[en] ⁸⁵Kr concentration in air in the vicinity of the reprocessing plant was measured when it was released from the plant stack during the hot-test operation using PWR spent fuels. Charcoal absorption method was devised for this experiment as a rapid, simple and inexpensive technique for the measurement of ⁸⁵Kr concentration at about 10^-9 μCi/cm³. Special air samplers were located at few kilometers distant from the stack and the air was collected for an hour at a flow-rate of 1.5 liters per minute. About thirty air samples were taken and analyzed for ⁸⁵Kr concentration successfully. The performance of sampling and analytical methods employed was good, although some improvements were found to be necessary. An example is that an air-collection bag should be made of ''saran'' so that the leakage be minimized. Usually in the atmospheric diffusion study sulfur hexafluoride gas is used as an air-tracer, and analytical procedure for the gas concentration down to 10^-3 ppb is well established. In this experiment SF₆ gas was injected into the stack during the discharge of ⁸⁵Kr and the concentration in sampled air was also determined. The results show a good correlation between ⁸⁵Kr and SF₆ concentration in sampled air. (author)