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Defence in depth: reactors



Now we have worked through several examples of how to calculate the basic rating. This slide is a repeat from earlier in this module and reminds you that having derived the basic rating, you now need to consider additional factors. These were covered in the overview module.

As the first question is answered, rating events for reactors at power follows the steps shown here. 

What safety provisions have been affected?

The basic rating depends on assessing the status of safety provisions in the plant.
- It is about initiators and safety functions

The wider issues are; human performance and safety management.

Additional factors are about the wider safety management issues, depending mainly on failures of personnel and procedures.

A 'basic rating' is assessed from the first step and a 'final rating' is derived from considering the additional factors. Additional factors were explained in the overview module.