PSI - Issue 60

Keshav Mohta et al. / Procedia Structural Integrity 60 (2024) 36–43 Author name / Structural Integrity Procedia 00 (2019) 000 – 000

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The analysis method is graphically depicted in Fig. 2.

Fig. 2. Analysis method for structural integrity assessment of Calandria

5. Case studies on Indian PHWRs With the analysis method mentioned above, the structural integrity assessment of Calandria of Indian PHWRs- Standard 220 MWe and 540 MWe configuration has been carried out and the duration of in-Calandria corium retention has been determined for a postulated accident scenario of unmitigated total loss of heat sink. The salient features of these studies are described here, and details maybe found in Mohta et al. (2017, 2020b). Thermal hydraulic analysis has been carried out using ASTEC V2.1 with suitable adaptation for PHWR specific geometry and features. Various heat exchanges modeled for the analysis are shown in Fig. 3. Based on the transient temperature time histories obtained from the thermal analysis, the elastic visco-plastic finite element analysis with geometric and material non-linearity has been carried out to assess the structural response of the Calandria. The FE model comprises of integrated Calandria- end shield assembly, as shown in Fig. 4., to correctly account for the realistic component stiffness, temperature distribution and boundary conditions. The time line of key events based on the thermal and structural assessment of the Calandria assembly during the accident progression is furnished in Table 1 for Standard 220 MWe and 540 MWe Indian PHWRs. The case studies show reasonable time frame for operator action due to in-Calandria corium retention, and highlight the advantages of several heat sinks (moderator, end shield water, vault water) and low power density in PHWRs.