Which of the following is a conservative assumption used to bound the design basis events?

• A. Worst case single failure of equipment
• B. Adverse consequences is typically defined as cladding damage
• C. Non-safety equipment not available during an accident
• D. Equipment providing no capability if not fully operable

Answer: (A)

A fundamental way designers bound design basis events is to assume the worst-case single failure of equipment. This conservative stance ensures safety functions must perform even when one component unexpectedly fails, thanks to redundancy and margins built into the system. By focusing on a single, credible failure, engineers can demonstrate that safety goals are met under that worst-case scenario, which in turn bounds all less severe or more complex events.

The other descriptions describe outcomes or conditions rather than the bounding practice itself. Cladding damage is a possible consequence, not the assumed bound used to define the event. Assuming non-safety equipment is unavailable during an accident or that equipment provides no capability unless fully operable are not the standard conservative bounding assumptions used to define design basis events.