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

SUB-CHAPTER : 16.2PRE-CONSTRUCTION SAFETY REPORTCHAPTER 16: RISK REDUCTION AND SEVEREACCIDENT ANALYSESPAGE : 26 / 295Document ID.No.EPR-0002-0162 Issue 04To study the effect of the porosity of the melt, water penetration depth (i.e. fragmentation) andfuel temperature, these parameters were varied without consideration of any boronconcentration in the cooling water and the most reactive configuration, k ∞ ≈ 1.21, was found toresult from a porosity of 44%, a water penetration depth of 51.6 cm and a fuel temperature of70°C (conservative case).When 2300 ppm natural boron concentration was considered the reactivity was found to bek ∞ ≈ 0.82.The most reactive porosity will decrease due to the competing effect between absorber andmoderator. It was found that the highest eigenvalue k ∞ with boron occurs at a porosity of 24%(70°C fuel temperature, 2300 ppm boron concentration, 24% porosity and 51.6 cm waterpenetration depth).For this very conservative configuration results k ∞ ≈ 0.93, i.e. large margins to criticality exist.Thus also higher enrichments do not result in recriticality during ex-vessel melt stabilisation..