PSI - Issue 54

Oleksii Ishchenko et al. / Procedia Structural Integrity 54 (2024) 241–249 Yaroslav Dubyk et al./ Structural Integrity Procedia 00 (2023) 000 – 000

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For this purpose, a special procedure for CFD-Post was developed using the Perl language, the essence of which is as follows. A curvilinear generatrix is constructed for the core barrel, which geometrically corresponds to the middle surface between the internal and external ones. Each generatrix curve of the outer and inner surface is divided into a finite number of points, so that the arc length is equal. After this, the canonical shape of the ray is found, which is assumed to be orthogonal to the internal generatrix at the point that intersects the external curve. The center line reference point coordinates are calculated from the condition that the distance to each of the considered nodes of the generatrices is equal. This method allows one to obtain consistent external and internal nodes from which you can calculate the difference in static pressure and dynamic pressure of flow deceleration (dynamic component). To calculate the forces and moments projections on each of the coordinate axes (OX, OY, OZ), summation is carried out in azimuth. The direction cosines on the curved section of the elliptical bottom are considered, allowing us to obtain the resultant (integral loads) distribution in the axial direction. This method allows to neutralize the influence of an uneven computational mesh on the calculation of surface integrals and solves the problem of projecting data onto a curved surface. 3. Structural integrity assessment

Fig. 4. Generalized specification for calculating dynamic loads on reactor elements.

For the strength calculation, FEM was created in ANSYS, which included CB and other RVI, and consisted of 57116 shell elements and 5417 beam elements (shown in Fig. 5). These types of elements were chosen due to geometry's complexity and large number structural elements. Also, the geometry was simplified by lowering the Young’s modulus , it allowed us to remove perforations in CB bottom, plates and forgings of the Block of Guide Tubes. Such simplification is done considering retaining the overall element stiffness. RVI support elements like vibration damping brackets, upper CB keys, fuel assemblies heads were replaced by springs with corresponding stiffnesses (all simplifications shown in Fig. 5). For the CB geometry model (except core bottom which is considered very rigid), plastic strengthening was applied according to the power law. The strengthening diagram for CB material is obtained using steel properties for forgings according to PNAE G-7-002-86 (1989). One of the ideas was to compare obtained FEM results with the analytical solution Dubyk et al. (2018), Dubyk et al. (2020). In such case CB is schematized as a thin cylindrical shell with parameters L = 8.73 m; R = 1.775 m; h = 0.06 m . Clamped-Simply Supported (C-S) is used as boundary conditions: clamped at the CB bottom, since thin shell is connected to relatively rigid CB bottom and simply supported at the upper part of CB. The both models are compared using natural frequency analysis Dubyk et al. (2018). The limitation of the analytical solution is use of elastic material model, nevertheless, it is very useful in parametric studies. Both models (FE model and approximate calculation scheme) were used for further CB stress-strain state dynamic calculation during ‘col d leg’ LB LOCA, using pressure drop from CFD results.