Experimental investigations on leak flow rate characteristics of water through axial artificial microcracks of steam generator tubes under back pressure conditions

Leak-before-break (LBB) analyses on tube microcracks are benificial for preventing small loss of coolant accident (SLOCA) in nuclear power plants. Currently, experimental investigations on leak flow rate characteristics of room temperature water through axial artificial microcracks of steam generator tubes under back pressure conditions are carried out for the following range: 0 < P_in ≤ 15.5 MPa, 0 < P_out ≤ 8.0 MPa, 1005 ≤ Re ≤ 85092, 3.54 ≤ δ/D_h ≤ 4.38, 0.13 mm ≤ W ≤ 0.16 mm, 1.01 mm ≤ δ ≤ 1.09 mm. Experimental results show that the recommended conservative value of working pressure in slit tubes (P_in) should be smaller than 9.0 MPa because irreversible expansion deformation of microcracks with a crack openning displacement of 0.15 mm will occur when P_in > 9.0 MPa. The leak flow rate is proportional to the square root of differential pressure in and out of slit tubes (ΔP) and crack openning displacement (W) when the back pressure (P_out) is equal to atmospheric pressure. However, leak flow rates increase with a decreasing back pressure first and then become a constant value for a given P_in. Each of pressures in slit tubes possess a corresponding critical ΔP. In a general, a new correlation was developed to predict 97.5% percent of leak flow rate data of water through axial artificial microcracks of steam generator tubes under back pressure conditions with a maximum deviation of ±4.0%.