Hanford Waste Encapsulation: Strontium and Cesium

The strontium and cesium fractions separated from high-radiation-level wastes at Hanford are converted to the solid strontium fluoride and cesium chloride salts, doubly encapsulated, and stored underwater in the Waste Encapsulation and Storage Facility. A capsule contains ∼70 000 Ci (2.59 PBq) of ¹³⁷Cs or 70 000 to 140 000 Ci (2.59 to 5.18 PBq) of ⁹⁰Sr. Materials for fabrication of process equipment and capsules must withstand a combination of corrosive chemicals, high radiation dosages, and, frequently, elevated temperatures. The two metals selected for capsules, Hastelloy C-276 for strontium fluoride and Type 316L stainless steel for cesium chloride, are adequate for prolonged containment. Additional materials studies are being done both for licensing strontium fluoride as source material and for second-generation process equipment.