Long half-lives relevant to nuclear waste disposal
JRC scientists standardised the activity concentration of three fission products (129I, 151Sm, and 166mHo) potentially present in nuclear waste. This work will result in new and eventually more accurate determination of the half-lives of these three radionuclides.
Accurate nuclear decay data, such as half-lives, are important input parameters in the development of technical solutions for safe long-term disposal of nuclear waste. 129I is a fission product of 235U considered as one of the most important dose contributors in the nuclear waste disposal storages in the future. 151Sm is produced during the irradiation of uranium fuel rods in nuclear reactors. 166mHo is produced in nuclear fuel as a result of the neutron activation of erbium admixtures, which is added to the fuel to improve the burn out of the uranium.
The currently available data in the literature on the 129I, 151Sm, and 166mHo half-lives are either scarce or inconsistent, and new measurements are needed to obtain accurate values with reliable uncertainties. For such long-lived nuclides, the half-life value is best obtained by independently measuring the activity concentration and the mass concentration of the given radionuclide in the same solution.
One of the aims of the European Metrology Research Program (EMRP) project "Metrology for Radioactive Waste Management (MetroRWM)", executed in 2011-2014, was to determine the half-lives of the three long-lived radionuclides, 129I, 151Sm, and 166mHo. In the course of the project, the radionuclide activity concentrations were determined using standardisation techniques, following the highest level of accuracy and precision in collaboration with national metrology institutes.
At the JRC-IRMM, the activity concentrations were measured both by the Triple-to-Double Coincidence Ratio (TDCR) Liquid Scintillation Counting (LSC) method and the CIEMAT/NIST efficiency tracing LSC method.