Decommissioning of nuclear reactors requires determination of all remnant long-lived isotopes that were produced during their long functioning time of the respective facilities. Radiocarbon (14C) is such an isotope (T1/2 = 5730 yr), widely produced by neutron reactions in a thermal column of a nuclear reactor. Accelerator mass spectrometry (AMS) uses 14C for precise dating of up to 50,000 years old archaeological artifacts. This study presents a premier AMS measurement of high concentrated 14C samples that are strictly forbidden in laboratories dedicated to perform 14C dating. The determined 14C activities range from the natural level (isotopic ratio 14C/12C = 1.2 × 10–12) up to values of 10,000 times higher. 14C bulk and depth profile concentrations were measured in the thermal column disks of a decommissioned nuclear reactor. Results have shown that the 14C concentration in the thermal column, close the reactor core is about 75 kBq/g and decreases to 0.7 Bq/g and the end of the column. Such AMS measurements are applicable for decommissioning and waste management of nuclear reactors.
