The neutron-proton capture cross section at the neutron laboratory velocity of 2200 m/sec has been determined from the time decay of the thermalized neutron population following short bursts of fast neutrons in water samples of widely varying sizes. Use of an intense pulsed neutron beam enables elimination of many of the problems encountered in earlier experiments. The present result for this cross section is 332.6 + 0.7 mb, which is the most precise of any result obtained by this method and is comparable in accuracy and consistent with the most accurate values determined by any method.NUCLEAR REACTIONS p(n, y)d, E=0.0253 eV; measured Lifetimes of thermal neutrons in water samples of various sizes; deduced o,

A detailed evaluation of the fuel-burnup dependent power distribution and the scram reactivity for the PIUS reactor design has been performed. The analyses were carried out using the CPM lattice physics and NODE-P2 core neutronics/thermal-hydraufics codes, and are based on the information provided in the PIUS Preliminary Safety Information Document.Cycle depletion calculations were performed for a set of nine representative initial core loadings and the threedimensional core power distributions were determined. These calculations indicate that the PIUS radial FAh and total Fa power peaking is stronger than that indicated by the PIUS reference-design values.The scram reactivity resulting from the injection of highly borated pool water was calculated for a series of timedependent linear ramp and square-wave pool flows. The three-dimensional distribution of the borated pool water throughout the core was modeled and the spatial reactivity effects of the distributed boron were determined. For pool flows that increase as a linear ramp, the spatial reactivity effects of the distributed boron were very small. In this case, a constant core-average boron reactivity coefficient can be used to model the PIUS scram reactivity.

The preconceptual design of the APT Li-A1 target system, also referred to as the Spallation-Induced Lithium Conversion (SILC), target system, is summarized in this report. The. system has been designed to producea "3./8 G9al '' quantit3t of tritium,using the 2.00-mA, 1.0: GeV pr(Jton beam emerging from the LANL-designed LINAC. The SILC target system consists of a beam expander, a heavy-water-cooled lead spallation neutron source assembly surrounded by light-water-cooled Li-A1 blankets, a target window, heat removal systems, and related safety systems. The preconceptual design of each of these major components is described. Descriptions are also provided for the target fabrication, tritium extraction, and waste-steam processes. Performance characteristics are presented and discussed.

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