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Hunter, Timothy

Publications and source records attributed to Hunter, Timothy.

9 records
All sourcesNASA NTRSDOE OSTI
DOE OSTI2020

Drying Spent Magnox Fuel for Interim Dry Storage

Spent Magnox fuel is usually stored under water for shielding and cooling following use in-reactor, but the storage water can react with Magnox clad fuel and cause corrosion and forms a sludge which generates a secondary waste product. One option to prevent unwanted corrosion and avoid expensive waste management is to dry the wet fuel. This project aims to test a drying process which will convert wet and corroded Magnox fuel to a stable form to demonstrate viability for conversion from wet to dry storage. Samples of corroded Magnox supplied by National Nuclear Laboratory. Corrosion product retrieved by various methods including dry scraping, ultrasonic treatment to form sludge and sludge drying to isolate suspension. TGA undertaken on Sample 1 and Sample 2, with brucite and hydromagnesite for comparison. Both samples showed ∼10% mass loss up to 250 deg. C attributable to water held in sample. Mass loss from dehydroxylation which liberates further water in both samples. TGA data plotted alongside chemically pure brucite and hydromagnesite shows expected similarities/differences between Sample 1(mostly brucite) and Sample 2 (brucite/hydromagnesite mixture). Following treatment, dried samples observed to slowly gain mass in ambient conditions. Presumed to be hygroscopic absorption of air water vapour as effect is reversible, with similar effect observed for hydromagnesite and brucite. Etched Magnox vacuum dried for 3.5 h at 90 deg. C to test for reaction with residual water - some discoloration but no noticeable corrosion observed. Drying etched Magnox metal to observe surface effects/corrosion during drying process.

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DOE OSTI2020

Development of Acoustic Backscatter for In Situ Monitoring of Nuclear Sludge Wastes During Transfer - 20117

This paper presents an overview into the use of acoustic backscatter systems (ABS) for the in situ characterization of nuclear waste sludge concentration, size and aggregation, highlighting key achievements from the University of Leeds. Previous projects funded through the Engineering and Physical Sciences Research Council (EPSRC) UK and Innovate UK are firstly reviewed and linked to current research within the new TRANSCEND consortium. Detailed are a number of developments at various stages of technology readiness level, from the use of ABS to monitor small-scale sludge settling in columns, to large-scale jet-mixing and waste transfer operations. Current work with Sellafield Ltd will see new technology and world leading analysis methods deployed to measure the consolidation of complex wastes currently undergoing containment, the first time full industrial utilization of these systems has been achieved. (authors)

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DOE OSTI2020

Drying Wet Stored and Corroded Magnox Fuel for Interim Dry Storage - 20187

To investigate the feasibility of drying corroded Magnesium alloy clad nuclear fuel, the corrosion products of inactive and unirradiated Magnox simulant dry corrosion product and dried corroded Magnox sludge were characterised by X-ray diffraction and thermogravimetric analysis. XRD identified brucite in the dried corrosion product and both brucite and hydromagnesite in the sludge. TGA identified mass loss on dehydration of ∼9.1% up to 250 deg. C and 27.9% from dehydroxylation up to 440 deg. C, with total mass loss of 41.9% up to 800 deg. C for the dried corrosion product. The sludge TGA showed 8.3% mass loss up to 250 deg. C from dehydration, 7.5% up to 330 deg. C from dehydroxylation and 31.4% mass loss up to 47.2% for decarbonation, with total mass loss of 49.2% up to 800 deg. C. Water removal up to 1.8 g was performed by cold vacuum drying (40 deg. C-120 deg. C) on a ≅14.8 g (wet) corroded Magnox sample. The process was monitored by observing pressure, dew point, temperature and gas flow changes supported by measuring the sample mass loss as water is removed. From these tests, it was observed that the dried corroded Magnox displayed some hygroscopic capacity which has implications for water retention following vacuum drying and the length of exposure required to achieve the desired dryness. Whilst at higher temperatures the water was removed faster, the increased temperature also risks the fuel cladding undergoing unwanted chemical reactions with the residual water during the process. However, at lower temperatures the achievable levels of dryness were reduced. Therefore, from these observations this work has identified that there is a temperature balance that may be necessary to optimise the drying process with respect to allowing the greatest level of dryness whilst restricting unwanted chemical reactions. (authors)

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DOE OSTI2019

Use of In Situ Acoustic Backscatter Systems to Characterize Spent Nuclear Fuel and its Separation in a Thickener - 19288

To aid in the transportation, dewatering and storage of radioactive UK legacy waste sludges at Sellafield Ltd., the application of an Acoustic Backscatter System (ABS) was investigated in this study, as a method for monitoring suspended solids concentration and consolidation of cohesive and aggregated sludges (that form the basis of many wastes at Sellafield). An ABS represents a particularly promising technology, as they can be used with minimal intrusion, to measure both particle size and concentration depending on prior system knowledge, through inversion of the return echo voltage response of pulse-echo signals in the MHz range. To assess the application for continuous, high concentration (∼30 % v/v) thickened wastes, an ABS was utilised to characterise a pseudo-steady state laboratory thickener over hours, using flocculated calcite as a representative test material. Measurements were taken both horizontally through a consolidated bed using a 1 MHz transducer and vertically downwards with a 2 MHz transducer to measure sediment concentration above the settled bed and track bed height via the interface reflection. Characterisation of flocculated aggregate diameters was initially determined to be ∼510 μm, using an in-line Focussed Beam Reflectance Measurement (FBRM) device. The submerged 2 MHz probe indicated that there were only limited changes to the dispersion concentration or size over time. Changes in settled bed density, due to increasing bed height and changes in the underflow flow rate, were qualitatively measured via differences to the acoustic signal attenuation over time. An initial increase in attenuation with bed height was observed as the bed densified due to local compression. Once an equilibrium bed height was reached, the acoustic attenuation remained fairly constant with time, although the bulk underflow density was reduced with the increase in underflow rate. The solids residence time in the bed, determined from a transitive volume-balance model, was found to be ∼3200 s for pseudo-steady state operation at a maintained bed height of ∼0.175 m. Results of the study highlight the potential the ABS as a remote process monitoring tool for both relatively dilute suspensions and concentrated thickened mineral sludges, with potential applications across waste processing sites at Sellafield. (authors)

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DOE OSTI2019

Erosion and Mobilisation of Highly Active Simulant Suspensions using Impinging Vertical Jets - 19378

Based on the nuclear industry in the U.K., storage of nuclear waste poses a particularly complex challenge. Specifically, this research is concerned with post-PUREX (Plutonium Uranium Redox Extraction) high level waste, known as HAL (Highly Active Liquor), containing nitric acid and a host of fission products. HAL is concentrated, and stored in HASTs (Highly Active Storage Tanks) at the HALES (Highly Active Liquor Evaporation and Storage) facility at the Sellafield site, UK. HASTs are large concrete containers designed to keep the HAL cool and continually circulated prior to vitrification for permanent storage and disposal. Without comprehensive understanding of how this HAL is behaving within the HASTs, a multitude of issues could arise, and understanding such issues is the basis of this research. Components of the HAL begin to form solid particles in the HASTS, and impinging vertical liquid jets are used to mobilize the sedimented particle bed to reduce hot-spot formation. Experimental validation of the jets and associated modelling is required to assess the jets efficacy, and by considering the erosion based on dimensionless parameters, will allow the results to be scaled. This is of particular interest due to the wide reaching applications to all industries that require utilisation of impinging jets, for mass or heat transfer. An experimental rig of 0.5 m{sup 3} has been used to experimentally model the central jet of the HASTs. A spherical glass simulant (SiO{sub 2}, spherical) of various sizes has been used for the initial non-cohesive particle testing, and modelling. Each experiment used 8 different jet diameters. Dimensionless analysis takes the form of the erosion parameter, Ec, which allows comparison of systems of different scales and a means of correlating multiple simulants against one another, so patterns are easily identifiable. Part of the dimensionless analysis was also to deduce the modified Shields parameter from vane viscometry to allow for a comparison of erosion behaviour taking into account particle properties, flow properties and the overall influence these have on the erosion profile. Particle size distribution was found to have a direct effect on yield stress and modified Shields parameter, with larger particles being dominated by inertial forces and past a certain size threshold surface forces appear to dominate. Ec data found the larger glass simulants to behave as expected for a non-cohesive particles, however surface forces also appear to be present for the smaller size distributions. (authors)

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DOE OSTI2018

Cake Permeability of Waste Simulants found in the Highly Active Storage Tanks at Sellafield - 18676

Caesium Phosphomolybdate (CPM) and Zirconium Molybdate (ZM) are two compounds causing issues within the Highly Active Storage Tanks (HASTs) at Sellafield. CPM has the potential to cause 'hot spots' possibly affecting the integrity of the tanks due to its settling and radioactive properties. ZM is thought to cause mobility issues when it is re-suspended by the jet ballasts in the HASTs. CPM and ZM were synthesised following the method published by Paul. The permeability method followed was published by Loginov. Conclusions: CPM has a higher overall cake resistance; Suggests a more open network for the ZM bed than the CPM bed; Cubes would be expected to pack tighter than spheres, suggesting the orientation of the cubes has some effect on the packing; In future the use of 2 M nitric acid instead of water will be explored as this is the natural conditions found in the HASTs.

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DOE OSTI2016

Utilizing a Novel Acoustic Backscatter Array to Characterize Waste Consolidation and Settling in a Horizontal Flow Clarifier - 16051

As part of a collaboration between the University of Leeds, Sellafield Ltd and MMI Engineering Ltd, bespoke acoustic instrumentation and numerical simulation methods have been established to optimize nuclear legacy waste transfers. Specifically, a new ultrasonic measurement system has been developed, allowing suspended particle concentration and consolidation to be measured remotely. This technology has been combined with computational fluid dynamics (CFD) modelling of settling particulate systems, permitting full characterization, simulation and prediction of sludge separation processes. Presented here are experimental and numerical results on the transport and settling behavior of non-active nuclear-analogue suspensions in two flow geometries: gravitational settling of glass dispersions in a 250-liter column; and transport and sedimentation of flocculated calcite in a close-to-full-scale clarifier (9 m{sup 3} total volume and 4.8 m{sup 2} length). In addition, details of the design, construction and calibration of a custom-built Ultrasonic Array Research Platform (UARP) are described. Settling column results suggested that particle concentration changes could be simulated with good accuracy by a CFD model (developed using the open source OpenFOAM framework) when compared to measured samples. Large-scale clarifier trials were used to assess the effectiveness of the UARP controller with an attached in situ acoustic backscatter array (ABA). The ABA consisted of 8 transducers angled down at 20 deg. to the vertical, pulsing at 2-2.5 MHz in cycles (covering 1.8 m total depth). In comparison to a range of sampled concentrations across the length of the clarifier, results confirmed that the UARP-ABA system was highly successful at characterizing these complex flows over several hours of operation, allowing visualization of depth-wise bulk density changes and bed build-up over time. Collectively, this work highlights the capability of these tools to monitor and optimize a number of current waste transfer operations at Sellafield, with further potential applications for solid-liquid separations across waste, water treatment and minerals engineering industries. (authors)

12 MANAGEMENT OF RADIOACTIVE AND NON-RADIOACTIVE W↗
DOE OSTI2016

Gas Retention and Release from Nuclear Legacy Waste - 16449

The retention of gas within corroded magnox sludge waste at Sellafield, UK and secondary reprocessing waste at Hanford, USA has significant economic and safety implications for decommissioning various nuclear legacy buildings, including the magnox swarf storage silos and first generation magnox storage pond. A series of laboratory scale gas retention tests within magnesium hydroxide soft sediments have revealed a 4-51 Pa yield stress range where consolidated beds could retain sufficient gas to become buoyant with respect to a water supernatant. Density inversion could lead to a Rayleigh-Taylor style instability which could result in an upward transfer of radioactive material from the consolidated bed. The applicable yield stress range suggests that such rollover events may occur in weaker sediment than previously hypothesized, based on current understanding of the fluidization and stable channel mechanisms for gas release from weak and very strong sediments respectively. X-ray computed tomography images of gas retained by 7 Pa yield stress soft sediment reveal both a stable foam layer at the top of the bed and regions dense with micro-bubbles which could provide pathways for gas transport through the bed. Extension of these pathways, hidden below the surface of the sediment, to the container walls and the foam layer could represent a novel mechanism for gas release from intermediate strength sediments of <100 Pa yield stress. (authors)

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