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In this paper a model to predict the ultimate failure of TRISO-coated fuel particles under hypothetical core heatup events is proposed. Features of the model include the ability to treat the statistical variation of the number of coated fuel particles and to make a thermodynamic estimation of the stoichiometry of irradiated UO{sub 2} kernels and the equilibrium CO pressures. The model predictions agree well with the results of postirradiation heating tests. The thermal creep of pyrolytic carbon, however, must be taken into account to further improve the accuracy of the prediction.

3′-Deoxyseldomycin 5 (2), 2′-deamino-3′-epiamino-3′-deoxyseldomycin 5 (14), and 2′,3′-epimino-2′-deamino-3′-deoxyseldomycin 5 (15) were prepared from seldomycin 5 (1). Treatment of hexa-N-ethoxycarbonyl (ecb)-3′-O-tosylseldomycin 5 with sodium borohydride in DMSO gave the corresponding N-ecb-derivatives of 2, 14, and 15. Removal of the ecb groups of these compounds with aq potassium hydroxide gave the free bases 2, 14, and 15, respectively. Structure determination of the products was performed by means of MS, CMR, PMR, and chemical reactions. It was found that 2 exhibits a more potent and broader antibacterial activity than the parent compound 1, and 14 shows unique antibacterial spectrum against resistant strains, whereas 15 has almost no activity.

3′-Episeldomycin 5 (7) was synthesized from seldomycin 5. Reaction of hexa-N-ethoxycarbonylseldomycin 5 (2) with o-nitrobenzenesulfonyl chloride gave penta-N-ethoxycarbonylseldomycin 5-2′,3′-epicyclic carbamate (3) in one step. Hexa-N-ethoxycarbonyl-3′-O-tosylseldomycin 5 or hexa-N-ethoxycarbonyl-3′-O-mesylseldomycin 5, prepared from 2, was also converted into 3 by being heated in weakly basic solvents such as N,N-dimethylformamide or pyridine. Compound 3 was hydrolyzed to give 7. Structure of 7 was confirmed by PMR, CMR, MS, and Δ[M] values. Compound 7 was found to be active against resistant bacteria which carry 3′-O-phosphorylating enzymes. Δ[M] values for vicinal amino groups were shortly discussed.

The structures of seldomycin factors 1 and 2 have been determined by consideration of chemical degradation and spectral properties. Factor 1, also known as XK-88-1, is shown to be 6-O-(2-amino-2-deoxy-alpha-D-xylopyranosyl) paromamine (1) and factor 2, also known as XK-88-2, is shown to be 4'-deoxy-neamine (2). Mass spectral evidence has been obtained that suggests the most probable structure for seldomycin factor 3, also known as XK-88-3, is 6'-amino-6'-deoxyseldomycin factor 1 (12).

3′-Episeldomycin 5 (7) was synthesized from seldomycin 5. Reaction of hexa-N-ethoxycarbonylseldomycin 5 (2) with o-nitrobenzenesulfonyl chloride gave penta-N-ethoxycarbonylseldomycin 5-2′,3′-epicyclic carbamate (3) in one step. Hexa-N-ethoxycarbonyl-3′-O-tosylseldomycin 5 or hexa-N-ethoxycarbonyl-3′-O-mesylseldomycin 5, prepared from 2, was also converted into 3 by being heated in weakly basic solvents such as N,N-dimethylformamide or pyridine. Compound 3 was hydrolyzed to give 7. Structure of 7 was confirmed by PMR, CMR, MS, and Δ[M] values. Compound 7 was found to be active against resistant bacteria which carry 3′-O-phosphorylating enzymes. Δ[M] values for vicinal amino groups were shortly discussed.