PSI - Issue 37

M. Annor-Nyarko et al. / Procedia Structural Integrity 37 (2022) 225–232 Author name / Structural Integrity Procedia 00 (2019) 000 – 000

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3.2. Heat transfer coefficient estimation The heat transfer coefficient (h) of the injected emergency coolant interaction with the inner RPV was estimated using Equation1 (Holman, 2010; Schlichting and Gersten, 2017) h = Ck ( D 2 ρ 2 μ gβ∆T 2 Pr) n (1) where C = 0.590, n = 0.3 and k=0.6096 W/m K are assumed. In this study the heat transfer coefficient was conservatively estimated to be 8450 W/m 2 °C 3.3. ASME curve for the material fracture toughness The fracture toughness of the RPV material is quantified the ASME approach expressed in Equation 2 K IC = 36.46 + 3.083exp[0.036(T − ART NDT + 56)] (2) where ART NDT is the mean value of the adjustment in reference temperature caused by irradiation. ART NDT = 70°C is selected based on the calculation of end of life fluence of the selected PWR in accordance with R.G. 1.99 and 10 CFR 50.61(He and Isozaki, 2000; USNRC, 1988) 3.4. Fracture mechanics submodel The fracture mechanics node-based submodel shown in Fig.4. (b) which consist of the maximal stress location was created from the results of a direct coupled thermo-mechanical analysis shown in Fig. 4. (a). The submodel incorporated all the boundary conditions of the full RPV model by interpolating the temporal displacements obtained from the global model as mechanical boundary conditions on the boundaries of the submodel during the co-simulation phase. The mesh of the model was sensitively determined to ensure computational efficiency and accuracy. An axial semi-elliptical surface crack with a depth of one-fourth the RPV wall thickness and an aspect ratio ⁄ = 0.3 was assumed in this study. The integrity parameter; stress intensity factor (K 1 ) was then estimated at the deepest crack point using both M-integral method implemented in the proposed Abaqus-FRANC3D Co-simulation. Also, the SIF was estimated using the conventional VCCT method.

Fig. 4. (a) Maximum stress location at the inlet nozzle-vessel wall intersection (b) Abaqus-FRANC3D fracture mechanics submodel with inserted surface crack