[en] To investigate the effect of heat treatment on the microstructure and corrosion characteristic of a Zr-Nb alloy, specimens prepared through various kinds of processing and heat treatment were used. Autoclave corrosion test under the steam condition at 400 deg C, microhardness test and O/M and SEM studies have been carried out. The corrosion characteristics of heat treated specimens were compared in relation to their microstructures to clarify the relationship between microstructure and corrosion characteristic. In Zr-1Nb-0.2Cu alloy the corrosion characteristic was observed to be significantly affected by heat treatment and the introduction of cold rolling after β-quenching was indicated to increase the corrosion resistance probably because the formation of precipitate was influenced by that process. The corrosion characteristics of Zr-Nb alloys was thought to be controlled by the characteristics of precipitates formed during processing

[en] Effects of intermediate annealing, final annealing and texture on the corrosion of the advanced nuclear fuel cladding. The corrosion characteristics of the alloy was highly influenced by final annealing than intermediate annealing, and the corrosion resistance increased with increasing the final annealing temperature. From the result on the corrosion test for the alloy with similar microstructure and different texture characteristics, the corrosion resistance in the early stage of corrosion was highly affected by texture and corrosion resistance increased when (0002) texture normal to the corrosion surface was well developed. However, the effect of texture decreased when corrosion was proceeded. It is suggested that texture of the alloy plays an important role in corrosion behavior at early stage of corrosion though the corrosion behavior is dominated by oxide characteristics when thick oxide was formed

[en] At present, Zircaloy-4 is widely used as a cladding material for PWRs. However, the demanding operating conditions such as high burnup, extended fuel cycle, high temperature and high pH coolant condition make it unacceptable of the use of Zircaloy-4. In this regard, KAERI have developed 6 advanced cladding tubes and the performance tests on the new tubes are underway. Creep resistance is one of the life-limiting factors of a cladding material. In this paper, the tube creep results are described, which was performed at 350 .deg. C and 400 .deg. C temperatures, and applied hoop stress range of 100-150MPa. The creep resistance was strongly influenced by final annealing temperature in such way that recrystallized tube showed low creep strain than stress-relieved one by a factor of 3, while the effect of intermediate annealing on creep strength was very little. The alloying content of Sn and Nb dominated the creep resistance. The KAERI claddings showed superior or comparable creep resistance to Zircaloy-4 tube

[en] The corrosion resistance of Zr-Nb-Sn-Fe-X alloys were evaluated by the autoclave tests under the environments of 360 .deg. C water, 360 .deg. C LiOH 70 ppm solution and 400 .deg. C steam. The mechanical properties of those alloys were also investigated by tensile tests and creep tests. The corrosion resistance of the alloys in the water and the LiOH solution showed similar behavior, while they are superior to that of Zircaloy-4 in LiOH solution. The alloys, which have much in alloying content, showed better properties in tensile strength and creep resistance due to alloying effect. The final heat treatment of the alloys at 470 .deg. C and 520 .deg. C has little differences in corrosion behavior but much in mechanical strength and creep strength because the heat treatment at 470 .deg. C has more dislocation barrier than that at 520 .deg. C

[en] Phase transformation characteristics and corrosion resistance were evaluated for the advanced Zr fuel claddings containing Nb and the corrosion characteristics of the intermediate product in manufacturing process was examined. From the result obtained by DSC, it was shown that the α/β transformation in D cladding was proceeded in the temperature range of 770 to 945 .deg. C, which was consistent with the result of TEM observation. The corrosion resistance of D claddings was shown to be superior to A, B and zircaloy-4 claddings and increased with decreasing the final annealing temperature. From the result on the corrosion test for the intermediate products in manufacturing process, corrosion resistance increased when (0002) texture normal to the corrosion surface was well developed. It is suggested that corrosion resistance of Zr alloys can be improved by controlling the crystallographic texture through the change of processing parameter as well as controlling the heat treatment condition

[en] The Improvement of the corrosion resistance of nuclear fuel claddings is the critical issue for the successful development of the high burn-up fuel. KAERI have developed the K-claddings having a superior corrosion resistance by controlling the alloying element addition and optimizing the manufacturing process. The comparative evaluation of the corrosion resistance for K-claddings and the foreign claddings was performed and the effect of the heat treatment on the corrosion behavior of K-claddings was also examined. Corrosion tests were carried out in the conditions of 360 .deg. C pure water, PWR-simulating loop and 400 .deg. C steam, From the results of the corrosion tests, it was found that the corrosion resistance of K-claddings is superior to those of Zry4 and A claddings and K6 showed a better corrosion resistance than K3. The corrosion behavior of K-cladding was strongly influenced by the final annealing rather than the intermediate annealing, and the corrosion resistance increased with decreasing the final annealing temperature

[en] To elucidate the correlation between the oxide impedance and corrosion characteristics of the Zr-xNb alloys, the long term corrosion test in high temperature / high pressure aqueous solution and the impedance test in the room temperature sulfate solution were performed. β-quenched plate specimens were heat-treated at 570 .deg. C for 500 hours to get the α+β_Nb phase and the at 640 .deg. C for 10 hours to get the α+β_Zr phase. The impedance test was conducted in sulfate solution for the initial corrosion test specimen (WG = 30 mg/dm²). To evaluate the impedance date, 4 types of equivalent circuits were constructed by 5 parallel and serial RC elements. By using the equivalent circuits, the thickness of the inner and outer layers were calculated and the electric resistance of each layers were estimated. The corrosion behaviour of Zr-xNb alloys were quite different depending of the annealing condition and Nb-content. The corrosion resistance of the β_Nb phase contained high Nb alloys were excellent rather than β_Zr phase contained high Nb alloys. The electric resistance of the outer layer of β_Zr phase contained high Nb alloy was twice larger than that of β_Zr phase contained high Nb alloy, and in the case of outer layer 30% larger. So, the long term corrosion behaviors in high temperature could be estimated well by using the impedance test results

[en] To evaluate the effect of both intermediate and final heat treatments on the tensile properties of new KAERI cladding tubes, four kinds of the tubes(UE, UF, UG and UH) were manufactured and the tensile tests of those tubes were carried out with the strain rate 4.2X10-3/s at room temperature and 400 .deg. C. The effect of intermediate heat treatment on the claddings was a little, but that of final one was distinguishable showing that the higher the final heat treatment was the lower both the yield strength and the ultimate tensile strength was, and the elongation was vice versa. The tensile strength of the tubes was equivalent to or over than that of Zry-4 but the tensile elongation of the tubes was larger by about 2.6-4.3%

[en] The mechanical properties of Zr0.4Nb0.8SnFeCrMn alloy, which is under development as one of the candidate alloys for advanced fuel cladding material, were evaluated at various final thermo-mechanical treatments including cold-working and annealing temperature. The microstructure and pole distribution were observed using optical microscopy and X-ray, respectively. Tensile and creep tests were carried out at ambient temperature and 400 .deg. C, respectively. As a result of texture analysis, basal pole was directed to normal direction, while prism pole was to rolling direction. The significant reduction of ductility was observed in stress-relieved specimen of transverse direction than that of rolling direction, but the difference was disappeared as the degree of recrystallization increased. The anisotropic behavior along to the direction of applied stress was seems to be highly associated with prism pole distribution. Further discussion was given to the effect of thermo-mechanical treatments in terms of strain hardening rate, θ and characteristics of toughness. Creep test result showed that recrystallization decreased the thermal creep strength at the test regime of 400 .deg. C and 150 MPa

[en] To evaluate the effect of both intermediate and final heat treatments on the burst properties of the new cladding tubes, four kinds of tubes were manufactured and undergone the burst tests at room temperature and 400 .deg. C. The effect of intermediate heat treatment on the claddings was a little with 13% at most, but that of final one was distinguishable. So, higher final heat treatment made the claddings have lowered the ultimate hoop strength and increased total circumferential and uniform burst elongation. But if the claddings were finally annealed above 510 .deg. C, it appeared that the re-crystallization of the tubes had the trend less