Some major highlights of the passive safety design features in the SCOR, structured in accordance with the various levels of defence in depth [IV-5, IV-6], are brought out below.

Level 1: Prevention of abnormal operation and failure

• Integral design of the primary circuit;

• Internal CRDMs;

• Relatively low core power density;

• Elimination of soluble boron reactivity control system;

• Substantially negative moderator temperature reactivity coefficient throughout the whole burnup cycle. Level 2: Control of abnormal operation and detection of failure

• Large coolant inventory in the main coolant system, large thermal inertia of the primary circuit;

• Substantially negative moderator temperature reactivity coefficient throughout the whole burnup cycle.

Level 3: Control of accidents within the design basis

• For a steam line rupture, no possibility of return to criticality and no need for safety injection;

• Large inventory of water inside the RPV; long term cooling by the RRP systems in a passive mode during LOCA;

• For a steam generator tube rupture, no steam release to the atmosphere (steam is condensed in a dedicated pool);

• Primary circuit has no soluble boron; therefore, no risk of dilution by water of the secondary circuit;

• Natural circulation heat removal during a loss of flow accident (LOFA);

• Increased reliability of decay heat removal system achieved through the use of natural convection.

Level 4: Control of severe plant conditions, including prevention of accident progression and mitigation of severe accident consequences [48]

Level 5: Mitigation of radiological consequences of significant release of radioactive materials

The following features help in passively bringing down the containment pressure and in minimizing any releases from the containment following a LOCA:

• As large break LOCAs are eliminated by design, the maximum break size in LOCA is limited by 2 x 50 mm;

• Relatively small, inerted, pressure suppression containment;

• Relatively small fuel inventory;

• Increased retention of fission products (flooding of reactor cavity, dedicated pool for steam condensation under a steam generator tube rupture, etc.).