1. ERMSAR 2012, Cologne March 21 – 23, 2012 Institut de Radioprotection et de Sûreté Nucléaire (IRSN), Cadarache, France Institute of Nuclear Technology and Energy Systems, (IKE) Stuttgart University, Germany Royal Institute of Technology (KTH), Stockholm, Sweden Contact : georges.repetto@irsn.fr, rudi.kulenovic@ike.uni-stuttgart.de weimin@kth.se Investigation of Multidimensional Effects during Debris Cooling G. Repetto, T. Garcin (IRSN), M. Rashid *, R. Kulenovic (IKE), Weimin Ma, Liangxing Li (KTH) * presenter

2. ERMSAR 2012, Cologne March 21 – 23, 2012 Debris bed coolability plays an important role in the termination and stabilization of a severe accident. Towards the quantitative understanding of debris bed coolability, many experiments (IKE-IRSN-KTH) have been conducted to investigate two- phase flow and heat transfer in particle beds Introduction 2 The table summarizes briefly, some conditions of those experiments related to coolability of debris beds: POMECO at Stockholm, DEBRIS at Stuttgart, PRELUDE at Cadarache.

3. ERMSAR 2012, Cologne March 21 – 23, 2012 3 POMECO-FLPOMECO-HT PRELUDE-HT DEBRIS Reflooding Facilities Water tank Test section Outlet steam line

4. ERMSAR 2012, Cologne March 21 – 23, 2012 4 Instrumentation : reflooding tests 170 mm 50mm Water injection Overflow line Water storage tank (Bottom- Flooding) Ceramic cylinder Quartz glass External Mid radius Central PRELUDE-HT DEBRIS In PRELUDE, simultaneous measurements of steam flow rate, and pressure drop across the bed provide complementary data that allow “cross-checking” and contribute to improve our understanding of quenching of a particle bed Thermocouples inside the debris bed, in different (axial and radial) locations allow a fine view of the different phases of the transient and are useful to follow the quench front propagation.

5. ERMSAR 2012, Cologne March 21 – 23, 2012 5 DEBRIS Experiments Boiling / Dryout Experiments with down comer installation in the center of the bed a) a) Closed down comer (top-flooding) b) b) Open down comer (bottom-flooding / natural circulation) c) c) Perforated down comer (lateral flow of water to the bed) (a)(b)(c) ceramic balls “debris” water pool down comer

6. ERMSAR 2012, Cologne March 21 – 23, 2012 6 Polydispersed particle bed, System pressure 1, 3 and 5 bar - no qualitative effect on pressure drop behavior - higher vapor density and small change in latent heat - higher DHF increased coolability Lateral-flooding may lead to steam flow into the down comer DEBRIS Experiments

7. ERMSAR 2012, Cologne March 21 – 23, 2012 7 DEBRIS Quenching Experiments Polydispersed particle bed, bed height 640 mm Top-flooding, initial maximum bed temperature 432 °C Two distinct quenching phases realized

8. ERMSAR 2012, Cologne March 21 – 23, 2012 8 DEBRIS Quenching Experiments Polydispersed particle bed, initial maximum bed temperature 631 °C Water supplied to the bottom of the bed from an overlying water tank at a height of ~ 950 mm Near wall thermocouples indicate faster quench front progression -75 0 75 Radius [mm] Bed Height [mm] Temperature °C

9. ERMSAR 2012, Cologne March 21 – 23, 2012 DEBRIS Experiments- Summary Boiling and dryout experiments with water have been performed in volumetrically heated debris bed varying the - flow conditions (top- and bottom-flooding) and system pressures (1, 3 and 5 bar) and measuring - pressure gradient along bed height, temperature distribution and dryout heat flux Quenching experiments at different flow conditions (top- and bottom-flooding) and initial superheating temperatures at ambient pressure - quench time and the behaviour of quench front progression Air / Water cold experiments - single - and two - phase pressure drop measurements - single - and two - phase pressure drop measurements 9

10. ERMSAR 2012, Cologne March 21 – 23, 2012 Almost 1000°C during the reflooding phase Those results qualified PRELUDE HT facility Water velocity = 2 m/h at 870°C This test corresponds to the worst thermal hydraulics conditions for the outlet steam line : - HT for the debris ( 860-990°C) - High power deposition (300 W/kg) - Low flow rate (2 m/h) First example : B2 mm Results PRELUDE HT (1/5) 10 The PRELUDE facility, in operation since mid of 2009, has been modified in 2011 to increase the performance regarding the power deposition and the initial temperature of the debris bed up to 1000°C.

11. ERMSAR 2012, Cologne March 21 – 23, 2012 with higher water velocily = 5 m/h at 900°C Second example : B4 mm Results PRELUDE HT (2/5) 11 While the general behavior of the reflooding is not strongly changed by the increase of temperature, the experiment performed at 900°C has shown the highest water/steam conversion factor never reached up to now (> 90%), even more that was foreseen by the pre-calculation. Higher peak steam flow rate in the short term and reflooding longer in long term (more important stored energy) with a higher total steam production

12. ERMSAR 2012, Cologne March 21 – 23, 2012 Results PRELUDE HT (3/5) 12 Illustration of the quench front propagation (timing for quenching identified when thermocouples reached the saturation conditions). The existence of a quasi steady propagation of the quench front is verified for most of the tests. The faster quench front velocity in the periphery versus the centre outlines the 2D behaviour of the reflooding process. Comparaison with DEBRIS tests regarding the Quench front propagation

13. ERMSAR 2012, Cologne March 21 – 23, 2012 Water flow rate Tests 2011 : 12 Tests 2010 : 10 Test 117 The impact of the bypass which could change T/H conditions for the fluidisation will be studied in the beginning of 2012, using a larger PRELUDE test section Nevertheless, those results give preliminary information of their impacts on the PEARL tests matrix The fluidisation domain has been estimated for various particles size : B4, B2 et B1 as function of the thermal hydraulics conditions (T, Q) 22 tests with Ø2mm diameter Results PRELUDE HT (4/5) 13 When the steam produced during the reflooding create drag force higher to gravitational force of the debris, fluidisation phenomenon could occure and was observed in PRELUDE experiments

14. ERMSAR 2012, Cologne March 21 – 23, 2012 with injection flow rate 2 m/h with injection flow rate 5 m/h Effect of temperature and power deposition Results PRELUDE HT (5/5) 14 The effect of the initial debris temperature has shown an impact on the peak of the steam flow rate during the first stage of the reflooding whereas the(specific power maintained during the transient) has a stronger impact during the second stage of the reflooding and consequently on the duration of the complete quenching of the debris bed, which is in agreement with the more important stored energy

15. ERMSAR 2012, Cologne March 21 – 23, 2012 While the general behavior of the reflooding is not strongly changed, the High Temperature Tests in PRELUDE HT, up to 900°C, outlined very high water/steam conversion factor during the first stage of the Reflooding The impact of the power deposition, which simulated the residual neutron power has a stronger impact during the end of the transient Simultaneous measurements of steam flow rate, temperature evolution and pressure drop across the bed provide complementary data that allow “cross- checking” and contribute to improve our understanding of quenching of a particle bed with bottom cooling injection Regarding Fluidisation, the open questions are the probability to occur in the Reactor case, according to the thermal hydraulics in the partially degraded core, the heat transfers which could increase the efficiency of the Reflooding. Conclusion in PRELUDE 15

16. ERMSAR 2012, Cologne March 21 – 23, 2012 Objective: To study the friction laws and dryout heat flux of particulate beds packed with non-spherical particles 16 BedParticlesFacilityBed shapeεTest Focus 1 Cylinders: 3 x 3 / mm (diameter x length) POMECO-FL Cylindrical: 90 x 635 / mm (diameter x length) 0.34Single-phase flow Effective diameter 2 Cylinders: 3 x 3 / mm (diameter x length) POMECO-HT Cuboidal: 200 x 200 x 620 /mm (L x W x H) 0.34 Two-phase flow: top-flooding &bottom fed Dryout heat flux POMECO Experiments

17. ERMSAR 2012, Cologne March 21 – 23, 2012 1–Hu & Theofaneous model 2–Schulenberg & Műller model 3–Reed model 4–Lipinski model 1–Lipinski model 2–Reed model POMECO-FL POMECO-HT Single phase flow testTop flooding testBottom fed tests Results POMECO 17

18. ERMSAR 2012, Cologne March 21 – 23, 2012 The tests on the POMECO-FL facility show that for a particulate bed packed with non-spherical particles such as cylinders, the effective particle diameter can be represented by the equivalent diameter of the particles, which is the product of Sauter mean diameter and the shape factor. Given the diameter obtained from the test on POMECO-FL facility, the dry-out heat flux obtained in POMECO-HT test is well predicted by the Reed’s model for a top-flooding bed. The bottom injection improves the dry-out heat flux significantly and the prediction of the Reed model is more conservative with increasing flow rate of the bottom injection. 18 Conclusion in POMECO

19. ERMSAR 2012, Cologne March 21 – 23, 2012 Future Work 19 2D quenching experiments with down comer installation in the center of the bed The PRELUDE results will be extended in 2012 with reflooding experiments of heterogeneous porous media (mixture of particles of different diameter, non spherical particles) in the larger test section (PRELUDE 2D including a bypass) and different mode of water injection to prepare PEARL experiments, in a the largest Debris Bed and very challenging configuration never performed up to now Benchmark reflooding experiments at IKE-DEBRIS and IRSN-PRELUDE Investigation of friction laws with Air / Water cold experiments at IKE-DEBRIS

20. ERMSAR 2012, Cologne March 21 – 23, 2012 The European Research Project on Severe Accidents SARNET: Severe Accident Research NETwork of Excellence) Acknowledgement: 20 Thank you for your attention