Byung-Kwon Choi

Out-of-pile and In-pile Perfomance of Advanded Zirconium Alloys (HANA) for High Burn-up Fuel

The performance of the advanced Zr alloys (HANA) for a high burn-up fuel has been evaluated in the out-of-pile and in-pile conditions. The corrosion resistance of the HANA claddings was superior to Zicaloy-4 in a PWR-simulating loop condition. The improved corrosion resistance of the HANA claddings was attributed to the fine distribution of the precipitate. HANA claddings showed a higher creep resistance as compared to Zircaloy-4 from the thermal creep test. The deformation behavior of HANA in a LOCA condition was similar to Zircaloy-4. Threshold ECR value of HANA was higher than the conventional value of 17% in Zircaloy-4, which is mainly due to the fact that the Nb decreases the oxidation rate as well as the hydrogen pickup. Fretting wear test revealed that HANA claddings have a similar wear resistance to Zircaloy-4. From the irradiation test up to burn-up of about 12 GWd/MtU, HANA claddings showed a better corrosion resistance as well as a better creep resistance than Zircaloy-4. The in-pile corrosion resistance of the HANA claddings was improved by 40–50% as compared to Zircaloy-4 on the basis of the oxide thickness measurements.

Joining of Be to Ferritic-Martensitic Steels with Diffusion Barrier Interlayer

Abstract A joining of Be to ferritic-martensitic steels (FMS) is an essential process in the fabrication of ITER test blanket module (TBM). The diffusion barrier layers together with the coated interlayer were applied to the HIP joining of Be and FMS in order to develop the interlayer technology for the fabrication of ITER TBM. Multiple layers formed due to an excessive diffusion of elements in the interface region in the absence of a diffusion barrier layer. Such a complicated interface structure consisting of brittle phases in part would be very prone to fracture even at low stress levels. A Cu foil or a HIPed CuCrZr layer applied as a diffusion barrier was effective to retard the diffusion between Be and FMS. It was revealed that the diffusion barrier layers helped to improve the joining properties by reducing the possibility to form diffusion layers in the interface, which made the Be/FMS joint have an appreciable joining strength.

INVESTIGATION ON THE CORROSION BEHAVIOR OF HAHA-4 CLADDING BY OXIDE CHARACTERIZATION

The microstructure, the corrosion behavior and the oxide properties were examined for Zr-1.5Nb-0.4Sn-0.2Fe-0.1Cr (HANA-4) alloys which were subjected to two different final annealing temperatures: 470°C and 570°C. HANA-4 was shown to have s-enriched phase with a bcc crystal structure and Zr(Nb,Fe,Cr)₂ with a hcp crystal structure with s-enriched phase being more frequently observed compared with Zr(Nb,Fe,Cr)₂. The corrosion rate of HANA-4 was increased with an increase of the final annealing temperature in the PWR-simulating loop, 360°C pure water and 400°C steam conditions, which was correlated well with a reduction in the size of the columnar grains in the oxide/metal interface region. The oxide growth rate of HANA-4 was considerably affected by the alloy microstructure determined by the final annealing temperature.