Nuclear Power/Protective Barriers in power plants
In what part of a nuclear power plant is it important to have a protective barrier against oxygen, water, gases, oil or greases or other substances?
As with any industrial setting, you need the standard protection for motors, pumps, and electrical equipment (protect from corrosion due to water). We use cleanliness control programs to ensure anything we use is clean and free of grease and other contaminants.
On the nuclear side, we don't want oxygen in the primary coolant water or the non-radioactive feed water because of corrosion. There are no special protective barriers on the primary (reactor) side because it is a sealed system. On the secondary side, we use seals along all the pump shafts and other places, but that is primarily to keep the water in. Since the water is at a high pressure, the oxygen cannot enter.
There are two places where oxygen can enter systems: the main condenser and the electrical generator. The main condenser collects the steam from the main turbines and condenses it back to water that will be pumped back to the steam generators (boilers). We want the condenser to be at a vacuum for higher thermodynamic efficiency, so we have seals to keep the air out and special ejectors that remove any air that might have collected there.
The main generator is cooled with hydrogen. To prevent air from entering and mixing with the hydrogen to form an explosive gas mixture, we have special labyrinth seals to keep the hydrogen in and the oxygen out.
The only other place we take special care is the primary side (the reactor coolant system and the reactor itself). We use a "foreign material exclusion" program to keep everything out that shouldn't be there. We don't want to drop tools, bolts, or anything else in the systems where they were get battered around by the coolant flow and cause damage to components.
If you need any of this explained or any more detail, please let me know.