High-energy imaging: an asset in active photon interrogation

The Photon Activation and Irradiation System (SAPHIR) platform is used to develop methods for characterizing radioactive waste packages through active photon interrogation. It mainly consists of an electron accelerator and a conveyor for handling waste packages weighing several tons. The accelerator generates an intense flow of high-energy photons through braking radiation (Bremsstrahlung), aiming it at a conversion target. This photon beam is then used to “interrogate” the waste packages.
In recent years, LIST has developed several methods based on detection of delayed neutrons and delayed gamma rays. These methods have been used successfully to characterize the radiological contents of different types of waste packages. One of LIST’s short-term objectives is to expand the range of methods that can be used with SAPHIR, enabling it to benefit from their complementarity and optimize the active photon interrogation process.

Using conventional X-ray films

Regardless of which non-destructive method is used to characterize a waste package’s radiological contents, X rays (two-dimensional images) or tomographs (three-dimensional images) of the package’s contents provide precious information that can reduce the uncertainties of measurements. They can validate and optimize them, mainly by making use of heterogeneities, the simulations used to assess the activity of radioelements. Depending on the package’s size, these imaging methods require the use of isotopic sources (60Co) or a linac electron accelerator. If a linac is used, we then talk of high-energy imaging (IHE).
It has then been a matter of finding out whether SAPHIR could be used to produce high-energy images ofwaste packages. The feasibility of doing so was demonstrated in a ANDRA super control at the end of 2008. The analyzed package was a CBFC-2 shell 1 m in diameter, 1.5 m high and weighing a total of 1.8 tons. The shell contained a 400 litre drum immobilized in a concrete envelope 14 cm thick. LIST’s teams obtained a complete image of the package in this way. Several interesting points were revealed (variations in thickness at various points in the drum, the presence of a clamp on its top, etc.) and the fact that the 400 litre drum was completely filled was confirmed.
At the beginning of 2009, new tests were performed on a 870 litre model package representing the packages stored in the CEDRA facility at the CEA’s Cadarache site. EPID (Electronic Portal Imaging Device), a new detection system used in real-time imaging, was successfully tested in taking these measurements. Through the use of high-energy imaging, it will now be possible to enhance and optimize the characterization of radioactive waste packages through active photon interrogation. ANDRA is already interested in this method of producing quantitative and qualitative measurements through the same system (a single accelerator used for imaging and active photon interrogation), and it has decided to finance R&D in this field in 2009.