Nitric oxide (NO), a free radical present in biological systems, can have many detrimental effects on the body, from inflammation to cancer. Due to NO’s short half-life, detection and quantification is difficult. The inability to quantify NO has hindered researchers’ understanding of its impact in healthy and diseased conditions. Single-walled carbon nanotubes (SWNTs), when wrapped in a specific single-stranded DNA chain, becomes selective to NO, creating a fluorescence sensor. Unfortunately, the correlation between NO concentration and the SWNT’s fluorescence intensity has been difficult to determine due to an inability to immobilize the sensor without altering its properties. Through the use of a recently developed sensor platform, systematic studies can now be conducted to determine the correlation between SWNT fluorescence and NO concentration. This paper explains the methods used to determine the equations that can be used to convert SWNT fluorescence into NO concentration. Through the use of the equations developed in this paper, an easy method for NO quantification is provided. The methods outlined in this paper will also enable researchers to develop equations to determine the concentration of other reactive species through the use of SWNT sensors.

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The current UK concept for a low- or intermediate-level nuclear waste repository includes a largely cementitious backfill. The cement provides a high pH environment in which the general corrosion rate of the metal canisters is reduced and the solubilities of many nuclides low. It has previously been assumed that this high pH will exist for a period of 107 years, however cement will degrade due to leaching of the solid components and attack from aqueous species in groundwater. In this paper we describe the preliminary stages of a model of the degradation of cement in a repository. The modelling involves the incorporation of a thermodynamic description of cement[2] into the static code PHREEQE[5]. This is then used in a coupled chemistry-transport model of simple leaching of cement using the code CHEQMATE[4]. This preliminary modelling also provides a useful verification of CHEQMATE as a direct comparison with a THCCDM (a coupled code based on CHEMTRN) model is possible. Results from this preliminary model suggest that the fall in pH due to leaching is slow. The model is sufficiently flexible to form the basis of more detailed investigations of the effect of groundwater interactions on the degradation of cement.

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A model of the progress of radionuclides through a porous sorbing material is presented. This model couples a surface complexation model of sorption process with a transport simulation in the CHEQMATE code. The chemical model has been shown to reproduce adequately trends observed in batch sorption experiments. In this paper, the coupled model has been applied to a through-diffusion experiment of uranium in London clay. The predictions show a significant variation in calculated Rd across a 9 mm clay sample over a timescale of 100 days, suggesting that a quoted Rd may only be applicable for a limited range of space and time in this evolving system. The model will later be used to investigate possible limitations to the simple Rd approach in repository safety assessment modelling.