Simulated Reactor Coolant Research Articles

Development of Fatigue Crack Growth Prediction Model in Reactor Coolant Environment

In order to conduct effective and rational maintenance activity of components in nuclear power plants, it is proposed to manage fatigue degradation based on crack size corresponding to an extent of cumulative fatigue effect. This study is aimed at developing a prediction model for fatigue crack growth in simulated reactor coolant environment. In order to investigate influence of reactor coolant environment on crack initiation and crack growth, two-step replica observations were conducted for environmental fatigue test specimens (type 316 stainless steel) subjected to three kinds of strain range. Crack initiation, growth, and coalescence were observed in the experiments. It is clarified that crack coalescence is one of the dominant factors causing fatigue life reduction, and fatigue life reduction depends on crack size and distance of two coalescing cracks. Then, a model was developed for predicting statistical crack initiation and growth behavior. The relationship between dispersion of crack initiation life and strain range was approximated by the Weibull model to predict crack initiation. Then, the statistical crack growth was modeled using the relation of crack growth rate and strain intensity factor. Furthermore, the crack coalescence was taken into account to the crack growth prediction considering the distance between two cracks. Finally, the crack growth curve, which is the relationship between crack size and operation period, was derived through Monte Carlo simulation with the developed model. The crack growth behavior and residual life in the simulated reactor coolant environment can be reviewed by the crack growth curve obtained with crack initiation, and the growth model developed was compared with the fatigue test results.

X‐ray photoelectron study of oxides formed on Ni metal and Ni‐Cr alloy surfaces under electrochemical control at 25 °C and 150 °C

AbstractThe oxide chemical composition on metallic Ni and NiCr alloy electrodes has been studied for changes in simulated reactor coolant solution chemistry, through a range of oxidizing potentials and pH settings at 25 °C and 150 °C. Even under strongly reducing conditions, the Ni surface has a 2‐nm layer of oxide and hydroxide from which further oxides form, depending on the subsequent oxidative step. For basic (normal operating) pH conditions and under oxidation potentials near 0 volts (vs. SCE), a predominantly Ni(OH)2 layer is formed that appears to remain relatively stable up to at least 48 hours of oxidation at 150 °C. For the NiCr alloy, similar stability is imparted by a thin film of Cr(OH)3/ Cr2O3 and Ni(OH)2./NiO. Under milder oxidizing (but still basic) conditions, the surface is stabilized by a thin film that is mostly Ni(OH)2/NiO. Under neutral solution conditions, the same oxide/ hydroxide films do not seem to be as effective in stabilizing the surface. Copyright © 2017 John Wiley & Sons, Ltd.

Temperature effects on low-cycle fatigue behavior of SA533B steel in simulated reactor coolant environments

The low-cycle fatigue (LCF) tests were conducted on SA533B steel at a strain rate of 0.4% s −1 in simulated reactor coolant environments. A significant temperature effect on fatigue life was observed with the specimens tested in the water environment with saturated oxygen; the fatigue lives varied with temperature in the range from 150 °C to 300 °C. However, little or no dependence of fatigue life on temperature was noted in the water environment with oxygen content of 213 ppb. At any test temperature, the steel specimens endured the longest fatigue life when tested in air, but, in contrast, they were observed to have the shortest one in the water environment with saturated oxygen. It implies the fatigue–corrosion interaction plays a significant role in determining the fatigue life of SA533B steel. The results of X-ray diffraction (XRD) analysis showed that the constituents of corrosion products were strongly affected by both temperature and dissolved oxygen content of the water environment. Furthermore, the same factors also affected the fracture appearances of fatigue-tested specimens. The dynamic strain aging (DSA) effect on fatigue life is also discussed in this report.

Dynamic Response of Hot/Cold Liquid Interfaces to Pump Speed Perturbations in a Thermal-Hydraulic Loop Simulating a PIUS-type Reactor.

The operation of a PIUS-type reactor requires controlling the reactor pump speed to keep stationary the hot/cold liquid interfaces between the reactor coolant and cold borated water. The dynamic response of the interface location to pump speed perturbations is analyzed for an experimental loop simulating a PIUS-type reactor. The transfer function between the pump speed and the interface location is obtained by perturbing and Laplace-transforming the one-dimensional fluid momentum equations. The analytical results agree well with experimental data taken from the same facility. It is shown that the magnitude of the phase lag in the response of the interface location, which needs to be considered in designing a pump speed controller, primarily depends on the fluid inertia in the loop, the density lock flow area, and the density difference between the simulated reactor coolant and borated water.

Evaluation of High-Temperature Alloys for Helium Gas Turbines

Because of the high thermal and mechanical stresses in components of a helium turbine coupled directly to a high-temperature reactor and the stringent nuclear safety requirements, an extensive materials development program has been undertaken. The candidate alloys for turbine blades and hot ducts (nickel- and molybdenum-base alloys) and for rotors (1% CrMoV and 12% chromium steels) have been tested under the expected service conditions.The results of creep/rupture, fatigue, and fracture mechanics tests on turbine blade and rotor materials are presented. The gas/metal reactions that occur in the simulated reactor coolant gas and the decontamination behavior of components are also discussed. In addition the development of a molybdenum-base alloy for turbine blading is reported.