The turbines don't vent unless they are throttling down or in an emergency shutdown and would never do it if the system uses water that came from the reactor. They run closed loop systems where the reactor heat transport fluid (d2o in the candu reactors I work on. But can be regular water) this system circulates between the reactor and a heat exchanger. The heat exchanger passes the thermal energy into regular water (unless it is the type that feeds direct to the turbine but I have no experience with that type) regular water is then turned to steam and heads to the turbines. There is normally a high pressure turbine which is the smallest, after the steam passes through that there is still lots of energy in the steam so it is sent to a drying system (I have never worked on that so I don't know exactly what it does) and then the steam comes back into the low pressure turbines. The ones I work on have 1 hp and 3 lp turbines. The 2 steam pipes feeding into the hp are about 2.5ft in diameter and carry a total of about 1.6 million hp of energy. From the low pressure turbines the steam goes to a condenser. It is just another heat exchanger where they pump cold water through tubes surrounded by the steam. The steam condenses and drops to the bottom where it cycles back via pumps to the first heat exchanger to be turned back to steam in a closed loop. The cooling water gets warm from the exchange and gets pumped into cooling ponds were it can be released back into the lake once it reaches a certain temperature. If you see a cooling tower like in the Simpsons. That is like having an air cooled car vs a water cooled car. The steam goes to the inside of the tower in tubes. It stays in its closed loop but warms the air up. The warm air rises causing cooler air to be sucked in the bottom. The steam you see rising is not the steam from the turbines, it is from the air changing temperature.