A decontamination technique for the primary cooling circuit of the research type nuclear reactor

Accumulation of radioactive corrosive materials in the primary loop of reactors will lead to elevated radiation level in workplace, increased maintenance and repair costs, and greater difficulty in later decommissioning. This study analyzed the contaminants deposited on the inner walls of pipes serving a reactor by Raman microscopy. The results show that the main contaminants were FeCO3 and “green rusts” and γ-FeOOH may exist. A laboratory decontamination experiment was conducted on samples from the contaminated piping using two decontaminants: decontaminant A, composed primarily of HNO3, and decontaminant B, composed primarily of H2C2O4. The structural material of the reactor’s cooling circuit piping restores its metallic luster after decontamination, demonstrating the effectiveness of the two decontaminants. The contaminants identified can be divided into two categories: soft materials that were easy to remove and hard materials that were firmly attached to pipe wall. The curves describing the activity of 137Cs present in the solutions reveal that the decontamination process with decontaminant A or B consisted of a rapid reaction stage and a slow reaction stage. This indicates that there could be various oxides in the contaminants. An online decontamination experiment was performed on an analog primary loop. The monitoring data suggests that the decontamination method determined under laboratory conditions is applicable to online decontamination of operating cooling loops of reactors. Furthermore, the study found that the fluctuations caused by liquid motion within large devices can affect the activity of 137Cs in the solutions. [Display omitted] •The research on the primary cooling circuit decontamination technology was reported.•We used laser micro-raman spectroscopy to observe the radioactive sediments.•We determined the end point of cleaning according to the radioactivity level change.•We carried out the decontamination experiment on a large analog cooling circuit.