Thorium dioxide:  properties and nuclear applications

Belle, J.

doi:10.2172/5986642

Cited by 99 publications

(55 citation statements)

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“…Density data for the other uranium phases described in the technical literature were obtained from Roberts et al (1990) by calculation from XRD spacings. (b) Hardness data were obtained from Roberts et al (1990) except for irradiated uranium metal fuel ) and UO 2 (Belle 1961). (c) These formulas are based on more recent structure assessments and differ slightly from the formulas provided in the original reference (Wang and Xu 2000).…”

Section: Uranium Phase Observations In the Present Testingmentioning

confidence: 99%

Hydrothermal Testing of K Basin Sludge and N Reactor Fuel at Sludge Treatment Project Operating Conditions

Delegard¹,

Schmidt²,

Thornton³

2007

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Executive SummaryFive bench-scale tests (~50 ml each) were conducted in sealed, un-agitated reaction vessels using sludge samples collected from the K East Basin and particles/coupons of irradiated N Reactor fuel (also from the K Basins). These tests were designed to evaluate and understand the chemical changes that may be occurring under the hydrothermal conditions (e.g., 7 to 72 h at 185°C) of the Sludge Treatment Project (STP) corrosion process and the effects that any changes would have on sludge rheological properties. The two sludge formulations used in these tests were selected to represent nominal (vs. bounding) compositions of the two major sludge feed streams to the STP process. The scoping tests were not designed to evaluate engineering aspects of the process.The hydrothermal treatment affected the chemical and physical properties of the sludge. In each test, significant uranium compound phase changes were identified, resulting from dehydration and chemical oxidation and reduction reactions. Physical properties of the sludge were significantly altered from their initial, as-settled, sludge values including, shear strength, settled density, weight percent water, and gas retention.The high uranium content sludge (~70 wt% uranium) set up to form a very stiff solid that exhibited very high shear strength (120,000 to 170,000 Pa) after hydrothermal treatment at 185°C for 7 to 10 hours under static (unstirred) conditions. Shear strengths of untreated sludge range from about 270 to 8100 Pa. Also, the hydrothermal treatment reduced the water content in the settled sludge by about 20 wt%. The treated sludge was difficult to remove from the Teflon test vessels, with sludge firmly adhering to the Teflon vessel surfaces. The strength of the treated sludge was further evaluated by agitation in water. In a 600-ml beaker, with 400 ml water at ~30°C, the diameters of agglomerates were reduced by about 40 to 50% after 1 hour of agitation with a 5.08-cm (2-in.) diameter impeller rotated at a tip speed of 80 cm/s.Further static tests with lower uranium-content sludges (~16 wt% uranium) run 72 h at 185°C produced softer solids with 9,000 to 16,000 Pa shear strengths. While some sludge adhered to the Teflon liner, it was not tenaciously bound. The agglomerates from these tests were relatively weak and, in some cases, were disintegrated with a gentle stream of water. The water content in the settled sludge was not significantly affected by the hydrothermal treatment.Chemical phase alteration, observed by X-ray diffraction, scanning electron microscopy, and energy dispersive spectrometry, gave evidence that solids dissolution followed by precipitation was responsible for the increased strengths of the sludge products. The presence of organic ion exchange resin (OIER) and polymer flocculent (constituents known to be in K Basin sludge) in the lower uranium-content sludge did not appear to have a significant impact on the physical behavior of the post-treated sludge.Four irradiated uranium metal fuel coupons were included in on...

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Section: Uranium Phase Observations In the Present Testingmentioning

confidence: 99%

Hydrothermal Testing of K Basin Sludge and N Reactor Fuel at Sludge Treatment Project Operating Conditions

Delegard¹,

Schmidt²,

Thornton³

2007

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“…Changes to the crystal structure have been reported under nuclear reactor irradiation conditions for some uranium oxides (Belle 1961). Additionally, @.mage to the lattices of minerals found in nature because of either self-irradiation or external radiation has been reported (Lustman 1961).…”

Section: Uranium Oxidesmentioning

confidence: 99%

“…Materials with the fluoriterelated structure (e.g., U02 and PuOZ)are not susceptible to radiation-induced amorphization (Weber et al 1998, Belle 1961 Irradiation of crystals can result in increased ionic diffision. Examples include cation diffusion, which is enhanced in UOZand mixed oxide fkels by reactor irradiation.…”

Section: Amorphizationmentioning

confidence: 99%

Radiolytic Effects on Fluoride Impurities in a U{sub 3}O{sub 8} Matrix

Icenhour¹

2000

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The safe handling and storage of radioactive materials require an understanding of the effects of radiolysis on those materials. Radiolysis may result in the production of gases (e.g., corrosives) or pressures that are deleterious to storage containers. A study has been performed to address these concerns as they relate to the radiolysis of residual fluoride compounds in uranium oxides. The interactions of radiation with crystalline solids, based on the bonding characteristics of the crystal, are described to enhance the understanding of radiolytic effects in uranium oxides. Samples of U02F2wH20 and U~08 (with -1.4 wt YO fluorine content) were irradiated in a 'Co source and in spent nuclear fiel (SNF) elements from the High Flux Isotope Reactor (HFIR) at Oak Ridge National Laboratory. Container pressures were monitored &roughout the irradiations, and gas and solid samples were analyzed after the irradiations. The irradiation of U02F2~xH20 produced 02-with G(02)-values ranging from 0.007 to 0.03 molecules 02 produced per 100 eV. Neither F2 nor HF was produced by the irradiations. Chemical analysis of solid samples showed that some of the uranium was reduced from U(W) to U(IV). A saturation damage limit for the U02F2SXH20was demonstrated by using the HFIR SNF elements, and the limit was found to be 7-9°/0(at -108 radlh). It is shown that the covalently bonded oxygen is more susceptible to radiation darnage than is the ionically bonded fluorine. Irradiation of U@8 (with -1.4 wt 'XO fluorine content) resulted in neither gas production nor a pressure increase. These experiments led to the conclusion that U@8 is safe during 10ng-tem'Istorage fiOm overpressurization and the production of corrosives caused by gamma radiolysis of residual fluorides.

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“…Mishra et al [44] reports the addition of maximum 15 wt% of the (Th, 30%U)O 2 MOX sintered rejects recycled via mechanical micronisation process (crushed and attritor milled) for fabrication of fuel. [29]. However, presence of UO 2 in the ThO 2 matrix has caused its oxidation thus giving (Th, U)O 2+x .…”

Section: Mechanical Micronisationmentioning

confidence: 99%

An Integrated Process for Recycling of ThO<sub>2</sub> Based Mixed Oxide Rejected Nuclear Fuel Pellets

Singh¹,

Khot²,

Kumar³

et al. 2017

WJNST

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This paper presents a study on the process engineering aspects of relevance to the industrial implementation of ThO 2 and (Th, U)O 2 mixed oxide (MOX) pellet type fuel manufacturing. The paper in particular focuses on the recycling of thoria based fuel production scrap which is an economically important component in the fuel manufacturing process. The thoria based fuels are envisaged for Advanced Heavy Water Reactor (AHWR) and other reactors important to the Indian Nuclear Power Programme. A process was developed for recycling the chemically clean, off-specification and defective sintered ThO 2 and (Th, U)O 2 MOX nuclear fuel pellets. ThO 2 doesn't undergo oxidation or reduction and thus, more traditional methods of recycling are impractical. The integrated process was developed by combining three basic approaches of recycling namely mechanical micronisation, air oxidation (for MOX) and microwave dissolution-denitration. A thorough investigation of the influence of several variables as heating method, UO 2 content, fluoride and polyvinyl alcohol (PVA) addition during microwave dissolution-denitration was recorded on the product characteristics. The suitability evaluation of the recycled powder for re-fabrication of the fuel was carried out by analyzing the particle size, BET specific surface area, phase using XRD, bulk density and impurities. The physical and chemical properties of recycled powder obtained from the sintered (Th 1-y , U y )O 2 (y; 0 -30 wt%) pellets advocate 100% utilisation for fuel re-fabrication. Recycled ThO 2 by integrated process showed distinctly high sinterability compared to standard powder evaluated in terms of surface area and particle size.

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Thorium dioxide: properties and nuclear applications

Cited by 99 publications

References 0 publications

Hydrothermal Testing of K Basin Sludge and N Reactor Fuel at Sludge Treatment Project Operating Conditions

Hydrothermal Testing of K Basin Sludge and N Reactor Fuel at Sludge Treatment Project Operating Conditions

Radiolytic Effects on Fluoride Impurities in a U{sub 3}O{sub 8} Matrix

An Integrated Process for Recycling of ThO<sub>2</sub> Based Mixed Oxide Rejected Nuclear Fuel Pellets

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Thorium dioxide: properties and nuclear applications

Cited by 99 publications

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Hydrothermal Testing of K Basin Sludge and N Reactor Fuel at Sludge Treatment Project Operating Conditions

Hydrothermal Testing of K Basin Sludge and N Reactor Fuel at Sludge Treatment Project Operating Conditions

Radiolytic Effects on Fluoride Impurities in a U{sub 3}O{sub 8} Matrix

An Integrated Process for Recycling of ThO&lt;sub&gt;2&lt;/sub&gt; Based Mixed Oxide Rejected Nuclear Fuel Pellets

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An Integrated Process for Recycling of ThO<sub>2</sub> Based Mixed Oxide Rejected Nuclear Fuel Pellets