Large-break loss of coolant accident LOCA

Large pipes are eliminated by design, thus eliminating the large-break loss of coolant accident (LOCA) design basis accident. 

By adopting the integrated primary system design and the HHTS without reactor coolant pumps and main coolant pipelines, the possibility of accidents that may cause fuel failure, such as a large-break loss of coolant accident (LOCA), rod ejection (R/E), loss-of-flow (LOF) and locked rotor (L/R), is essentially eliminated. During the normal operation, the water level in the reactor vessel is controlled by injection from the charging pumps. However, since the diameter of the pipes connected to the primary system (reactor vessel) is less than 10 mm, water level can be maintained to submerge the top of the core without any injection. 

A typical large dry containment is shown in Fi re 4.1-3. A large dry containment is designed to contain the blowdown mass and energy from a large break Loss-of-Coolant Accident (LOCA), assuming any single active failure in the containment heat removal systems. 

Safety. A large inventory of radioactive fission products is present in any reactor fuel where the reactor has been operated for times on the order of months. In steady state, radioactive decay heat amounts to about 5% of fission heat, and continues after a reactor is shut down. If cooling is not provided, decay heat can melt fuel rods, causing release of the contents. Protection against a loss-of-coolant accident (LOCA), eg, a primary coolant pipe break, is required. Power reactors have an emergency core cooling system (ECCS) that comes into play upon initiation of a LOCA. 

---