Colloquia

Samenvatting

With the life extensions and ageing of nuclear reactors worldwide, the need for Long-Term Operation (LTO) projects increases. The concrete in the High Flux Reactor (HFR) in Petten, the Netherlands, is also a subject to these projects. This study assesses the use of Acoustic Emission (AE) to evaluate various reactor concretes.

To assess the useability of AE, relations from literature are compared to an experimental study. This experimental study is done on concrete cores that are drilled from various places in the reactor building. Both high-density pool shielding and standard concrete cores are extracted from the reactor. These concretes have been exposed to various combinations of environmental and operating conditions. These conditions include leakage, drying, and radiation.

To evaluate the difference various concrete mixtures, and operating and environmental conditions have on the results of an AE study, cores with variations in one variable are needed. To this end, fresh concrete cores are made. The mixture differences entail two different water-to-cement ratios and two different maximum aggregate sizes. To simulate environmental and operating conditions, the concrete is oven dried.

In a three point bending test, the concrete cores are increasingly loaded until failure. AE signals are captured from the crack growth in the concrete using an AE sensor that is attached to the surface of the material. The signals from crack growth are time-synced to the force that is applied to the material.

It is found that the standard concrete can be evaluated with AE, while this is not possible for the high-density cores. For all concrete except for the high-density, trends are found in the data. When comparing crack growth mechanisms using a graph of the average frequency (AF) as a function of the rising angle (RA), the utilisation of concrete can be evaluated close to fracture. With the usage of the number of crack growths per force level, the utilisation can be evaluated over a wider range. Furthermore, from the fresh and standard reactor concretes, relations can be found between mixture, and environmental and operating conditions.

The use of AE in concrete evaluation in the reactor is found to be possible on standard concrete, it is not possible for the high-density cores. The state of the concrete can be evaluated using the number of signals per force level, the water content of the concrete does influence the number of signals that are expected.