Plant Operations, Maintenance, and Testing
Modes and limits
Operations run on Technical Specifications organized by mode (PWR Mode 1 power operation through Mode 6 refueling; BWR definitions differ in detail). Each Limiting Condition for Operation has a required action with a completion time. Know the default rules: 10 CFR 50.36-derived TS 3.0.2 and 3.0.3 govern what to do when an LCO is not met and when to enter a shutdown mode. Shutdown margin is a core parameter - typical PWR limits are around 1.3% Δk/k with the highest-worth rod assumed stuck out, and BWRs roughly 0.38% Δk/k.
Testing and maintenance
Surveillance requirements cover periodic testing, calibration, and IST per ASME OM through 10 CFR 50.55a. Motor-operated valve testing, diesel generator loading, and accumulator checks are classic exam items. The maintenance rule (10 CFR 50.65) requires risk-significant systems to be monitored and kept in a condition consistent with design basis.
Startup and ascension
After refueling: criticality via boron endpoint or rod withdrawal, then hot-zero-power physics testing (isothermal temperature coefficient, control rod worth), then power ascension with flux map calibration.
Traps
- Applying completion times as extensions of LCO entry rather than deadlines.
- Mixing PWR and BWR mode definitions.
- Assuming surveillance test intervals can be extended freely; TS restrictions apply.
Worked example
An LCO is entered at 08:00 with a 72-hour completion time. If the action cannot be met, the TS 3.0.3 default typically requires initiation of shutdown within 1 hour and reaching a safe mode within a specified longer window - do not read the 72 hours as permission to keep operating.