(A) study on the method and process for removal of radioactive corrosion product from NPP using its magnetic property

Abstract

It is important to emphasize that the current trend to longer fuel cycle (1824 month) has complicated the dilemma of finding optimum chemical condition for the primary coolant because of some problems such as increase of radioactive corrosion product, possibility of axial offset anomaly and so on. Radioactive corrosion products which are generated by the neutron activation of general corrosion products at a nuclear power plant are the major source of occupational radiation exposure. There are several ways to reduce the radiation levels around the primary water system. For example, improving the coolant purification system, operating at high pH, the adopting materials with low levels of cobalt in the primary coolant system and decontaminating the primary system more frequently. The representative method for CRUD reduction is the high pH operation that controls the deposition of general corrosion products using solubility difference in the primary coolant system. The pH value of 7.4 has been suggested as suitable pH value in many experiments and researches. However, it is difficult to operate on the high pH chemistry at the long term fuel cycle (1824 month cycle) due to high boron concentration. The concentration of lithium that works as chemical agent with boron in order to control pH of the primary coolant is restricted because of possibility of Li-Zr stress corrosion cracking related to nuclear fuel damage. Therefore, it is important to emphasize that current movement to long term fuel cycle has increased the difficulty of pH optimization. Amounts of CRUD generation at long term fuel cycle expect to increase compared to 12 month fuel cycle owing to difficulty of high pH operation. Not only passive ways for CRUD reduction but also active methods for CRUD removal are required at a long term fuel cycle. During the power operational period, the crud in the primary coolant is generally removed at the chemical volume control system (CVCS), which controls the concent...