Visualization of B4C/SS Eutectic Reaction and Liquefaction for Code development & validation

Transcription

1 Visualization of B4C/SS Eutectic Reaction and Liquefaction for Code development & validation May Shota UEDA, Hiroshi MADOKORO, Byeongnam JO, Masahiro KONDO, Koji OKAMOTO Department of Nuclear Engineering and Management The University of Tokyo

2 Contents 1. Introduction 2. Experimental setup 3. Visualization experiments 4. Results 5. Conclusion 19/05/2015 2

3 Introduction

4 Background Fukushima Daiichi Simulation results of Fukushima Daiichi accident reported by TEPCO. The complete failure of the control blades probably happened in the rather early phase of the Fukushima accident. To prevent the recurrence of the severe accident and enhance its safety, clarifing the failure mechanism of control blades is really important. 19/05/2015 4

5 Absorber material in BWR[1][2] BWR fuel Control blade Absorber rod B 4 C powder Stainless Steel BWR uses B 4 C as the absorber material B 4 C is filled in the stainless steel tube Stainless steel tubes are installed in control blade 5

6 Early liquefaction due to B4C/SS eutectic reaction Melting point B 4 C ~2720K Stainless Steel ~1730K B 4 C/SS eutectic ~1500K Relocation of control blade[3] Melting temperatures of B4C & SS are 2720 K and 1730 K, respectively. Melting temperature of eutectic material is lower than the original materials. When the temperature exceed 1500K, the eutectic material starts to melt suddenly. Control rods melt firstly among other components. 19/05/2015 6

7 Objective In spite of its importance, few experimental research had been performed(ex: P. Hofmann (KIT) and H. Uetsuka (JAEA)). In the past, no visualization of the phenomena was reported. Difficult to know the dominant phenomenon during the liquefaction. Cannot characterize the phenomena in simulations. Visualizing reaction layer growth in order to create a database for simulation. Acquire the qualitative and quantitative information by image analysis. Provide boundary conditions( e.g. Temperature, Heat transfer ) 19/05/2015 7

8 Experimental

9 Specimen B4C powder is stuffed between SS plate. Filling rate was 47 %. We focused on the side SS plates during the experiments. Stainless Steel Plate B4C powder

10 42 mm 10 mm 15 mm Specimen(cont d) Specimen that has B4C powder between SS plates. Specimen was 4 mm in width & 35 mm in height. Measured the temperature with 4 thermocouples Front view Side view Tungsten heater Tungsten heater Specimen TCs TCs 2 mm 2 mm 4 mm 19/05/

11 Experimental setup Heat up the test piece with tungsten heater. Radiation heat transfer Sheathed thermocouples. Ar atmosphere inside the test facility. Power supply + Glass window Electrode Heater Heater Camera SS/B4C Electrode Ar Gas 19/05/

12 Visualization experiments

13 Conditions for each test case Average Temp. [ C] Case 1 L s s Case 1 R s s Case 2 R s Case 3 L s Case 3 R s σ shows the average temperature and standard deviation of each test case. Due to the different temperature of test piece in left and right side, which were analyzed separately and indicated by L and R. 19/05/

14 Temperature history B/L thermocouple was broken due to the reaction Temperature [ ] Top/Left Top/Right Bottom/Left Bottom/Right IR camera Time [s] 19/05/

15 Results of experiments On the left side, the eutectic reaction started and later it also started on the right side. Molten material invaded B4C region enhancing the diffusion. SS plates started to melt. Liquefied SS enhanced the diffusion of B4C. 19/05/

16 Results of experiments (cont d) The side SS plates were drastically molten. The middle part of the T.P. was molten due to not uniform heat flux profile in height direction. 2 cm Back plate does not melt because we coated it with cement. Result of the reaction 19/05/

17 The plots of results Correlation between the reaction layer thickness and the square root of time. Each plots obeyed a parabolic rate law. 19/05/

18 Arrhenius plots of experimental results The reaction rate constants for B 4 C powder/ss were obtained in the previous studies (Hering and Hofmann, 1994; Nagase et al., 1997). An obvious discontinuity in the temperature dependence of the parabolic rate law constant is seen between 1200 and 1225 C (Nagase et al., 1997). This discontinuity exists because the minimum melting temperature of Fe-B system is 1174 C and it starts to melt when it exceeds this temperature with certain amount of mixture. 19/05/

19 Conclusion The eutectic reaction between B4C powder & SS has been visualized. The temperature history during the experiment has been obtained. Qualitative knowledge about the growth of reaction zone has been obtained. The new correlation was proposed between 1181 and 1208 C 19/05/

20 Thank you for your attention! 19/05/

21 References [1] TOSHIBA Corporation, Advanced Boiling Water Reactor What s ABWR Control Rods and Control Rod Drive, m, (accessed ) [2] World Nuclear Association, Nuclear Fuel Fabrication, nuclear.org/info/nuclear-fuel-cycle/conversion-enrichment-and- Fabrication/Fuel-Fabrication/, (accessed ) [3] L. Sepold, S. Hagen, P. Hofmann and G. Schanz, Behavior of BWR-type Fuel Elements with B4C/Steel Absorber Tested under Severe Fuel Damage Conditions in the CORA Facility, Forschungszentrum Karlsruhe, FZKA-7447, 2009 [4] M. Kondo and Seiichi Koshizuka, Improvement of stability in moving particle semi-implicit method, International Journal for Numerical methods in Fluids, Vol. 65, p (2010) [5] Диаграммы состояния двойных металлических систем (4 тома), [6] Asril Pramutadi Andi Mustari and Y. Oka, Molten uranium eutectic interaction on iron-alloy by MPS method, Nuclear Engineering and Design, Vol. 278, p (2014) 19/05/