The interactions of several high-yield fission products with the SiC coating were studied in laboratory experiments by doping simulated fuel kernels with selected fission product elements before Triso coating. The resulting particles were annealed in a thermal gradient and SiC-fission product interactions were observed and quantified using metallography, radiography, scanning and transmission electron microscopy, and electron microprobe analysis. The results of these studies are discussed in terms of predicting SiC performance and fuel behavior during irradiation.

Etude du probleme de la corrosion des tubes echangeurs de chaleur dans les fours a lit fluidise. Determination des phases en equilibre en differents points de la zone de reaction. Application a un alliage inoxydable Fe−Cr−Ni−Mn ayant la composition de l'acier inoxydable 304; role des oxydes et sulfures resultant de la presence de CaSO 4

This paper applies recently developed thermodynamic techniques to a theoretical analysis of the corrosion of heat-exchanger tubes in the fluidized-bed coal combustor. These techniques permit determination of the equilibrium phases at any location, or series of locations, in a reaction zone from two sets of data. One set is the aggregate elemental composition at any position in the interface, which can be experimental, such as from a microprobe analysis, or theoretical, such as from an assumed model of reaction zone compositions. The second set is the value of the Gibbs free energy of formation for each of the condensed and gaseous species that could conceiveably exist in the system. Analysis of the subject system at the Fe-Cr-Ni-Mn composition of type 304 stainless steel suggests that the presence of a CaSO/sub 4/ deposit on 304 SS is a sufficient condition for reactions that produce oxides and sulfides. Formation of Ni/sub 3/S/sub 2/ in the reaction zone is indicated, which infers the presence of the deleterious 910 K Ni-liquid-Ni/sub 3/S/sub 2/ eutectic, as has been suggested from experimental work. In addition, the presence of CaFe/sub 2/O/sub 4/ spinel, first considered here, appears to be necessary for the formation of sulfides of manganesemore » and iron, which are observed experimentally. Other information includes identification of equilibria controlling sulfur and oxygen pressures within the reaction zone andvariation of the equilibrium phase concentrations across the interface, the latter information being a potentially useful guide to experimental identification of reaction product phases.« less

The reaction rate of either NdC/sub 2/ or LaC/sub 2/ kernels with SiC in coated particles similar to those used in a High-Temperature Gas-Cooled Reactor (HTGR) is essentially identical with that observed in irradiated, TRISO-coated HTGR fuel particles containing UC/sub 2/. The reaction apparently results from destructive distillation of the rare-earth dicarbide in the kernel, transport of rare-earth metal gas down the temperature gradient, formation of the dicarbide at the SiC-pyrocarbon interface, and solution of the SiC in the dicarbide along the SiC grain boundaries. The reaction rate necessary to cause SiC coating failure in four years would apparently be achieved at temperatures above approximately 1565K. It appears that much less than 0.003 of the fissile fuel could fail from this reaction; this compares with a proposed large HTGR design failure fraction of approximately equal to 0.0039 for the fissile fuel.

Nuclear fuels for the high‐temperature gas‐cooled reactor (HTGR) consist of spherical kernels of actinide compounds contained in gaslight pyrolytic carbon and SiC. The fuel kernels migrate up the temperature gradient and into the coating layers. A theoretical analysis of in‐reactor migration data indicates that a solid‐state diffusion process controls the migration rate in fissioned Th 0.84 U 0.16 C 2 , UO 2 , ThO 2 , PuO 2‐x , and Th 0.8 U 0.2 O 2 particles. The theoretically based kernel migration coefficient (KMC) measured in units (cm/s) °K 2 ( o K/cm)‐ 1 , is thus used to correlate the laboratory and in‐reactor data. The KMC values for Pu‐containing particles may be dependent on the initial and in‐reactor O/Pu values. The other in‐reactor KMC values were apparently not dependent on the extent of fission, the fission of either 233 U or 235 U, or the presence of an SiC coating layer. Laboratory KMC values were obtained for unirradiated ThO 2 , UO 1.65 N 0.25 ,UC 2 ThC 2 , and Th 0.84 U 0.16 C 2 particles and generally appeared to be consistent with in‐reactor data.

Mass-spectrometric measurements of CO contained in irradiated UO2 kerneled HTR fuel particles are summarized and evaluated. The oxygen release O/F (atoms per fission) at the end of irradiation is found to be a function of irradiation time t (days) and irradiation temperature T (particle surface temperature, °C); no dependence upon the type of nuclide fissioned (uranium or plutonium) could be found. Within the limits of 66 < t < 550 days, 950 < T < 1525°CandO/F <0.40 fU + 0.85 fPu (fU, fPu are the fractions of fissions in uranium and plutonium, respectively) the oxygen release can be represented by the empirical expression log{(O/F)/t2} = −0.21–8500/(T + 273).A tentative model explaining this result is proposed.

Publisher Summary This chapter describes a useful procedure for the purification of several tRNA's from calf liver. A combination of chromatographic methods, BD-cellulose, reversed-phase, and DEAE-Sephadex, is employed to achieve the purification. Rat liver serine tRNA, purified by partition chromatography, is the only mammalian tRNA that has been sequenced. The procedure described in this chapter was developed so that a number of mammalian tRNA's could be purified in adequate quantities to permit determination of the nucleotide sequence, use as substrate for modifying enzymes, and identification of enzymatic recognition sites. Double-label experiments to identify which isoaccepting species of a tRNA has been isolated are performed on each tRNA product using RPC-5 minicolumns. The final purity of each tRNA product is defined as the respective amino acid acceptance per 3'-terminal adenosine nucleoside.

This chapter describes methods for the preparation of crude tRNA and aminoacyl-tRNA synthetase from calf liver. These methods were developed for the purification of calf liver tRNA's. These methods are rapid and simple and can be readily scaled up to yield larger quantities. Calf liver was selected as it yields a more active crude tRNA preparation than beef liver s and is readily available. Tests with hog liver and chicken liver showed that the methods are generally applicable to all liver sources and probably to similar tissue materials. Analysis of the crude tRNA for amino acid-accepting activity showed activity for all 20 amino acids and a total activity of 64%. This is a minimum value as the assay conditions were not optimized for the individual amino acids. These methods for the preparation of liver tRNA's and aminoacyl-tRNA synthetases have proved dependable and reproducible in our hands. They can be readily scaled up or down to yield other quantities of these materials.

Five tRNAs (aspartic acid-2, leucine-1, lysine-2, phenylalanine, and serine-3) were isolated from crude calf liver tRNA by chromatographic procedures involving benzoylated DEAE-cellulose, reversed-phase chromatography, and DEAE-Sephadex A-50. Calculated activities (amino acid acceptance per 3′-terminal adenosine) were from 87 to 102 %. Crude calf liver tRNA contains much smaller quantities of RNA contaminants than crude tRNA from the mature beeves. The procedures for the preparation of the crude tRNA and chromatographic steps for isolation of these five tRNAs are amenable to scale-up for the preparation of larger samples.

The five chromatographically resolvable leucine tRNA's of Escherichia coli were purified by aminoacylation, chemical derivatization, benzoylated DEAE-cellulose (BD-cellulose) chromatography, basic hydrolysis, reversed-phase chromatography, and DEAE-Sephadex chromatography. The leucine tRNA-1, -3, -4, and -5 were estimated to be 80–100 % pure. The leucine tRNA-2, present in only minor amounts, was less pure. In ribosome binding experiments, leucine tRNA-1 and -2 recognized the codon CUG and leucine tRNA-5 recognized UUG. The leucine tRNA-3 and -4 did not recognize any of the known leucine codons. The method is amenable to scaleup and could be used to prepare large quantities of purified leucine tRNA's. The four arginine tRNA's from E. coli were also recovered by this method but they were less pure, possibly due to chemical damage in the derivatization step.

Improved separation of tRNA's by reversed-phase chromatography has been achieved through the use of a new plastic support, polychlorotrifluoroethylene. Two new chromatographic systems, designated RPC-5 and RPC-6, yield sharper separation of multiple isoaccepting tRNA's and less overlap of adjacent tRNA peaks. These are more applicable for preparatory-scale tRNA separations or identification of isoaccepting tRNA species than the previous diatomaceous-earth-supported, reversed-phase chromatography systems.

ADVERTISEMENT RETURN TO ISSUEPREVArticleNEXTTwo additional reversed-phase chromatographic systems for the separation of transfer ribonucleic acids and their application to the preparation of two formylmethionine and a valine transfer ribonucleic acid from Escherichia coli BJoseph F. Weiss, R. L. Pearson, and A. D. KelmersCite this: Biochemistry 1968, 7, 10, 3479–3487Publication Date (Print):October 1, 1968Publication History Published online1 May 2002Published inissue 1 October 1968https://pubs.acs.org/doi/10.1021/bi00850a024https://doi.org/10.1021/bi00850a024research-articleACS PublicationsRequest reuse permissionsArticle Views51Altmetric-Citations84LEARN ABOUT THESE METRICSArticle Views are the COUNTER-compliant sum of full text article downloads since November 2008 (both PDF and HTML) across all institutions and individuals. These metrics are regularly updated to reflect usage leading up to the last few days.Citations are the number of other articles citing this article, calculated by Crossref and updated daily. Find more information about Crossref citation counts.The Altmetric Attention Score is a quantitative measure of the attention that a research article has received online. Clicking on the donut icon will load a page at altmetric.com with additional details about the score and the social media presence for the given article. Find more information on the Altmetric Attention Score and how the score is calculated. Share Add toView InAdd Full Text with ReferenceAdd Description ExportRISCitationCitation and abstractCitation and referencesMore Options Share onFacebookTwitterWechatLinked InRedditEmail Other access optionsGet e-Alertsclose Get e-Alerts

regulate the accumulation in.viva of the total enzyme, if the This communication describes the experimental conditions which decrease in concentrations of the apo-or oxidized holoenzymes yielded excellent resolution of 14 amino, acid-specific tRNAs on speeds synthesis or slows degradation of the enzyme protein.one type of hydroxyapatite column.REFEREiYCES Hydroxyapatite was prepared as described by Levin (6) and a 1.