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

SUB-CHAPTER : 16.2PRE-CONSTRUCTION SAFETY REPORTCHAPTER 16: RISK REDUCTION AND SEVEREACCIDENT ANALYSESPAGE : 202 / 295Document ID.No.UKEPR-0002-162 Issue 042.5.4.3. Results of the COCOSYS calculation2.5.4.3.1. Containment pressureThe pressure time history for the SB(LOCA) case is shown in Sub-section 16.2.2.5 -Figure 7.The relevant phases are:• First pressure peak at the beginning of the event (1.45 bar at 1800 seconds).Subsequently, the pressure decreases due to strongly decreasing steam andwater release.• Second pressure increase due to the release from the leak after ~135,000seconds.• Occurrence of a short pressure peak of 1.6 bar after quench tank disk rupture(~167,000 seconds).• Ex-vessel phase with MCCI in the reactor pit after initial vessel failure from~168,700 seconds – ~180,200 seconds.• Core melt quenching in the core catcher (starting at ~180,500 seconds) causes asignificant pressure peak (3.6 bar at ~181,800 seconds) because of the(assumed) high steam production rate of 100 kg/s.• Pressure decrease due to cessation of steam production during the filling of thecore catcher (from ~181,800 seconds – 185,000 seconds).• Continuation of pressure decrease in the containment during the heat-up of thewater inventory in the core catcher (without steam production).• Enhanced pressure decrease after start of two trains of the EVU [CHRS] at~188,400 seconds.• Beginning of steam production in the core catcher due to the decay heat of thecore melt at ~202,000 seconds. Pressure rises to 1.4 bar.• Long term rate of pressure decrease is 0.002 bar/hour.At all times, the pressure remains well below the design pressure (5.5 bar), see Sub-section16.2.2.5 - Table 11.The local pressure differences in the containment are very small in relation to the absolutepressure.