Regional Basic Professional Training Course in Korea

❙ 497 ❙
8-A. Deterministic Accident Analysis (Non‐LOCA)
RCS cool‐down, following reactor trip, leads to a rapid decrease in pressurizer
water volume and the SI signal is initiated on low pressurizer pressure. The SI
signal automatically terminates normal feedwater supply and initiates auxiliary
feed water system (AFWS) actuation.
The SG blowdown liquid monitor and/or the condenser off‐gas air ejector radiation
monitor will alarm, indicating a sharp increase in radioactivity in the secondary
system and will automatically terminate SG blowdown.
The reactor trip automatically trips the turbine; if offsite power is available, steam
dump valves open permitting steam to the condenser while in a loss of offsite
power steam dump valves close. Following turbine trip, the steam flow rapidly
decreases and the SG pressure rapidly increases, resulting in the steam discharge to
the atmosphere through the SG relief and safety valves.
Following reactor trip, continued action of the auxiliary feedwater supply from the
condensate storage tank (CST) and borated SI flow from the refueling water
storage tank (RWST) provides a heat sink to absorb the decay heat.
For the SGTR, it is expected that the accident diagnostics and isolation procedure can be
completed within 30 minutes of event initiation, considering the indications provided at
the control board, together with the magnitude of break flow. However, it is assumed in
the analysis that the operator action initiates 30 minutes after initiation of the accident,
isolating the faulted SG, followed by reduction of the RCS temperature and pressure to
the shutdown cooling or residual heat removal (RHR) condition.
8.5.7. Radioactive Release from a Subsystem or Component
For a PWR, the initiating events that can result in readioactive release from a subsystem