Fission product diffusion in ig-110 graphite

The threat of global climate change and resultant disasters has never been higher. The promises made by many countries of carbon neutrality by 2050 will be impossible to achieve without nuclear technology. Global public support for nuclear energy is at its highest level in modern history but is still severely hampered by perceptions of safety and issues involving nuclear waste and proliferation. The Fukushima disaster of 2011 and the attack on Ukraine by the Russian Federation in 2022 only served to highlight the dangers of older reactor technology and the potential for large releases of radioactivity either by accident or intentional sabotage. For these reasons most countries have a keen interest in improved reactor technologies, particularly in regards to safety, as they plan to build, or continue building, their nuclear fleets. Generation-IV reactors are characterized by improved safety, economics, and proliferation resistance compared to current light water reactor designs. The hightemperature gas-cooled reactor (HTGR) exemplifies these characteristics with the additional benefit of process heat production capabilities. Past and current demonstration reactors have proved the technical feasibility of the design and several future reactors are set to enter demonstration phases as early as the late 2020s. Despite strong performance in past and present reactors, there remains several unknown variables, particularly in regards to fission product behavior and transport under differing reactor conditions. Due to the robust nature of the tristructural isotropic fuel particles used in HTGRs, as well as the large amount of graphite comprising the core, there is little risk of a reactor meltdown. Instead, the primary safety consideration of HTGRs is the release of radioactive materials from the core, either during normal operation or an off-normal event. Most fission and activation products will be completely retained in either the fuel particle or the surrounding matrix graphite; a few, however, have a demonstrated ability to migrate through all core structures and deposit onto cooling system components. This poses a danger to reactor workers and, if the closed coolant circuit were to be compromised, the public. With that in mind, it is essential to fully understand the transport parameters of these select radionuclides in every component of the reactor core, including the core structural graphite. This work has measured effective diffusion coefficients of Sr, Ag, Pd, Eu, and Cs in IG-110 structural graphite. A time-release method was utilized to measure these diffusion coefficients at temperatures up to 1973 K using an inductively-coupled plasma mass spectrometer. The effective diffusion coefficients here reported can be used to aid predictive fission product transport programs.Includes bibliographical references

Magnetic Levitation and Noncoalescence of Liquid Helium

We describe experiments in which drops of liquid helium-4, as large as 2 cm in diameter, are magnetically levitated. We have found that, when two or more drops are levitated in the same magnetic trap, the drops often remain in a state of apparent contact without coalescing. It appears that this effect is caused by the slow evaporation of liquid from the drops

Can a charged ring levitate a neutral, polarizable object? Can Earnshaw's Theorem be extended to such objects?

Stable electrostatic levitation and trapping of a neutral, polarizable object by a charged ring is shown to be theoretically impossible. Earnshaw's Theorem precludes the existence of such a stable, neutral particle trap.Comment: 11 pages, 1 figur

Artificial tektites: an experimental technique for capturing the shapes of spinning drops

Determining the shapes of a rotating liquid droplet bound by surface tension is an archetypal problem in the study of the equilibrium shapes of a spinning and charged droplet, a problem that unites models of the stability of the atomic nucleus with the shapes of astronomical-scale, gravitationally-bound masses. The shapes of highly deformed droplets and their stability must be calculated numerically. Although the accuracy of such models has increased with the use of progressively more sophisticated computational techniques and increases in computing power, direct experimental verification is still lacking. Here we present an experimental technique for making wax models of these shapes using diamagnetic levitation. The wax models resemble splash-form tektites, glassy stones formed from molten rock ejected from asteroid impacts. Many tektites have elongated or ‘dumb-bell’ shapes due to their rotation mid-flight before solidification, just as we observe here. Measurements of the dimensions of our wax ‘artificial tektites’ show good agreement with equilibrium shapes calculated by our numerical model, and with previous models. These wax models provide the first direct experimental validation for numerical models of the equilibrium shapes of spinning droplets, of importance to fundamental physics and also to studies of tektite formation

A report on the laboratory performance of the spectroscopic detector arrays for SPIRE/HSO

We report the performance of the flight bolometer arrays for the Spectral and Photometric Imaging REceiver (SPIRE) instrument to be on board of the Herschel Space Observatory (HSO). We describe the test setup for the flight Bolometric Detector Assembly (BDA) that allows the characterization of its performance, both dark and optical, in one instrument's cool down. We summarize the laboratory procedure to measure the basic bolometer parameters, optical response time, optical efficiency of bolometer and feedhorn, dark and optical noise, and the overall thermal conductance of the BDA unit. Finally, we present the test results obtained from the two flight units, Spectroscopic Long Wavelength (SLW) and Spectroscopic Short Wavelength (SSW)

The Science Performance of JWST as Characterized in Commissioning

This paper characterizes the actual science performance of the James Webb Space Telescope (JWST), as determined from the six month commissioning period. We summarize the performance of the spacecraft, telescope, science instruments, and ground system, with an emphasis on differences from pre-launch expectations. Commissioning has made clear that JWST is fully capable of achieving the discoveries for which it was built. Moreover, almost across the board, the science performance of JWST is better than expected; in most cases, JWST will go deeper faster than expected. The telescope and instrument suite have demonstrated the sensitivity, stability, image quality, and spectral range that are necessary to transform our understanding of the cosmos through observations spanning from near-earth asteroids to the most distant galaxies

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

The Science Performance of JWST as Characterized in Commissioning

This paper characterizes the actual science performance of the James Webb Space Telescope (JWST), as determined from the six month commissioning period. We summarize the performance of the spacecraft, telescope, science instruments, and ground system, with an emphasis on differences from pre-launch expectations. Commissioning has made clear that JWST is fully capable of achieving the discoveries for which it was built. Moreover, almost across the board, the science performance of JWST is better than expected; in most cases, JWST will go deeper faster than expected. The telescope and instrument suite have demonstrated the sensitivity, stability, image quality, and spectral range that are necessary to transform our understanding of the cosmos through observations spanning from near-earth asteroids to the most distant galaxies.Comment: 5th version as accepted to PASP; 31 pages, 18 figures; https://iopscience.iop.org/article/10.1088/1538-3873/acb29