Helium leak detection and other nondestructive tests of closure welds proved unreliable for the EBR-II fuel rods. A system was developed which used pressure decay in a miniature pressure chamber as a measure of weld leakage. Analysis of pressure decay rate permitted determination of leak size. Spurious signals resulting from leakage of the test system produced an abnormal ultimate test chamber pressure. These were readily differentiated from fuel rod leaks. The sensitivity of the tests is approximately 5 × 10−6 standard cubic centimeters of helium per second. Higher sensitivity may be obtained by variation of the technique and of the equipment. The influence of vapor contamination of leak capillaries was investigated and correlated with surface tension phenomena. The test has been successfully applied to a variety of fuel elements and incapsulated specimens with small internal void spaces.