FURTHER IMMOBILIZATION OF STABILIZED ALPS SEDIMENT PHOSPHATE WASTE WITH POWDER METALLURGY HOT ISOSTATIC PRESSING FOR FUKUSHIMA DECOMMISSIONING

Abstract

The decommissioning of the Fukushima Daiichi nuclear power plant presents a great challenge in terms of waste management owing to the presence of various radionuclides and waste materials, including large amounts of radioactive sediment waste from the advanced liquid processing system (ALPS). The durability of the waste form is crucial for the safety of final disposal. Phosphate waste (ALPS phosphate) is a candidate material for stabilizing the carbonate and iron co-precipitation slurry wastes from ALPS. To enhance waste form durability, we propose using a composite form that encases primary waste, the ALPS phosphate in a secondary metallic matrix for protection from corrosion under a repository environment. The simulated ALPS phosphate (main composition of Ca:Mg:Fe:P=2:3:1:5, doped Cs, Sr, Eu, and Ce) was synthesized, using hot isostatic pressing (HIP), a powder metallurgy method, at 1000 °C and 175 MPa for 3 h and a composite waste form was obtained. Metallographic measurements and elemental analyses revealed that the powdery stainless steel was well sintered, and transformed into an ingot matrix, whereas the ALPS phosphates and their decomposition products were individually dispersed and confined within the metal matrix. According to a simple corrosion model, the composite waste form described is expected to have a long enough lifetime to ensure a safe, final disposal.