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Experience is described at the Savannah River plant for the separation and purification of Np237 and Pu238 from irradiated neptunium targets, and for the separation and purification of Np2 37 from irradiated natural and enriched uranium. Most of the processing is by anion exchange in relatively small equipment that was installed by novel techniques in the canyons of the large radiochemical separations buildings. Separations of neptunium from uranium are accomplished by modifications tp solvent extraction flowsheets. The performance of the process and equipment is given for each operation. Significant changes made to achieve excellent yields and purity of products are discussed. Characteristics of anion exchange resins that are used are correlated with process performance. » program to manufacture Pu238, an alpha emitter well suited for use in power generators in space vehicles, was assigned to the Savannah River plant (SRP) in 1959. Pu238 is produced by neutron irradiation of Np237 which has previously been separated from irradiated uranium. Ion ex-. change and solvent extraction processes were developed at the VOL. 3 NO. 4 OCTOBER 1964 315

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Incidents and accidents occurring in nuclear facilities, transport accidents or malevolent actions associated with radioactive material may involve a release of airborne radionuclides. For these situations, a realistic assessment of the radiological consequences for the public is of great importance with respect to adequate emergency measures. Within this context, the determination of the spatial distribution of the resulting airborne concentration as well as of the deposition of radionuclides on the ground, vegetation and building surfaces are necessary prerequisites. For such calculations, advanced atmospheric dispersion models are increasingly used. Their characteristics and fields of application are presented.