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A program to develop a metal hydride based hydrogen isotope separation process began at the Savannah River Laboratory in 1980. This semi-continuous gas chromatographic separation process will be used in new tritium facilities at the Savannah River Site. A tritium production unit is scheduled to start operation in 1993. An experimental, large-scale unit is currently being tested using protium and deuterium. Operation of the large-scale unit has demonstrated separation of mixed hydrogen isotopes (55% protium and 45% deuterium), resulting in protium and deuterium product streams with purities better than 99.5%. 3 refs., 4 figs.
Production scale separation of tritium from other hydrogen isotopes at the Savannah River Site (SRS) in Aiken, SC, has been accomplished by several methods. These methods include thermal diffusion (1957--1986), fractional absorption (1964--1968), and cryogenic distillation (1967-present). Most recently, the Thermal Cycling Absorption Process (TCAP), a metal hydride based hydrogen isotope separation system, began production in the Replacement Tritium Facility (RTF) on April 9, 1994. TCAP has been in development at the Savannah River Technology Center since 1980. The production startup of this semi-continuous gas chromatographic separation process is a significant accomplishment for the Savannah River Site and was achieved after years of design, development, and testing.
A new analytical method is proposed for measuring the deuterium to hydrogen ratio (D/H) of non-stoichiometric water in hydrous minerals via pyrolysis facilitated gas-chromatography-isotope ratio mass spectrometry (GC-IRMS). Previously published analytical methods have reported a poorly understood nonlinear dependence of D/H on sample size, for which any accurate correction is difficult. This sample size effect been variously attributed to kinetic isotope fractionation within the mass spectrometer and peripheral instruments, ion source linearity issues, and an unstable H_3^+-factor or incorrect H_3^+-factor calculations. The cause of the sample size effect is here identified by examinations of individual chromatograms as well as bulk data from chromatographic peaks. It is here determined that it is primarily an artifact of the calculations employed by the manufacturer's computer program, used to both monitor the functions of the mass spectrometer and to collect data. Ancillary causes of the sample size effect include a combination of persistent background interferences and chromatographic separation of the isotopologues of molecular hydrogen. Previously published methods are evaluated in light of these findings. A new method of H_3^+-factor and D/H calculation is proposed which makes portions of the Isodat software as well as other published calculation methods unnecessary. Using this new method, D/H is measured in non-stoichiometric water in chert from the Cretaceous Edwards Group, Texas, as well as the Precambrian Kromberg Formation, South Africa, to assess hydrological conditions as well as to estimate the maximum average surface temperature during precipitation of the chert. Data from Cretaceous chert are consistent with previously published data and interpretations, based upon conventional analyses of large samples. Data from Precambrian chert are consistent with maximum average surface temperatures approaching 65°C during the Archean, instead of the much lower temperatures derived from erroneous methods of sample preparation and analysis. D/H is likewise measured in non-stoichiometric water in silicified basalt from the Precambrian Hooggenoeg Complex, South Africa. Data are shown to be consistent with D/H of the Archean ocean similar to present day values.
The separation of isotopes has always been a challenge because of their identical size, shape and thermodynamic properties. Nowadays, the extraction of deuterium is performed e.g. by the Girdler Sulfid process or cryogenic distillation, which lead to low separation factors (below 2.5) in combination with high energy costs. The standard way to produce helium-3 is to skim it as a byproduct of the radioactive tritium decay. In this thesis, two alternative approaches have been investigated for the separation of light isotopes, Quantum Sieving and Chemical Affinity Sieving . While Quantum Sieving is based on confinement in small pores, Chemical Affinity Sieving relies on strong adsorption sites. Both methods use the mass difference of the isotopes, which is related to their zero-point energy. The microporous metal-organic frameworks are excellent candidates for studying these quantum effects due to their well-defined pore structure and the possibility to introduce strong adsorption sites directly into the framework. The samples have been exposed to an isotope mixture and the adsorbed quantity of each isotope was detected by low-temperature thermal desorption spectroscopy (TDS). The ratio of the desorbed amount of the isotopes leads directly to the selectivity (separation factor). The selectivity is determined as a function of exposure time and temperature and exhibits the highest value of 25 observed for hydrogen isotopes at temperatures well above the boiling point of liquid nitrogen.
Intermetallic compounds with the CaCu.sub. 5 type of crystal structure, particularly LaNiCo.sub. 4 and CaNi.sub. 5, exhibit high separation factors and fast equilibrium times and therefore are useful for packing a chromatographic hydrogen isotope separation colum. The addition of an inert metal to dilute the hydride improves performance of the column. A large scale mutli-stage chromatographic separation process run as a secondary process off a hydrogen feedstream from an industrial plant which uses large volumes of hydrogen can produce large quantities of heavy water at an effective cost for use in heavy water reactors.