MECHANICAL ASPECTS CONCERNING THERMAL FATIGUE INITIATION IN THEMIXING ZONES OF PIPING

摘要

Following the incident (through-wall crack and crazing zones) of May 1998 on the principal mixing zone ofthe residual heat removal system at CIVAUX nuclear plant, EDF has initiated a R&D programme to understandthe incident and assess the risks of damage on other nuclear plant mixing zones. The programme includesdifferent sectors of developments : assessment of temperature fluctuations in mixing zones, study of high-cyclethermal fatigue behaviour of austenitic steel and development of mechanical methodologies for damageassessment and propagation of crazing zones (thermal striping).The paper develops the mechanical part of the programme. It describes analytical thermal fatigue testsperformed on a pipe structure using the bench test INTHERPOL. It also describes an attempt to calculate thespatial and temporal variations of fluid thermal fluctuations in a mixing zone like CIVAUX, using a Large EddySimulation method (LES). Distribution of temperature in the wall is evaluated in the same calculation. Thisresult is used afterwards to estimate the stress variations on the pipe by using finite elements calculation orsimplified methods.