SYNROC PROCESS FOR URANIUM RICH WASTE FROM 99 MO PRODUCTION

摘要

The Australian Nuclear Science and Technology Organisation (ANSTO) irradiates Uranium (U) targets tornproducern99 99Mo, the precursor to radiopharmaceutical Mo, 99m 99mTc. A process to convert the U-rich dissolverrnwaste, from the U-targets, into a durable synroc type ceramic has been demonstrated at laboratory scalernby ANSTO and the Idaho National Engineering and Environmental Laboratory (INEEL). Synroc is arnparticular kind of “synthetic rock,” developed in 1978 by the late Professor Ted Ringwood of thernAustralian National University. It is an advanced ceramic comprising geochemical stable natural titanaternminerals, which have immobilized uranium and thorium for millions of years. These mineral structuresrncan incorporate and immobilize nearly all of the elements present in high-level radioactive waste (HLW).rnA joint effort between ANSTO and the INEEL was conducted to evaluate 1) a fluidized-bed to calcine thernU-bearing liquid waste surrogate solutions mixed with a synroc precursor and 2) conversion of the calcinerninto synroc via hot isostatic pressing (HIPing).rnTc. The feasibility study was completed using a lanthanide-rich non-radioactive surrogate of the U-rich wastern(a nitrate based solution), combined with a titanate-rich precursor suspension. Having prepared 20-Lrnbatches of feed solutions for the calcination trials, they were calcined in a HrnH2/N /N2 reducing atmosphere atrn575-620°C with an electrically heated 82 mm diameter fluidized-bed reactor. The feed was spray driedrnand calcined on a starting bed of 200-400 μm Synroc B precursor particles. A series of calcination testsrnwere performed, achieving >90% bed turnover to the desired synroc precursor.rnNon-volatile (Sr, Ba, Ca, K, Ce, La, Nd, Pr, Al, and Ni) elements in the surrogate HLW feed wererneffectively converted to an oxide calcine product, with minimal generation of fines in the bed. Bedrnparticulate growth was well behaved with the production of homogeneous spherical particles suitable forrnbed fluidization and feed spray coating. Fines generation was reduced to approximately 10% of the oxidernproducts produced by the liquid feed. The fines were efficiently collected by a cyclone separator andrnsintered metal blowback filter (>99% solids disengagement). The fines and bed were collected forrnphysical and chemical analysis. Residual nitrate levels in the calcined bed were less than 0.5 wt%, whichrnis a prerequisite for HIPing. The partitioning efficiency of potentially volatile radioactive Ru and Cs inrnthe calcine product was greater than 99.98%.rnThe synroc precursor calcine was mixed with 2 wt% of powdered titanium metal in a steel can. It is thenrnevacuated, sealed, and hot isostatic pressed (HIPed) at 1250°C. The HIPing process produced arnchemically durable, homogeneous (at the 50 micron scale) ceramic having nearly 100% theoreticalrndensity, and a waste loading of approximately 35 wt% was achieved. The physical and chemicalrncharacteristics of the HIPed sample were evaluated. Scanning Electron Microscopy (SEM) reveal arnhomogeneous crystalline synroc was produced. Waste form durability is predictably superior to those ofrnalternative vitrified waste forms.;