Nuclear safeguards inspectors collect samples containing dust particles at nuclear facilities and other locations, using a process known as environmental sampling.
Such samples, in the form of cotton swipes, contain uranium particles that can reveal information about the current and past activities at a nuclear facility and verify whether a state is abiding by its legal commitment not to divert nuclear material from peaceful activities or engage in undeclared nuclear activities.
The JRC-Karlsruhe started environmental sample analysis in 90’s and was one of the first laboratories in the IAEA’s network of laboratories for particle analysis.
Sample collection
Environmental sampling for safeguards is based on the principle that every process, no matter how leak tight, emits small amounts of material to the environment. This was demonstrated successfully after the Gulf War, during the IAEA’s programme “93+2”, when environmental samples were collected from the vicinity of Iraq’s destroyed nuclear facilities.
Environmental sampling is performed using cotton swipes (10cm x 10 cm). The amount of radioactivity in the uranium particles is undetectable, thus they can be easily transferred to laboratories for analysis.
The Large Geometry Secondary Ion Mass Spectrometry Laboratory
The Large Geometry Secondary Ion Mass Spectrometry Laboratory (LG-SIMS laboratory), which is a state of the art technique for uranium particle analysis, was established at the JRC-Karlsruhe in a joint effort with DG-ENER in 2013.
The LG-SIMS allows in a first step to localise the uranium particles in a matrix of millions of dust particles and to determine their approximate 235U enrichment.
In the second step, precise microbeam measurements are performed on all uranium isotopes simultaneously to obtain the isotopic composition of micrometer sized particles. All this can be performed within 24 hours.
Sample preparation
First, the swipe is screened by Monochromatic Micro-focusing X-Ray fluorescence (MMXRF) to identify the uranium rich areas on the swipe.
After that, the dust is transferred to a graphite planchet using a vacuum impactor technique.
The work is performed in a clean room using disposal glove-bags and other single-use tools to avoid cross-contamination.
Measurement uncertainties and quality control
The LG-SIMS laboratory at the JRC-Karlsruhe has an ISO17025 accreditation, which calls for strict working protocols and therefore ensures accurate and precise results.
The performance of the laboratory is monitored frequently by proficiency tests. Typically achieved uncertainties are below 0.1% for the 235U enrichment and below 1% for the minor isotopes, 234U and 236U.
Due to the excellent precision and the possibility to detect inhomogeneities in samples, LG-SIMS is applied also for nuclear forensic analysis.
