The progression of the accident along with the degradation parameters are tabulated in Table 4. Primary pressure is shown in Fig. 2. As soon as LOCA is initiated, primary pressure drops sharply due to large inventory loss (Fig. 3) in RCS. Depressurization of RCS is faster in higher break sizes. In case of small break (50 mm) pressure oscillates around 8 MPa up to 4000 s and then decreases slowly. This is due to mismatch between core heat generation and energy taken out through the break and steam generator. Fig. 4, Fig. 5 show the pressure and inventory transients for similar cases with hydro-accumulator injection. A delayed depressurization and loss in inventory is evident for medium (150 mm) and small (50 mm) break cases whereas for large break case (850 mm) the trend is similar as observed without HA injection cases. The time required for total core uncovery (Table 4) also shows the effect of HA injection on primary side inventory.