Characteristics of Wear Products From Fueling Machine Ram Balls at Darlington
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Abstract
Introduction of dissolved and particulate Stellite ram balls wear products into the primary heat transport system during fueling machine on-power channel operations may result in a significant additional contribution to the reactor Co-60 fields. The heavy water auxiliary system (HWAS) associated with each Darlington fueling machine (FM) trolley is currently equipped only with a 1 µm filter; despite a roughed-in provision, no ion exchange purification is employed. Minimizing the introduction of ram balls wear products into the Primary Heat Transport (PHT) system by more effective filtration and by using ion exchange columns in the HWAS would reduce their contribution to the Co-60 source term. This paper presents an assessment of the adequacy of the present filter and the benefit of installing ion exchange capability in the HWAS. These assessments were performed by analyzing samples of FM water drawn from the HWAS. Both the loading and the particle size distribution of Stellite wear products in the samples were determined. Following successive filtration through a range of filter sizes down to 0.1 μm, the filtered water samples were exposed to mixed bed ion exchange resins to determine the dissolved ionic loading present. In addition, smears taken from filter housings during filter change-out and a cut-out sample from a spent filter were analysed to determine the elemental compositions and gamma activity make-up of the particulate present. These data were combined with dose rate data for the corresponding spent filters to obtain estimates for the generation rate of ram balls wear product. While the data developed were insufficient to assess the merits of replacing the current filter with a 0.1 µm filter, installation of a mixed bed ion exchange column in the HWAS would be beneficial and is, therefore, recommended.
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