1 kg gives kg Fe with 7.5*10 5 J and kg Al 2 O 3 with 1.5*10 6 J.

ERMSAR 2012, Cologne March 21 – 23, 2012 Max. concrete erosion: Metal: axial 15 cm, lateral 6,5 cm; Oxide: lateral 5 cm. Significant concrete erosion by the oxide melt: approx. 17 l (E dec = 76 MJ). V er (met.)~ 15 l (E dec = 69 MJ). Fig. 8: Section of the MOCKA1.7 crucible.

ERMSAR 2012, Cologne March 21 – 23, 2012 Conclusions Destruction of the concrete structure at low heat fluxes. BETA/COMET like ratio of axial to lateral concrete erosion by a metal melt for a siliceous concrete. Significant lateral concrete erosion by the oxide melt (not observed in BETA/COMET experiments). Possible future tests: Study of the MCCI on a siliceous concrete with rebars. Investigate the concrete ablation ratio in rectangular, half-cylinder and inverse crucibles.