C-14 HIGH CONCENTRATION MEASUREMENTS WITH RELEVANCE FOR DECOMMISSIONING OF NUCLEAR REACTORS

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 (C-14) is such an isotope (T-1/2 = 5730 yr), widely produced by neutron reactions in a thermal column of a nuclear reactor. Accelerator mass spectrometry (AMS) uses C-14 for precise dating of up to 50,000 years old archaeological artifacts. This study presents a premier AMS measurement of high concentrated C-14 samples that are strictly forbidden in laboratories dedicated to perform C-14 dating. The determined C-14 activities range from the natural level (isotopic ratio C-14/C-12 = 1.2 x 10(-12)) up to values of 10,000 times higher. C-14 bulk and depth profile concentrations were measured in the thermal column disks of a decommissioned nuclear reactor. Results have shown that the C-14 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.