PSI - Issue 59

Yaroslav Dubyk et al. / Procedia Structural Integrity 59 (2024) 36–42 Dubyk and Zvirko/ Structural Integrity Procedia 00 (2019) 000 – 000

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3. In-Vessel scenario results The IVMR scenario was considered for WWER-440 reactor, discussed previously in Dubyk and Antonchenko (2020). Mechanical and physical properties of the RPV steel are taken according to International Atomic Energy Agency (2008), multi-linear isotropic hardening model (MISO) is used, creep is described by the modifies time hardening model. As a calculation scenario a LBLOCA + Station Blackout is considered with a maximum heat flux on the internal surface ~ 1 MW/m 2 . The BC conditions for the internal surface are heat fluxes (obtained from MELCORE) and Temperature and HTC for the outer RPV surface (obtained using RELAP). The cavity is assumed flooded (external temperature ~ 100 °C), and the main circulation loop is depressurized , corium mass ~90 tons. For analysis the 2D axisymmetric model is used Dubyk and Antonchenko (2020), which consisted from 44969 nodes and 14662 elements PLANE183, model was limited at the height of supporting elements, where it was fixed in axial direction. The analysis is done in two variants:  Only RPV melting is considered, i.e. elements with temperature above the 1400°C (melting point) were „killed‟  Melting and corrosion are considered, i.e. in the addition to previous elements are „killed‟ according to Eq(2) procedure. An incubation period of 12000 s is considered (see eq.1). Before we move to the comparison between two variants, it is necessary to give a characterization of the RPV „ carrying zones‟. For any time step, we can divide the residual wall into three zones (see Fig.2):  Hight- temperature zone (1000 to 1400°C), it is a zone with high deformation, which do not carry any load, moreover according to Eq.(1) it may be also called „corrosion zone‟ .  Zone of creep relaxation (500 to 1000°C) , it is a zone with limiting carrying capacity with developed plastic and creep strains.  Load-carrying zone (below 500 °C), a „cold part‟ of the remaining wall thickness. The thickness of this zone determines the RPV possibility to withstand the mechanical loads, including possible overpressure.

Fig. 2. RPV cross-section with zones indication. Time = 23400 seconds, Heat Flux ~0.45MW/m 2 , calculations without corrosion.