The Effect of Operational Factors on Phase Formation Patterns in the Light-Water Reactor Pressure Vessel Steels

Abstract

This paper presents the results of atom probe tomography studies on radiation-induced phase formation in light-water reactor pressure vessel steels after neutron irradiation under various conditions in comparison with the literature data. The given irradiation conditions are fluence (10–100) × 1022 m−2, flux (5–2700) × 1014 m−2s−1 and irradiation temperature (50–400) °C. The composition of the studied steels varies in a wide range for the elements significantly affecting radiation and thermal resistance of steels: Ni in the range of 0.2–6.0 wt.%, Mn–0.03–1.1 wt.%, Cu–0.01–0.16 wt.%, and P–0.01–0.03 wt.%. The number density, volume fraction, size, composition, and nucleation sites of precipitates are determined. The regularities of the effect of various operational factors on the phase formation in these steels have been analyzed and revealed. The study shows that in materials with high copper content, Cu-rich precipitates are formed by a radiation-enhanced mechanism. In materials with low copper content, their formation upon irradiation at 300 °C occurs by a radiation-induced mechanism since the main nucleation sites are point defect clusters formed in cascades. At the same time, the density, volume fraction, and composition of the precipitates depend on the steel composition (Ni and Mn content). In the steel with increased Ni content up to 5 wt.% but with ultra-low Mn content ≤ 0.03 wt.%, it is possible to suppress the formation of Ni-Si-Mn precipitates under irradiation.

Analysis of Shift in Nil-Ductility Transition Reference Temperature for RPV Steels Due to Irradiation Embrittlement Using Probability Distributions and Gamma Process

“…This continuous exposure leads to the gradual degradation of their material properties [2], manifesting as irradiation embrittlement. At the microscopic level, neutron irradiation causes the formation of defects such as vacancies, interstitial atom point defects, and clusters, which leads to the precipitation and segregation of solute atoms, notably with Cu-rich precipitates and P element segregation [3][4][5]. From a macroscopic perspective, RPV steels experience embrittlement, evidenced by an increase in nil-ductility transition reference temperature (RT NDT ) [5], a reduction in upper-shelf energy, and diminished fracture toughness.…”