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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2. Interaction between Corium and Reactor Pressure Vessel The systematic experimental studies of the interaction between the corium and RPV steel, was caried out during some EU projects (Bechta et al., 2009) and (Pivano et al, 2019). Such study requires complicated test facilities, and those data is unique. The corrosion process can be described by three phases (Bechta et al., 2008): incubation and acceleration (formation and accumulation of liquid phase, corium crust impregnation), corrosion and then saturation. During the incubation phase the corrosion depth is negligible, and time of the process can be described by the equation:   8000 200 70 , inc n t C s    (1)

Here n C   The steady-state corrosion process and saturation is described by the equation: n C  oxidation index, 70 30

dh

4

0.46 10

, T T mm s  /



 

(2)

int

B

dt

Here dh dt  corrosion rate, for 70 ; int T  temperature on the corrosion front, °C, 1440 30 n C  

int B T T  

B T  temperature of the final corrosion front position, °C According to the experiments Bechta et al. (2006) the minimum value of 1090 B T  °C s recommended for calculations. Eq. (2) can be used for conditions of reactor presser vessel interaction with both oxide and metallic parts of the suboxidized corium pool. Both melting and corrosion contribute to thinning of RPV wall during the IVMR scenario. To account for it a special technique of „element killing‟ is implemented in the ANSYS code to simulate the wall ablation. The process is illustrated in Fig. 1 , i.e. the RPV wall profile is updated regularly during the analysis, by „killing‟ ements which temperature exceed the melting limit or which are corroded through.

Fig. 1. Element birth and death technics for melting and ablation.

It is worth mentioning that for simulation purpose a refine mesh, particularly in the area of expected ablation should be used. It is also recommended to refine the mesh during the sensitivity study, to be confident in the ablated RPV profile.