Phenomena | WWER-1000/V320 Design features and prevention and mitigation measures | |
Design features | Additional prevention and mitigation measures | |
Core melt | • Active medium and low-pressure safety injection (TQn3 and TQn2); • Passive Hydro Accumulators; • Emergency boron injection (TQn4). | • Additional diesel generators; • Qualification of some systems to operate as safety systems (TK system); • Water injection in reactor core or SG by mobile fire protection equipment in extreme conditions. |
Core melt under high pressure | • Primary depressurization system; • Safety valves; • Spray system. | • Qualification of some systems operates as safety systems (YR and TK). |
Pressure vessel failure | • In-vessel retention (by in-vessel injection of water). | • By external vessel cooling with water |
External steam explosion | • None. The cavity is dry. | • Need additional investigation in case of flooding of cavity for In-Vessel Melt Retention(IVMR). |
Basemat melt-through | • In-vessel melt retention by water injection. | • Plugging all ionization chamber channels located in the walls of the reactor vessel cavity; • Ex-vessel measures (see below). |
Containment overpressure | • Containment spray (earlier phase); • Larger containment free volume. | • Containment venting system (scrubber). |
Hydrogen detonation | • Larger containment free volume. | • Hydrogen recombiners; • Long term containment management (risk for late phase release). |
Containment bypass | • Accident management (for Primary to Secondary (PRISE) events using appropriate procedures). | • Ex-vessel measures (corium spreading, corium cooling by water supplying); • Long term cooldown of corium. |
Accident in spent fuel pool (SFP) | • Water level and temperature monitoring; • Emergency water supply system. | • Even SFP heat distribution; • Water injection in SFP by mobile fire protection equipment in extreme conditions. |