17 Search Results

The development of remote controlled methods for manufacturing EBR-II fuel elements was influenced by many interacting factors. Radiation levels within the process cell have been predicted to range from 10³ to 10⁷ rad per hour. Radiation damage to organic lubricant, electrical insulations, elastic seals, and protective coatings precludes the use of many standard machine components. Heat generated in the fuel by absorbed radiation makes forced cooling necessary in many operations. Oxygen must be exluded from all operations where the fuel is exposed. Equipment must be designed for remote maintenance and component replacement within the limitation of available manipulators. The EBR-IImore » fuel consisted of fissium alloy pins sodium bonded in stainless steel tubes. Precision casting was chosen as the basis for refabricating the fuel pins. Remote controlled equipment was developed to cast, assemble, and inspect the EBR-II fuel elements. Radiation resistant, plug-in machine components were developed to give reasonable life expectancy and to allow remote maintenance and replacement.« less

Here, an iron-based amorphous metal with good corrosion resistance and a high absorption cross section for thermal neutrons has been developed and is reported here. This amorphous alloy has the approximate formula Fe_49.7Cr_17.7Mn_1.9Mo_7.4W_1.6B_15.2C_3.8Si_2.4 and is known as SAM2X5. Chromium, molybdenum, and tungsten were added to provide corrosion resistance, while boron was added to promote glass formation and the absorption of thermal neutrons. Since this amorphous metal has a higher boron content than conventional borated stainless steels, it provides the nuclear engineer with design advantages for criticality control structures with enhanced safety. While melt-spun ribbons with limited practical applications were initiallymore » produced, large quantities (several tons) of gas-atomized powder have now been produced on an industrial scale, and applied as thermal-spray coatings on prototypical half-scale spent-nuclear-fuel containers and neutron-absorbing baskets. These prototypes and other SAM2X5 samples have undergone a variety of corrosion testing, including both salt-fog and long-term immersion testing. Modes and rates of corrosion have been determined in various relevant environments and are reported here. While these coatings have less corrosion resistance than melt-spun ribbons and optimized coatings produced in the laboratory, substantial corrosion resistance has been achieved.« less

After the successful test of the first long Nb₃Sn quadrupole (LQS01) the US LHC Accelerator Research Program (LARP, a collaboration of BNL, FNAL, LBNL and SLAC) is assessing training memory, reproducibility, and other accelerator quality features of long Nb₃Sn quadrupole magnets. LQS01b (a reassembly of LQS01 with more uniform and higher pre-stress) was subjected to a full thermal cycle and reached the previous plateau of 222 T/m at 4.5 K in two quenches. A new set of four coils, made of the same type of conductor used in LQS01 (RRP 54/61 by Oxford Superconducting Technology), was assembled in the LQS01more » structure and tested at 4.5 K and lower temperatures. The new magnet (LQS02) reached the target gradient (200 T/m) only at 2.6 K and lower temperatures, at intermediate ramp rates. The preliminary test analysis, here reported, showed a higher instability in the limiting coil than in the other coils of LQS01 and LQS02.« less

In this study, an overview of the High-Performance Corrosion-Resistant Materials (HPCRM) Program, which was cosponsored by the Defense Advanced Research Projects Agency (DARPA) Defense Sciences Office (DSO) and the U.S. Department of Energy (DOE) Office of Civilian and Radioactive Waste Management (OCRWM), is discussed. Programmatic investigations have included a broad range of topics: alloy design and composition, materials synthesis, thermal stability, corrosion resistance, environmental cracking, mechanical properties, damage tolerance, radiation effects, and important potential applications. Amorphous alloys identified as SAM2X5 (Fe_49.7Cr_17.7Mn_1.9Mo_7.4W_1.6B_15.2C_3.8Si_2.4) and SAM1651 (Fe₄₈Mo₁₄Cr₁₅Y₂C₁₅B₆) have been produced as meltspun ribbons (MSRs), dropcast ingots, and thermal-spray coatings. Chromium (Cr), molybdenum (Mo),more » and tungsten (W) additions provided corrosion resistance, while boron (B) enabled glass formation. Earlier electrochemical studies of MSRs and ingots of these amorphous alloys demonstrated outstanding passive film stability. More recently, thermal-spray coatings of these amorphous alloys have been made and subjected to long-term salt-fog and immersion tests; good corrosion resistance has been observed during salt-fog testing. Corrosion rates were measured in situ with linear polarization, while the open-circuit corrosion potentials (OCPs) were simultaneously monitored; reasonably good performance was observed. The sensitivity of these measurements to electrolyte composition and temperature was determined. The high boron content of this particular amorphous metal makes this amorphous alloy an effective neutron absorber and suitable for criticality-control applications. In general, the corrosion resistance of such iron-based amorphous metals is maintained at operating temperatures up to the glass transition temperature. These materials are much harder than conventional stainless steel and Ni-based materials, and are proving to have excellent wear properties, sufficient to warrant their use in earth excavation, drilling, and tunnel-boring applications. Large areas have been successfully coated with these materials, with thicknesses of approximately 1 cm. The observed corrosion resistance may enable applications of importance in industries such as oil and gas production, refining, nuclear power generation, shipping, etc.« less

Here, the performance of the Intel iPSC/860 hypercube and the Ncube 6400 hypercube are compared with earlier hypercubes from Intel and Ncube. Computation and communication performance for a number of low-level benchmarks are presented for the Intel iPSC/1, iPSC/2, and iPSC/860 and for the Ncube 3200 and 6400. File I/O performance of the iPSC/860 and Ncube 6400 are compared.

Once top quarks are found, because they are heavy they will allow many new tests of the standard model (SM) and new probes of physics at the 100-GeV scale. In this paper we show how to test the standard-model QCD predictions for the transverse polarization of a top quark produced at the Fermilab Tevatron, Superconducting Super Collider, CERN Large Hadron Collider, and the Next Linear Collider. We also examine the most general form of the W – t – b vertex, and show how to detect effects of non-SM operators. Ways of detecting non-SM CP-violation effects in either the productionmore » or the decay of the top quarks and top antiquarks are examined.« less

The authors discuss an investigation to determine analytically if the performance of concrete beams and columns in a hydrocarbon pool test fire would differ significantly from their performance in a standard test fire. The investigation consisted of a finite element analysis to obtain temperature distributions in typical cross sections, a comparison of the resulting temperature distribution in the cross section, and a strength analysis of a beam based on temperature distribution data. Results of the investigation are reported.

The taste thresholds for saccharin (sweet), hydrochloric acid (sour), sodium chloride (salt), and quinine hydrochloride (bitter) were determined in 32 adult Wistar rats, 8 rats for each taste material, before and after a 50 R, 250-kVp x-ray exposure to the tongue. Taste thresholds were obtained using a behavioral technique employing lateral hypothalamic stimulation for the reward stimulus. The preirradiation taste threshold values for saccharin 0.001%, NaCl 0.002%, HCl 0.001%, and quinine hydrochrolide 0.0001% were 3-6 times lower than previously reported values. Satiation for the reward stimulus (lateral hypothalamic stimulation) did not occur so that detection of the transient nature ofmore » the effect was accomplished with frequent daily taste threshold determinations. All animals experienced a 10-fold decrease in taste sensitivity within 24 hours following the x-ray exposure and all threshold values returned to preirradiation levels within 72 hours. The speed of onset and duration of the transient alteration in taste thresholds was dependent upon the particular taste substance under investigation. A study of the rate of tritiated thymidine incorporainto the taste bud confirmed the 10-day average life span for a taste bud cell and indicates that the immediate low dose radiation effect on taste is independent of taste bud cell renewal kinetics. Morphological study of the taste buds failed to reveal an anatomical explanation for the observed radiation change in taste acuity.« less

A general framework is derived for studying differential operations in renormalized perturbation theory. The method makes possible a simple, unified derivation of the renormalization group and Callan-Symanzik equations, as well as a direct test for broken symmetries (including broken scale invariance), without the necessity of defining currents and deriving their generalized Ward identites. A second-order differential equation of the Callan-Symanzik type is derived using similar methods.

The possibility that the electromagnetic current has an isotensor component, has never been excluded. Further, to be sure, if an I = 2 electromagnetic current existed, it would have rather peculiar properties provided one wants to maintain the usual structure of the charge operator. (In particular, the elastic electric isotensor form factors must vanish at zero momentum transfer.)