New approaches for sludge management in the nuclear industry

Hastings, Jeremy J.; Rhodes, D.W.; Fellerman, Andy S.; McKendrick, D.; Dixon, Chris

doi:10.1016/j.powtec.2006.10.015

Cited by 21 publications

(23 citation statements)

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“…Cavity expansion theory states that the greater the mechanical strength of the soft sediment, characterized according to its shear yield stress, τ , and shear modulus, G , the greater the resistance to expansion of the host pore Many natural marine sediments and waste in longstanding nuclear legacy facilities are characterized by fine grain sizes and many have consolidated to high yield stresses (

τ < 1

kPa) over several decades and thus present considerable resistance to the above two mechanisms. Under these conditions the excess bubble pressure may rise until it exceeds the combined compressive and tensile strengths of the sediment, forming cracks along the direction of minimum compressive stress by a process of tensile fracture .…”

Section: Introductionmentioning

confidence: 99%

Yield stress dependency on the evolution of bubble populations generated in consolidated soft sediments

et al. 2017

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Retention of hydrogen bubbles within consolidated soft sediments represents an important safety consideration for the management of legacy nuclear wastes due to the potential for acute gas release. Gas retention sufficiently reduced the bulk density of intermediate yield stress (<800 Pa) sediments for the bed to become buoyant with respect to an aqueous supernatant, potentially inducing Rayleigh-Taylor instabilities. X-ray computed tomography revealed that beds of 7-234 Pa yield stress retained very similar, steady state size distributions of mature bubbles, limited to 9 mm equivalent spherical diameter, for long residence times. This implied a dominant gas release mechanism dictated by the pore to millimeter scale bubble population, not previously identified in such weak sediments and unrelated to the bubbles' buoyant force. At 1112 Pa yield stress, large bubbles of up to 20 mm diameter were observed to grow through induction of lateral cracks, facilitating gas transport to the bed periphery, thereby limiting the maximum void fraction, while nonhomogeneous gas generation promoted the formation of low density regions rich with microbubbles which similarly provide pathways for gas release.

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τ < 1

Section: Introductionmentioning

confidence: 99%

Yield stress dependency on the evolution of bubble populations generated in consolidated soft sediments

et al. 2017

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“…Colloidal materials such as gels and pastes can exhibit both elastic ͑solidlike͒ and viscous ͑liquidlike͒ behaviors and these are frequently further complicated by a nonlinear dependence on the flow rate. 3 Blockages of radioactive material in engineering equipment are particularly undesirable and plant must be designed to run for its lifetime with little or no intervention. The rheology of concentrated liquid-solid suspensions is therefore central to the optimal design of pumps and pipelines involved in their transport.…”

Section: Introductionmentioning

confidence: 99%

“…Furthermore, since the suspension fluid is composed of particles that are of a significant size compared to the nominal colloidal particles the latter are subject to a depletion interaction, not present for real colloids whose size is normally many times that of the suspension fluid molecular size. 3 Furthermore, the colloidal particles become ordinary DPD particles in the limit of zero core size and there is therefore a link with a recently developed parametrization for the conservative part of the interaction. To some extent both drawbacks may be partially compensated by the DPD particles that reside on the colloid surface, but this has never been directly studied.…”

Section: Introductionmentioning

confidence: 99%

Dynamic simulations of colloids by core-modified dissipative particle dynamics

Whittle

Travis

2010

The Journal of Chemical Physics

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We develop a core-modified dissipative particle dynamics model of colloidal systems which includes an extra term to counteract depletion forces. Results are presented covering the full range of volume fractions. Radial distribution functions for the suspending fluid are shown to change significantly as the volume fraction of colloid increases. Equilibrium results for the long-time diffusion coefficient behave as expected, but the short-time coefficient is anomalous. The form of the equilibrium stress correlation functions is discussed and the derived Green-Kubo viscosities are compared with expected semiempirical forms. For nonequilibrium shear-field simulations we find that the system temperature is not adequately controlled by the dissipative particle dynamics (DPD) thermostat alone. Results using three alternative auxiliary thermostats are compared; a naive choice leading to a string phase at high shear rate. Using a thermostat based on relative particle velocities, the model reproduced the four classical regions of colloid rheology: a first Newtonian plateau, a shear-thinning region, a second Newtonian plateau, and finally a shear-thickening region at high strain rate. The most unexpected result of this exercise is that the core-modified DPD model without auxiliary thermostat almost exactly follows the same curve despite recording a temperature increase of a factor approximately 2.5 over the range.

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“…Sand was chosen as a model particulate material for comparison with existing studies (e.g. Aderibigbe and Rajaratnam, 1996;Ansari et al, 2003;Kobus et al, 1979;Rajaratnam, 1982;Sequeiros et al, 2007;Yeh et al, 2009); while magnesium hydroxide was chosen as a general relevant simulant for the grain fractions of 'legacy' sludge wastes present in various U.K. nuclear waste stores (Hastings et al, 2007). Although the highly active fission particulates within the HASTs themselves may be generally finer (McArthur et 4` al., 2005), larger cohesionless materials were chosen to better allow the assessment of system scale and the performance of the ultrasonic velocity profiler.…”

Section: Methodsmentioning

confidence: 99%

The influence of system scale on impinging jet sediment erosion: Observed using novel and standard measurement techniques

Hunter¹,

Peakall

Unsworth³

et al. 2013

Chemical Engineering Research and Design

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Jet impingement as a method for eroding particulate beds and maintaining sediment in suspension is an important process for a host of industries, particularly in nuclear waste processing, where such systems to disperse and mix particulate beds have a number of advantages over other approaches.Existing work has utilised fairly rudimentary techniques for the measurement of erosion depths and here we demonstrate a new technique for measuring both static and dynamic erosion of cohesionless particulates under an impinging jet, using ultrasonic Doppler velocimetry. This approach is tested on both quartz sands and on a range of Mg(OH) 2 particulates that are key simulants for nuclear waste facilities, such as the Highly Active Storage Tanks at Sellafield, U.K. A critical jet height was found to exist that balanced the impingement velocities and total entrained jet volume to maximise erosion. The effect of system scale was also considered by normalising steady-state crater depths and sizes, with erosion being enhanced in the small scale, possibly due to increased turbulent recirculation. Additionally, velocity profiles and acoustic backscatter were used to determine both steady-state crater profiles and kinetic changes in bed-depths with time, and highlighted important differences between static and dynamic measurements of erosion depth.

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New approaches for sludge management in the nuclear industry

Cited by 21 publications

References 0 publications

Yield stress dependency on the evolution of bubble populations generated in consolidated soft sediments

Yield stress dependency on the evolution of bubble populations generated in consolidated soft sediments

Dynamic simulations of colloids by core-modified dissipative particle dynamics

The influence of system scale on impinging jet sediment erosion: Observed using novel and standard measurement techniques

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