i ii Front Cover CaptionThe figure on the front cover illustrates "dynamic control" of electron transfer rates at short distances. The graph compares existing rates with two theoretical ideas: 1) nonadiabatic theoretical predictions that rates will continue to increase as electronic coupling increases, and 2) dynamical theoretical predictions that rates will be limited by solvent motions. Proposed experiments would measure rates in the region in which the theories differ.

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Executive Summary Research ObjectivesThe direct measurement of the chemistry in reactor cores is extremely difficult. The extreme conditions of high temperature, pressure, and radiation fields, are not compatible with normal chemical instrumentation. There are also problems of access to fuel channels in the reactor core. For these reasons, all reaction vendors and many operators have extensively used theoretical calculations and chemical models to model the detailed radiation chemistry of the water in the core and the consequences for materials. The results of these model calculations can be no more accurate than the fundamental information fed into them, and serious discrepancies remain between model calculations and reactor experiments [1,2,3]. For proposed supercritical water cooled reactors, there is barely any information available to begin construction of a radiolysis model for the anticipated pressure (250bar) and temperatures

Self-reaction of the hydrated electron Rate constant Yield of H 2 Linear energy transfer (LET) Monte Carlo track chemistry calculationsIt has been a longstanding issue in the radiation chemistry of water that, even though H 2 is a molecular product, its "escape" yield g(H 2 ) increases with increasing temperature. A main source of H 2 is the bimolecular reaction of two hydrated electrons (e − aq ). The temperature dependence of the rate constant of this reaction (k 1 ), measured under alkaline conditions, reveals that the rate constant drops abruptly above ~150°C. Recently, it has been suggested that this temperature dependence should be regarded as being independent of pH and used in hightemperature modeling of near-neutral water radiolysis. However, when this drop in the e − aq self-reaction rate constant is included in low (isolated spurs) and high (cylindrical tracks) linear energy transfer (LET) modeling calculations, g(H 2 ) shows a marked downward discontinuity at ~150°C which is not observed experimentally. The consequences of the presence of this discontinuity in g(H 2 ) for both low and high LET radiation are briefly discussed in this communication. It is concluded that the applicability of the sudden drop in k 1 observed at ~150°C in alkaline water to near-neutral water is questionable and that further measurements of the rate constant in pure water are highly desirable.