Transactions of the 17 th International Conference on Structural Mechanics in Reactor Technology (SMiRT 17) Prague, Czech Republic, August 17 –22, 2003 Paper # P01-4 1 Evaluation of Ultimate Load Bearing Capacity of the Primary Containment of A Typical 540MWe Indian PHWR Ray Indrajit, Roy Raghupati, Verma U.S.P., Warudkar A.S. Nuclear Power Corporation of India Ltd., India ABSTRACT This paper presents the analysis of the Inner Containment Structure (ICS) of a typical 540 MWe Indian PHWR for the purpose of evaluating its ultimate load bearing capacity (ULBC) under beyond postulated design basis accident (DBA) scenario. The methodology adopted for the non-linear analysis of the prestressed concrete ICS including the various issues, viz. behaviour of concrete under compression and tension, tension stiffening, cracked shear modulus etc. have also been discussed in this paper. The effect of accident temperature on ULBC has been studied and discussed in this paper. This paper also discusses about the study carried out for mesh sensitivity of the finite element (FE) discretisation on ULBC of ICS in the non-linear range. Based on the detailed analysis, the factor of safety of the ICS under beyond postulated DBA scenario has been evaluated. INTRODUCTION The typical Indian PHWRs of 540MWe series are having a double containment system. The ICS is prestressed concrete and the outer containment structure (OCS) is reinforced concrete. The ICS is a cylindrical structure of 63.0m height, capped with a prestressed concrete segmental spherical dome with two large openings to facilitate the replacement of SG should it be needed at later date. The OCS is a reinforced concrete structure having similar shape of that of ICS and covers the ICS completely (Fig.-1). The ICS is designed against the postulated DBA pressure (14.4 T/m 2 (g)) and temperature due the various postulated accident scenario viz. LOCA, MSLB etc. A non-linear analysis of the IC has been carried out considering the reinforcements & prestressing steel embedded in the concrete in order to study the factor of safety available for the ICS beyond the postulated DBA scenario. The analysis model has been developed using a degenerated layered shell element in which the reinforcements/prestressing steels are modelled using a smeared approach. Various aspects of behaviour of reinforced/prestressed concrete under tension and compression viz. tension stiffening, compression behaviour of the concrete etc., have been accounted for using the state of the art knowledge available in the literature. This paper presents a comprehensive description of the analytical model used in the evaluation of the ULBC of the ICS under beyond postulated DBA scenario with due consideration to the aspect of analytical modeling of the behaviour of the reinforced concrete shell under tension & compression. The behaviour of the ICS has been presented in this paper at different stages of loading beyond the design pressure. The behaviour of the ICS at different stages of loading beyond the design pressure considering constant accident temperature has also been discussed in this paper. The problem is highly non-linear and the analysis results are sensitive to the FE discretisation of the structure. The adequacy of the FE discretisation considered in the analysis is established by mesh sensitivity analysis. The same is also discussed in this paper. The additional factor of safety of the design of the ICS beyond the postulated DBA with and without accident temperature has been discussed in this paper. ANALYSIS METHODOLOGY Geometrical Idealisation The containment is a thin shell structure. Therefore, the stresses developed due to different loads are mainly membrane in nature and the normal stresses in thickness direction are negligible. Radial (transverse) tensile stresses do develop in the ICS by means of embedded curved prestressing cables (curvature effect). Radial tensile stresses also occur due to transition in thickness of the shell at the discontinuities (transition effect) and due to presence of voids due to cable sheath (stress concentration effect). The radial tensile stresses are more during the construction time and reduce under the internal pressure due to accident condition. Since the magnitude of the radial stresses both under compression and tension is almost negligible under accident condition, a shell model using 8 noded degenerate quadratic shell element has been adopted for evaluating the non-linear response of the structure. Transverse shear deformations are considered in the element formulation with the assumption that the normal to the mid-surface of the element remains straight but not necessarily normal during deformation. Three
Evaluation of Ultimate Load Bearing Capacity of the Primary Containment of A Typical 540MWe Indian PHWR
Jun 27, 2023
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