A long, long time ago.... there used to be a happy group of engineers that designed nuclear plants for utilities....
No more...
Check ASME NB/NC/ND 3600 for a general definition of the three pipe classes. each plant required what was called a PFSAR and an FSAR ( preliminary and final safety analysis report) These were the documents that contained what is commonly called the Design Criteria for the plant.
Within the PFSAR or FSAR was the definition of the classification of safety systems and thier ASME "Class"
