Fracture toughness and crack growth rates of irradiated austenitic stainless steels.

Abstract

Austenitic stainless steels (SSs) are used extensively as structural alloys in the internal components of reactor pressure vessels because of their superior fracture toughness properties. However, exposure to high levels of neutron irradiation for extended periods leads to significant reduction in the fracture resistance of these steels. Experimental data are presented on fracture toughness and crack growth rates (CGRs) of austenitic SSs irradiated to fluence levels up to 2.0 x 10 21 n/cm 2 (E > 1 MeV) (ª3.0 dpa) at ª288°C. Crack growth tests were conducted under cycling loading and long hold time trapezoidal loading in simulated boiling water reactor (BWR) environments, and fracture toughness tests were conducted in air. Neutron irradiation at 288°C decreases the fracture toughness of the steels; the data from commercial heats fall within the scatter band for the data obtained at higher temperatures. In addition, the results indicate significant enhancement of CGRs of the irradiated steels in normal water chemistry BWR environment; the CGRs for irradiated steels are a factor of ª5 higher than the disposition curve proposed for sensitized austenitic SSs. The rates decreased by more than an order of magnitude in low-dissolved-oxygen BWR environment.

Crack growth rates of irradiated austenitic stainless steel weld heat affected zone in BWR environments.

“…19,20 Crack growth rates a factor of ≈5 higher than the disposition curve proposed in NUREG-0313 21 for sensitized austenitic SSs in water with 8 ppm dissolved oxygen (DO) have been observed. The CGRs of Type 304L SS irradiated to 0.9 and 2.0 x 10 21 n/cm 2 (1.35 and 3.0 dpa) and of Type 316L SS irradiated to 2.0 x 10 21 n/cm 2 (3 dpa) were comparable.…”

“…The experimental J Ic for this material and those obtained earlier 19 for two commercial heats (C19 and C16) in air are plotted as a function of neutron exposure in Fig. 50.…”

“…5,16 However, the beneficial effect of decreased DO was not observed in a test on Type 304L SS irradiated to 2 x 10 21 n/cm 2 , although it is possible that this different behavior is associated with the loss of constraint in the specimen due to the high applied load. 19 This report presents experimental data on the CGRs of Types 304L and 304 SS weld HAZ specimens irradiated to ≈5.0 x 10 20 n/cm 2 (E > 1 MeV) (≈0.75 dpa) at ≈288°C. The irradiations were carried out in a He environment in the Halden heavy water boiling reactor.…”

Crack growth rates and fracture toughness of irradiated austenitic stainless steels in BWR environments.

“…1a and b, respectively. 2,3,[11][12][13][14][15][16][17][18][19][20][21][22][23][24][25][26][27] The fast reactor data show a rapid decrease in fracture toughness at a neutron dose of 1-2 dpa (Fig. 1a); the neutron dose at the onset of the rapid decrease varies with the chemical composition and heat treatment of the steel.…”

“…* Similar test results under LWR conditions are limited. 2,27 The effect of neutron exposure (in dpa) on the fracture toughness J Ic of austenitic SSs irradiated at 350-450°C (662-842°F) up to ! 25 dpa in fast reactors and BWRs is shown in Figs.…”