Reactor Operations and Control
Domain 2 covers maneuvering the reactor from subcritical through power operation: rod and boron worth, startup rate, period, power defect, and closed-loop control of temperature, pressure, and level.
Core rules
- Approach criticality by boron dilution or rod withdrawal in small steps; verify counts and inverse-count-rate behavior before adding positive reactivity.
- Startup rate (SUR) in decades per minute = 26.06 / stable reactor period in seconds. A shorter period means faster power change; a negative period means power is decreasing.
- Differential rod worth is pcm per inch; integral worth is the sum over the stroke. Boron worth is negative pcm per ppm; dilution adds positive reactivity.
- Power defect is the reactivity change from zero to full power due to Doppler and moderator feedback; it is compensated by rod withdrawal or dilution.
- Tavg control and axial offset control are coupled: rod motion affects both power distribution and temperature. Steam generator level is controlled by feedwater, not by rod motion.
Worked example
A reactor is on a 100 s stable period. SUR = 26.06/100 = 0.26 decades per minute; doubling time = 0.693 × 100 = 69 s. If operators need −300 pcm and boron worth is −8 pcm/ppm, they must add 300/8 = 37.5 ppm boron. That is a calculated change, not a license to skip reactivity verification.
Traps
Using SUR = 26.06 × period inverts the relationship. Confusing period with doubling time is common. Overborating for a small power defect can force a long dilution and delay startup. Treating pressurizer level as a direct measure of RCS inventory ignores charging, letdown, and shrink/swell.