Full-Core GCMR Coolant Depressurization Transient

Unlike the single-channel blockage transient, which has localized effects, the coolant depressurization transient is a global event that impacts the entire GCMR core. Within 13 seconds of the transient event's initiation, the coolant outlet pressure in all channels drops linearly from 7 MPa to ambient pressure (i.e., 0.1 MPa, see Figure 1). Simultaneously, the coolant velocity decreases from 15 m/s to 0.1 m/s (see Figure 2).

This event significantly reduces the global heat removal capacity of the GCMR, leading to a substantial temperature increase. Similar to the single coolant channel blockage case, temperature feedback during the high-temperature transient leads to a rapid decrease in reactor power, as shown in Figure 3. The GC-MR almost loses all of its original operating power within 400 seconds, along with a maximum temperature increase in fuel by approximately 50 K.

Figure 3: Time evolution of reactor power during a coolant depressurization transient