During the last decades, the nuclear and non-nuclear industry has produced a considerable amount of low and intermediate level radioactive wastes. These waste packages will be safely disposed in a final repository under strict acceptance requirements (e.g. the radiological and material characterization) defined by national licensing and supervisory authorities. The material characterization of waste packages can be performed based on existing documentation or, if the documentation is insufficient, on further destructive or non-destructive analysis. Non-destructive methods are to be preferred because destructive methods lead to higher exposures of operating personnel as well as costs. For the non-destructive material analysis, the speaker presents an innovative non-destructive technology called QUANTOM® (QUantitative ANalysis of TOxic and non-toxic Materials) based on prompt and delayed gamma neutron activation analysis (P&DGNAA). This technology is able to identify, verify and quantify the amount of hazardous and non-hazardous substances in 200-l radioactive drums, which is needed for a final disposal characterization.
In Germany, low and intermediate level radioactive wastes are currently stored on surface in intermediate storages. Due to the phasing-out of the German nuclear power plants and dismantling activities a considerable increase in low and intermediate level radioactive wastes is expected. Finally, such wastes will be disposed underground in the geological repository Konrad, which is planned to go into operation in 2027. The federal company for radioactive waste disposal BGE (Bundesgesellschaft für Endlagerung) is responsible for the qualification of radioactive packages in Konrad. However, waste producers from the nuclear industry have the possibility to transfer their qualified wastes to the BGZ (Bundesgesellschaft für Zwischenlagerung) already from 2020 until Konrad goes into operation.
Only qualified packages regarding the radiological inventory and the material composition can be delivered and subsequently emplaced in Konrad. Material characterization means that the materials in the drums need to be categorized into groups of substances (material vectors) and the mass fraction of this substances must be quantified. Legacy wastes are usually problematic: the existing documentation is poor and not sufficient to satisfy the requirements regarding the material characterization. Besides, the documented material vector may not coincide with the true material vector of the drum.
Until today, the material characterization of legacy wastes is done based on documentation and by destructive methods. Such methods are time-consuming and expensive. Additionally, they will lead to a repackage of the waste, which results in even more restrictive requirements and subsequently increase the total volume of the wastes. We propose a non- destructive technology: a fully automated measurement device based on prompt and gamma delayed neutron activation analysis called QUANTOM®.
QUANTOM® is developed for the non-destructive assay of 200-l waste drums with a maximum weight of 1 t. The drums are positioned in the middle of a lifting turntable in order to perform a full scan of the drum. The drums are irradiated with neutrons, which are emitted by a Deuterium-Deuterium (D-D) neutron generator. The neutrons are moderated with high-purity graphite to reach their thermal and epithermal energies before they hit and activate the content of the drums. The prompt- and delayed- gamma rays induced by neutron captures in the drum are detected by two
n-type High-Purity Germanium (HPGe) detectors. These gamma rays are then analyzed to identify and quantify the element fractions of the material in the drum. The documented material content of the drum can finally be checked (i.e. plausibility check) and even complemented. The whole measurement device is surrounded by a shielding of borated polyethylene and can be integrated in a 25’ standard steel container. The first prototype of QUANTOM® is in operation since October 2020.
The main benefits of QUANTOM® are listed below:
• Non-destructive multi-element analysis with high sensitivity (ppm-range) of the entire matrix
• Fast measurement process (2h-4h per waste drum) with high measurement precision
• No repackaging and no increase of waste volume
• Reduction of costs (min. 50% per waste drum) compared to destructive analysis processes
• Minimizing the transportation of radioactive waste drums and radiation exposure of the operation staff.
In the presentation the speaker will outline the instrumental design of the QUANTOM® measurement device for the material characterization for final disposal and present the results of the validation campaign with non-radioactive and radioactive waste drums. The validation campaign with non-radioactive reference materials was performed in cooperation with the department Nuclear Analysis and Radiography of the Centre for Energy Research in Budapest, which measured the reference materials in a research reactor.
The joint project QUANTOM is funded by the German Federal Ministry of Education and Research under grant number 15S9406A / B / C. The responsibility for the content of this publication lies with the project partners.