Doel 3 & Tihange 2 - Some Peer-reviewed Scientific Papers & Reports

14

J. Koutskf', K. ~pllchal

EXPER IMENTAL

The experiments were done on the low-alloy CrMoV and CrNiMoV steels which are current ly used for light water reactor pressure vessels. The material compos i t ion of the steels is given in Table 1. Tensile tests were conducted at a strain rate of 8.3 x 10-4s -t on cylindrical tensile specimens of diameter d = 4 mm and working section length l = 20 mm. For cons tant load testing the me thod of delayed fracture was used with cylindrical 60° V-notched specimens of dimen- sions d~ = 3.5 ram, d2 = 5 mm and l = 17.5 mm and notch radius 0.05 ram. Both series of tests were per formed at room temperature. The specimens were irradiated in an irradiat ion rig using a hel ium envi ronment at temperatures of 130, 180 and 290°C for fast neut ron fluences of 2.6-4.9 x 1023nm -2 (E > 0.5 MeV). Uni rradiated specimens prior to tensile test were hydrogen-charged for 1h at room temperature in 1N H2SO4 solut ion (with addi t ion of 30ppm As203). The delayed fracture test was carried out only on uni rradiated notched specimens which had been hydrogen-chargedunder constant load in 1N H2SO4 with current densities of 10, 100, 300 and 3000Am -2. The hydrogen content was determined by vacuum extract ion of mel ted specimens in an adapted BALZERS EAH-220 analyzer. The specimens had been stored in liquid ni t rogen before tensile testing or hydrogen content determinat ion.

RESULTS

Hydrogen and radiationembrittlement

The mechanicalpropert ies of the CrMoV steel depend on the extent of i rradiat ion- induced defects, on the hydrogen content and on hydrogen charging parameters. The influence o f irradiat ion becomes evident as radiat ion strengthening of the steel which increases with decreasing irradiat ion temperature in the range 290-120°C. Fr om the data given in Table 2 this is obvious; for example, for the samples irradiated at 130°C to fluence 9 x 102anm -2, the yield st rength (Rp)o. 2 increases by 59% and the tensile strength Rm by 41%. The influence of hydrogen was not observed at concent rat ions up to