[en] Bucklings derived from activation measurements in the ZED-2 reactor are given for 19-element natural uranium metal assemblies. Measurements were made in triangular arrays of 55 assemblies at pitches in the range 20 to 40 cm. 'Coolants' used were: (1) D2O of moderator purity, (2) He to simulate a voided condition. Bucklings obtained with He as coolant are higher than those for D2O coolant for the pitches investigated. (author)