Which of the following is a PWR indication of a design basis accident (DBA)?

• A. Unusual Increase in Containment Pressure
• B. Decreased Reactor Coolant System Pressure
• C. All ECCS Pump Start
• D. Reactor May Empty and Depressurize

Answer: (A)

In a PWR, a design basis accident is a scenario that challenges containment and requires the plant’s emergency systems to respond. The clearest signal of such an event is a rise in containment pressure. As the reactor coolant system experiences a transient (like a LOCA or other pressure-relieving event), steam and gases are released into the containment and the containment relief paths allow pressure to build. This pressure rise inside the containment is a direct indicator that the plant is experiencing an event designed to be mitigated by the safety systems, so operators watch containment pressure as a primary cue to initiate DBAs procedures and ECCS actions.

Decreased reactor coolant system pressure can occur during a LOCA, but it’s a symptom of the break itself rather than the containment-side indicator that operators use to recognize a DBA. Automatic ECCS pump starts happen in response to the event and are not a single, defining signal. The phrasing about the reactor emptying and depressurizing isn’t a standard, direct indicator used to identify a DBA.