Development of alpha-emitting large area radioactive surface sources tailored for decommissioning

Abstract

The reliability of contamination measurements during decommissioning and dismantling (D&D) of used nuclear facilities is of the utmost importance for the rest of the process and an efficient waste management. Therefore, the surface contamination monitors used have to be calibrated on-site, regularly, with the use of reference sources. Additionally,​ the performance of novel surface contamination monitors designed for D&D may need to be assessed in-lab, without access to restricted D&D sites. For these two scenarios, there is a need for new reference sources that could compare to real contaminated surfaces in term of size, level of contamination, but also shape and roughness, while being traceable to national standards and without labile contamination. The approach described herein is the encapsulation of radionuclides in the matrix of an epoxy resin. Surface sources are obtained by pouring the liquid resin in molds of desired size and geometry. Any radionuclide can be scavenged, even volatile ones, as long as they can be processed in aqueous form. The activity used to spike the resin is traceable and was compared with the emission rate of particles measured using a primary method of standardization, the coincidence technique. For alpha emitting radionuclides, the source efficiency is low, around 1%, but the relation between activity and surface emission rate has proven robust at different activity levels and source thickness. The uniformity of the sources is below 90%, for sources larger than 100 cm 2, however large area modular pixelated sources with uniformity of around 90% could be obtained by assembling several smaller sources. Additionally, the sources prepared have shown no or very low labile contamination, using dry and wet smear tests. This allows their use without any cover layer, and is very beneficial for their use in harsh on-site environments. The sources prepared do not comply with most of the standard ISO 8769 requirements, which regulates the characteristics of metrological reference sources. However, they can be applied to the specific needs of the decommissioning and dismantling process.