Application of Coating Technology on the Zirconium-Based Alloy to Decrease High-Temperature Oxidation Hyun-Gil Kim*, Il-Hyun Kim, Jeong-Yong Park, Yang-Hyun Koo, KAERI, 989-111 Daedeok-daero, Yuseong-gu, Daejeon, 305-353, Republic of Korea *Corresponding author: hgkim@kaeri.re.kr
Accident-tolerant fuel claddings (ATFC) The breakthrough to the challenge facing nuclear fuels of LWR after Fukushima Dai-ichi accident involves the development of accident-tolerant fuels. Fukushima accident New requirements have been emerged on the performance of fuel to provide a more extended safety margin. One of the research efforts to enhance the accident-tolerance of nuclear fuels relies on the improvement in the oxidation resistance of claddings with the reduction of hydrogen emission. Hydrogen explosion Zr + 2H 2 O ZrO 2 + 2H 2 2
Technical issue Technical issues to development of ATFC Normal operation condition - High burn-up (higher corrosion/creep resistance) - Load follow (higher strength/fatigue resistance) Zr-based alloys Accident condition - High temperature oxidation (lower oxidation rate) - High temperature ballooning (higher creep/deformation resistance) Surface modified Zr alloys - Zr alloy + surface alloying, coating Hybrid materials - Zr alloy + thermo-stable materials (SiC, Nb, Mo ) Full ceramic materials - SiC/SiC f composite - Others (?) Increasing challenges - Fabrication - Economy - Verification Time to development 3
Challenges to ATFC Application of new materials raises many issues on the performance and the integrity of the claddings. - Oxidation resistance - Adhesion to the matrix - Phase stability up to high temp. - Thermal expansion coefficient - Neutron economy - Thermal conductivity - Irradiation susceptibility - Tube fabricability - Unknowns Zr alloys Surface modification 4
Cladding Y 2 O 3, SiC, Cr 3 C 2, N, C, Si, Cr Cladding Y 2 O 3, SiC, Cr 3 C 2, N, C, Si, Cr Cladding Y 2 O 3, SiC, Cr 3 C 2, N, C, Si, Cr Y 2 O 3, SiC, Cr 3 C 2, N, C, Si, Cr Concept of surface modification technology 1. Coating of corrosion resistance material on cladding 2. Mixing of coated material into cladding 3. Additional coating of corrosion resistance material Coating method develop. Vacuum evaporation Plasma spray Laser beam scanning (with coated powder) Combine of coating methods Mixing method develop. Laser beam scanning Ion implantation Annealing Additional coating method develop. Vacuum evaporation Plasma spray Laser beam scanning with coated powder Annealing Performance evaluation Corrosion test : up to 1200 o C (normal operation and LOCA-simulated conditions) Adhesion test : thermal cycle (thermal expansion), mechanical deformation and impact Micro-structural analysis 5
Oxide Carbide Materials Phase Transform. Temp. ( o C) Melting Point ( o C) Thermal Expansion Coff. (x 10-6 K) Thermal Conductivity (W/mK) Y 2 O 3 none 2690 8.1 1.0 SiO 2 Depend on pressure 1600 12.3 1.3 Cr 2 O 3 none 2400 9.0 2-5(coating) Al 2 O 3 none 2072 8.4 5-25(bulk) ZrO 2 M(970)/ T(1205)/Cubic 2130 10.1 1.8-3.0 Cr 3 C 2 none 1895 10.3 13 SiC(CVD) none 2545 <5 330 ZrC none 3540 7.01 12 Nitride ZrN none 1960 7.24 10 Metal Consideration of coating materials Neutron Cross Section (barn) 1.28(Y) 0.0002(O) 0.177(Si) 0.0002(O) 3.05(Cr) 0.0002(O) 0.231(Al) 0.0002(O) 0.182(Zr) 0.0002(O) 3.05(Cr) 0.0035(C) 0.177(Si) 0.0035(C) 0.185(Zr) 0.0035(Cr) 0.185(Zr) 1.9(N) Cr none 1907 4.9 93.9 3.05(Cr) Si none 1414 2.6 149 0.177(Si) Substrate Zr HCP(863)/BCC 1850 7.2 10 0.185(Zr) 6
Phase diagram of coating material and Zr Zr-Si Zr-Cr 7
Consideration of coating technologies Plasma spray method Laser beam scanning method Plasma spray Laser beam scanning 8
High temperature oxidation test Temperature was increased at 50 o C/min to 1200 o C, maintained at 1200 o C for 2000s and then Ar gas-cooled. Steam was supplied right after the temperature reached 1200 o C. 9
Weight Gain, mg/dm 2 Oxidation behavior of selected coating materials 10000 1000 100 Metal Cr Si wafer SiO 2 10 1 0 500 1000 1500 2000 2500 Time, s 10
Analysis of Si-coated layer by PS 1pass 3pass 6pass Si-layer 100 m 100 m 100 m 11
Comparison of Si-coated layer by PS and PS+LBS PS PS+LBS Si layer Epoxy Si-Zr mixed layer 50 m 12
Analysis of Si-coated layer by PS+LBS Si-Zr mixed layer Si and mixed grain (5~20 at% Si; 80~95 at% Zr) 50 m Coated surface direction grain (~99 at% Zr) 13
Oxidation behavior of Si-coated samples 10000 Weight Gain, mg/dm 2 1000 100 10 Si-coated by PS Si-coated by PS + LBS 1 0 500 1000 1500 2000 2500 Time, s 14
Si-coated layer by PS after oxidation 1pass 3pass 6pass Si-layer ZrO 2 Si-layer ZrO 2 Si-layer ZrO 2 200 m 200 m 200 m 200 m 15
Comparison of oxidation resigons Zr PS PS+LBS ZrO 2 Si-layer -Zr(O) ZrO 2 Si-Zr mixed layer 200 m 200 m 200 m 16
Comparison of oxidation characteristics PS PS+LBS After oxidation Si-layer spalled region Epoxy ZrO 2 Si-Zr mixed layer Before oxidation PS PS+LBS Si layer Epoxy Si-Zr mixed layer 50 m 50 m 17
Analysis of Si-Zr mixed layer after oxidation Oxidized Si-Zr mixed layer Pt Oxidized Si-Zr mixed layer Large grain region O: 30~40 at% Si: 5~20 at% Zr: 40~65 at% ZrO 2 -Zr(O) 200 m 200 m Slim grain region O: 20~30 at% Si: 5~20 at% Zr: 50~75 at% FIB damage 18
Future plan Verification of coating materials (Si and Cr) Simplified of coating method (Powder supplied LBS) 1) Control of the coated thickness, composition, and phase Manufacture of tube samples Performance test of surface coated tube samples - Very high temperature oxidation test higher than 1200 o C - Strength and creep ballooning test at high temperature - Basic physical performance test - Others 1) Zr alloys Surface modification 19
Summary Coating techniques both the coating methods and coating materials to reduce the oxidation rate of zirconium-based alloy in a high-temperature steam environment were studied. After 1200 o C test in steam environment, the SiO 2 showed the highest oxidation resistance among the tested materials, and Si was more effective than Cr from the viewpoint of oxidation resistance. Plasma spray (PS) and laser beam scanning (LBS) after a PS were selected as the coating method, and the Si was chosen as a coating layer for the surface coating material on zirconiumbased alloy. PS coating technique has problems such as the formation of pores in the Si-coated layer and the interface oxidation caused by low adhesion property. By the LBS treatment, the pores in the Si-coated layer by PS were successively removed, and the interface oxidation was suppressed by the formation of the diffusion bonding between substrate and Si-Zr mixed layer. Oxidation resistance of the Si-Zr mixed layer is superior to that of, and a good adhesion property can be obtained. Thus, the hydrogen generation of zirconium alloy by an excess oxidation reaction in a high-temperature steam environment can be considerably reduced by the application of the Si coating technology of PS + LBS treatments. 20
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