KONBiN’03 The 3-rd Safety and Reliability International Conference FINITE ELEMENT SYSTEM MODELLING AND PROBABILISTIC METHODS APPLICATION FOR STRUCTURAL SAFETY ANALYSIS ROBERTAS ALZBUTAS, GINTAUTAS DUNDULIS, RONALD F. KULAK Lithuanian Energy Institute, Lithuanian Energy Institute, Argonne National Laboratory robertas@mail.lei.lt , gintas@isag.lei.lt , rfkulak@anl.gov Abstract: A probability-based approach is presented as the integration of probabilistic methods and deterministic modelling based on the finite element method. An existing finite element software package was linked to an existing probabilistic package to analyze the complex mechanics and to perform the transient nonlinear analysis of impact problems. The developed methodology is applied to the analysis of a whipping group distribution header and subsequent impacts with adjacent headers; this is a postulated accident for the Ignalina Nuclear Power Plant RBMK-1500 reactors. The uncertainties of material properties, component geometry data and loads were taken into consideration. The probabilities of failure of the impacted header and of the header support-wall from uncertainties in material properties, geometry parameters and loading were estimated. Key words: Finite Element Method, Probabilistic Finite Element Analysis, RBMK- 1500, Pipe Whip Impact 1. INTRODUCTION The Ignalina Nuclear Power Plant is a twin-unit RBMK-1500, graphite moderated, boiling water, multichannel reactor [1]. In comparison to Western power plants, RBMK-type reactors contain thousands of pipelines. Sometimes several high-energy pipelines are located in one compartment. A guillotine rupture of one of these high-energy pipelines raises serious safety concerns about possible severe damage to neighbouring pipelines and to the adjacent building structures. The group distribution header (GDH) is one of the critical components of the reactor safety system for the RBMK-1500. The GDH must function not only during normal operation, but also in case of an accident. Emergency core cooling system (ECCS) piping is connected to the GDH piping. In case of an accident, coolant passes through the ECCS and GDH piping. A deterministic analysis of this problem was presented in [2]. It is well known that the values for material parameters are uncertain. The uncertainty of strength parameters is especially characteristic for concrete materials. The random effects, which are associated with material properties, pipe geometry and concrete walls, were incorporated into the analysis. The probabilistic analysis of neighbouring piping failure and support-wall failure after a GDH guillotine break were carried out.