Evaluation of Synroc-C as a second-generation waste form

The durability of a crystalline titanate waste form, Synroc-C, was evaluated as a second-generation waste form by leach testing. Tests using both monolith and high surface area powdered samples were used with silicate water and brines at 90/sup 0/C and 150/sup 0/C for up to 90 days. In addition, low surface area-to-volume ratio, 1-day leach tests were conducted between 90/sup 0/C and 250/sup 0/C to determine forward-direction leach rates and activation energies. Dissolution rates of Cs, Mo, Ba, and U indicated that Synroc-C generally performed about an order of magntidue better than uranium-doped 76-68 glass. The release of Cs and Mo from Synroc-C, at least initially, may be primarily from intergranular regions of the material. The activation energy for the release of these elements from glass was about 9 kcal/mol but less than 3 kcal/mol for Synroc-C. In long-term tests, uranium dissolution may be controlled more by the formation of uranium alteration products than by release from the waste form

Volatility and entrainment of feed components and product glass characteristics during pilot-scale vitrification of simulated Hanford site low-level waste

Commercially available melter technologies were tested for application to vitrification of Hanford site low-level waste (LLW). Testing was conducted at vendor facilities using a non-radioactive LLW simulant. Technologies tested included four Joule-heated melter types, a carbon electrode melter, a cyclone combustion melter, and a plasma torch-fired melter. A variety of samples were collected during the vendor tests and analyzed to provide data to support evaluation of the technologies. This paper describes the evaluation of melter feed component volatility and entrainment losses and product glass samples produced during the vendor tests. All vendors produced glasses that met minimum leach criteria established for the test glass formulations, although in many cases the waste oxide loading was less than intended. Entrainment was much lower in Joule-heated systems than in the combustion or plasma torch-fired systems. Volatility of alkali metals, halogens, B, Mo, and P were severe for non-Joule-heated systems. While losses of sulfur were significant for all systems, the volatility of other components was greatly reduced for some configurations of Joule-heated melters. Data on approaches to reduce NO{sub x} generation, resulting from high nitrate and nitrite content in the double-shell slurry feed, are also presented

Durability of double-shell tank waste grouts

This report summarizes results of studies conducted in FY89 to assess the durability of grouted DST waste. This is in support of WHC`s grout disposal program to determine the physical/chemical properties of simulated DST grouts cured for extended time periods at elevated temperatures. This report presents results of tests on simulated DST grout samples cured up to 6 months at 75 to 95 C. All the testing and characterization were done on a single formulation of DS slurry feed grout. The simulated waste was the same as in the Nov. 1988 pilot- scale test of grout processing. The dry blend (47 wt% slag, 47 wt% class F fly ash, 6 wt% type I/II portland cement) was mixed with the simulated waste at a mix ratio of 9 lb/gal. Resultant grout slurry was cast into molds and cured at 100% RH at 75, 85, and 95 C. Leach resistance and compressive strength decreased with curing times and temperatures. The samples absorbed water during curing (up to 9 wt%) as a result of osmotic pressures caused by the high salt content within the grout, and this may have caused microcracking and reduced strength. Cracking due to increased internal pressures from salt crystallization also may have occurred as the samples cooled from curing

Characterization of double-shell slurry feed grout produced in a pilot-scale test

Current plans for disposal of the low-level fraction of selected double-shell tank (DST) wastes at Hanford, Washington include grouting. Grout disposal in this context is the process of mixing low-level liquid waste with cementitious powders. and pumping the resultant slurry to near-surface, underground concrete vaults. Once the slurry is in the vaults. the hydration reactions that occur result in the formation of a highly impermeable solid product that binds and encapsulates the radioactive and hazardous constituents. Westinghouse Hanford Company (WHC) operates the Grout Treatment Facility (GTF) for the US Department of Energy (DOE). Pacific Northwest Laboratory(a) (PNL) provides support to the Grout Disposal Program through laboratory support activities, radioactive grout leach testing. performance assessments, and pilot-scale tests. A pilot-scale test was conducted in November 1988 using a simulated Double-Shell Slurry Feed (DSSF) waste. The main objective of the pilot-scale test was to demonstrate the processability of a DSSF grout formulation that was developed using laboratory equipment and to provide information on scale-up. The dry blend used in this test included 47 wt% class F fly ash, 47 wt% blast furnace slag, and 6 wt% type I/II portland cement. The dry blend was mixed with the simulated waste at a ratio of 9 lb/gal and pumped to a 2800-gal, insulated tank at about 10.4 gpm. Samples of simulated DSSF waste. dry blend, grout slurry, and cured grout were obtained during and after the pilot-scale test for testing and product characterization. Major conclusions of these activities are included

Assessment of dome-fill technology and potential fill materials for the Hanford single-shell tanks

This study is part of a task that will identify dome-fill materials to stabilize and prevent the collapse of the structures of 149 single- shell tanks (SSTs). The SSTs were built at the Hanford Site in Washington State and used between 1944 and 1980 to store radioactive and other hazardous wastes. In addition to identifying suitable fill materials, this task will develop the technology and methods required to fill the tanks with the selected material. To date, basalt is the only candidate fill material with any testing conducted for its suitability as a dome-fill material. Sufficient data do not exist to select or eliminate basalt as a candidate material. This report documents a review of past dome-fill work at the Hanford Site and of other pertinent literature to establish a baseline for the dome-fill technology. In addition, the report identifies existing dome-fill technology, preliminary performance criteria for dome-fill technology development, potential testing strategies, and potential fill materials. As a part of this study, potential fill materials are qualitatively evaluated and a list of preliminary candidate fill materials is identified. Future work will further screen these materials. The dome-fill task work will ultimately contribute to the development of a final waste form package and the safe isolation of wastes from the Hanford Site SSTs

Interactive leach tests of UO/sub 2/ and spent fuel with waste package components in salt brine

Spent fuel is being considered as a waste form for disposal in a repository located in salt. To adequately model spent fuel performance as a waste form that may be contacted by brine in a repository, it is necessary to describe the leach (dissolution) behavior of spent fuel and the chemical interactions of the released radionuclides with their environment. To this end, leach tests were conducted on: UO/sub 2/ in Permian Basin salt brine or deionized water at test temperatures of 25, 75, and 150/sup 0/C. Some tests were done in the presence of ductile cast iron, which is a representative overpack material, and/or oxidized Zircaloy, which is the usual fuel cladding material. Spent fuel (H.B. Robinson) in Permian Basin salt brine at 25 and 75/sup 0/C. Some of the tests were conducted in the presence of ductile cast iron. The release values for leach periods up to 60 days were determined for systems utilizing both UO/sub 2/ and spent fuel. This report is based upon data obtained during 1982 and 1983. The larger temperature dependence of the leach behavior that was observed for deionized water than was observed for brine is difficult to interpret on the basis of our knowledge. Differences in UO/sub 2/ alteration products may be involved. For example, the existence of sodium uranates is likely in the brines but not possible with deionized water. Differences in ionic strength may also play a role. Observations derived from the leach tests performed in brine include: (1) the presence of iron coupons had no effect on total release of uranium from either spent fuel or UO/sub 2/ but did reduce solution concentrations, and (2) 100 to 200 times more uranium was released from spent fuel than from UO/sub 2/ per unit of geometric surface area

The nitrogen footprint of organic food in the United States

We estimated the reactive nitrogen (Nr) lost per unit food Nr consumed for organic food production in the United States and compared it to conventional production. We used a nitrogen footprint model approach, which accounts for both differences in Nr losses as well as differences in productivity of the two systems. Additionally, we quantified the types of Nr inputs (new versus recycled) that are used in both production systems. We estimated Nr losses from organic crop and animal production to be of comparable magnitude to conventional production losses, with the exception of beef. While Nr losses from organic vegetables are possibly higher (+37%), Nr losses from organic grains, starchy roots, legumes are likely of similar magnitude to conventional production (+7%, +6%, -12%, respectively). Nr losses from organic poultry, pigmeat, and dairy production are also likely comparable to conventional production (+9%, +10%, +12%, respectively), while Nr losses from organic beef production were estimated to be higher (+124%). Due to the high variability and high uncertainty in Nr efficiency in both systems we cannot make conclusions yet on the statistical significance of these potential differences. Conventional production relies heavily on the creation of new Nr (70%-90% of inputs are from new Nr sources like synthetic fertilizer), whereas organic production primarily utilizes already existing Nr (0%-50% of organic inputs are from new Nr sources like leguminous N fixation). Consuming organically produced foods has little impact on an individual's food N footprint but changes the percentage of new versus recycled Nr in the footprint. With the exception of beef, Nr losses from organic production per unit N in product are comparable to conventional production. However, organic production requires the creation of less new Nr, which could reduce global Nr pollution.FWN – Publicaties zonder aanstelling Universiteit Leide