[en] Byproduct cesuim was recovered from Hanford nuclear waste following removal of the plutonium product and recovery of the enriched uranium from the spent nuclear fuel. The major incentive for recovery of the cesium, along with strontium, was reduction of the heat-generation rate in the waste tanks. Removal of these two heat-producing chemical species results in more than 90% reduction in heat generation in neutralized waste from 1-year-old fuel, and thus, much lower temperatures result in the tanks. The cesium was recovered from the Hanford waste stream beginning in 1967 and was purified and encapsulated from 1974 to 1983, resulting in 1576 capsules containing a total of about 75 MCi of ¹³⁷Cs. Although these capsules were designed to ease the handling of the waste, they also have substantial potential for use in industrial irradiators. The use of the WESF capsules to meet the demands of the medical industry turned out to be the most viable option, and several companies petitioned the US Department of Energy to obtain this material. To date, two commercial firms are using WESF cesium capsules in three commercial irradiation facilities. A third firm has recently leased a small amount of cesium. A total of 38 MCi in over 700 WESF capsules has been leased. 7 refs., 3 figs