Hot Isostatic Compaction of Graphite

The effects of temperature, pressure, and graphite starting material on the density, isotropy, and strength of dense graphite material prepared by hot isostatic compaction of graphite powders were examined. Process equipment was developed to permit operation at temperatures up to 2700 C under a 1600-atom isostatic pressure of inert gas . The isotropy of graphite compacts was determined by neutron diffraction. Relatively isotropic, high-purity graphites were produced having modest isotropic tensile strength and extremely high density (up to 2.24 g per cm3, or 99 per cent of theoretical)

GAS-PRESSURE BONDING OF ZIRCALOY-CLAD FLAT-PLATE URANIUM DIOXIDE FUEL ELEMENTS

A solid-state bonding technique involving the use of gas pressure at elevated temperatures was investigated for the preparation of compartmented Zircaloy-clad flat-plate uranium dioxide fuel elements. These investigations involved development of methods for the surface preparation and assembly of fuel- element components for bonding, determination of optimum bonding parameters, development of barrier coatings for uranium dioxide to prevent reaction with Zircaloy, and extensive testing and evaluation of the bonded fuel elements. During the course of this work, the process was continually modified and refined in an effort to improve the quality of the bonded element and decrease the cost of fabrication. The surface-preparation studies indicated that satisfactory bonding could be obtained consistently with both machined and belt-abraded components. Belt abrasion is more economical and was used as the standard technique in the development phases of the program. Initially the elements were assembled into a stainless steel or Ti-Namel envelope which was evacuated and sealed prior to bonding. Later studies showed that the quality of bonded elements could be improved and process costs decreased by edge welding the Zircaloy components to form a gastight assembly that was then bonded without use of a protective envelope. Further cost reductions were incorporated into the process by the use of piece Zircaloy components to form the picture frame. Optimum bending with a minimum core-to-cladding reaction was achieved by pressure bonding at 1500 to 1550 deg F for 4 hr using a helium gas pressure of 10,000 psi. A postbonding heat treatment for 5 min at 1850 deg F in a salt bath promoted additional grain growth at the bond interface during the alpha-to-beta transformation. Barrier layers of graphite. chronaium, iron. molybdenum, nickel, niobium, palladium, and various oxides were investigated to prevent reaction between the UO/sub 2/ core and Zircaloy cladding. Graphite, in the form of a sprayed and buffed coating, and chromium were found to be relatively effective barriers. The graphite coating was easy to apply and less expensive than a chromium electroplate. (auth

The genomic landscape of balanced cytogenetic abnormalities associated with human congenital anomalies

Despite the clinical significance of balanced chromosomal abnormalities (BCAs), their characterization has largely been restricted to cytogenetic resolution. We explored the landscape of BCAs at nucleotide resolution in 273 subjects with a spectrum of congenital anomalies. Whole-genome sequencing revised 93% of karyotypes and demonstrated complexity that was cryptic to karyotyping in 21% of BCAs, highlighting the limitations of conventional cytogenetic approaches. At least 33.9% of BCAs resulted in gene disruption that likely contributed to the developmental phenotype, 5.2% were associated with pathogenic genomic imbalances, and 7.3% disrupted topologically associated domains (TADs) encompassing known syndromic loci. Remarkably, BCA breakpoints in eight subjects altered a single TAD encompassing MEF2C, a known driver of 5q14.3 microdeletion syndrome, resulting in decreased MEF2C expression. We propose that sequence-level resolution dramatically improves prediction of clinical outcomes for balanced rearrangements and provides insight into new pathogenic mechanisms, such as altered regulation due to changes in chromosome topology

The James Webb Space Telescope Mission

Twenty-six years ago a small committee report, building on earlier studies, expounded a compelling and poetic vision for the future of astronomy, calling for an infrared-optimized space telescope with an aperture of at least $4m$. With the support of their governments in the US, Europe, and Canada, 20,000 people realized that vision as the $6.5m$ James Webb Space Telescope. A generation of astronomers will celebrate their accomplishments for the life of the mission, potentially as long as 20 years, and beyond. This report and the scientific discoveries that follow are extended thank-you notes to the 20,000 team members. The telescope is working perfectly, with much better image quality than expected. In this and accompanying papers, we give a brief history, describe the observatory, outline its objectives and current observing program, and discuss the inventions and people who made it possible. We cite detailed reports on the design and the measured performance on orbit.Comment: Accepted by PASP for the special issue on The James Webb Space Telescope Overview, 29 pages, 4 figure

FURTHER DEVELOPMENT OF GAS-PRESSURE BONDING OF ZIRCALOY-CLAD FLAT-PLATE URANIUM DIOXIDE FUEL ELEMENTS

The effects of core barrier coatings, void spaces, and surface-cleaning techniques on the quality of Zircaloyclad flat-plate UO/sub 2/ fuel elements prepared by gas-pressure bonding were investigated. Techniques were developed for the application of barrier layers of chromium by a vapordeposition process and of crystalline carbon by a pyrolytic process. These coatings, together with a graphite coating previously developed, were evaluated in pressure-bonded fuel elements for their effectiveness in preventing coreto-cladding reaction and for their general production feasibility. Crystalline carbon coatings 15 to 40 mu in. thick and chromium coatings 25 to 40 mu in. thick were determined to be satisfactory. In the stady of the flow of cladding-plate material into void spaces in the picture-frame assembly, it was established that excessive flow, and consequent thinning of the cladding, can be minimized by individually compartmentalizing the cores with Zircaloy ribs. This design resulted in maximum restriction of the effects of a cladding failure in service. Quantitative data on the maximum amount of void space resulting from manufucturing tolerances or from chipped fuel cores that is tolerable in cladding failure in service. Quantitative data on the maximum amount of void space resulting from manufucturing tolerances or from chipped fuel cores that is tolerable in elements of this design were obtained. In stadies of surface-cleaning technlques, it was found that a final multistep rinsing cycle resulted in bonds consistently free of evidence of contamination. (See also BMI-1374.) (auth

Further development of gas-pressure bonding of zircaloy-clad flat-plate uranium dioxide fuel elements /

"Contract No. W-7405-eng-92.""UC-25 Metallurgy and Ceramics (TID-4500, 15th Ed.).""May 11, 1960.""Report No. BMI-1436."Includes bibliographical references (p. 57).Work performed by the Battelle Memorial InstituteMode of access: Internet

Gas-pressure bonding of stainless steel-clad UO₂ flat-plate elements /

"Contract No. W-7405-eng-92.""UC-25 Metals, Ceramics, and Materials (TID-4500, 18th Ed.).""October 5, 1962.""Report No. BMI-1597."Includes bibliographical references (p. 24)Work performed by the Battelle Memorial InstituteMode of access: Internet

Gas-pressure bonding of flat-plate fuel assemblies /

"Contract No. W-7405-eng-92.""UC-25 Metallurgy and Ceramics (TID-4500, 14th Ed.).""January 20, 1959.""Report No. BMI-1312."Includes bibliographical references (p. 43).Work performed by the Battelle Memorial InstituteMode of access: Internet

Oxidation resistance of oxide-coated UO₂ microspheres /

"April 2, 1963."Includes bibliographical references (p. 22)Work performed by the Battelle Memorial InstituteMode of access: Internet

Gas-pressure bonding of zircaloy-clad flat-plate uranium dioxide fuel elements /

"Contract No. W-7405-eng-92.""UC-25 Metallurgy and Ceramics (TID-4500, 14th Ed.).""August 28, 1959.""Report No. BMI-1374."Includes bibliographical references (p. 105-106).Work performed by the Battelle Memorial InstituteMode of access: Internet