Albert K. Fischer

The trio experiment

The TRIO experiment is a test of in-situ tritium recovery and heat transfer performance of a miniaturized solid breeder blanket assembly. The assembly (capsule) was monitored for temperature and neutron flux profiles during irradiation and a sweep gas flowed through the capsule to an analytical train wherein the amounts of tritium in its various chemical forms were determined. The capsule was designed to operate at different temperatures and sweep gas conditions. At the end of the experiment the amount of tritium retained in the solid was at a concentration of less than 0.1 wppM. More than 99.9% of tritium generated during the experiment was successfully recovered. The results of the experiment showed that the tritium inventories at the beginning and at the end of the experiment follow a relationship which appears to be characteristic of intragranular diffusion.

Vapor Pressure of Bismuth

The total vapor pressure of bismuth as determined in the temperature range 1196°—1268°K by the quasistatic and boiling‐point methods is represented by logp(torr) = − (9150.3/T)+7.6327. The bismuth vapor density as found by the transpiration method is 3.05×10−3 g/liter at 1173°K. A combination of the pressure and density data yields an average molecular weight of the vapor at 1173°K of 328 which implies 57 mole % Bi2 and 43 mole % Bi in the vapor, and partial pressures of 0.29 and 0.39 torr for the monatomic and diatomic species, respectively. The standard enthalpies of dissociation of Bi2(g) and of vaporization of liquid to monatomic and diatomic species are 47.8, 50.3, and 52.8 kcal/mole, respectively. The results are compared with those of other workers.

Thermodynamics of Li2O and other breeders for fusion reactors

Thermodynamic calculations have been made to compare the thermochemical performance of the fusion reactor breeder blanket materials, Li/sub 2/O, LiAlO/sub 2/, and Li/sub 4/SiO/sub 4/ in the temperature range 900 to 1300K and in the oxygen activity range 10/sup -25/ to 10/sup -5/. In general, LiAlO/sub 2/ offers advantages over Li/sub 2/O, and Li/sub 2/O in turn appears better than Li/sub 4/SiO/sub 4/. The protium purge technique of enhancing tritium release is explored for the LiAlO/sub 2/ system. Oxygen activity is an influential variable in these systems and must be considered in executing and interpreting measurements on rates of tritium release, the chemical form of the released tritium, diffusion of tritiated species and their identities, retention of tritium in the condensed phase, and solubility of hydrogen isotope gases. Surface adsorption is seen as a potentially significant contributor to tritium inventory.

Desorption of H2O and H2 from steel and LiAlO2 by temperature programmed desorption

Abstract Temperature programmed desorption (TPD) measurements with a steel sample tube and helium sweep gas are in progress to provide data describing the kinetics of desorption of H2O(g) and H2(g) from ceramic tritium breeders. Preliminary blank experiments indicated that the steel can be a reactive participant with H2O being consumed and H2 being evolved. There is also evidence of some dissolution of H2 in the steel. However, it is possible to stabilize the steel in the absence of added H2 so that useful desorption measurements with H2O(g) can be made. Initial work was on the LiAlO2-H2O(g) system. Fresh samples of LiAlO2 bear large amounts of adsorbed H2O. TPD spectra were measured for LiAlO2 that had been equilibrated in a helium stream with 200 ppm H2O(g) at temperatures from 473 to 773 K. Several techniques of data analysis were applied, questions of possible peak overlap still remain to be resolved. An activation energy for desorption of H2O(g) of approximately 120 kJ/mol appears to be associated with the sample equilibrated at 673 K. This result agrees with the value reported in the literature for decomposition of LiOH, and suggests that some sites on LiAlO2 might resemble sites on Li2O in their adsorptive properties. For a 773 K equilibration, the activation energy of desorption appears considerably higher.

Thermodynamics of the Li2O fusion reactor breeder

Abstract Lithium oxide is one of the candidate tritium breeders for a fusion reactor. A computational survey, using experimentally measured activity coefficients for LiOH in Li 2 O, was made of the thermodynamic behavior of Li 2 O as a fusion reactor breeder blanket material. All significant species involved in establishing an equilibrium state, including those generated from the effects of H-T exchange, are included in the analysis. Oxygen activity, particularly at values less than approximately 10 −15 , is a variable that was found to strongly influence the balance of the molar quantities and activities of various species. These relationships are important in assessing the HT-HTO balance in the gas phase, the enhancement of tritium release by protium purging, the vaporization of LiOH/LiOT and Li, and the effects of elemental lithium and LiT in the condensed phase.

Studies of surface adsorption on LiAlO2

Computational and experimental approaches are being taken to understanding surface adsorption/desorption effects on tritium inventory and release. The computational survey integrates a thermodynamic treatment of surface adsorption and bulk phase effects such as solubility and gas phase composition. The system T/sub 2/O:T/sub 2/:LiAlO/sub 2/ was examined. The calculations indicate that surface adsorption can be expected to contribute most to tritium inventory under the conditions of lower temperatures and higher oxygen activities. Higher temperature and lower oxygen activity favor lower surface inventory. In the experimental work, a high temperature gas chromatograph was constructed in order to measure the H/sub 2/O:H/sub 2/ surface adsorption isotherms and the solubility of hydroxide in LiAlO/sub 2/. Preliminary data indicate that at 478K approximately 15% of the surface is covered for a partial pressure of H/sub 2/O of approximately 52 Pa. Calculated values can be obtained that are in reasonable agreement with this.

Thermochemical comparison of the effectiveness of protium purging of fusion breeders

The tritium breeders for a fusion reactor, Li/sub 2/0, LiAl0/sub 2/, and Li/sub 4/Si0/sub 4/, are compared on a thermochemical basis in respect to their response to protium purging. Two oxygen activity levels, established by H/sub 2/O:H/sub 2/ ratios of 100: 1 and 1:100 are considered at the temperatures 900 and 1300K. In terms of tritium release (all gaseous forms), LiAl0/sub 2/ is better than Li/sub 2/0 and this in turn better than Li/sub 4/Si0/sub 4/. At 900K, Li/sub 2/0 and LiA10/sub 2/ release more tritium than at 1300K. Li/sub 4/Si0/sub 4/ releases more tritium at 1300K than at 900K.

Quasistatic Vapor Pressure Measurements on Reactive Systems in Inert Atmosphere Box

What is effectively a single tube adaptation of the quasistatic method of measuring vapor pressure has been devised. The method is suitable for use in an inert atmosphere box in studying air sensitive systems. The applicability and limits of operation of the technique are described. Precision and accuracy were checked against a known system, pure sodium.

Adaptation of an ion microprobe for ion bombardment of liquid metals

A technique involving a new substage assembly was developed to permit an ion microprobe mass analyzer (IMMA) to be used as an ion bombardment facility for molten metals (lithium) without harm to the instrument from the hot, reactive samples.

Temperature programmed desorption from LiAlO2 treated with H2

Temperature programmed desorption (TPD) measurements have been made of H2O and H2 desorption from LiAlO2 treated at 923 K with He-H2 mixtures containing 990, 495, and 247 vppm H2. Desorptions were into sweep gases of pure He and into He-H2 mixtures. The H2O and H2 desorption peaks were shown to be the sums of first order subpeaks which had reproducible desorption activation energy and pre-exponential terms. For H2O desorption, the activation energies were 96, 117, and 134 kJ/mol (23, 28, and 32 kcal/mol). (Earlier work had identified an additional peak with an activation energy of 75 kJ/mol (18 kcal/mol.) Enhancement of desorption of H2O by H2 in the sweep gas was confirmed. The enhancement results not from modifying the activation energies and pre-exponential terms for the various sites but from changes in the populations of sites participating in the desorption process so that sites with lower activation energies are increasingly involved. For those runs with He as the sweep gas, desorption of H2 could be observed. The subpeaks involved had activation energies within approximately 4 kJ/mol (1 kcal/mol) higher than the analogous peaks for H2O desorption.