Recommendation for linearization procedure in nuclear pressure vessel-nozzle intersections

Abstract

The pressure vessel design is a fundamental step during the construction of new pressurized water reactors (PWRs). In these facilities, several safety requirements are necessary to guarantee the protection of workers, community and environment against the release of radioactive materials. The Design by Analysis is the procedure presented in the ASME Code, Section III, for nuclear components, which consist of rigorous analysis and classification of all types of stresses and loading conditions to incorporate smaller safety factors increasing the general safety. The limits presented in the ASME Code, Section III, were based on the shell theory. However, precise rules for achieving the various stress categories, in solid finite element analysis, have not been implemented yet in the code. For this reason, this work presents a methodology for the linearization procedure of elastic stresses in pressure vessel-nozzle intersections. Therefore, a vessel was modelled in tridimensional solid finite elements, analyzed and verified as a nuclear component. Then, a discussion of how to perform the code verifications was presented, as well as a mapping of stresses. The lines that were constructed in pressure vessel between transition and structural elements in the longitudinal plane (0º) and lines in structural elements in the nozzle in the transversal plane (90º) present higher stresses and are compared with the ASME Code, Section III limits.