High Level Nuclear Waste at the Savannah River Site— Past, Present, and Future

Abstract

The Savannah River Site (SRS) operated five heavy water nuclear reactors and two separation canyons for the production of nuclear materials for defense, special isotope production and space programs. These operations produced more than 100 million gallons of high-level nuclear waste (HLW), which has been stored in underground carbon steel tanks. The highly alkaline HLW consists of three forms; precipitated metal hydroxides and hydrous metal oxides referred to as sludge, supernatant liquids or supernate, and crystalline sodium salts referred to as saltcake that are formed upon evaporation and cooling of waste supernates. The current inventory of HLW at SRS is about 38 million gallons. Disposition of the HLW seeks to immobilize more than 99% of the radioactivity in a highly durable borosilicate glass wasteform. Concentrated liquid and saltcake are retrieved and pretreated to remove cesium, strontium, and alpha-emitting radionuclides. The separated radioactive components transfer into the Defense Waste Processing Facility (DWPF) for vitrification along with the sludge fraction of the HLW. The decontaminated liquid waste transfers into the Saltstone Production Facility (SPF) for incorporation into a cement wasteform for onsite disposal as a low-level waste. The DWPF began radioactive service in 1996 and to date has produced more than 3250 glass canisters. The SPF began radioactive operations in 1990 and has immobilized more than XX million gallons of decontaminated waste liquids. Two pilot-scale pretreatment facilities, the Actinide Removal Process (ARP) and the Modular Caustic Side Solvent Extraction Unit (MCU) began radioactive operations at SRS in 2008. The ARP facility uses an inorganic ion exchanger, monosodium titanate (MST), to remove 90Sr and alpha-emitting radionuclides (principally 238Pu, 239Pu, 240Pu and 237Np). Following treatment with MST, the waste passes into the MCU for removal of radio-cesium using a calixarene extractant. The Salt Waste Processing Facility (SWPF), currently under construction will use these same processes to treat the HLW at a throughput of about 7 million gallons per year beginning in 2014. A new initiative, referred to as the Small Column Ion Exchange (SCIX) process is under development to accelerate pretreatment of salt wastes at SRS. The SCIX operation uses an inorganic ion-exchanger, crystalline silicotitanate (CST) for the separation of cesium and strontium from waste solutions. This separation technology will feature two small ion-exchange columns located within a high-level waste tank.