Repair Welding of Irradiated Reactor Vessel Steel by Low Heat Input GTAW and LBW

摘要

Weldability in neutron-irradiated low alloy steel for a reactor (pressure) vessel has been studied by a temper-bead welding technique using low-heat-input GTAW and LBW(YAG). The base and weld metals of low alloy steel with clad or without clad were irradiated up to 1.4×10~(24) n/m~2 (>1 MeV) at 290 ℃, which approximately corresponds to the maximum neutron fluence of a 60-year-operation plant's vessel. The mechanical property tests, such as tensile, impact side bend and hardness, were carried out after the repair-welding. The weld cracking did not occur in base and weld metals of irradiated low alloy steels during the repair-welding by GTAW and LBW. Small porosities were formed in the first and second layers of the repair weld metal. Only a few porosities were found in weld metal compared with in base metal. From the results of mechanical properties, the weld metal of low alloy steel could be welded up to a He concentration of 12.9 appm, while the base metal could be done up to only 1.7 appm He. On the other hand, weld cracks occurred in stainless steel and Ni base alloy clad on low alloy steel caused by He bubble formation Based on these results, the rule of repair-welding procedure selection was proposed for the reactor (pressure) vessel.