Abstract: A method and apparatus for locating defective nuclear fuel elements is disclosed. Fuel elements that are to be tested are enclosed in a test chamber, filled with water. Air is pumped or pulled into the chamber, entering through a gas sparger at the bottom of the chamber and displacing a portion of the water above the fuel element. This reduces the pressure in the vessel, forms an air pocket above the fuel element and purges the water surrounding the fuel element of fission gases released from defective fuel elements. The activity of sample gas drawn from the chamber is continuously monitored to indicate fission gas content. In subsequent steps the pressure in the chamber is further reduced with a vacuum pump and gas drawn from the air pocket above the fuel for testing is recirculated and allowed to continuously purge the water surrounding the fuel elements of fission gases released from defective fuel elements.