12.100. This accident is caused by any event that requires reactor trip combined with a station blackout, i. e., the loss of all power, as well as the loss of capability of the secondary system to remove heat from the primary circuit. Under such circumstances, with no means for normal heat removal, the primary system pressure would rise until the relief value system would initiate blowdown. Subsequent events for a TMLB’ accident could follow those given above for the AB accident. However, in a more realistic vari­ation, designated as a TMLB accident, electrical power is assumed to be recovered in 1 to 3 hours. Should this be the case, meltdown and the subsequent scenario might be avoided.

Containment bypass accidents (V)

12.101. This is an accident category in which the containment would be compromised by such possibilities as the failure of a series of valves con­necting the high-pressure reactor coolant system with the low-pressure portions of the emergency core cooling system leading outside the con­tainment. In this category, the event scenario and consequences depend greatly on the design details of the specific reactor system. It should be noted that in the Three Mile Island accident, there was some containment compromise through the level control and purification system (§12.179).