Ag-110m contamination in PWRs: EMECC feedback and OSCAR simulations

Overview & Synopsis

Reducing collective dose is a critical objective for all nuclear plant operators. To achieve this, the CEA, in collaboration with EDF and Framatome, has been developing a code for over 50 years to calculate the contamination of PWR circuits, known as OSCAR. Additionally, the CEA has conducted surface contamination measurements of PWR circuits through the EMECC campaigns (operational feedback from 76 units, totaling 440 reactor cycles). Co-58 and Co-60 are typically the two most concerning radionuclides in PWR systems. However, the EMECC campaigns have also revealed that Ag-110m can be a significant radiocontaminant in certain parts of auxiliary systems, posing major challenges for operators, such as increased collective dose, higher maintenance costs, and extended unit outages. A previous NPC 2016 paper highlighted lessons on silver behavior from EMECC campaigns [1]. This paper summarizes those findings: during oxygenation, Ag-110m dissolves from primary surfaces and precipitates on colder auxiliary system parts. Additionally, Ag-110m sampled via NSS often misrepresents its volume activity in the primary system. These findings are further complemented by feedback from the last 10 years of EMECC campaign. The paper also presents OSCAR simulations of Ag-110m transfer within PWR circuits, which confirm these findings and provide insights into the unique behavior of Ag-110m. Finally, based on EMECC feedback from France and abroad, as well as OSCAR simulations, a comprehensive strategy will be proposed to prevent the recontamination of auxiliary systems by Ag-110m during the oxygenation process.