Neutron Radiographic Investigations of Hydride Blisters Grown on Zr- 2.5Nb Pressure Tube Spool Piece Under Stimulated Condition of In- Reactor Pressure and Temperature

The present work has been carried out with an aim to have a thorough understanding of the mechanism of blister formation and the resulting degradation in the serviceability of the component under simulated in-reactor condition of pressure and temperature. A 220 MWe Indian PHWR Zr-2.5Nb pressure tube spool piece of 165 mm length was charged with a homogeneous hydrogen concentration using lithium hydroxide solution at 300 °C followed by growth of multiple hydride blisters at 10 different locations on the pressure tube outside surface by maintaining cold spots. This blistered tube was subjected to burst test by pressurizing the tube in steps of 20 kg/cm2 for 10 minutes up to 380 kg/cm2 at which it burst with sound. The failed tube was examined by neutron radiography, scanning electron microscopy, surface profiling, video microscopy and digital imaging for characterizing the cracked and un-cracked blisters. Neutron radiographs of the hydride blisters were recorded using NR facility at Apsara, a 200 kW swimming pool type reactor using transfer technique with 25 μm Gd neutron converter screen. The details of NR investigations done are reported in this paper.