Concrete behavior in reactor envelope of a nuclear power plant at temperatures upto200°C

Abstract EN

In this contribution, the properties of concrete at Temelin nuclear power plant (Czech Republic) are introduced.

The concrete specimens from Temelin NPP were manufactured at the construction site, then stored at 20°C and 100% R.H.

for 28 days and exposed to temperatures of 40°C, 60°C, 100°C, and 200°C.

It was found that the loss in mechanical properties of concrete is influenced by its degradation through changes induced in basic processes of cement hydration and hardening of the bonding system in the cement paste under the action of elevated temperatures.

At 200°C, the bonding system of concrete has already lost approximately three quarters of the water content bound in C-S-H and C-A-H gel-like hydrate phase.

The Ca(OH)2 content, determined by the intensity of diffraction line at 4.91 A, is decreased by approximately 5 times at 200°C compared to that at 20°C/100% R.H.

— 28 days — cure.

This decrease in volume of the hydrate phase and Ca(OH)2 is closely connected with the coarsening of the pore structure of concrete, because the bound water mass is replaced at elevated temperatures by air voids.

At 200°C, the remainder of non-decomposed hydrate phase and Ca(OH)2 represents the binding material supply, giving concrete its residual utility properties.