Kinetics and transient absorption spectra of pyrene-and 1 -chloropyrene-triethylamine (TEA) systems, in the presence and absence of cyanide ions, have been studied b y a nanosecond timeresolved laser flash photolysis method in dry acetonitrile at room temperature. Schemes for c h loropyrene-triet hylami ne-and c h loropyrene-triet hylami ne-CNsystems have been developed and individual rate constants determined either b y direct measurements or by use of computer analysis of the experimental decay curves. The reaction results in the dehalogenation of chloropyrene t o yield pyrene as the reaction product, but high quantum yields (0.2-0.4) are obtained only in the presence of cyanide ions. The hydrogen atoms which replace the chlorines originate from the solvent. This was determined b y deuterium labelling. The reaction proceeds via an exciplex t o radical ions, which recombine to form ion pairs. Cyanide ions attract chlorohydropyrene radicals, which are mainly formed in the reaction between chloropyrene anion radicals and the solvent. The cyanohydropyrenyl radicals formed are in equilibrium with the relatively stable cyanopyrene anion radicals and, b y cleavage of the cyano radicals, yield the reaction product.Paper 1/03584C

Diffusivities of Cs and Sr in concretes and in mixtures of sodium bentonite and crushed rock were measured.The order of magnitude of the apparent diffusivities (Da) for Cs and Sr in concretes was 10-14-10-13 m 2 /s and in the mixtures of bentonite and crushed rock 10-13-10-11 m 2 /s. The calculated effective diffusivities (De) in the mixtures of bentonite and crushed rock seemed in some cases to exceed the corresponding values in water, which suggests that the pore diffusion/sorption model cannot explain the transport phenomena in all cases.The experiments where the sorption factors were varied in the diffusion samples suggest that the nuclides diffuse also while being sorbed. A combined pore diffusion-surface diffusion model has been used to explain the transport and the corresponding diffusivities have been evaluated. This paper will give the measured diffusion and sorption data and discuss the models used to describe diffusion in porous sorbing agents.

A laboratory method for measurement of diffusion of radionuclides inconcretes and compacted bentonite has been developed. In this method a tracer is introduced through one end into the cylindrical sample closed in a tube and preequilibrated with water. After the introduction period of the tracer the tube is sealed hermetically and the concentration profiles of the radionuclides are measured periodically from the outside of the sample using a collimated detector. Diffusivities are calculated from the activity profiles by fitting the theoretical curve with the measured profile. The paper will give diffusion data for Co, Sr and Cs in some concrete products and for Co and Cs in compacted sodium bentonite.