STRESS CORROSION CRACKING SENSITIVITY OF IRRADIATED FERRITIC STEEL IN BWR COOLANT CONDITIONS

摘要

Stress corrosion cracking of low alloyed steel 22NiMoCr37 is evaluated with the goal to determine crack growth rate in irradiated steel under conditions simulating closely conditions of BWR RPV under operation. Testing with both unirradiated and irradiated specimens gives full experimental matrix that enables to separate particular influences on the stress corrosion cracking in base metal and heat affected zone. For the experiment, in pile BWR experimental loop has been built at Nuclear Research Institute, Rez. Special attention was devoted to H_2O_2 determination in the vicinity of the samples. To achieve this three items were realized - technical installations, measurements and modeling of radiolysis. Special sampling lines for H_2O_2 measurements and ECP electrodes in pipes are used. Hydrogen peroxide is measured in different mode of reactor and loop operation. Comparison of modeling and measurement enables to calculate H_2O_2 along the loop and near testing specimens. 2T CT specimens have been chosen in order to achieve high level of loading. The irradiation rig has been built for pre-irradiation of specimens to the fluence of 1.5xl0~(18) n/cm~2 (E>lMeV). During the experiment, specimens are loaded by cyclic and constant load. Crack growth is monitored by means of potential drop measurement and COD. The first results obtained from the in pile and out of pile preliminary tests of unirradiated specimens are presented in the paper.