Abstract
The lifetime extension of the nuclear power stations is considered as an energy challenge worldwide. That is why, the risk analysis and the study of various effects of different factors that could potentially represent a hazard to a safe long term operation are necessary. The methodology for fatigue dimensions of the Pressurized Water Reactor components (PWR) is based on the use of design curves established from test carried out in air at 20 °C on smooth specimens by integrating safety coefficient that covers the dispersion of tests associated with the effects of structures. To formally integrate these effects, some international codes have already proposed and suggested a modification of the austenitic stainless steels fatigue curve combined with a calculation of an environmental penalty factor, namely Fen, which has to be multiplied by the usual fatigue usage factor. The aim of this paper is to present a new device “FABIME2E” developed in the CEA-LISN in collaboration with EDF and AREVA. These new tests allow quantifying accurately the effect of PWR environment on semi-structure specimen. This new device combines the structural effect like equi-biaxiality and mean strain and the environmental penalty effect with the use of PWR environment during the fatigue tests.
Highlights
Introduction and aimThe question of assessing the margins and safety factors in the fatigue analyses which are widely used today (ASME BPV III, RCC-M, JSME, EN-13445-3, etc... [1,2,3,4]) is a very challenging one.The fatigue rules used today in the nuclear industry were initially built and integrated into the ASME code in the 1960s
The first device (FABIME2) is devoted to study the effect of biaxiality and mean strain/stress on the fatigue life
Compared to FABIME2, specification changes for FABIME2E device mainly focused on the following points: – specimen is in contact with a Pressurized Water Reactor components (PWR) environment, – an operating temperature of 340 °C, – a maximum pressure up to 350 bar, Fig. 8
Summary
The question of assessing the margins and safety factors in the fatigue analyses which are widely used today (ASME BPV III, RCC-M, JSME, EN-13445-3, etc... [1,2,3,4]) is a very challenging one. To reduce the specimen diameter, the thickness is varying along the radius to initiate a fatigue crack at a specimen center and the possibility to increase the thickness has been kept The objective of this first fatigue test was to dissociate the effect of the mean stress and equi-biaxial state loading. It was used to optimize the geometry of a disk specimen refined in its center It was used as a circumferentially embedded diaphragm with an applied pressure on both sides in order to obtain an equivalent strain in each loading direction in the plane (Fig. 3). The experimental device called “FABIME2’’ is divided into four parts: – fatigue cell which contains the spherical bending specimen, – pressure generating system until 100 bars, – electrical enclosure, – homemade software developed under LABVIEW that provides control and acquisition data during the tests. In order to obtain a homogeneous austenitic phase, the sheet was subjected to a thermal treatment: keeping at high temperature (between 1050 and 1150 °C) followed by rapid cooling
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