Multi Stud Tensioner for BWR (Boiling Water Reactor)

The detensioning and tensioning work of a BWR Multi Stud Tensioner is one of the main tasks during the plant outages of a BWR. The concept for a boiling water Multi Stud Tensioner is comparable to a pressurized water reactor Multi Stud Tensioner. The tensioning technology principle is the same. The difference is that in accordance to the plant procedures only a certain amount of the RPV studs has to be removed for further material investigations. It means the main task and the focus is the detensioning and tensioning of RPV studs.

Therefore, the Multi Stud Tensioner is used for detensioning / tensioning of all reactor studs at the same time, with the same tensioning force. During the detensioning or tensioning process, digital measurement gauges monitor and record the elongation at each RPV stud.
All elongation measurement data and pressure data of the tensioning process are logged and memorized.

The MST also has another important function that saves a lot of time, radiation exposure dose, and effort for the operator and finally reduces the outage cost.

With this function, all RPV nuts are turned off simultaneously and transferred to the support ring of the MST with an integrated support device in the process of RPV detensioning. In between the detensioning and tensioning process the RPV nuts are easily unloaded and the inner threads are easily cleaned.

For the tensioning process, all RPV Nuts are transported with the integrated support device to the RPV and turned onto the RPV studs.

A typical operating time for detensioning or tensioning the Reactor Pressure Vessel is between 100 minutes and 150 minutes. It includes the 100 % automatically RPV nut turning and tensioning or detensioning the RPV studs.

The RPV studs (most of the time a fourth part of the Reactor studs) have to be turned by a separate Stud Turning Robot. The RV Stud Turning Robot has an own driving mechanism for moving forward from one RV stud to the next. During the whole Stud turning and positioning procedure the RV Stud Turning Robot is secured to prevent from falling down.