Investigation of flow and heat transfer in a large-scale spent nuclear fuel cooling pond

The recent focus on nuclear power has led to the need for more efficient and economical methods of operating the Spent Nuclear Fuel (SNF) cooling ponds as well as complying with the strict safety and environmental legislations imposed by the IAEA and the UK Government. Like many other industrial applications, the design and operation of the SNF cooling ponds have evolved from experience; trial and error. Since the stored materials in such ponds are radioactive, it is very difficult to perform experimental studies. As a result, a rigorous scientific study based on fundamental principles has to be performed. The present research explores analytically and numerically the main processes that take place across the pond installation. The body of the present study includes four main parts: the first part is involved in modelling the heat loss from the free water surface, mainly due to evaporation, using analytical and single-phase numerical approaches, which represents a critical factor in the modelling of the large-scale cooling ponds. The predicted results were in good agreement with experimental data available in open literature. In the second part, a thermal model using Microsoft Excel spreadsheet was developed for the cooling pond based on an analytical approach. The well-mixed hypothesis was adopted to describe the water zone as well as the humid air zone. Also, the ventilation system was considered within this model. The developed spreadsheet tool was validated against reliable data available for Maine Yankee pool as well as temperature measurements collected from the Sellafield site. This spreadsheet tool is able to describe the transient behaviour with low computational cost, allowing many "what-if" scenarios to be rapidly investigated. In the third part, Computational Fluid Dynamics (CFD) was used to model the cooling pond at both macro and micro levels. The macro level modelling involved in developing a CFD model for Sellafield’s cooling pond where the fuel regions were approximated to porous medium. The computational domain was produced for the water zone only, where the humid air zone was introduced to the model by coupling of the spreadsheet model with the CFD model. This model was validated and used to examine the distribution of water temperature to confirm the reliability of the adopted well-mixed approach in the analytical model. The outcomes from the CFD and spreadsheet models were used to provide some boundary conditions to the micro-level model of the fuel assemblies. The modelling methodology of the fuel assemblies was partially validated with experimental data for heat transfer around vertical cylinder. The maximum temperature of the water within the rack arrangement was determined under various conditions and a correlation was proposed. Finally, a sensitivity study was performed using Taguchi method and the statistical method of ANOVA to assess the influence of the cooling systems as well as the environmental conditions on the thermal performance of the cooling pond. The spreadsheet model was implemented to carry out the calculations. The outcomes from this study were presented in the form of recommendations that may be able to aid the organisation to manage their cooling pond more efficiently and safely during the normal operating conditions as well as recovery from an accident scenario

Evaluating airborne and ground based gamma spectrometry methods for detecting particulate radioactivity in the environment: a case study of Irish Sea beaches

In several places, programmes are in place to locate and recover radioactive particles that have the potential to cause detrimental health effects in any member of the publicwho may encounter them. A model has been developed to evaluate the use of mobile gamma spectrometry systems within such programmes, with particular emphasis on large volume (16 l) NaI(Tl) detectors mounted in low flying helicopters. This model uses a validated Monte Carlo code with assessment of local geochemistry and natural and anthropogenic background radiation concentrations and distributions. The results of the model, applied to the example of particles recovered from beaches in the vicinity of Sellafield, clearly show the ability of rapid airborne surveys conducted at 75 m ground clearance and 120 kph speeds to demonstrate the absence of sources greater than 5 MBq 137Cs within large areas (10–20 km2 h−1), and identify areas requiring further ground based investigation. Lowering ground clearance for airborne surveys to 15 m whilst maintaining speeds covering 1–2 km2 h−1 can detect buried 137Cs sources of 0.5 MBq or greater activity. A survey design to detect 100 kBq 137Cs sources at 10 cm depth has also been defined, requiring surveys at b15 m ground clearance and b2 m s−1 ground speed. The response of airborne systems to the Sellafield particles recovered to date has also been simulated, and the proportion of the existing radiocaesium background in the vicinity of the nuclear site has been established. Finally the rates of area coverage and sensitivities of both airborne and ground based approaches are compared, demonstrating the ability of airborne systems to increase the rate of particle recovery in a cost effective manner. The potential for equipment and methodological developments to improve performance are discussed

Mechanisms of inorganic carbon-14 attenuation in contaminated groundwater: Effect of solution pH on isotopic exchange and carbonate precipitation reactions

Radioactive 14C is a significant contaminant associated with nuclear fuels and wastes that is potentially highly mobile in the environment as dissolved inorganic carbonate species. This study investigated the mechanisms by which dissolved inorganic 14C is retained in surface and groundwater environments via precipitation and isotopic exchange reactions. Precipitation of calcite in the presence and absence of nucleation sites is considered along with isotopic exchange with both atmospheric CO2 and solid carbonates. Precipitation occurs at calcite supersaturation values of SICAL > 1.5 in the absence of nucleation sites and SICAL > 0–0.5 in the presence of nucleation sites, suggesting that precipitation of 14C-bearing carbonates is much more likely in subsurface environments where nucleation sites are abundant. The maximum 14C removal in solid isotopic exchange experiments occurred after approximately 2 weeks equilibration. In these experiments the amount of 14C removed from solution was proportional to the amount of calcite surface area present, and removal from solution was equivalent to rapid equalisation of the isotope ratio in an 8–10 Å active surface layer. Although the reactivity of natural carbonates may be lower than the calcite samples used in this study, these results suggest isotopic exchange with solids will be an important 14C retardation mechanism in subsurface environments containing only modest TIC concentrations. These results suggest that if inorganic 14C is released into sub-surface environments, both precipitation and solid phase isotopic exchange can result in non-conservative 14C-DIC transport and 14C contamination may persist in groundwater for decades following accidental releases. In contrast, in experiments open to atmosphere with pH values below 9.3, complete loss of dissolved inorganic 14C was very rapid and occurred with timescales of 10's of hours. 14C loss was due to a rapid exchange of dissolved 14C species with 12CO2 (g) and the kinetics of 14C removal increased as pH values were lowered (i.e. atmospheric isotopic exchange was first order with respect to the concentration of carbonic acid present). Thus these results suggest that release of inorganic 14C to surface waters with pH values <9.3 would result in rapid exchange with 12CO2 (g) and 14C would not persist in the aqueous environment, whereas 14C-DIC released to saturated subsurface environments may persist close to the release site for decades due to precipitation and solid phase exchange reactions preventing/retarding transport with the groundwater

How benchmarking can support the selection, planning and delivery of nuclear decommissioning projects

Nuclear Decommissioning Projects and Programmes (NDPs) are jeopardized by several risks, long schedule and cost estimates that lay in the range of hundreds of billions of pounds. Moreover, in some countries, these estimates keep increasing and key stakeholders have a limited understanding of the determinants that engender this phenomena. Benchmarking refers to the process of comparing projects in order to identify best practices and generate ideas for improvement. However, even if it is the envisaged approach to tackle the decommissioning challenges (and due to the NDPs’ uniqueness), until now, benchmarking has been only partially used. This paper proposes an innovative methodology to benchmark decommissioning projects, both from the nuclear and non-nuclear industry, within the UK and worldwide. From this cross-sectorial and cross-country analysis, it is possible to gather a list of key NDPs’ characteristic and statistically test their correlation with the project performance. The ultimate aim of the research underpinning this paper is to investigate the possible causation between the NDPs’ characteristics and the NDPs’ performance and to develop guidelines to improve the selection, planning and delivery of future NDPs

Sellafield

SIGLEAvailable from British Library Lending Division - LD:1769.7F(INIS-mf--9100)(microfiche) / BLDSC - British Library Document Supply CentreGBUnited Kingdo

Objectives and scope of the joint funded BNFL/DOE product evaluation development programme

Department of the Environment commissioned research on radioactive waste management 1989/90SIGLEAvailable from British Library Document Supply Centre- DSC:3614.604(DOE/RW--89.050) / BLDSC - British Library Document Supply CentreGBUnited Kingdo

The application of ultrasonic techniques to the quality checking of encapsulated radioactive waste

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The use of magnetite for decontaminating alpha containing effluents

SIGLEAvailable from British Library Document Supply Centre- DSC:9091.9F(PCMRP--85/P14) / BLDSC - British Library Document Supply CentreGBUnited Kingdo

Progress report for 1986/87 from the Waste Treatment and Disposal Working Party covering joint BNFL/DOE funded work

Intermediate Level Waste Research ProgrammeAvailable from British Library Document Supply Centre- DSC:3614.604(DOE/RW--88.056) / BLDSC - British Library Document Supply CentreSIGLEGBUnited Kingdo