Experimental Study of Core Melt In-Vessel Retention (INVECOR) - ISTC Project K-1265

1. ISTC project K-1265:Experimental study of core melt in-vessel retentionIN-VEssel COrium Retention (INVECOR) Presented by Vladimir Zhdanov IAE NNC RK 5th Eurasian conference “Nuclear science and its application”, October, 14 – 17, 2008 Ankara, Turkey

2. Presentation contents • Background • Main directions of work and results • Design of experimental section for INVECOR test • Major directions of LAVA-B facility modernization • Testing of Zr-coating technique on graphite surface • Creation of INVECOR test conditions • Test with one plasmatrons • Test section design (RPV model) • Conclusions

3. INVECOR project general information Collaborators Project participants and coordination IRSN, France ITU-JRC, EU CEA, France FZR,Germany Pisa University,Italy FZK, Germany Coordinator Steering committee ISTC, Moscow Operation Agent: IAE NNC RK, Kazakhstan

4. Background In vessel core degradation during the severe accident Metal/oxide stratification in the molten pool “Classical” representation In-vessel configuration with inverted metal stratification Schematic diagram of reactor core following TMI-2 accident MASCA observation

5. Test scenario using LAVA-B facility • Corium composition: UO2+ZrO2+Zr • Corium mass: up to 60 kg • Corium temperature: up to 3000 deg. C • Heating technique: induction heating in the “hot crucible” • Height of melt dropping: 1,7 m

6. Design of experimental section for INVECOR test External electrode Directing cone for corium discharge Thermal screen Gained power of single plasmatrons • Up to 16 kW with argon-gas • Up to 19 kW with nitrogen • Total power approx. 90 kW Maximum time of plasma burning - Up to 2,5 hours Coaxial plasmatrons (5 units) Internal electrode Graphite Plasmatrons nozzles Lower part of external electrode (protected with Zr) Corium pool RPV model (1:8) Wall thickness 50 mm Zone of electric arc burning Design of coaxial plasmatrons nozzles

7. Subtasks to be performed Graphite crucible coating Electric melting furnace Copper electrode design Facility pressure vessel Electrode nozzles design, testing and coating Experimental section RPV model design and calculation DAS improvement Major directions of LAVA-B facility modernization

8. Testing of protective coating on graphite surfaces (1) Main objective of coating – to prevent the interaction between graphite and corium component at high temperature Technique of coating consists in spreading of molten zirconium along the protected graphite surface with subsequent zirconium carbiding Surfaces to be protected are: • inner surface of the melting crucible • Outer surface of the external nozzle of the coaxial plasmatrons Graphite crucibles of different dimensions with protective coating on internal surface

9. Testing of protective coating on graphite surfaces (2) Corium C-30 Re-melting Corium C-30 Initial components Corium C-50 Initial components Corium C-30 Re-melting Results of protective coating testing against molten corium attack 2600 deg. C Time 30 minutes 2600 deg. C Time 40 minutes 2800 deg. C Time 60 minutes 2600 deg. C Time 90 minutes

10. Melting of UO2 2850C Melting of ZrO2 2690C 2600C Formation of ceramic U-Zr-O melt 2400C Formation of -Zr(O)-UO2 and U-UO2 monotectics Start of UO2 dissolution by molten Zircaloy – formation of metallic (U-Zr-O) melt Melting of -Zr(O) 1975C  1850C Melting of zirconium (by different authors) 1760C 1450C Melting SS+Zr eutectic 1420C Melting of stainless steel and Inconel Eutectics Fe–Zr formation 1300C Start of rapid Zircaloy oxidation by H2O – uncontrolled temperature escalation Eutectics Ni–Zr, formation 1200C First eutecticsNi–Zr, Fe–Zr formation 940C Creation of INVECOR test conditions (1) Temperature of corium/steel interface should be higher than 950 deg. C to creation of conditions for physico-chemical interaction between corium and RPV steel

11. Creation of INVECOR test conditions (2) Design of RPV model Corium pool pre-calculation using profile thermal insulation on the outer RPV model surface Design of RPV model

12. Test with one plasmatrons (1) Main objectives • Testing of thermal insulation efficiency • Testing of protective coating reliability against prototypic corium attack at high temperature • Finding the ways of coaxial plasmatrons power increase • Testing of electrode nozzles life-time to estimate the duration of integral INVECOR test

13. Test with one plasmatrons (2) Scheme of experimental cell Result on pre-calculation at plasmatrons power 18 kW

14. Test with one plasmatrons (3) Temperature of the inner vessel wall Assembled plasmatrons (lower part of graphite nozzle is covered with Zr)

15. Test with one plasmatrons (4) Cross section of the experimental cell and results of phase analysis

16. Test with one plasmatrons (5) State of protective coating on the graphite surface after test Coated electrode nozzle before test Protective coating after test

17. 16 Erosion rate/energy input, g/(GJmin) ARV-1 14 R4340 12 10 8 6 4 2 0 0,215 0,235 0,255 0,275 0,295 0,315 0,335 Electric current in the arc, kA Test with one plasmatrons (6) Relative erosion rate of internal electrode depending on current in the arc

18. Test with one plasmatrons (7)

19. Test section (RPV model) Outside view of test section including device for decay heat modeling Longitudinal section of experimental assembly

20. Conclusions • Experimental facility LAVA-B in IAE NNC RK is able the modeling of different scenarios of severe accident in LWR using 60 kg of prototypic corium, namely: • FCI for in-vessel condition; • FCI for ex-vessel condition; • MCCI with imitation of decay heat in corium using induction heating; • Behavior of corium pool on the lower head of pressure vessel with imitation of decay heat in corium using plasmatrons device. • Experimental technique allows to provide the correct corium composition in above tests and specific scenario condition.