Radiolytic products of the coolant in light-water reactors play an important role in the corrosion of the metal in the primary coolant circuits. It requires a good understanding of the water radiolysis behaviour due to spent fuel to optimize the water chemistry control strategies during shutdown and cooldown. Since it is difficult to measure or observe the radiolytic species and electrochemical corrosion potential (ECP) in the primary coolant circuits directly, simulations are performed using water chemistry code LwrChem. The model is based on the theory of water radiolysis and electrochemical corrosion. The stable oxidation radiolytic species concentrations including O2 and H2O2 and ECPs at closely spaced points around the primary coolant circuits of Chinese 900 MWe PWR under various operation conditions during shutdown are calculated. The result shows that the ECPs are higher during shutdown than during power operation, and the ECPs out of core regions are lower than those in the core. Under higher lithium concentration conditions, more hydrogen peroxide are consumed with OH−, also there are less oxygen decomposed by hydrogen peroxide, resulting with lower ECPs. From the 291 ℃ hot shutdown case to 130 ℃ cold shutdown case, the ECPs are getting higher and even positive, forming oxidation environment. The results of this work provide a reference for optimizing the water chemistry strategies during shutdown and cooldown.