SCC Investigation of Pre-Irradiated Core Shroud Weld HAZ Specimens under Simulated BWR Environmental Conditions in a Research Reactor

摘要

$1VGB PowerTech e. V., Essen, Germany$2Vattenfall Europe Nuclear Energy GmbH, Hamburg, Germany$3EnBW Kernkraft GmbH, Philippsburg, Germany$4RWE Power AG Essen , Germany$5Nuclear Research Institute Rezplc, Czech Republic$6Nuclear Physics Institute CAS, Czech Republic; ;Crack growth rate, BWR normal water chemistry, neutron irradiation, austenitic stainless steel, heat-affected zone This paper presents final results of a project aiming to produce reliable crack growth data on the Nb-stabilized austenitic stainless steel 1.4550 (A347) under the simultaneous influence of BWR-coolant and neutron/gamma irradiation. In order to obtain appropriate and realistic experimental data for power plant components, the investigated test material was cut from an original Siemens KWU BWR RPV core shroud and crack growth data were generated in a large scale test loop integrated into a research reactor that ensured water chemistry and radiochemical conditions as close as possible to those of a BWR power plant. The focus was on the HAZ of the mid-section circumferential core shroud weld joint H4, which was also characterized by residual stress measurements. In the frame of the pre-irradiation program, four CT specimens were pre-irradiated in inert gas in a slab type reactor rig. Then EAC tests were performed in the research reactor at Rez under conditions as near as possible to operational conditions in a commercial BWR reactor (NWC, 288°C, 200 ppb O_2). A test loop consists of an in-pile channel and an out-of-pile channel, which enables simultaneous testing of two CT17 specimens in each channel. The loop is equipped with different sensors and sampling lines to determine the thermodynamic, water chemical and radiation conditions during the tests. The crack growth behavior of each specimen was continuously recorded using the potential drop and COD methods. The tests started with in-situ cycling of the specimens followed by a period with active constant load, when a crack growth was indicated. Crack growth rates of HAZ materials pre-irradiated to 6.0×10~(20) and l.5×l0~(21) n/cm~2 (E > 1 MeV), i.e. 0.9 and 2.3 dpa, were 2 to 8 times higher than the corresponding non-irradiated base material values under constant load. The HAZ CGR data were very similar to the CGR data of 1.4550 (A347) base metal irradiated to an equivalent fluence level. The experimental data are evaluated and presented together with fractographical and metallographical investigations.