Scram setpoint

An experimenter makes an error loading a rabbit sample. Injection of the sample results in a 100 millisecond period. If the scram setpoint is 1.25 MW and the scram delay time is 0.1 seconds, WHICH ONE of the following is the peak power of the reactor at shutdown (Assume rabbit system is operational for this question.)... 

List eight of the ten conditions that cause a relay scram. (Setpoints are not required.)... 

Control rod withdrawal at normal operation is analyzed. The reactivity worth of the withdrawn CR cluster is conservatively assumed as 1.3%dk/k. The same withdrawal speed as of PWRs (114 cm/min) is taken. The CR cluster is withdrawn until the reactor power reaches the scram setpoint (120% of rated power). The inserted reactivity is 0.69. The calculation results are shown in Fig. 6.32. The power increasing rate is small due to the reactivity feedbacks from the water density and fuel temperature. The cladding temperature increases by only 10°C because the main coolant flow rate is increased by the control system so as to keep the main steam temperature. If the control system is not considered, the increase in the temperature is about 110°C. The influence of the CR worth is small because the inserted reactivity before the reactor scram is almost the same [5]. 

The primary purpose of the RPS is to automatically scram the reactor if safety setpoints are exceeded. The RPS performs this fimction by unlatching the control rods for a fast gravitational insertion of all nine control rods. To ensure rod insertion, the RPS simultaneously activates the rod drive-in motors which drive in the control elements. Upon positive indication of control element insertion (decreasing flux), the RPS trips the primary pumps as part of the scram sequence. 

List 5 SCRAMS that are NOT based on neutron measuring channel signals. Setpoints are not required. 

The restart criteria require that transient and accident analyses include the assumption that mitigating systems are not actuated until the most conservative setpoint is reached. The Action Plans discuss setpoints and the time delays allowed for scram. In responding to the staff s inquiry, WSRC has indicated that worst-case setpoints are assumed for the analyses and, in particular, for the scram or the actuation of the Supplementary Shutdown System (SSS). WSRC further assured the staff that it has prepared specific calculations containing tables for all trip setpoints used for its analyses and that WSRC is currently developing a setpoint methodology document. Determination of setpoints is an open item. 

Since the peaks of pressure, power, and temperature appear in a very short time scale within 1 s, only the SRVs are effective to mitigate them. The reactor scram starts after the peaks come. The results of sensitivity analysis are shown in Table 6.13. The maximum pressure depends oti the SRV setpoint. The maximum power is not sensitive to the density coefficient because the increase in the coolant density itself is small. The increase in the cladding temperature is not sensitive to either parameter. 

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