Simulation experiments for radiologic inspection inside a nuclear reactor

Experiments were performed in a gamma cell to simulate radiologic inspection inside a CANDU nuclear power reactor. Radiation in the gamma cell is similar, both in magnitude and directions, to that in a shut down CANDU reactor. The inspection consists of detecting garter spring spacers used to maintain the gap between pressure tubes and calandria tubes in CANDU reactors. A shielding head made of tungsten alloy was placed inside a pressure tube. A glass scintillator was used as the gamma radiation detector. The scintillation light travelled through a fiber-optic light guide to the radiation-free environment outside the gamma cell, where the light was detected by a light sensor. Earlier experiments used a high-resolution CCD (charge coupled device) camera to capture images transferred through a high-resolution fiberscope. Later experiments used silicon photodiodes to measure the intensity of the light transferred through a fiber bundle that was made in-house. The light intensity approach was found to be more suitable for the detection of garter springs. The removal of the garter spring resulted in an immediate increase in the intensity of the scintillation light. Experimental results in the gamma cell show great promise for constructing a real-time garter spring detection tool for use in CANDU reactors.