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

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SUB-CHAPTER : 16.2PRE-CONSTRUCTION SAFETY REPORTCHAPTER 16: RISK REDUCTION AND SEVEREACCIDENT ANALYSESPAGE : 205 / 295Document ID.No.UKEPR-0002-162 Issue 042.5.5.3.2. Containment temperatureVery significant local temperature differences arise in the containment (Sub-section 16.2.2.5 -Figure 13) during rapid steam releases. Later on, in the long term steaming phase, thetemperature differences are reduced to small values (< 15°C).Sub-section 16.2.2.5 - Figure 14 shows the liner surface temperature for the dome (zoneAc7) and a lower annular compartment (zone Ac4) with respect to the gas temperature. Theliner temperatures remain below 150°C, with the exception of a short period after core meltquenching.The IRWST water temperature of the surface layer, the bottom layer and the saturationtemperature (with respect to the containment pressure) are shown in Sub-section 16.2.2.5 -Figure 15. The IRWST water coming from the bottom layer, which is fed into the core catcherin the long term steaming phase is significantly sub-cooled. The sub-cooling decreases from80°C at ~20,000 seconds to 25°C at ~100,000 seconds.2.5.5.3.3. Containment humidityLarge local humidity differences arise in the containment (see Sub-section 16.2.2.5 -Figure 16) until start of EVU [CHRS]. After this, the accessible rooms become saturated veryquickly and the humidity in the equipment rooms increases. Later on, in the long termsteaming phase, the equipment rooms are in a saturated state or close to saturation.2.5.6. ConclusionThree representative scenarios that may cause pressurisation of the containment after asevere accident have been analysed:• A LB(LOCA) scenario that leads to early and fast pressurisation.• A SB(LOCA) scenario with fast secondary cooldown, where heat is transferred tothe SG for a long period of time, and pressurisation of the containment startsonly after 40 hours.• A LOOP scenario with steam release through the RPT (reactor pressure tank)and transient pressurisation between the above mentioned scenarios.In all three severe accident scenarios analysed the containment pressure remains clearlybelow the containment design pressure of 5.5 bar.High gas temperature occurs only for short time (during MCCI and during the quenchingphase in the reactor pit and in the spreading room) in a few containment regions.In all cases the water in the IRWST remains clearly below 150°C in the upper layer andbelow 100°C in the lower pool layer.
SUB-CHAPTER : 16.2PRE-CONSTRUCTION SAFETY REPORTCHAPTER 16: RISK REDUCTION AND SEVEREACCIDENT ANALYSESPAGE : 206 / 295Document ID.No.UKEPR-0002-162 Issue 04SUB-SECTION 16.2.2.5 - TABLE 1Basic containment model - accessible zones [Ref]ZoneVolumeDescription Name No [m 3 ]Lower annular rooms Loop 1&2 Ac1 19 650Lower annular rooms Loop 3&4 Ac2 20 650Middle annular rooms Loop 1&2 Ac3 21 5300Middle annular rooms Loop 3&4 Ac4 22 5100Upper annular rooms Loop 1&2 Ac5 23 2300Upper annular rooms Loop 3&4 Ac6 24 1850Dome Ac7 25 45800Access Ac8 26 550Staircase south Ac9 27 400Staircase north Ac10 28 400Elevator Ac11 29 150Hot piping Ac12 30 650Sum accessible zones Ac1-Ac12 63800
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16.2 - Severe Accident Analysis (RRC-B) - EDF Hinkley Point

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