[en] The nonrandom packing of fuel rod debris around and above the surviving fuel rod segments is analyzed for a degraded core with the spacer grids modeled as a porous floor. The irregular shape of the debris is simulated by assuming that all of the spherical particles terminate their migration within the debris bed at their first two-point contact. Comparing computational results with experimental data for nonrandom packing verified the analytical approach. Specific calculations for the TMI-2 geometry reveal an average (horizontally integrated) nonrandom packing density between the fuel rods of approx. 0.30. If simulated vibrations are imposed, this value increases to 0.50. If the debris bed builds up above the fuel rod stubs, the average (horizontally integrated) packing density above these rods is approx. 0.38 without vibrations; loosely packed gravel has an average packing density of 0.45

[en] Highlights: • The thermal performance of a single-row heat exchanger was investigated. • Grid generated turbulence (GGT) was experimentally characterized. • GGT increased heat transfer in the single-row heat exchanger. • Flow visualizations showed vast changes in flow field under elevated free-stream turbulence. - Abstract: The thermal performance of single-row heat exchangers is generally considered to be inferior to multi-row heat exchangers. It is therefore desirable to optimize the former; especially for those cases which cannot accommodate an alternative. In this study, the heat transfer performance of a single-row circular-finned tube heat exchanger was investigated experimentally under elevated disturbance levels. Specifically, grid-generated turbulence (GGT)—the characteristics of which had been measured beforehand with a hot-wire anemometer—was applied to a clean-flow benchmark case and measurements taken at the heat exchanger outlet. It was shown that when the grid is positioned appropriately, a mean enhancement (in global Nusselt number) of up to 11% can be achieved. Flow visualizations revealed the flow structures responsible for the increase in heat transfer.

[en] The authors have been studying the effects of radiation on poly(methylmethacrylate), PMMA, which has been used as a resist in computer chip microlithography. In contrast to predictions based on solution photochemistry of related compounds, they have found by careful spectroscopic study of the irradiated polymer leads to four different kinds of double bonds. These ester cleavage reactions do not necessarily lead to rupture of the backbone, a necessary condition for efficient use as a resist. They find evidence that not only does the state (solution vs. film) upon which irradiation is carried out affect the product distribution, but also that the stereochemistry of PMMA (atactic vs isotactic) plays a role

[en] As the need for higher operating temperatures increases, there will be a greater need for materials that can withstand +2,000 C and oxidizing conditions. Y₂O₃, a high-temperature oxide, was selected on the basis of its high melting point and resistance to surface recession at 2,000 C. The need for processing such a high temperature material demands alternative approaches to production of reliable parts. Hot isostatic pressing offers a route to reliable production of parts for high temperature applications. This study developed empirical relationships to account for the shape of particles and attempts to modify the Ashby, Easterling and Arzt model by incorporating the morphological characteristics into the description of effective pressure on the particle contacts

[en] A numerical method has been formulated to analyse aligned and random backscattered spectra to determine the random fraction chi(z) of aligned MeV ion beams in single crystals. The analysis takes account of the difference in stopping power between channeled and random trajectories, the variations of stopping power and scattering cross sections with energy and a deviation of backscattered spectra from single scattering theory. The results of calculations for 1 MeV H⁺ spectra from Si and Au are presented and compared to those obtained from the commonly used analysis which takes the ratio of the aligned and random spectra. The results show that the detailed numerical method is required in the analysis of the spectra at backscattered energies less than approximately 0.7 k²E₀, where k² is the usual kinematic scattering factor, if a reasonable precision (< 10%) is to be maintained in chi(z) at these larger depths. (orig.)

[en] The effects of two highly purified human leukocyte interferons (IFN-A and IFN-AD) on drug-metabolizing capacity in mice have been investigated. IFN-AD was found to produce significant changes in antipyrine half-life, assessed by analysis of ¹⁴CO₂ exhalation rates following 14C-antipyrine administration. By contrast, IFN-A, which has considerably less antiviral potency than IFN-AD, was found to have no effect on antipyrine half-life. The administration regimen was found to markedly alter the effects seen with IFN-AD. When IFN-AD was given as single daily doses (5 X 10(7) units/kg/day X 3 days), the half-life of antipyrine increased by a mean of 40% (from 21.0 to 28.9 min). However, when a smaller daily dose (3 X 10(7) units/kg/day) was given as a continuous infusion, the antipyrine half-life increased by more than 3-fold (from 20.8 to 68.5 min) after 3 days of administration. Continued infusion for a further 3 days produced no additional change in antipyrine half-life. These results demonstrate that human leukocyte interferons can significantly inhibit hepatic metabolic activity in vivo

[en] Consolidation of high temperature materials to full density by press and sinter methods is limited to relatively simple shapes. Powder injection molding (PIM) allows complex shapes to be formed but presents problems with sintering to full density. Using hot isostatic pressing with PIM would allow complex geometry to approach full density or even achieve full density. Previous investigations with Y₂O₃ powders using PIM forming techniques and conventional sintering resulted in densities of 92--96% of theoretical. Containerless HIP'ing sintered samples increased density to 99% of theoretical. HIP densification of debound PIM samples would eliminate high temperature sintering to close the surface porosity to allow containerless HIP'ing. This investigation explores methods of canning and HIP'ing debound PIM samples of Y₂₃

[en] The radiation-induced decomposition of syndiotatic (st) and isostatic (it) poly(methyl methacrylate) (PMMA) to yield irradiation products (PMMA(d)) resulting from hydrogen abstraction from alpha-methyl or methylene groups to form main chain (M double-bond) or side chain (S double-bond) double bonds is studied by conformational analysis. Relative minimum energy conformations of the st- and it-isomers of PMMA as free molecules are studied. The isomers of PMMA(d) have relative minima in an overall linear (L) chain as well as a global minimum in a bent (B) form. The impact of the change of a tetrahedral C atom to a trigonal C atom upon double bond formation on the conformational energy is fundamental to the understanding of the results. The experimental results are explained by the following theoretical observations. In reactions involving only overall linear conformations, side chain double bond formation is favored because of the resulting large increase in steric repulsion between polymer units in main chain double bond formation. In reactions proceeding to bent conformations, however, the decreased steric interaction yields both main and side chain double bond formation within 6.3 kcal/mol for the st-PMMA(d) isomer and 2.2 kcal/mol for the it-PMMA(d) isomer. Reactions on surfaces are assumed to be constrained to the overall linear conformation of the starting material, PMMA. Prevention of both M double-bond and S double-bond degradation products is desired for microlithographic applications. Increased solubility arising from main chain scission (MCS) is desired, and both M double-bond and S double-bond for that reason are undesirable with respect to resist sensitivity. It is proposed that the troublesome S double-bond process can be attenuated or eliminated by replacing alpha-CH₃ with alpha-CF₃, thus enhancing the distribution of products toward MCS

[en] The nonrandom packing of fuel rod debris around and above the surviving fuel rod segments in a degraded core is analyzed with the spacer grids being modeled as a porous floor. The irregular shape of the debris is simulated by assuming that all of the spherical particles terminate their migration within the debris bed at their first two-point contact. The analytical approach is verified by comparing the computational results with experimental data for nonrandom packing. Specific calculations for the TMI-2 geometry reveal an average (horizontally integrated) nonrandom packing density between the fuel rods of approximately 0.30. If simulated vibrations are imposed, this value increases to 0.50. If the debris bed builds up above the fuel rod stubs, the average (horizontally integrated) packing density above these rods achieves a value of approximately 0.38 without vibrations; loosely packed gravel has an average random packing density of 0.45

[en] The RPI linac, originally built for neutron time-of-flight research, has been modified to allow both low and high electron energy beam radiation studies to be carried out on semiconductors and polymers over the energy range from 5 to 70 meV. Dose rates exceeding 10¹¹ rad/s (Si) are achieved. The L-band microstructure of the accelerator allows for micropulses of 38 ps with 2x10¹³ rad/s in the pulse for high dose rate effects studies. Both in-house and external user programs are being carried out in semiconductors radiation effects. High injection effects, recombination mechanisms, and space charge and internally generated fields are being studied at high electron dose rates. Preliminary experiments have been made using the electron beam for radiation curing of polymer material. The high electron and photon energies available allow for greater depth-dose radiation curing control than previously obtainable in thick sections of polymer compounds. Electron and photon dosimetry measurements are also performed to correlate radiation effects with electron and photon energy spectra. (orig.)