In the nuclear industry, dismantling activities in nuclear decommissioning leads to the generation of vast amounts of contaminated metallic waste, whose decontamination could enable the recycling and reuse of such scrap metals, thus minimizing the environmental footprint of dismantling activities. This thesis focuses on improving the advanced PHADEC process recently proposed by Ansaldo Nucleare to manage contaminated metallic scraps, which foresees the final conditioning of the contamination in an effective waste form as the iron phosphate glass (IPG). The decontamination process consists of 4 different stages. After removing the superficial contaminated layer by a pickling process and the chemical adjustment of the so-obtained ferrous solution, contaminants are recovered in a solid form by an electrochemical precipitation process. The effectiveness of such a step has been further improved by adding co-precipitants that, in some cases, lead to better precipitation and decontamination yields. Finally, the precipitate, a wet, contaminated iron phosphate sludge, was directly treated at a high temperature to obtain an IPG wasteform. The process has been studied at the Laboratory of Radiochemistry and Radiation Chemistry at the Department of Energy of Politecnico di Milano employing pristine steel scraps and stable isotopes of the radioactive contaminants and process byproducts. The final glass has been analyzed using inductively coupled plasma mass spectrometry (ICP-MS), X-ray diffraction, and X-ray fluorescence spectroscopy to monitor parameters relevant to the vitrification step. The so-obtained IPG waste form has been tested for chemical durability by an ASTM standard method at 90°C for 7days, and the release of contaminants was evaluated by ICP-MS analyses. The results obtained are promising, but further studies are required to find optimal experimental conditions to implement the process at an industrial scale.
Le attività di smantellamento nell’ambito del decommissioning nucleare portano alla generazione di enormi quantità di rifiuti metallici contaminati, la cui decontaminazione potrebbe consentire il riciclo e il riutilizzo di tali rottami metallici, minimizzando così l'impronta ambientale delle attività di smantellamento. Questa tesi si concentra sul miglioramento del processo avanzato PHADEC recentemente proposto da Ansaldo Nucleare per gestire i rottami metallici contaminati, che prevede il condizionamento finale della contaminazione in una forma di rifiuto efficace come il vetro ferro-fosfatico (IPG). Il processo di decontaminazione consiste in 4 diverse fasi. Dopo la rimozione dello strato contaminato superficiale mediante un processo di decapaggio e l’aggiustamento delle necessarie caratteristiche chimiche della soluzione ferrosa così ottenuta, i contaminanti vengono recuperati in forma solida mediante un processo di precipitazione elettrochimica. L'efficacia di tale fase è stata ulteriormente migliorata dall'aggiunta di co-precipitanti che in alcuni casi portano a una migliore precipitazione e resa di decontaminazione. Il precipitato, un fango ferro-fosfatico umido contenente i contaminanti, è stato trattato direttamente ad alta temperatura per ottenere il vetro IPG. Il processo è stato studiato presso il Laboratorio di Radiochimica e Chimica delle Radiazioni del Dipartimento di Energia del Politecnico di Milano per mezzo di rottami di acciaio non contaminati e isotopi stabili dei contaminanti radioattivi. I sottoprodotti del processo così come il vetro finale sono stati analizzati utilizzando la spettrometria di massa al plasma accoppiato induttivamente (ICP-MS), la diffrazione dei raggi X e la spettroscopia di fluorescenza a raggi X al fine di monitorare i parametri rilevanti per l’ottenimento di una buona vetrificazione. I vetri IPG così ottenuti sono stati sottoposti a test per valutarne la stabilità chimica seguendo un metodo ASTM e il rilascio di contaminanti è stato valutato tramite analisi ICP-MS. I risultati ottenuti sono promettenti, ma ulteriori studi sono necessari per individuare condizioni sperimentali ottimali per l’implementazione del processo su scala industriale.
Innovative management of contaminated metallic waste via electrochemical precipitation and conditioning into iron phosphate glass
BASAVARAJ, AKASH
2021/2022
Abstract
In the nuclear industry, dismantling activities in nuclear decommissioning leads to the generation of vast amounts of contaminated metallic waste, whose decontamination could enable the recycling and reuse of such scrap metals, thus minimizing the environmental footprint of dismantling activities. This thesis focuses on improving the advanced PHADEC process recently proposed by Ansaldo Nucleare to manage contaminated metallic scraps, which foresees the final conditioning of the contamination in an effective waste form as the iron phosphate glass (IPG). The decontamination process consists of 4 different stages. After removing the superficial contaminated layer by a pickling process and the chemical adjustment of the so-obtained ferrous solution, contaminants are recovered in a solid form by an electrochemical precipitation process. The effectiveness of such a step has been further improved by adding co-precipitants that, in some cases, lead to better precipitation and decontamination yields. Finally, the precipitate, a wet, contaminated iron phosphate sludge, was directly treated at a high temperature to obtain an IPG wasteform. The process has been studied at the Laboratory of Radiochemistry and Radiation Chemistry at the Department of Energy of Politecnico di Milano employing pristine steel scraps and stable isotopes of the radioactive contaminants and process byproducts. The final glass has been analyzed using inductively coupled plasma mass spectrometry (ICP-MS), X-ray diffraction, and X-ray fluorescence spectroscopy to monitor parameters relevant to the vitrification step. The so-obtained IPG waste form has been tested for chemical durability by an ASTM standard method at 90°C for 7days, and the release of contaminants was evaluated by ICP-MS analyses. The results obtained are promising, but further studies are required to find optimal experimental conditions to implement the process at an industrial scale.File | Dimensione | Formato | |
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https://hdl.handle.net/10589/188500