Spent nuclear fuel as a waste form for geologic disposal: Assessment and recommendations on data and modeling needs

This study assesses the status of knowledge pertinent to evaluating the behavior of spent nuclear fuel as a waste form in geologic disposal systems and provides background information that can be used by the DOE to address the information needs that pertain to compliance with applicable standards and regulations. To achieve this objective, applicable federal regulations were reviewed, expected disposal environments were described, the status of spent-fuel modeling was summarized, and information regarding the characteristics and behavior of spent fuel was compiled. This compiled information was then evaluated from a performance modeling perspective to identify further information needs. A number of recommendations were made concerning information still needed to enhance understanding of spent-fuel behavior as a waste form in geologic repositories. 335 refs., 22 figs., 44 tabs

Engineering-scale test 4: In situ vitrification of toxic metals and volatile organics buried in INEL soils

An engineering-scale in situ vitrification (ISV) test was conducted on soils containing a mixture of buried waste materials expected to be present at the Idaho National Engineering Laboratory (INEL) subsurface disposal area (SDA). The test was part of a Pacific Northwest Laboratory (PNL) program to assist INEL in treatability studies of the potential application of ISV to mixed transuranic wastes at the INEL SDA. The purpose of this test was to determine the feasibility of using ISV to vitrify soils containing a mixture of buried hazardous heavy metals (Ag, As, Ba, Cd, Cr, Hg, Pb, Se), with stainless and carbon steels, nonhazardous combustibles, and organics in the form of cemented sludge/grease mixtures. Specific objectives included determining the destruction and removal efficiency of hazardous volatile organics, determining the distribution of hazardous heavy metals between vitrified components, soils, and the ISV off-gas system, determining the leachability of the vitrified product, and evaluating electrode coatings. Actual site soil from INEL was used in the test and a basalt block was placed at a depth of 66 cm (26 in.) below the soil surface. The basalt was included to simulate basalt layers below the SDA and to evaluate bonding of the glass to basalt and possible contaminant transport into the basalt. 5 refs., 11 figs., 13 tabs

Bacterial community structure and variation in a full-scale seawater desalination plant for drinking water production

Microbial processes inevitably play a role in membrane-based desalination plants, mainly recognized as membrane biofouling. We assessed the bacterial community structure and diversity during different treatment steps in a full-scale seawater desalination plant producing 40,000 m3/d of drinking water. Water samples were taken over the full treatment train consisting of chlorination, spruce media and cartridge filters, de-chlorination, first and second pass reverse osmosis (RO) membranes and final chlorine dosage for drinking water distribution. The water samples were analyzed for water quality parameters (total bacterial cell number, total organic carbon, conductivity, pH, etc.) and microbial community composition by 16S rRNA gene pyrosequencing. The planktonic microbial community was dominated by Proteobacteria (48.6%) followed by Bacteroidetes (15%), Firmicutes (9.3%) and Cyanobacteria (4.9%). During the pretreatment step, the spruce media filter did not impact the bacterial community composition dominated by Proteobacteria. In contrast, the RO and final chlorination treatment steps reduced the Proteobacterial relative abundance in the produced water where Firmicutes constituted the most dominant bacterial group. Shannon and Chao1 diversity indices showed that bacterial species richness and diversity decreased during the seawater desalination process. The two-stage RO filtration strongly reduced the water conductivity (>99%), TOC concentration (98.5%) and total bacterial cell number (>99%), albeit some bacterial DNA was found in the water after RO filtration. About 0.25% of the total bacterial operational taxonomic units (OTUs) were present in all stages of the desalination plant: the seawater, the RO permeates and the chlorinated drinking water, suggesting that these bacterial strains can survive in different environments such as high/low salt concentration and with/without residual disinfectant. These bacterial strains were not caused by contamination during water sample filtration or from DNA extraction protocols. Control measurements for sample contamination are important for clean water studies