Presentation of a New Methodology of Chained Computations usingInstationary 3D Approaches for the Determination of Thermal Fatigue in aT-Junction of a PWR Nuclear Plant

摘要

Thermal fatigue of the coolant system of PWR plants is a major issue for nuclear safety. The problem is especiallyrnaccute in mixing zones, like T-junctions, where a large difference of water temperature between the two entry branchesrnand the high level of turbulence can lead to large temperature fluctuations at the wall. Until now, studies on this matterrnhave been tackled at EDF using steady methods. The purpose of this paper is to present a new methodology of chainedrncomputations, that allows to take into account the unsteady and 3D effects of the problem, and apply it to the ResidualrnHeat Removal (RHR) system. A development version of EDF finite volume CFD tool Code_Saturne is used torncompute the fluid flow with a L.E.S. Model, which gives access to the instantaneous temperature fluctuations.rnCode_Saturne is coupled to the finite element thermal code Syrthes, which propagates the temperature fluctuations intornthe wall thickness. Then, the instantaneous temperature field inside the wall is transferred to EDF thermomechanic toolrnCode_Aster, to perform mechanical computations that yield the instantaneous mechanical stresses seen by the Tjunctionrnand the following elbow. The results of this first study are promising, although this method is still largelyrnunder development and validation.