16.2 - Severe Accident Analysis (RRC-B) - EDF Hinkley Point

SUB-CHAPTER : 16.2PRE-CONSTRUCTION SAFETY REPORTCHAPTER 16: RISK REDUCTION AND SEVEREACCIDENT ANALYSESPAGE : 201 / 295Document ID.No.UKEPR-0002-162 Issue 042.5.4. SB(LOCA)2.5.4.1. Time history and input data for the in-vessel phaseThe SB(LOCA) scenario considered is defined as follows:• 5 cm diameter (20 cm²) SB(LOCA) in a cold leg,• four steam generators fed by AFW,• partial secondary cooldown with four SG initiated at RIS [SIS] signal for 20minutes,• fast secondary cooldown with four SG initiated 30 minutes after reactor scram,• no opening by the normal PZR bleed valves,• opening of the severe accident dedicated valve when maximum core outlet gastemperature exceeds 650°C,• no LHSI,• no MHSI,• accumulators available.The time history of key events for the in-vessel phase is shown in Sub-section 16.2.2.5 -Table 9 from MAAP-4.04 calculations.2.5.4.2. Time history and input data for the ex-vessel phaseThe time history of key events for the ex-vessel phase is given in Sub-section 16.2.2.5 –Table 10.After vessel failure at ~168,700 seconds the core melt pours into the reactor pit and MCCIbegins. Steam, hydrogen, CO 2 and CO are produced and released into the containment. Thegeneration of these gases is modelled using COSACO. Because of the high temperatures inthe pit, instantaneous combustion of the generated hydrogen and CO in a standing flame isassumed.At ~180,200 seconds, the melt gate fails and the liquid core melt/concrete mixture flowsdown into the core catcher. During MCCI in the core catcher, steam, hydrogen, CO 2 and COare produced and released into the containment. Again, the generation of these gases ismodelled using COSACO. Because of the high temperatures in the core catcher,instantaneous combustion of the generated hydrogen and CO in a standing flame isassumed.The activation of two EVU [CHRS] trains is considered at ~188,400 seconds (12 hours afterthe core outlet temperature reaches 650°C).MCCI continues in the core catcher until all sacrificial concrete is consumed at~188,600 seconds.