CSB investigators discovered the reactor vessel's automated vent valve was almost completely closed, and that it was designed to open so it could relieve pressure and maintain the setpoint.

The relief valve's function is to protect the reactor from overpressure in the event of a trip — a sudden shutdown. It would release steam to relieve pressure within the reactor.

Each reactors locking collar has a unique key which ensures only that key can be used to open that specific individual reactor. With customer safety paramount, each individual PressureSyn reactor is ...

The 685-megawatt reactor was closed for work on one of the unit’s four safety relief valves, Williams said. “The leak was captured inside the plant as designed and was not a threat to workers ...

"One of our relief valves was not operating properly," said SCE&G spokeswoman Rhonda O'Banion. Right now, two new nuclear reactors are under construction at the site.