Radiological characterization of neutron-activated metal wastes from nuclear power stations

Three different methods for determining the long-lived radionuclide contents of highly neutron activated metal wastes are being compared and assessed using samples of pressurized-water reactor (PWR) and boiling-water reactor (BWR) spent fuel disassembly hardware and control rods. These methods include: 1) empirical analyses involving sampling and laboratory measurements; 2) direct assay techniques; 3) calculation methods. These techniques are discussed and the results of the comparisons made to date are presented. The agreement between empirical versus calculational methods for the disassembly hardware was generally within 10% to 50%, and rarely exceeded a factor of 2.5, especially near the fueled region of the reactor core. However, large discrepancies between the measured versus calculated concentrations were observed for⁵⁹Ni and⁶³Ni at the end fittings of the fuel assembly hardware, where the calculations underestimated the concentrations by factors varying from about 8 to 28. The calculation errors are believed to be due to inadequate cross section data for the nickel isotopes.Pacific Northwest Laboratory is operated for the U. S. Department of Energy by Battelle Memorial Institute under Contract DE-AC06-76RLO 1830.     

Plasma Thermal Conversion of Methane to Acetylene

This paper describes a re-examination of a known process for the direct plasma thermal conversion of methane to acetylene. Conversion efficiencies (% methane converted) approached 100% and acetylene yields in the 90–95% range with 2–4% solid carbon production were demonstrated. Specificity for acetylene was higher than in prior work. Improvements in conversion efficiency, yield, and specificity were due primarily to improved injector design and reactant mixing, and minimization of temperature gradients and cold boundary layers. At the 60-kilowatt scale cooling by wall heat transfer appears to be sufficient to quench the product stream and prevent further reaction of acetylene resulting in the formation of heavier hydrocarbon products or solid carbon. Significantly increasing the quenching rate by aerodynamic expansion of the products through a converging–diverging nozzle led to a reduction in the yield of ethylene but had little effect on the yield of other hydrocarbon products. While greater product selectivity for acetylene has been demonstrated, the specific energy consumption per unit mass of acetylene produced was not improved upon. A kinetic model that includes the reaction mechanisms resulting in the formation of acetylene and heavier hydrocarbons, through benzene, is described.     

Polymicrobial Biofilm Inhibition Effects of Acetate‐Buffered Chitosan Sponge Delivery Device

Polymicrobial biofilm‐associated implant infections present a challenging clinical problem. Through modifications of lyophilized chitosan sponges, degradable drug delivery devices for antibiotic solution have been fabricated for prevention and treatment of contaminated musculoskeletal wounds. Elution of amikacin, vancomycin, or a combination of both follows a burst release pattern with vancomycin released above minimum inhibitory concentration for Staphylococcus aureus for 72 h and amikacin released above inhibitory concentrations for Pseudomonas aeruginosa for 3 h. Delivery of a vancomycin, amikacin, or a combination of both reduces biofilm formation on polytetrafluoroethylene catheters in an in vivo model of contamination. Release of dual antibiotics from sponges is more effective at preventing biofilm formation than single‐loaded chitosan sponges. Treatment of pre‐formed biofilm with high‐dose antibiotic release from chitosan sponges shows minimal reduction after 48 h. These results demonstrate infection‐preventive efficacy for antibiotic‐loaded sponges, as well as the need for modifications in the development of advanced materials to enhance treatment efficacy in removing established biofilm.

     

The least number of edges for graphs having dihedral automorphism group

The least (and greatest) number of edges realizable by a graph having n vertices and automorphism group isomorphic to D_2m, the dihedral group of order 2m, is determined for all admissible n.     

Conservative methods for the Toda lattice equations

We are concerned with the numerical integration of the Todalattice equations by using different conservative methods. Numericalexperiments suggest that the global error for isospectral schemesdecreases exponentially with time but it is almost constantfor either symplectic or more general integrators. We providea theoretical explanation for these experimental findings.