Determination of ¹⁴C, ⁵⁵Fe, ⁶³Ni and gamma emitters in two different types of activated reactor pressure vessel (RPV) steel samples were carried out. The gamma emitters were analysed using HPGe detectors with ISOCS and standard geometry calibrations. Two radioanalytical procedures for the ¹⁴C, ⁵⁵Fe, ⁶³Ni analysis were developed using inactive samples and activated samples were analysed using modified procedures. A Monte Carlo code was used for the modelling of the activation results. The obtained measured and calculated results were comparable.

This paper reports the results obtained during an intercomparison exercise for the determination of difficult to measure radionuclides in activated reactor pressure vessel (RPV) steel samples. In total, eight laboratories participated analysing ¹⁴C, ⁵⁵Fe and ⁶³Ni activity concentrations in RPV steel. In addition, some laboratories also analysed ⁶⁰Co activity concentrations. Corresponding activity concentrations were also determined using activation calculations. Robust statistical techniques were utilised for the analysis of the results according to ISO 13528 standard. The results showed good agreement for ⁵⁵Fe and ⁶³Ni results whereas ¹⁴C results had significant differences. ⁶⁰Co results were in quite good agreement.

The objective of the study has been to estimate the residual activity in the decommissioning waste of the TRIGA Mark II–type research reactor FiR 1 in Finland. Neutron flux distributions were calculated with the Monte Carlo code MCNP. These were used in the ORIGEN-S point-depletion code to calculate the neutron-induced activity of materials at different time points by modeling irradiation history and radioactive decay. Knowledge of the radioactive inventory of irradiated materials is important in the planning of the decommissioning activities and is essential for predicting the radiological impact to personnel and the environment. Decommissioning waste consists mainly of ordinary concrete, aluminum, steel, and graphite parts. Results include uncertainties due to assumptions on material compositions and lack of some detailed operational history data. Comparison to activity inventory estimates of two other decommissioned research reactors is also presented.

The objective of the study has been to verify the calculated residual activity in the decommissioning waste of the TRIGA Mark II–type research reactor FiR 1 in Finland. Knowledge of the radioactive inventory of irradiated materials is important in the planning of decommissioning activities and is essential for predicting the radiological impact to personnel and the environment. Measurements are performed for low active material samples from outer parts of the reactor. Methods include gamma spectrometric measurements, composition measurements with mass spectrometry, oxidation measurements of especially ¹⁴C in graphite, and full combustion measurements of lithium-enriched shielding materials. Results are compared to estimates calculated with a combined Monte Carlo model of the reactor and a point-depletion code modeling the irradiation history. Decommissioning waste consists mainly of ordinary concrete, aluminum, steel, and graphite parts. Only preliminary measurements of low active samples are reported so far, but the same methods will be used later for characterizing and classifying dismantling waste. Some discussion of characterization requirements and future sampling is also included.