The Wolsung unit 1 plant is a pressurized heavy water type reactor (PHWR). In this plant the membranes are used to remove dissolved oxygen from the end shield cooling system. This system re-circulates water that is used to cool the reactor wall. The cooling system is filled with carbon steel balls that are used to prevent radiation exposure to the workers during a refueling period. Dissolved oxygen is controlled in order to prevent corrosion of the piping and carbon steel balls in the system.
Historically hydrazine treatment was used to control the dissolved oxygen in the end-shield cooling system. Engineers associated with the plant investigated other technologies in an effort to overcome some of the limitations of using hydrazine.
Hydrazine reacts with dissolved oxygen to form water and nitrogen. Unreacted hydrazine decomposes to produce ammonia, nitrogen, and at high temperatures, hydrogen. The formation of hydrogen gas is a potential hazard. In addition, hydrazine is considered a health risk and the engineers wanted to limit employee exposure to the chemical.