Long Term Durability Testing of Simulated Iron-Phosphate Nuclear Waste Glass
- PDF / 396,597 Bytes
- 6 Pages / 612 x 792 pts (letter) Page_size
- 20 Downloads / 220 Views
II3.22.1
LONG TERM DURABILITY TESTING OF SIMULATED IRON-PHOSPHATE NUCLEAR WASTE GLASS H. Haworth1, D.J. Wronkiewicz1, and D.E. Day2, 1Department of Geology and Geophysics and 2 The Graduate Center for Materials Research; University of Missouri - Rolla; Rolla, MO.
ABSTRACT An iron phosphate base glass and a simulated Hanford Tank Farm B (TFB) waste loaded iron phosphate glass were reacted under both Product Consistency Test (PCT) and Vapor Hydration Test (VHT) conditions. Solution aliquots were collected following reaction of the TFB glass after the completion of a PCT at 90ºC for time periods of 7, 49, 185, 274, and 365 days. Normalized element release patterns for sodium were highest of all the elements present, with values initially decreasing between 7 and 182 days and then increasing thereafter. Normalized release values for phosphorous declined between 49 and 182 days but increased thereafter, whereas calcium contents declined to and remained below the analytical detection limit after 182 days. Normalized element release patterns for Ce, Nd, and Fe were below 0.00045 g/m2 for all time periods tested. Amorphous iron oxide and elongate crystals (possibly apatite?) were noted as alteration products in both long-term PCT and short-term VHT formats. The VHT samples were reacted at 150°C for time periods of 3, 7, and 35 days for the base glass and 3, 7, 35, 91, 185, and 300 days using the TFB glass. Reacted samples were examined for alteration products, with an emphasis on identifying phases that could potentially occur during geologic disposal. The base glass reacted quickly under the VHT conditions. Phosphorous released from the base glass apparently formed phosphoric acid, which quickly lowered the solution pH to a value of one. The acidic nature of the fluids, in turn, led to an accelerated rate of glass corrosion. The addition of alkali and alkaline earth elements in the TFB glass prevented the low pH excursion seen in the base glass; possibly by ion exchange processes that remove hydrogen ions from solution, sequestering of phosphorous in alteration phases to prevent phosphoric acid formation, or both. This change led to a dramatic decrease in TFB glass reaction rates relative to the base glass composition. Alteration products included an amorphous iron precipitate and several crystalline phases. INTRODUCTION The safe disposal of radioactive wastes requires the development of durable waste forms that effectively isolate hazardous components from the biosphere for an extended period of time. Borosilicate glass is the waste form that has been chosen by many countries for the vitrification and disposal of their nuclear waste materials [1]. Certain high level waste streams, however, contain components that may have limited solubilities in a borosilicate glass matrix. Such components include phosphorous, sulfate, some heavy metals, and halide elements. Vitrification of waste streams containing high concentrations of these components may produce glasses with crystalline phase inclusions that have formed during cool
Data Loading...
