Differentiate 'design basis' from 'operating envelope.'

• A. Design basis defines intended design parameters; operating envelope defines the safe operational limits during routine operation.
• B. Design basis is the maximum safe operating limit; operating envelope is the structural design.
• C. Operating envelope defines material specifications; design basis covers production targets.
• D. Design basis equals operating procedures.

Answer: (A)

The main distinction is where the boundary lies between design intent and day-to-day safety in operation. The design basis is the set of design criteria and parameters that define what the plant is built to handle and how it should meet safety, performance, and reliability requirements. It covers intended design parameters such as allowable pressures, temperatures, materials of construction, design margins, codes and standards, and assumptions used during engineering.

The operating envelope, on the other hand, is the safe range of conditions under which the plant can operate during routine operation, including normal and foreseeable transient conditions. It is the practical window controlled by process controls, instrumentation, procedures, and safety systems, derived from the design basis and hazard analyses.

So the best statement captures that the design basis defines intended design parameters, while the operating envelope defines the safe operational limits during routine operation. The other options mix up these roles: the design basis is not simply the maximum safe operating limit, nor is the operating envelope the structural design, nor do the design basis and operating procedures are the same.