Photochemistry relevant to nuclear waste separations: a feasibility study

The feasibility of photochemically fractionating the actinides in nuclear waste processing is evaluated on a preliminary basis. The data indicate that there are potentially useful photoredox reactions. However, there is a serious lack of data on photochemical parameters for the solution conditions existing in nuclear waste processing. The problem areas relevant to photochemical processing are identified. The experimental areas that must be investigated in order to further evaluate the photochemistry are defined. A research and development program is outlined to determine whether these photochemical reactions can be successfully modified and adapted to a functional actinide fractionating process

General quantitative model for coal liquefaction kinetics: the thermal cleavage/hydrogen donor capping mechanism. [59 references]

A mechanism for coal liquefaction, based on the concept of thermal cleavage-hydrogen capping donor complexes, is proposed and the quantitative agreement between the derived rate laws and the kinetic data obtained from fifteen publications is presented. The mechanism provides rate laws which describe the preasphaltene, asphaltene, oil and gas time/yield curves for the coal liquefaction process. A simplistic dissolution model is presented and used to relate the proposed mechanism to the experimentally observed products. Based on the quality of the mechanistic fit to the reported coal liquefaction systems, which cover a diverse range of reaction conditions, coal types and donor solvent compositions, it is proposed that the donor solvent/thermal bond cleavage/hydrogen capping mechanism provides a good, quantitative description of the rate limiting process. Interpretation of the rate constant/temperature dependencies in terms of transition state theory indicates formation of the activated complex can involve either physically or chemically controlled steps. A uniform free energy of activation of 52 kcal was found for the diverse liquefaction systems indicating a common transition state describes the reactions. Thus the proposed mechanism unifies the diverse liquefaction kinetic data by using a set of uniform reaction sequences, which have a common transition state, to describe the conversion chemistry. The mechanism thereby creates a common base for intercomparison, interpretation and evaluation of coal conversion for the broad range of processes currently being investigated in the liquefaction field