7. Conclusions

6.2. Fragility curves of failure pressure

90 Recent Improvements of Power Plants Management and Technology

sure.

envelope.

The fragility curve of the failure pressure (see Figure 21) was determined performing 45 probabilistic simulations using the RSM approximation method with the experimental design CCD for 106 Monte Carlo simulations for each model and five levels of the overpressure. Various probabilistic calculations for five constant levels of overpressure next for the variable overpressure for gauss and uniform distribution were taken out. The nonlinear analysis of the steel technology structures was performed considering HMH-plastic criterion with the multilinear kinematic hardening stress-strain relations for various levels of the temperatures and the degradation of the strength. The uncertainties of the input data (Table 3) were

Figure 21. Fragility curves of the reactor-protective hood determined analytically for normal distribution with 5%

Figure 20. Sensitivity and trend analysis of the safety function of the reactor cover for uniform distribution of overpres-

The probability nonlinear analysis of the concrete containment failure was made for the overpressure loads from 250 to 500 kPa using the nonlinear solution of the reinforced concrete shelllayered elements. The CRACK program, which was developed by the author and implemented into the ANSYS system [3, 14–18], was used to perform the nonlinear analyses. The uncertainties of the load levels (temperature, dead and live loads), the material model of the composite structure (concrete cracking and crushing), reinforcement, and liner as well as other influences following from the inaccuracy of the calculated model and the numerical methods were taken into account in the Monte Carlo simulations [3]. The probability of the loss of the concrete containment integrity is less than 10<sup>6</sup> for the original structural model. The containment failure is equal to 0.050422906 for the overpressure of 275.5 kPa. The critical technology segment of the containment is the reactor-protective hood with the failure pressure pu.0.05 = 766.9 kPa. The mean value of pressure capacity of the reactor-protective hood is pu.0.50 = 891.8 kPa, the 95% upper bound is pu.0.95 = 973.6 kPa.
