Embrittlement Of Reactor Pressure Vessel Steels Research Articles

Dislocation density evaluation of three commercial SA508Gr.3 steels for reactor pressure vessel

Reactor pressure vessel (RPV) plays a crucial role in the safe operation of nuclear power plants (NPPs). However, RPV steels are generally subjected to high-energy neutron irradiation during the entire in-service lifetime, which causes the hardening and embrittlement of RPV steels. The dislocation density (ρ) is known to affect strongly the mechanical properties of RPV steels. The dislocation density of three commercial SA508 Gr.3 steels manufactured by different countries was thoroughly investigated by X-ray diffraction (XRD), electron backscattered diffraction (EBSD) and transmission electron microscopy (TEM). The dislocation densities of three SA508 Gr.3 steels calculated by XRD are as high as 1013 m−2 and consistent with results of tempered steels reported in prior studies. The results calculated by XRD match qualitatively with those obtained from TEM and kernel average misorientation (KAM) analysis of EBSD (EBSD-KAM).

Nondestructive Magnetic Adaptive Testing of nuclear reactor pressure vessel steel degradation

Inspection of neutron-irradiation-generated degradation of nuclear reactor pressure vessel steel (RPVS) is a very important task. In ferromagnetic materials, such as RPVS, the structural degradation is connected with a change of their magnetic properties. In this work, applicability of a novel magnetic nondestructive method (Magnetic Adaptive Testing, MAT), based on systematic measurement and evaluation of minor magnetic hysteresis loops, is shown for inspection of neutron irradiation embrittlement in RPVS. Three series of samples, made of JRQ, 15CH2MFA and 10ChMFT type steels were measured by MAT. The samples were irradiated by E>1MeV energy neutrons with total neutron fluence of 1.58×1019–11.9×1019n/cm2. Regular correlation was found between the optimally chosen MAT degradation functions and the neutron fluence in all three types of the materials. Shift of the ductile–brittle transition temperature, ΔDBTT, independently determined as a function of the neutron fluence for the 15CH2MFA material, was also evaluated. A sensitive, linear correlation was found between the ΔDBTT and values of the relevant MAT degradation function. Based on these results, MAT is shown to be a promising (at least) complimentary tool of the destructive tests within the surveillance programs, which are presently used for inspection of neutron-irradiation-generated embrittlement of RPVS.

Hardening and microstructure evolution in proton-irradiated model and commercial pressure-vessel steels

In an effort to understand the mechanisms of irradiation embrittlement of reactor pressure-vessel steels, hardening and microstructure evolution in a number of simple ferritic model alloys and complex bainitic steels irradiated with 3.2 MeV protons over a range of doses, dose rates and temperatures were characterized. Irradiations were conducted on selected model alloys to 1 dpa, which is a much higher dose than has been explored for neutron irradiations of these materials. Irradiation hardening was determined from Vickers hardness measurements, and the microstructures were characterized using small angle X-ray scattering (SAXS) in selected cases. At low-to-intermediate dose, the hardening trends in the proton-irradiated ferritic alloys without nickel were similar to those under neutron irradiation. Hardening also decreased with the proton irradiation temperature in this case, broadly consistent with neutron irradiation trends, and was generally relatively insensitive to dose rate. Quantitative differences were observed between the proton and neutron irradiations of model alloys and, to a lesser extent, complex steels, containing both copper and nickel. These differences can be rationalized by shifts in the hardening curves to higher dose, due to proton dose rates that are 700 or more times higher than for neutrons. Precipitate sizes in the proton-irradiated alloys generally increase with dose and are qualitatively similar to those observed in neutron-irradiated alloys. However, much larger scattering features were also detected at 1 dpa. All the alloys irradiated to this high dose were remarkably hardened by amounts from 490 to 740 MPa.

Preliminary Results On Ultrasonic Attenuation Detection Of Neutron Irradiation Embrittlement Of Nuclear Reactor Steel

ABSTRACTNeutron bombardment of reactor pressure vessel (RPV) steels causes reductions in fracture toughness in these steels, termed neutron irradiation embrittlement. Currently there are no accepted methods for nondestructive determination of the extent of the irradiation embrittlement nor the actual fracture toughness of the reactor pressure vessel. This paper provides preliminary results of an effort addressing the use of ultrasonic attenuation as a suitable parameter for nondestructive determination of irradiation embrittlement in RPV steels.