Abstract
X-ray computed tomography (X-ray CT) has been applied to non- destructively characterise changes in the microstructure of a concrete used in the pressure vessel structure of Advanced Gas-cooled Reactors (AGR) in the UK. Concrete specimens were conditioned at temperatures of 105 o C and 250 o C, to simulate the maximum thermal load expected to occur during a loss of coolant accident (LOCA). Following thermal treatment, these specimens along with an unconditioned control sample were characterised using micro-focus X-ray CT with a spatial resolution of 14.6 microns. The results indicate that the air void pore structure of the specimens experienced significant volume changes as a result of the increasing temperature. The increase in the porous volume was more prevalent at 250 o C. Alterations in air void size distributions were characterized with respect to the unconditioned control specimen. These findings appear to correlate with changes in the uni-axial compressive strength of the conditioned concrete.
Highlights
X-ray computed tomography (X-ray CT) has been applied to nondestructively characterise changes in the microstructure of a concrete used in the pressure vessel structure of Advanced Gas-cooled Reactors (AGR) in the UK
Concrete specimens were conditioned at temperatures of 105 oC and 250 oC, to simulate the maximum thermal load expected to occur during a loss of coolant accident (LOCA)
Advanced gas-cooled reactor (AGR) pressure vessels are constructed from high-strength ordinary Portland cement (OPC) - pulverised fuel ash (PFA) concrete
Summary
Advanced gas-cooled reactor (AGR) pressure vessels are constructed from high-strength ordinary Portland cement (OPC) - pulverised fuel ash (PFA) concrete. This material is subjected to temperatures of up to 87 oC during normal plant operation and must withstand temperatures of 250 oC during a LOCA [1]. Nasser and Marzouk [2] reported that after 6 months exposure to temperatures of between 71 oC and 149 oC, the residual strength of the material was increased significantly when compared to the 28 day strength. This was explained as being the product of enhanced hydration. This was thought to be as a result of the transformation of tobermorite gel to α-dicalcium silicates which are poorly binding
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