Reliability Assessment of Nuclear Containment Structure Prestressed by Unbonded Tendons

Abstract eng:
This study mainly focuses on reliability of nuclear containment, considering the gradual loss of prestressing force. The reliability analysis is performed for two parts of the containments, including the centre of containment wall and springline. Both meridian and hoop directional cracks are considered during the analysis. In order to satisfy the 60-service-years nuclear power plant design program in Korea, this study performed the curve-fitting with the measured data. Taking the 0-year prestressing force to have no loss, the expected prestressing forces from 1-year to 20-years are log-normally curve-fitted. For convenience use of prestressing loss model in reliability analysis, This study presented a rational and constant C.O.V value that represents the prestressing loss of Korean containments. Through-the-wall concrete cracking is considered as a limit state of containment. The limit state equation consist of four major items, including the stress from prestressing force, dead load, internal pressure and tensile strength of concrete. Both meridian and hoop directional throughthe- wall cracks are considered as the limit states for the analyses. The analyses are performed at springline and mid-height of containment wall. Reliability analysis is performed using the actual containment model in Korea. It has 20.24m radius and 60.47m height with 1.22m wall thickness. Commercial FEM software ABAQUS(ver 6.9) is used for evaluating stress level at each part of containment. The results showed that loss of prestressing force significantly affects the reliability of containment. The lowest structural reliability is evaluated at the mid-height of containment wall, showing the reliability index of 4.06 (Probability of failure: 2.5e-5) to 4.52 (Probability of failure : 3.1e-6). Also, the results revealed that containments are likely to fail with meridian directional crack, rather than hoop directional crack.

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