Jonathan Francis

Computational Fluid Dynamic Studies of Vortex Amplifier Design for the Nuclear Industry—I. Steady-State Conditions

In this paper computational fluid dynamics (CFD) techniques have been used to investigate the effect of changes to the geometry of a vortex amplifier (VXA) in the context of glovebox operations in the nuclear industry. These investigations were required because of anomalous behavior identified when, for operational reasons, a long-established VXA design was reduced in scale. The study simulates the transient aspects of two effects: back-flow into the glovebox through the VXA supply ports, and the precessing vortex core in the amplifier outlet. A temporal convergence error study indicates that there is little to be gained from reducing the time step duration below 0.1 ms. Based upon this criterion, the results of the simulation show that the percentage imbalance in the domain was well below the required figure of 1, and imbalances for momentum in all three axes were all below measurable values. Furthermore, there was no conclusive evidence of periodicity in the flow perturbations at the glovebox boundary, although good evidence of periodicity in the device itself and in the outlet pipe was seen. Under all conditions the modified geometry performed better than the control geometry with regard to aggregate reversed supply flow. The control geometry exhibited aggregate nonaxisymmetric supply port back-flow for almost all of the simulated period, unlike the alternative geometry for which the flow through the supply ports was positive, although still nonaxisymmetric, for most of the period. The simulations show how transient flow structures in the supply ports can cause flow to be reversed in individual ports, whereas aggregate flow through the device remains positive. Similar to the supply ports, flow through the outlet of the VXA under high swirl conditions is also nonaxisymmetric. A time-dependent reverse flow region was observed in both the outlet and the diffuser. It is possible that small vortices in the outlet, coupled with the larger vortex in the chamber, are responsible for the oscillations, which cause the shift in the axis of the precessing vortex core (and ultimately in the variations of mass flow in the individual supply ports). Field trials show that the modified geometry reduces the back-flow of oxygen into the glovebox by as much as 78. At purge rates of 0.65 m 3h the modified geometry was found to be less effective, the rate of leakage from the VXA increasing by 16-20. Despite this reduced performance, leakage from the modified geometry was still 63 less than the control geometry.

Computational Actuator Disc Models for Wind and Tidal Applications

This paper details a computational fluid dynamic (CFD) study of a constantly loaded actuator disc model featuring different boundary conditions; these boundary conditions were defined to represent a channel and a duct flow. The simulations were carried out using the commercially available CFD software ANSYS-CFX. The data produced were compared to the one-dimensional (1D) momentum equation as well as previous numerical and experimental studies featuring porous discs in a channel flow. The actuator disc was modelled as a momentum loss using a resistance coefficient related to the thrust coefficient (). The model showed good agreement with the 1D momentum theory in terms of the velocity and pressure profiles. Less agreement was demonstrated when compared to previous numerical and empirical data in terms of velocity and turbulence characteristics in the far field. These models predicted a far larger velocity deficit and a turbulence peak further downstream. This study therefore demonstrates the usefulness of the duct boundary condition (for computational ease) for representing open channel flow when simulating far field effects as well as the importance of turbulence definition at the inlet.

A Review of Vortex Amplifier Design in the Context of Sellafield Nuclear Operations

Vortex amplifiers have for over 30 years been used to ensure containment of glove-box ventilation in the event of a barrier breach, the most likely such breach being damage to the glove itself. Containment is achieved using fluidic principles to control the glove-box depression and ventilation rate under both normal and emergency conditions; in the event of such a breach vortex amplifiers can switch quickly between these two states without recourse to electrical, pneumatic or manual intervention. This paper begins by summarising the developments in vortex amplifier design used at the Sellafield site by successive companies engaged in fuel technology, reprocessing and decommissioning (British Nuclear Fuels PLC (BNFL), BNFL Engineering Limited, British Nuclear Group and Sellafield Limited). The main reasons for design changes have been practical issues of set-up, cleaning, filter and waste minimisation, and space limitations. The development culminates in the use of a smaller version of the vortex amplifier (VXA) which is a nearly exact geometrical scaling of its predecessor and which has been standard design for over a decade. Initial use of this device, the mini–VXA, led to a substantial increase in the amount of inert gas needed to maintain the required oxygen-depletion conditions within the glove-box, implying some escape of oxygen into the glove-box. The use of the mini–VXA introduced practical issues relating to (i) its control characteristics and (ii) the reverse flow of air in the supply port. Comparison with the published design specification demonstrates that the geometrical scaling process has led to a slightly hysteric characteristic. Tests conducted by the authors indicate (i) that the origin of the escaping oxygen is the control air feeding back through the supply ports and (ii) that a prototype chamber and orifice plate arrangement between the glove-box and mini–VXA significantly reduces the inert gas demand in normal usage. This prototype arrangement introduced problems in maintaining a clean environment in the chamber, so the chamber and orifice was substituted by a detachable cowl that enabled the mini–VXA to be located within the glove-box and provided access for cleaning.Copyright

The Emergence of Sustainable Practice Within Decommissioning

Despite the advance of sustainable practice and energy efficient techniques outside of the nuclear industry, at the start of the 21st Century there was a lack of published guidance aimed at their adoption at specifically nuclear facilities. Even with the establishment of the Nuclear Decommissioning Authority, there is very little guidance published on how to adopt sustainable practices during decommissioning. There have been instances where energy efficiency had affected design and operations decisions. Projects aimed at responsible housekeeping, switching off lights, and changes to the nuclear ventilation design philosophy illustrate a desire for action, but these activities were championed by interested and motivated employees. Sustainable practice had not at that time received a strategic lead that resulted in a management structure to enable a coordinated and concerted effort in sustainable practice. This paper traces the progress during the 20th and early 21st Centuries, whereby sustainable practice is now established within a much firmer foundation of case study, guidance and organisational structure; to embed sustainable practice within the United Kingdom’s current decommissioning programme. It looks at the development of relevant literature and, through interviews with key managers and external stakeholders, demonstrates (i) the degree to which two essential guidance documents (the NiCOP and CIRIA SD:SPUR) are permeating the industry, (ii) how the current work of the Characterisation and Clearance Group has evolved to influence the decontamination and dismantling planning procedures and (iii) the transition from identifying ‘free-release’ materials to actually releasing them for re-use in the community.Copyright

Numerical simulation of observed flow phenomena in the supply and control ports and associated feed channels of a mini-vortex amplifier

The trajectory and reach of jets issuing from tangential control ports at the periphery of a vortex amplifiers swirl chamber depend largely on design geometry, size and pressures applied. Excessive control port pressure causes these jets to extend too far across the face of the radial supply ports, to impact on the opposing supply port wall whereupon, they bifurcate to create back diffusion of control port flow along the supply port channels. Flow through vortex amplifier geometry is simulated using a baseline Reynolds stress turbulence model with Computational Fluid Dynamics (CFX) automatic wall treatment. Anisotropic stress and vortex stretching in the swirl chamber and outlet have not prevented convergence (based on normalised vortex amplifier residuals). Known flow structures are reproduced. This paper is focussed on simulation close to pressures needed for bifurcation. Just before the point on an operating characteristic at which bifurcated tangential flow appears, the recirculation zone crossing most of the radial supply stretches to intermittently cut off the radial flow. The steady state results indicate asymmetry between the four ports, as smoke visualisation tests also imply. The transient results are sufficient to demonstrate time-dependent structures and suggest periodicity of flow structures. The model can be used to inform design and operability studies. Moreover, a curious near-wall structure of spinning flow not previously reported has been predicted close to the axis and hugging the swirl chamber wall opposite the outlet, at radii within the forced part of the Rankine vortex.

Control Port Influence on Swirl, Operating, and Flow Characteristics of a Mini-Vortex Amplifier on Glove Box Service

The influence of control port geometry on swirl development, operating characteristics, global flow and momentum characteristics is studied experimentally. Shape and size of the control flow channels and the pressure applied at the tangential ports are critical in determining the trajectory of the jet issuing from the tangential ports; and deflection of radial flow, vortex strength and prevention of back diffusion along the radial supply ports. Dominance of control-to-exit area ratio is confirmed but a clear improvement in performance is noted for the practical site-based geometry that is not derived from this ratio, but from the shaped passages of the device. Flow and momentum characteristics provide additional design data. Lack of influence of supply-to-exit area ratio is demonstrated at lower ratios than advertised in literature. The relationship of Swirl number to output flow is demonstrated. The results imply a geometrical development that has led to practical improvements in vortex amplifier geometry on the scale of the mini-VA. Global flow and momentum characteristics provide insight into design and operation that is useful when avoiding back-diffusion in a mini-VA.

Computational Modelling of the Structural Integrity following Mass-Loss in Polymeric Charred Cellular Solids

A novel computational technique is presented for embedding mass-loss due to burning into the ANSYS finite element modelling code. The approaches employ a range of computational modelling methods in order to provide more complete theoretical treatment of thermoelasticity absent from the literature for over six decades. Techniques are employed to evaluate structural integrity (namely, elastic moduli, Poisson’s ratios, and compressive brittle strength) of honeycomb systems known to approximate three-dimensional cellular chars. That is, reducing the mass of diagonal ribs and both diagonal-plus-vertical ribs simultaneously show rapid decreases in the structural integrity of both conventional and reentrant (auxetic, i.e., possessing a negative Poisson’s ratio) honeycombs. On the other hand, reducing only the vertical ribs shows initially modest reductions in such properties, followed by catastrophic failure of the material system. Calculations of thermal stress distributions indicate that in all cases the total stress is reduced in reentrant (auxetic) cellular solids. This indicates that conventional cellular solids are expected to fail before their auxetic counterparts. Furthermore, both analytical and FE modelling predictions of the brittle crush strength of both auxteic and conventional cellular solids show a relationship with structural stiffness.

Advanced vehicular sensor system

Research into vehicle security control technology found that improved monitoring and security is required. As a result a viable security system needs to be in constant communication with a base station for monitoring purposes. Direct Sequence Spread Spectrum (DSSS) technology offers a secure solution, due to excellent interference suppression of non-gaussian noise and other similar interference. This paper offers an architecture that will utilize a hybrid wireless and Power Line Communication (PLC) medium as a solution. The research shows that using microprocessor technology to generate short message bursts utilising hybrid transmission mediums will allow for efficient and accurate transmission with low Bit Error Rates (BER).

Education and Industry Partnership: A Case Study of Co-Delivery

One of the essential elements for safe operation of a nuclear licensed site is the availability to the licensee in sufficient numbers of suitably qualified and experienced people to carry out and manage the operations and associated design work. In the last few years, there have been a number of reports to illustrate the recent and current problems of recruiting such people to work in the traditional locations for nuclear personnel in the North-West of England. Concern for the immediate future is exacerbated by a peculiar demographic of the people currently employed in positions demanding higher level skills. In response to the growing realization that there is an impending skills gap that needs to be filled, Sellafield Limited’s Talent Management team (and latterly with support of the NDA) have been working with a number of education and training providers to put in place bespoke courses aimed at overcoming this shortage. In the absence of a steady stream of willing graduates from technical and management courses, the primary strategy has been to encourage life-long learning and up-skilling amongst its employees, targeting those who, for whatever reason upon leaving school, missed their opportunity to study and progress to train at a high level, but who possess that potential and have now developed a keenness to proceed with that study in later life. One Foundation Degree has been selected for development of a unique approach to higher education. The work of University of Central Lancashire and its West-Cumbrian education and training partners has featured as a case study in other media, but this paper reports on a fresh development within that work: co-delivery. Co-delivery relates to a partnership of educationalists and industrialists, with an emphasis on industrial numbers on the course development steering group. The means by which a significant proportion of the course is strongly workplace related are presented and the benefits and problems that this introduces are discussed. The course uses the industry as a vehicle to communicate concepts and develop problem-solving skills. Rather than the major vocational aspects being confined to just a few ‘workplace’ modules, the industry permeates all modules and co-delivery is part of a good many. A report is also made on the areas of provision where the major capability and expertise is located in just a few industrialists; and how that aspect is learned within a co-delivery course.© 2009 ASME