Evaluation of the Risk of Damages in Mixing Zones: EDF R&D Programme

Abstract

Following the incident (through-wall crack and crazing zones) of May 1998 on the principal mixing zone of the residual heat removal system at CIVAUX nuclear plant, EDF has initiated a R&D programme to understand the incident and assess the risks of damage on other nuclear plant mixing zones. The programme includes different sectors of development: assessment of temperature fluctuations in mixing zones, study of high-cycle thermal fatigue behaviour of austenitic steel and development of mechanical methodologies for damage assessment and propagation of crazing zones (thermal striping). A series of tests is being performed in support of the programme. The paper develops the description of each sector of the programme: tests performed, on-site measurements and numerical interpretations. The first results are presented.

On the formation of crack networks in high cycle fatigue

“…Various components in nuclear power plants are subjected to thermomechanical loadings during their lifetime. Thermal striping was observed in the mixing zones of the auxiliary cooling system of nuclear power plants [1]. This is not troublesome as long as a fracture analysis indicates that the cracks will not grow notably during the remaining service life.…”

Experimental and numerical analysis of thermal striping in automotive brake discs

“…2 Authors generally agree that an increase in stress level results in an intensification of the crack network density and a decrease in the distance between cracks. 12 More recent studies 7,8,13,14 are connected with an incident that occurred in 1998 in the Civaux nuclear power plant, 15 where observations revealed the presence of thermal striping on the internal part of pipes of the cooling system. Their purpose was to improve the understanding of the failure and to develop efficient tools to simulate the evolution and criticality of a crack network.…”

Crack initiation under thermal fatigue: An overview of CEA experience. Part I: Thermal fatigue appears to be more damaging than uniaxial isothermal fatigue

“…It also occurs in different types of nuclear reactor components. In the case of pressurized water reactors (PWRs), networks of cracks may appear in auxiliary cooling lines, close to coldwater injection sites, in spite of the relatively small temperature fluctuations [4][5][6][7]. A multi-discipline strategy has been adopted by CEA to investigate thermal fatigue [8].…”