Doubling time is unit similar as in radioactive decay calculations. Doubling is defined as the amount of time it takes reactor power to double the initial power level. The reactor period is usually expressed in units of seconds or minutes. If the reactor period is known, doubling time can be determined as follows.
Doubling time = τe . ln2
τe = reactor period
ln2 = natural logarithm of 2
The smaller the value of DT, the more rapid the change in reactor power. The doubling time may be positive or negative. If the doubling time is positive, reactor power is increasing. If the value is negative, we talk about the halving time and reactor power is decreasing.
Suppose keff = 1.0005 in a reactor with a generation time ld = 0.01s. For this state calculate the reactor period – τe, doubling time – DT and the startup rate (SUR).
ρ = 1.0005 – 1 / 1.0005 = 50 pcm
τe = ld / k-1 = 0.1 / 0.0005 = 200 s
DT = τe . ln2 = 139 s
SUR = 26.06 / 200 = 0.13 dpm