Predictions of ultimate load capacity for pre-stressed concrete containment vessel model with BARC finite element code ULCA

Ultimate load capacity assessment of nuclear containments has been a thrust research area for Indian Pressurized Heavy Water Reactor (PHWR) power programme. For containment safety assessment of Indian PHWRs a finite element code ULCA was earlier developed at BARC, Trombay. This code has been extensively benchmarked with experimental results. The present paper highlights the analysis results obtained from code ULCA for Prestressed Concrete Containment Vessel (PCCV) that was tested at Sandia National Labs, USA in a Round Robin analysis. This test programme was co-sponsored by Nuclear Power Engineering Corporation (NUPEC), Japan and the US Nuclear Regulatory Commission (NRC). Three values of failure pressure predictions namely the upper bound, the most probable and the lower bound (all with 90% confidence) were made as per the requirements of the round robin analysis activity. The most likely failure pressure is predicted to be in the range of 2.95–3.15 Pd (Pd=design pressure of 0.39 MPa for the PCCV model) depending on the type of liners used in the construction of the PCCV model. The lower bound value of the ultimate pressure of 2.80 Pd and the upper bound of the ultimate pressure of 3.45 Pd are also predicted from the analysis. These limiting values depend on the assumptions of the analysis for simulating the concrete-tendon interaction and the strain hardening characteristics of the steel members. The experimental test has been recently concluded at Sandia Laboratory and the peak pressure reached during the test is 3.3 Pd that is enveloped by our upper bound prediction of 3.45 Pd and is close to the predicted most likely pressure of 3.15 Pd. This paper highlights the features of BARC code ULCA and addresses a few issues related to constitutive modeling of pre-stressed concrete structure that is relevant for ultimate load capacity prediction of nuclear containments. These would be useful for evaluation of the present numerical results with the test data obtained by Sandia National Laboratory.