Yong-Hwan Jeong

EFFECTS OF HEAT TREATMENTS ON MICROSTRUCTURES AND MECHANICAL PROPERTIES OF DUAL PHASE ODS STEELS FOR HIGH TEMPERATURE STRENGTH

In the present study, the effects of various heat treatments on the microstructure and mechanical properties of dual phase ODS steels were investigated to enhance the high strength at elevated temperature. Dual phase ODS steels have been designed by the control of ferrite and austenite formers, i.e., Cr, W and Ni, C in Fe-based alloys. The ODS steels were fabricated by mechanical alloying and a hot isostatic pressing process. Heat treatments, including hot rolling-tempering and normalizing-tempering with air- and furnace-cooling, were carefully carried out. It was revealed that the grain size and oxide distributions of the ODS steels can be changed by heat treatment, which significantly affected the strengths at elevated temperature. Therefore, the high temperature strength of dual phase ODS steel can be enhanced by a proper heat treatment process with a good combination of ferrite grains, nano-oxide particles, and grain boundary sliding.

PROPERTIES OF ZR ALLOY CLADDING AFTER SIMULATED LOCA OXIDATION AND WATER QUENCHING

In order to study the cladding properties of zirconium after a loss-of-coolant accident (LOCA)-simulation oxidation and water quenching test, commercial Zircaloy-4 and two kinds of HANA claddings were oxidized at temperatures ranging from 900℃ to 1250℃ and exposed for 300 s, and then cooled to 700℃ before quenching. Microstructural observations were made to evaluate the matrix characteristics with the chemical compositions after the LOCA-simulation test. Ring compression testing was then performed to compare the ductile behaviour of the HANA and Zircaloy-4 claddings. An X-ray diffraction (XRD) analysis was carried out for temperatures ranging from room temperature to 1250℃ for the oxide layer to verify the oxide crystal structure at each oxidation temperature.

IN-PILE PERFORMANCE OF HANA CLADDING TESTED IN HALDEN REACTOR

An in-pile performance test of HANA claddings was conducted at up to 67 GWD/MTU in the Halden research reactor in Norway over a 6.5 year period. Four types of HANA claddings (HANA-3, HANA-4, HANA-5, and HANA-6) and a reference Zircaloy-4 cladding were used for the in-pile test. The evaluation parameters of the HANA claddings were the corrosion behavior, dimensional changes, hydrogen uptake, and tensile strength after the claddings were tested under the simulated operation conditions of a Korean commercial reactor. The oxide thickness ranged from 15 to 37 mm at a high flux region in the test rods, and all HANA claddings showed corrosion resistance superior to the Zircaloy-4 cladding. The creep-down rate of all HANA claddings was lower than that of the Zircaloy-4 cladding. In addition, the hydrogen content of the HANA claddings ranged from 54 to 96 wppm at the high heat flux region of the test rods, whereas the hydrogen content of the Zircaloy-4 cladding was 119 wppm. The tensile strength of the HANA and Zircaloy-4 claddings was similarly increased when compared to the un-irradiated claddings owing to the radiation-induced hardening.

High Heat Flux Test of the KO Standard Mockups for ITER First Wall Semi-Prototype

Abstract The Korean standard mockups with beryllium tile were fabricated to perform the high heat flux test for the qualification test of ITER blanket first wall. These mockups include the 80 mm × 80 mm beryllium armor tiles joined to the CuCrZr heat sink with stainless steel cooling tubes by HIP (Hot Isostatic Pressing) technology. The high heat flux tests were performed in the Korea heat load test facility (KoHLT-1) with the averaged surface heat flux of 1.25 MW/m2 by using a graphite heater. Preliminary thermal and mechanical analyses were carried out to simulate the test conditions and to determine the number of cycles for the fatigue lifetime of the mockups. In our KoHLT-1 facility, the normal heat cycle was based on an expected heat flux of 1.25 MW/m2, and each mockup had to endure the 1,000 normal heat cycles in this heat flux in accordance with the mechanical simulation. In the cyclic heat flux tests, the maximum surface temperature of the beryllium tiles was controlled below 400 °C. As a result of these high heat flux tests with the acceptance criteria of the ITER blanket first wall, the manufacturing technologies of the Korean standard mockups will be utilized to develop the tokamak blanket for the international qualification procedure.