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Thesis (M.S.)--Oregon State University, 2009. / Printout. Includes bibliographical references (leaves 52-54). Also available on the World Wide Web.

Thesis (MScEng)--Stellenbosch University, 2013. / ENGLISH ABSTRACT: Production of graphite dust inside the Pebble Bed Modular Reactor (PBMR) influences the reactor operation negatively. Graphite is used as a moderator in the reactor core and the formation and transportation of graphite dust away from the reactor core decreases the amount of moderator which in turn has a negative impact on the reactor operation. High levels of radioactive dust may also contaminate reactor components which may pose a health risk to maintenance personnel. In this study a pressure vessel was designed and used to measure the wear of a graphite pebble in helium at elevated temperatures. By means of a multi-linear regression analysis a proper mathematical function was established in order to relate graphite wear to certain tribological parameters. These parameters were identified through a literature study. Discrete Element Modelling (DEM) was used to simulate the gravitational flow of graphite pebbles through the reactor core. The experimentally determined mathematical function was incorporated into the DEM simulation to estimate the annual mass of graphite dust to be produced by the PBMR pebble bed as a result of pebble-pebble interaction and pebble-wall interaction during refuelling. / AFRIKAANSE OPSOMMING: Die vorming van grafiet stof binne die korrelbed-modulêre reaktor (PBMR) beïnvloed die werking daarvan negatief. Grafiet word gebruik as 'n moderator in die reaktor kern en die vorming en vervoer van grafietstof weg van die reaktor kern lei tot 'n afname in die hoeveelheid moderator en dit het 'n negatiewe impak op die werking van die reaktor. Hoë vlakke van radioaktiewe grafietstof kontamineer ook reaktorkomponente wat 'n gesondheidsrisiko vir onderhoudspersoneel inhou. In hierdie studie was 'n drukvat ontwerp en gebruik om die slytasie van 'n grafietkorrel in helium by verhoogde temperature te meet. 'n Multi-lineêre regressie analise is dan gebruik om 'n wiskundige funksie daar te stel wat die verband tussen grafietslytasie en die eksperimentele parameters vas stel. Hierdie parameters was met behulp van 'n literatuurstudie geïdentifiseer. Diskrete Element Modellering (DEM) was gebruik om die gravitasionele vloei van grafietkorrels in die reaktor te modelleer. Die eksperimenteel bepaalde wiskundige funksie word in die DEM simulasie ge-inkorporeer om 'n skatting te maak van die jaarlikse massa grafietstof wat gevorm sal word in die PBMR korrelbed as 'n gevolg van korrel-korrel interaksie en korrel-wand interaksie gedurende hersirkulasie.

Diss. (sammanfattning) Linköping : Linköpings universitet, 2007. / Härtill 5 uppsatser.

Thesis (M. Phil.)--University of Hong Kong, 1996. / Includes bibliographical references (leaf 245-252).

<p>This project argues that the nuclear bomb has made speculation an integral part of representing the material world. The bomb’s capability to cause an unprecedented extent of destruction and the constant state of latent war between nuclear-armed countries (expressed through arms race and high alert readiness) created a reality where the disasters in the future must be constantly speculated to understand the contemporary world’s material state. The tens of thousands of nuclear warheads sleeping in silos and submarines are not just the sum of their material components, but also incredibly compressed embodiments of future disasters that may be released at a moment’s notice. Regardless of the likelihood of nuclear conflicts (with which this dissertation is not concerned), the weapon exerts its influence as one of the most catastrophic possibilities even as it remains dormant. In considering the implications of nuclear weapons, all nations and people on the planet think not of what they are, but what they can do. The weapon’s possible future states define its present significance.</p><p> The inherent oxymoron of the nuclear bomb is thus that despite its staggering materiality, it is fiction as well. Any representation of the bomb that ponders its sole purpose—mass destruction—is inevitably speculative. While the degrees in which they reference empirical data vary, the narratives from which people around the world from heads of nations to common citizens learn anything at all about nuclear weaponry are forms of fiction, ranging from fantastical literary fictions to strategic fictions attempting to represent the power of the weapon that is itself fantastical. Not all representations of the weapon or nuclear war are, of course, taken seriously. Apocalyptic nuclear events are often used in popular nuclear fictions as a convenient excuse for dismantling the existing social structures and providing interesting backdrops for survivalist stories. The very fact that imaginations of hypothetical nuclear disasters have become an overused cliché all the while proliferation remains an active threat, however, also indicates that the world has been living with the horrifying prospect of nuclear disasters for decades without an actual event of the kind—that, in other words, the weapon has existed mostly as a fiction. The introduction of the nuclear bomb to the world in this sense marks a critical point in history beyond which the speculated future outcomes of the productions in the present increasingly becomes an integral part of understanding the latter.</p><p>The central concept with which I articulate the relationship between the present and the future created by nuclear weaponry is “eventuality.” Eventuality is a narrativization process through which a historical event develops into an anticipated future event as the original event’s outcome. A story about a fictional World War III involving nuclear weapons, for example, is a form of eventuality. The conceptual usefulness of eventuality is that it articulates the historical trend in the post-1945 era as well as the more recent years of climate change, in which hypothetical future events are increasingly represented not just for the purpose of knowing the future itself, but also reassessing the history to date. Eventuality establishes a causal relation between an event and its hypothetical future outcome—or its “eventual” as I call it. By drawing a line of synthetic history extending beyond the present, eventuality as a narrativization process defines the direction in which history has been heading up to the present. Compared to the postmodernist understanding of the representation of the past, eventuality is concerned with how human productions in the present already creates the future and, consequently, how the very ways in which we conceive the present is influenced by the possible futures.</p><p>To discuss the concept of eventuality in detail, the first chapter examines time travel narratives as ideal instances of eventuality. Eventuality consists in two operations running in opposite temporal directions—speculatively writing the future (prospection) and assessing history in light of that speculated future (retrospection). The literary genre that embodies this exact pair of movements is the time travel narrative. H. G. Wells’s novel <i>The Time Machine </i>(1895), the first scientific time travel story, creates a critical legacy for the genre: the assumption that the entirety of time already exists. The conceptualization of the already-existing future is important because it emphasizes the causal relation between the present and the future—the future which the time traveler witnesses is the direct outcome of his present. In the movie adaptation produced during the Cold War, the dystopian course of history is rewritten to be a nuclear war narrative, which suggests that the time travel narrative as a base frame has been appropriated by the desire to speculate the future born with the nuclear bomb. Then decades later the <i>Terminator </i>movies develop the time travel narrative as an instance of eventuality even further by creating a scenario in which the future is no longer just an uncharted territory to be explored, but an active force that has a direct sway over the present’s world. </p><p>Along with literary fictions of nuclear disasters, strategic studies on nuclear conflicts also attempt to represent the nonexistent events of future disasters. The historical significance of the advent of wargaming, a major form of nuclear strategic fiction, is that even the comparatively scientific and empirical study of nuclear war funded by the U.S. military is fundamentally speculative. The very formation and development of wargaming, in other words, is an indication that the nuclear weapon brings with it unknown possibilities for the future. The legitimacy of a wargame’s findings is dependent on that of the future projection used in the scenario. But since the latter is itself speculative and thus cannot be proven, the narrative logic of a wargame is circular or self-referential. This circularity is exactly the structure of the synthetic history in the <i>Terminator </i>films, which is a form of eventuality in which the present creates the future and the future retrospectively redefines the present.</p><p>The nuclear bomb, finally, also contributed to the advent of ecological worldview with its ecocidal nature and sheer extent of destructive capability. Geosciences in the U.S. experienced a rapid growth following the second World War, as the military pursued global surveillance for nuclear activities. Some of the same scientists who developed the weapons also began to study the interactions between radiation and the human body, as the workers in the weapons production lines began to experience radiation sickness. This kind of research was soon expanded to the study of radiation’s ecological effects on a broader scale involving not just the human bodies but also other environmental entities, organic and inorganic. Civilian research projects, in the meantime, found a widespread impact of weapons tests, including the “bone seeker” radioisotopes accumulated in the human body. Lastly, in terms of the more general way of understanding the world, the cases of radiation exposures discovered far away from the sources offered people around the world points of reference with which they could conceive an ecologically interconnected network on a planetary scale. </p>

published_or_final_version / Mechanical Engineering / Master / Master of Philosophy

No / (137)Cs concentrations in ten species of foliose lichens collected within Tsukuba-city in August 2013 ranged from 1.7 to 35 kBq/kg. The relationships between (137)Cs in two dominant species, Dirinaria applanata and Physcia orientalis, and the air dose rate (muSv/h) at the sampling sites were investigated. (137)Cs in P. orientalis measured about 1 year after the Fukushima nuclear accident was correlated (r(2) = 0.80) more closely with the air dose rate than those measured after about 2 years (r(2) = 0.65), possibly demonstrating its continued value as a biomonitor to reflect ambient fall-out levels. In contrast, those of Dirinaria applanata were not correlated with the air dose rate in either year.