Regional Basic Professional Training Course in Korea

❙ 475 ❙
8-A. Deterministic Accident Analysis (Non‐LOCA)
8.2. INITIATING EVENTS AND THEIR
CATEGORIZATION
During the course of an AOO or a DBA, a number of different effects may challenge the
integrity of the barriers against uncontrolled release of radioactivity, by affecting the three
fundamental safety functions, control of reactivity, removal of heat from the fuel and
confinement of radioactive materials. These effects are also called ‘safety aspects’ of the
accident. Some potential safety aspects are listed below, covering the full spectrum of
consequences, from AOOs to DBAs, to BDBA, and to SAs:
• Reactor power excursions due to reactivity insertion;
• Reactor re‐criticality (local or global) after shutdown;
• Fuel enthalpy and temperature rise;
• Local fuel melting;
• Reduction of the departure from nucleate boiling ratio (DNBR) due to reduced
coolant flow or due to increased temperature or decreased pressure;
• Boiling crisis due to loss of coolant inventory;
• Overheating of fuel cladding;
• Zirconium–water reaction of the cladding;
• Deformation of and/or damage to the fuel cladding;
• Hydrogen production;
• Major fuel melting and core degradation;
• Primary or secondary system pressurization;