Corrosion products such as iron and nickel ions generated in the steam generator (SG) of a pressurized water reactor (PWR) deposit on the fuel rods in the reactor core, forming Chalk River Unidentified Deposits (CRUD). Activated by neutron irradiation in the reactor core, part of the CRUD layer transforms into radioactive substances, which are mainly ⁵⁸Co and ⁶⁰Co. Then the radioactive ⁵⁸Co and ⁶⁰Co are carried by the coolant into the entire primary loop. The existing research lacks a comprehensive modeling and discussion on the distribution of radioactive materials ⁵⁸Co and ⁶⁰Co in the primary loop. Predicting the content and distribution of radioactive materials ⁵⁸Co and ⁶⁰Co in the primary loop and assessing the impact of water chemistry and thermal parameters are of significant importance for radiation protection and core parameter design.

This study aims to explore the production and distribution of radioactive materials in the primary loop due to the deposition of CRUD in reactor core, with a typical PWR primary loop as the research subject.

Firstly, a predictive model for CRUD deposition and radioactive materials production distribution was established that encompassed CRUD deposition and radioactive material prediction. Then, the primary loop of PWR was simplified into five key nodes, i.e., the core, soluble corrosion products, SG, corrosion particulates, and erosion particles, to address the generation, migration, deposition, and growth of CRUD based on the principles of mass transfer and water chemistry. The proportion of particles returning coolant was controlled by the purification efficiency in the erosion particle node. Finally, the activation of CRUD and the migration, deposition, and erosion of radioactive materials at each node were correspondingly considered on the basis of the activation theory, and the distribution of radioactive materials in the primary loop was obtained by establishing and solving the mass transport balance equations for each node. Based on this established model, a comprehensive analysis was conducted on the influence of coolant flow rate, hydrogen content, and coolant inlet temperature.

The calculation results indicate that the radioactive materials inventory increases with an increase in coolant flow rate and hydrogen content. The impact of coolant flow rate and hydrogen content on the radioactive materials inventory of steam generators (SG) is 93.9% and 10% greater than the core. As the coolant inlet temperature increases by 8%, the radioactive materials inventory decreases by 9%, and its impact on the core is 19% greater than the SG. The model predictions for CRUD deposition and radioactive materials distribution closely align with the results obtained from the code CRUDSIM (Chalk River Unidentified Deposits SIMulation) with a difference less than 5%.

The results of this study demonstrate a significant influence of coolant flow rate, hydrogen content, and inlet temperature on the radioactive material content and distribution in the primary loop. Moderating coolant flow rates and reducing hydrogen concentrations are beneficial for lowering the content of ⁵⁸Co and ⁶⁰Co in SG. Conversely, increasing coolant inlet temperature effectively reduces the content of ⁵⁸Co and ⁶⁰Co in the core.