Pengaruh Rasio I/D terhadap Permulaan Flooding dan Fluktuasi Voltase Sinyal Tekanan Rezim Flooding pada Geometri Kompleks

A nuclear power plant operation requires reliability safety systems. Therefore, an accidental scenario such as the LOCA becomes a specific attention. This relates to a countercurrent flow phenomenon which permits the occurrence of a flooding regime. This study aims to investigate the effets of I/D ratios of the riser on the onset of flooding and time-series voltage fluctuations of differential pressure signals of the flooding regime on a complex geometry representing a PWR hot leg. The test section contains a combination of a horizontal, an elbow and an inclined pipes. Three I/D ratios containing 1.9 (R1), 3.9 (R2) and 8.3 (R3) were assesed. The tabulated data are expressed in the term of a flooding curve. Meanwhile, the statistical features of the time-series voltage fluctuations of the signals are presented on both PDF and PSD graphs. The results obtained show that the assesed I/D ratios do not conduct significance effects on the onset of flooding. On the other hand, there are trends which can be obtained from the time-series signals with the increase of the I/D ratio. Those trends can also be observed in the such statistical features; the PDF and PSD graphs, respectively.

Investigations on the Environmentally Assisted Fatigue Behavior of Steel Specimens for a Better Understanding of Component Fatigue in Nuclear Applications

The fatigue assessment of pressurized components is of high importance for the operation of nuclear power plants. However, the environmental influences on the fatigue behavior are highly discussed. On the one hand, laboratory specimens tested in high temperature water (HTW) conditions show a significant drop in fatigue lifetime, compared to tests at air environment, and question the conservatism of modern standards. On the other hand, the fatigue assessment methods based on uniaxial tensile testing seems to overestimate the fatigue damage of components during operation. To overcome these discrepancies, the environmental influences on material fatigue have to be better understood. Laboratory testing setups have to be adapted to the relevant loading conditions during power plant operation. Therefore, MPA Stuttgart is investigating the environmentally assisted fatigue (EAF) of steels under various loading conditions for smooth and notched specimens, as well as full scale component testing at HTW conditions. In this paper the results of ongoing research are presented. The low cycle fatigue experiments on steel materials for relevant nuclear applications are performed at air and under pressurized water reactor (PWR) environment. The shape of specimens, the loading spectra, loading rate and the multiaxiality of load are derived from piping components in power plant operation.

Analytical Approach to Sampling Estimation of Underwater Tunnels Using Mechanical Profiling Sonars

Hydroelectric power plants often make use of tunnels to redirect the flow of water to the plant power house. Such tunnels are often flooded and can span considerable distances. Periodical inspections of such tunnels are highly desirable since a tunnel collapse will be catastrophic, disrupting the power plant operation. In many cases, the use of Unmanned Underwater Vehicles (UUVs) equipped with mechanical profiling sonars is a suitable and affordable way to gather data to generate 3D mapping of flooded tunnels. In this paper, we study the resolution of 3D tunnel maps generated by one or more mechanical profiling sonars working in tandem, considering synchronization and occlusion problems. The article derives the analytical equations to estimate the sampling of the underwater tunnels using mechanical profiling sonars (scanning sonars). Experiments in a simulated environment using up to four sensors simultaneously are presented. We also report experimental results obtained by a UUV inside a large power plant tunnel, together with a first map of this environment using a single sonar sensor.