On the structural integrity assessment of cracked piping of PWR nuclear reactors primary systems

Abstract

The structural integrity assessment methods of cracked components manufactured with ductile materials request the evaluation of parameters of the Elastic–Plastic Fracture Mechanics (EPFM) and of the Limit Load Analysis (LL). The following simplified methods for evaluation of the ductile behavior of cracked piping systems are available in the literature and were considered in this work: J–T method (J-integral versus the tearing modulus T) [Paris, P.C., Johnson, R.E., 1983. A method of application of elastic–plastic fracture mechanics to nuclear vessel analysis. In: Elastic–Plastic Fracture: Second Symposium, vol. II, ASTM STP 803, pp. II-5–II-40], R6 method [Milne, I., Ainsworth, R.A., Dowling, A.R., Steward, A.T., 1988. Assessment of the Integrity of Structures Containing Defects. CEGB Report R/H/R6 – Revision 3, 1986. International Journal of Pressure Vessels and Piping 32, 3–104] and DPFAD method (Deformation Plasticity Failure Assessment Diagram) [Bloom, J.M., Malik, S.N., 1982. Procedure for the Assessment of the Integrity of Nuclear Pressure Vessels and Piping Containing Defects. EPRI Topical Report NP-2431, Research Project 1237-2, Electric Power Research Institute, CA, USA]. Calculation routines by Jong, R.P. [2004. Structural Integrity Assessment of Cracked PWR Piping Systems. M.Sc. Dissertation, Nuclear Technology Program, University of São Paulo (in Portuguese)], related to the above defined methods, were applied for the computation of the instability loads for some pipes of primary piping systems of Pressurized Water Reactors (PWR), with through-wall circumferential cracks, subjected to bending moments, made with high toughness steels. Changes in geometry and values of the materials properties were considered. The estimated instability loads (bending moments) obtained for the considered pipes were compared with experimental results obtained from the literature. From those comparisons, some conclusions and comments could be made, being the main focus of the work the aspects related to the characterization of the materials properties to the appropriate application of the methods to cracked piping of PWR primary systems, in evaluations of the LBB (Leak-Before-Break) concept.