Personnel operating a reactor plant must be aware of the heatup and cooldown rates for the system. If personnel exceed these rates, major damage could occur under certain conditions.

EO 1.12

IDENTIFY the basis used for determining heatup and cooldown rate limits.

EO 1.13

IDENTIFY the three components that will set limits on the heatup and cooldown rates.

EO 1.14

STATE the action typically taken upon discovering the heatup or cooldown rate has been exceeded.

EO 1.15 STATE the reason for using soak times.

EO 1.16 STATE when soak times become very significant.

Basis

Heatup and cooldown rate limits, as shown in Figure 6, are based upon the impact on the future fatigue life of the plant. The heatup and cooldown limits ensure that the plant's fatigue life is equal to or greater than the plant's operational life. Large components such as flanges, the reactor vessel head, and even the reactor vessel itself are the limiting components. Usually the most limiting component will set the heatup and cooldown rates.

Thermal stress imposed by a rapid temperature change (a fast ramp or even a step change) of approximately 20F (depending upon the plant) is insignificant (10⁶ cycles allowed depending upon component) and has no effect on the design life of the plant.

Figure 6 Heatup and Cooldown Rate Limits