Determination of the ¹⁴C Content in Activated Steel Components from a Neutron Spallation Source and a Nuclear Power Plant

Abstract

The (14)C content in activated steel components from the Swiss Nuclear Power Plant (NPP) Gösgen and the Spallation Neutron Source SINQ at the Paul Scherrer Institute is determined using a wet chemistry digestion technique and liquid scintillation counting for (14)C activity measurements. The (14)C activity of an activated fuel assembly steel nut from the NPP is further compared with theoretical predictions made on the basis of a Monte Carlo reactor model for this NPP. Knowledge of the (14)C inventory in these activated steel materials is important in conjunction with future corrosion studies on these materials aimed at identifying the (14)C containing organic compounds possibly formed in the cement-based near field of a repository for radioactive waste.

Analysis of 14C-bearing compounds released by the corrosion of irradiated steel using accelerator mass spectrometry

“…An irradiated steel nut segment (1 g) was immersed in 29.3 mL ACW solution in a polypropylene container and leached over a period of 1046 days (i.e., 2.87 years) in a hotcell under atmospheric (oxic) conditions. Characterisation of the used steel nut was reported in detail elsewhere 13 . It had a high dose rate (in the range of several tenth of mSv/h) due to the presence of activated metals (e.g.…”

“…It had a high dose rate (in the range of several tenth of mSv/h) due to the presence of activated metals (e.g. 60 Co), but its 14 C content was low (7.71 ± 1.08 nmol 14 C/g) 13 . The steel nut segment was removed from solution prior to the determination of 60 Co by gamma spectrometry and sampling of aliquots of the leaching solution for AMS measurements.…”

“…To date, there is no analytical approach available that allows a direct analysis of the speciation of 14 C-bearing organic corrosion products at the very low concentration levels required for corrosion studies with irradiated steel. The laboratory-scale set-up employed in the present work was limited to a sample size of 1 -2 g of irradiated steel due to the high dose rate of ~30 mSv/h/g of steel (mostly 60 Co) 13 . The 14 C concentration however is low (~18 kBq 14 C per g steel) 13 and the release rate of 14 C was estimated to range between a few femto-to a few picomoles 14 C per litre and day as a consequence of the very slow corrosion of steel (a few nm/year) 14,15 in alkaline solution.…”

“…The laboratory-scale set-up employed in the present work was limited to a sample size of 1 -2 g of irradiated steel due to the high dose rate of ~30 mSv/h/g of steel (mostly 60 Co) 13 . The 14 C concentration however is low (~18 kBq 14 C per g steel) 13 and the release rate of 14 C was estimated to range between a few femto-to a few picomoles 14 C per litre and day as a consequence of the very slow corrosion of steel (a few nm/year) 14,15 in alkaline solution. The aqueous 14 C concentration is further reduced when chromatographic fractionation is applied for the analysis of single 14 C-containing species due to dilution with the eluent.…”

Quantification of dissolved organic14C-containing compounds by accelerator mass spectrometry in a corrosion experiment with irradiated steel

“…A series of calibrations were performed on samples containing both 60 Co and 14 C with the aim to determine the contribution of 60 Co to the beta spectrum of 14 C. Note that 60 Co was found to be the main activation product in irradiated steel (Schumann et al 2014). To this end, 60 Co standards were analyzed both by gamma (energy window between 1050-1400 keV) and beta counting and a conversion factor accounting for the activity contribution of 60 Co to the 14 C spectrum in the energy window between 4 and 65 keV was assigned.…”