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

SUB-CHAPTER : 16.2PRE-CONSTRUCTION SAFETY REPORTCHAPTER 16: RISK REDUCTION AND SEVEREACCIDENT ANALYSESPAGE : 203 / 295Document ID.No.UKEPR-0002-162 Issue 042.5.4.3.2. Containment temperatureIn the first ~135,000 seconds the local gas temperature distribution in the containment isfairly homogeneous (Sub-section 16.2.2.5 - Figure 8). During the second leak release,quench tank disk rupture and core melt quenching phases (i.e. ~140,000 seconds – 200,000seconds), large local temperature differences arise in the containment. Later on, in the longterm steaming phase, the temperature differences reduce to small values (< 15°C).Sub-section 16.2.2.5 - Figure 9 shows the liner surface temperatures for the dome (zoneAc7) and a lower annular compartment (zone Ac4) with respect to the gas temperature. Formost or the transient, the liner temperature remains below 80°C. During core melt quenchingthe temperature peaks briefly at 125°C.The IRWST water temperature and the saturation temperature (with respect to thecontainment pressure) are shown in Sub-section 16.2.2.5 - Figure 10. The IRWST water,which is fed into the core catcher in the long term steaming phase, is significantly sub-cooledin both water layers. Sub-cooling decreases from 50°C in the in-vessel phase of 0 seconds –168,700 seconds to 40°C in the long term (ex-vessel phase).2.5.4.3.3. Containment humidityIn the first ~145,000 seconds, the local humidity distribution in the containment is fairlyhomogeneous at about 100% in the whole containment, see Sub-section 16.2.2.5 -Figure 11. During the second release, quench tank disk rupture and core melt quenchingphases (i.e. ~140,000 seconds – 200,000 seconds), there are significant differences in localhumidity. Later on, in the long-term steaming phase, the humidity differences reduce andeventually saturation is reached everywhere in the containment.2.5.5. LOOP2.5.5.1. Time history and input data for the in-vessel phaseThe LOOP scenario with loss of all 6 diesels is defined as follows:• loss of Main Feedwater System (ARE [MFWS]),• closure of Main Steam Isolation Valves (VIV [MSIV]),• loss of Startup and Shutdown System (AAD [SSS]),• opening of the severe accident dedicated valves when maximum core outlet gastemperature exceeds 650°C,• accumulators available,• availability of power latest after 12 hours.The time history of key events for the in-vessel phase is shown in Sub-section 16.2.2.5 –Table 12 from MAAP-4.04 calculations.