PSI - Issue 54

Oleksii Ishchenko et al. / Procedia Structural Integrity 54 (2024) 241–249 Author name / Structural Integrity Procedia 00 (2019) 000 – 000

248

8

Table 2. Result table. Max. Stress (Regime number)

r K

r S

I K , MPa· √m

ref  , MPa

Crack direction

n

Non-irradiated part

mx  (I) bx  (II) m   (III) b   (IV) mx  (V) bx  (VI) m   (VII) b   (VIII)

154.31 152.11 210.44 210.99 141.78 141.71 125.86 125.48

0.70 0.69 0.95 0.95 0.18 0.18 0.16 0.16

64.99 66.76 49.38 49.59 27.43 27.59 28.44 31.10

0.27 1.59 0.28 1.60

1.33 1.33

0.20 0.20

External

Irradiated part

0.33 2.87 0.33 2.85 0.34 2.80 0.38 2.58

Internal

Fig. 8. Failure assessment diagram (FAD) for the CB (a) upper part; (b) bottom part : markers “+” – circumferential crack, “X” – axial crack, “O” – outside crack, “□” – inside crack.

Conclusions This work presents the results of a comprehensive assessment of the impact on the VVER-1000 internals, accounting the core topology during the initial dynamics of the LOCA event. The analysis consists of two consecutive steps. The decompression wave movement in the reactor when the cold circulation leg breaks is calculated at the first step. The transient process analysis is carried out in a two-phase (heterogeneous in speed and temperature) formulation. For this purpose, the developed VVER-1000 CFD model is complemented by a special phase change model (SPCM). The proposed SPCM model is based on the classical thermal phase transition model of the two resistance type. It makes it possible to consider the effect of pressure changes and allows simulating surface vapor generation in a simplified core model. SPCM is tested on the classic Edwards test. The proposed phase change model is implicitly implemented in the VVER-1000 CFD model. Obtained for 1000 ms results differ significantly from those obtained in a single-phase formulation. The approximate (based on the thin shell vibrations) and detailed (Ansys FEM) analysis were compared. Plastic strengthening was specified for the FEM. The FEM was used to evaluate plastic deformation during the event and