Compton imaging to support a new robotic platform for mapping nuclear decommissioning sites

Abstract

The localisation, identification and remediation of hotspots in a nuclear decommissioning site is an important step in the decommissioning process. This ensures that operators, carrying out future decommissioning activities, will no longer be exposed to unneeded dose-uptake. The current practice for identifying hotspots is to use human operators for radiological measurements, but due to the high dose rate of the hotspots, special measures are necessary to protect workers and the available time to perform mapping and characterisation steps is limited. This not only introduces the risk of missing sources or performing inaccurate measurements and other specific ALARA related challenges, but it is a time consuming and inefficient way of mapping. Robots can be employed to automate this repetitive work of mapping and characterising to reduce the exposure of workers and increase the accuracy of the measurement. Within the current ‘energy transition funds’ project ARCHER (Autonomous Robotic platform for CHaractERisation), a robot platform was developed that aims at minimising the need for human intervention. This platform contains a lightweight CZT gamma spectrometer or a Compton camera for radiological mapping. ARCHER is executed by academic research partners (UHasselt and KU Leuven) in collaboration with industrial partners (Tecnubel and Magics) and financial support of the Belgian FOD Economy. Using a Compton camera reduces the need for excessive manoeuvres of the platform and, as measurements are performed relatively far away from the source, the chance of contaminating the platform is limited. Complementary, the CZT Spectrometer is also used for scanning the contaminated surfaces and identification of the hotspots. Lab-scale tests have been performed with a mapping routine. The CZT scanning approach was optimised for distance, measurement time and mapping performance. Cs-137 and Co-60 sources were used to simulate hotspots. Results show that sources could be localised with an accuracy of up to 5 mm. The Compton camera was subjected to the same tests and also showed that the Cs-137 sources could be localised. The provided presentation demonstrates initial results regarding the use of the ARCHER platform in a lab-scale environment. The use of the Compton camera has been found an added value to the currently used method in ARCHER. Future research will aim at further development of the used gamma imaging approach to detect a wider energy range. The robot platform itself will also go into the next development phase where in situ acceptance testing will be performed at an installation currently in decommissioning.