The Environmental Protection Agency (EPA) provides access to information on a variety of topics related to the environment and strives to inform citizens of health risks. The EPA also has an extensive library network that consists of 26 libraries throughout the United States, which provide access to a plethora of information to EPA employees, scientists, and researchers. The EPA implemented a reorganization project to digitize their materials so they would be more accessible to a wider range of users, but this plan was drastically accelerated when the EPA was threatened with a budget cut. It chose to close and reduce the hours and services of some of their libraries. As a result, the agency was accused of denying users the “right to know” by making information unavailable, not providing an adequate strategic plan, and discarding vital materials. This case study explores the background of the digitization project, the practices implemented, and the critiques of the project.

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The Environmental Protection Agency

Mobile colloids—suspended particles in the submicrometre size range—are known to occur naturally in ground water1, 2 and have the potential to enhance transport of non-soluble contaminants through sorption3. The possible implications of this transport mechanism are of particular concern in the context of radionuclide transport. Significant quantities of the element plutonium have been introduced into the environment as a result of nuclear weapons testing and production, and nuclear power-plant accidents. Moreover, many countries anticipate storing nuclear waste underground. It has been argued that plutonium introduced into the subsurface environment is relatively immobile owing to its low solubility in ground water4 and strong sorption onto rocks5. Nonetheless, colloid-facilitated transport of radionuclides has been implicated in field observations6, 7, but unequivocal evidence of subsurface transport is lacking3, 8, 9. Moreover, colloid filtration models predict transport over a limited distance resulting in a discrepancy between observed and modelled behaviour3. Here we report that the radionuclides observed in groundwater samples from aquifers at the Nevada Test Site, where hundreds of underground nuclear tests were conducted, are associated with the colloidal fraction of the ground water. The 240 Pu/239 Pu isotope ratio of the samples establishes that an underground nuclear test 1.3 km north of the sample site is the origin of the plutonium. We argue that colloidal groundwater migration must have played an important role in transporting the plutonium. Models that either predict limited transport or do not allow for colloid-facilitated transport may thus significantly underestimate the extent of radionuclide migration.

Migration of plutonium in ground water at the Nevada Test Site

This review provides a comprehensive evaluation of the state-of-knowledge of radiation effects in crystalline ceramics that may be used for the immobilization of high-level nuclear waste and plutonium. The current understanding of radiation damage processes, defect generation, microstructure development, theoretical methods, and experimental methods are reviewed. Fundamental scientific and technological issues that offer opportunities for research are identified. The most important issue is the need for an understanding of the radiation-induced structural changes at the atomic, microscopic, and macroscopic levels, and the effect of these changes on the release rates of radionuclides during corrosion.

https://www.cambridge.org/core/services/aop-cambridge-core/content/view/09D70E1FB1A625EC09BB98883C3A5ED3/S0884291400044411a.pdf/div-class-title-radiation-effects-in-crystalline-ceramics-for-the-immobilization-of-high-level-nuclear-waste-and-plutonium-div.pdf

Radiation effects in crystalline ceramics for the immobilization of high-level nuclear waste and plutonium

The geomeffy, bond valences, and polymerization ofhexavalent uranium polyhedra from 105 well-refined structures are analyzed. The Utu cation is almost always present in crystal stnrctures as part of a nearly linear (UOr)z* uranyl ion that is coordinated by four, five or six equatorial anions in an approximately planar arangement perpendicular to the uranyl ion, giving square, pentagonal and hexagonal bipyramids, respectively. The Utu-O7\" bond length (Oy,: uranyl-ion O atom) is independent of the equatorial anions of the polyhedra;-averages of all polyhedra tlat contain uranyl ions ffs; I6lIJ6f-Or. = 1.79(3), mg0.-.9 a,= 1.79(4), and t8lu6+-Our = 1.78(3) A. Not a[ r6lu6+ polyhedra contain uranyl ions; there is a continuous series of coordiaation polyhedr4 from square bipyramidal polyhedra with uranyl ions to holosymmehic octahedral geometry. The mUo* and t8lu6+ polyhedra invariably contaitl a uranyl ion. The equatorial U6.-0 (0: O,-, OH-) bond-lengths of uranyl polyhedra depend upon coordhation number; averages for all polyhedra are t6lu6+-dq = 2,28(5), rlUot-$* = 2.37(9), afi t8tlJ6+-$q2.47 (12) A. Cunently available bond-valence parameters for U& are unsatisfactory for determining bond-valence sums. Coordination-specific bond-valence paxameters have been derived for U6|, together with parameters applicable to all coordination geometries. The parameters give bond-valence sums for Ue of -6 vlr and reasonable bond-valences for Uc,-Ou, bonds. The bond-valence paraneters facilitate the recognition of Ua, U5+ and U6| catiotrs in refined crystal structures. The crystal-chemical consfraints ofpolyhedral polymerization in uranyl phases are discussed.

The crystal chemistry of hexavalent uranium; polyhedron geometries, bond-valence parameters, and polymerization of polyhedra

Publisher Summary It is noted that colloidal particles can be effectively transported through subsurface porous media under certain hydrogeochemical conditions. If present in large concentrations, mobile colloids can act as carriers for strongly sorbing contaminants and thereby provide an unretarded transport pathway for contaminants that are otherwise strongly retarded. This potential transport pathway can be considered in risk assessments of sites heavily contaminated with toxic chemicals, such as certain radionuclides, heavy metals, and hydrophobic organic compounds. The chapter reviews the current state of knowledge about the behavior of colloids in porous media and their role in contaminant transport. The chapter also identifies some important future research needs. Colloids are commonly defined as small particles or other entities with dimensions roughly between 1 nm and 1 μm. These size limits to dissolved molecules on one side and to larger suspended particles on the other side. Colloidal particles remain stable in suspension over long time periods, unless they coagulate to form larger aggregates or deposit onto surfaces of larger grains.

Mobile Subsurface Colloids and Their Role in Contaminant Transport

Ten-year results from unsaturated drip tests with UO2 at 90°C: implications for the corrosion of spent nuclear fuel

Uranium release and secondary phase formation during unsaturated testing of UO2 at 90°C

Insoluble plutonium- and americium-bearing colloidal particles formed during simulated weathering of a high-level nuclear waste glass. Nearly 100 percent of the total plutonium and americium in test ground water was concentrated in these submicrometer particles. These results indicate that models of actinide mobility and repository integrity, which assume complete solubility of actinides in ground water, underestimate the potential for radionuclide release into the environment. A colloid-trapping mechanism may be necessary for a waste repository to meet long-term performance specifications.

http://science.sciencemag.org/content/sci/256/5057/649.full.pdf

Colloid Formation During Waste Form Reaction: Implications for Nuclear Waste Disposal

Drip tests to measure radionuclide release from spent nuclear fuel are being performed at 90 °C at a drip rate of 0.75 ml every 3.5 days. The test conditions are designed to simulate the behavior of spent fuel under the unsaturated and oxidizing conditions expected in a potential repository at Yucca Mountain. The U, Pu, Cs, Sr, \"Tc, and I content in the leachate after 581 days of testing is reported. These data provide valuable information for estimating the release of long-lived radionuclides. A comparison is made between our results and those of other researchers. The \"Te release fractions are suggested to be representative of matrix dissolution.

The release of uranium, plutonium, cesium, strontium, technetium and iodine from spent fuel under unsaturated conditions

Corrosion of spent UO{sub 2} fuel has been studied in experiments conducted for nearly six years. Oxidative dissolution in vapor and dripping groundwater at 90 C occurs via general corrosion at fuel-fragment surfaces. Dissolution along fuel-grain boundaries is also evident in samples contacted by the largest volumes of groundwater, and corroded grain boundaries extend at least 20 or 30 grains deep (> 200 {micro}m), possibly throughout millimeter-sized fragments. Apparent dissolution of fuel along defects that intersect grain boundaries has created dissolution pits that are 50 to 200 nm in diameter. Dissolution pits penetrate 1-2 {micro}m into each grain, producing a ''worm-like'' texture along fuel-grain-boundaries. Sub-micrometer-sized fuel shards are common between fuel grains and may contribute to the reactive surface area of fuel exposed to groundwater. Outer surfaces of reacted fuel fragments develop a fine-grained layer of corrosion products adjacent to the fuel (5-15 {micro}m thick). A more coarsely crystalline layer of corrosion products commonly covers the fine-grained layer, the thickness of which varies considerably among samples (from less than 5 {micro}m to greater than 40 {micro}m). The thickest and most porous corrosion layers develop on fuel fragments exposed to the largest volumes of groundwater. Corrosion-layer compositions depend strongly on water flux, with uranyl oxy-hydroxides predominating in vapor experiments, and alkali and alkaline earth uranyl silicates predominating in high drip-rate experiments. Low drip-rate experiments exhibit a complex assemblage of corrosion products, including phases identified in vapor and high drip-rate experiments.

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John K. Bates

Papers

Ten-year results from unsaturated drip tests with UO2 at 90°C: implications for the corrosion of spent nuclear fuel

Uranium release and secondary phase formation during unsaturated testing of UO2 at 90°C

Colloid Formation During Waste Form Reaction: Implications for Nuclear Waste Disposal

The release of uranium, plutonium, cesium, strontium, technetium and iodine from spent fuel under unsaturated conditions

Oxidative Corrosion of Spent uo2 Fuel in Vapor and Dripping Groundwater at 90°C