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Appendix G Glossary annealing barn criticality criticality accident curie eutectic favorable geometry Missile material fission cross section a procedure to encourage the diffusion of a substance into a solid matrix by heating below the melting point a unit of area, equal to 1 0-24 cm2, used to measure nuclear cross sections the presence of a self-sustaining fission chain reaction an unplanned criticality a measure of the quantity of radioactive material in a sample, equal to 3.7 x 10~ disintegrations per second a mixture of two substances in the proportion that establishes a compound with the lowest possible melting point. The liquid is a single phase; the constituent solids separate upon equilibrium cooling. a shape of a container holding fissile material in which the geometric dimensions prevent a criticality excursion regardless of enrichment, concentration, or water-equivalent external reflection any mixture of Missile nuclides (uranium-233, uranium-235, and plutonium-239) capable of criticality a measure (in units of area) of the probability that a fission event occurs upon collision of a neutron and a Missile nucleus Gal

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G.2 AN EVALUATION OF DOE ALTERNATIVE FOR MSRE fluorination a process using any of a number of chemical agents to introduce fluorine into a substrate (producing fluoride compounds, as by halogen exchange or oxidation) getter a chemically active material that reacts to trap an evolved gas hycirofluorination a process using hydrogen fluoride (HF). In this application, ~ reoxidizes reduced centers that have been formed in the former melt. It does not take uranium to an oxidation state higher than IV. isobars nuclei of two different elements (i.e., differing atomic number Z) with the same mass number (A) kilogram a metric unit of mass liquidus line the boundary in a phase diagram of a binary system that separates a two-phase region from a single-phase liquid region mole a unit of measure equal to Avogadro's number of particles oxidation state a measure of the number of electrons needed to share in bonds to establish the electronic neutrality of the pure species psia literally, pounds per square inch absolute, a measure of pressure (a vacuum = 0 psia; atmosphere [atml = 14.7 psia) psig literally, pounds per square inch gauge, a measure of pressure from a gauge that compares to an ambient atmospheric reading (psi" = psia- 1 atm; 1 atm = 0 psi") radiolysis any chemical reaction induced by the effects of ionizing radiation reductant a substance participating in a chemical reaction by reducing, or adding an electron to, a species of interest, thereby lowering its oxidation state

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APPENDIX G GLOSSARY roentgen torr G.3 a unit of radiation exposure; currently defined as 2.58 x 10-4 coulombs per kilogram and derived historically as the amount of gamma radiation that produces 1 electrostatic unit of charge (via production of ions) in ~ cm3 of air at 1 atm and OC millimeters of mercury, a measure of pressure (latm=760torr)

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