In the nuclear pumped-lasers, the passage of these energetic charged particles through gas results in a non-uniform volumetric energy deposition. This spatial non-uniformity induces a gas motion, which results in density and hence refractive index gradients that affects the laser's optical behaviour. The motion of He-3 gas in a closed cavity is studied when it experiences transient and spatially non-uniform volumetric heating caused by the passage of He-3(n, p)H-3 reaction products. Gas motion is described by the radial velocity field of gas flow. Spatial and temporal variations of radial gas velocity are calculated for various tube parameters by using a dynamic energy deposition model. In the calculations, it is assumed that the laser tube is irradiated with neutrons from the pulse at a peak power of 1200 MW corresponding to a maximum thermal neutron flux of 8 x 10(16) n/cm(2) sn in the central channel of ITU TRIGA Mark II Reactor. Results are examined.