NUCLEAR-DEBRIS FORMATION at EDWARD C. FREILING, GLENN R. CROCKER, and CHARLES E. ADAMS. * U. S. Naval Radiological Defense Laboratory, San Francisco, California ABSTRACT This paper describes the present program, recent progress, anc future plans of the U. S. Naval Radiological Defense Laboratory (NRDL’ in the field of nuclear-debris formation. Two fallout-formation prediction systems have been programmed for computer calculation. The predictions represent great advancements over systems that do not account for fractionation, but much room remains for improvement. The greatest needs appear to be for the definition of particle-size distribution, the accounting for agglomeration effects, and the development of a kinetic approach. Preliminary steps in the development of a kinetic approach are described. A by-product of the prediction system is the calculation of unfractionated radiological properties. As an example of this work, decay rates, dose rates, and spectra are given for the most important case of #87fission produced by a thermonuclear neutron spectrum. Some results of correlating radiochemical data from fractionated samples of air-burst debris are discussed, but numerical results are reserved for a following paper* to facilitate comparison with correla- tions from other burst types. Preliminary laboratory investigations of fission-product interaction with various substrate materials are described. These show large negative deviations from Raoult’s law, particularly when the interaction is between a basic fission product and acidic substrate or an acidic fission product and basic substrate. *See paper by Glenn R. Crocker, Francis K. Kawahara, and Edward C. Freiling, this volume, 1