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De Villiers G.J.,Pebble Ltd | Treurnicht J.,Stellenbosch University | Dobson R.T.,Stellenbosch University
Applied Thermal Engineering | Year: 2012

The Pebble Bed Modular Reactor Pty. Ltd. (PBMR) has called for research into the possibility of distributed in-core temperature measurement. In this paper, several methods for distributed temperature measurement in high-pressure, -radiation and -temperature environments have been investigated by means of a literature study. The literature study revealed fiber-Bragg grating (FBG) temperature sensors to be the most feasible solution to the temperature measurement challenge. Various parameters affecting the propagation of light in optical fibers and consequently the FBG reflection profile was investigated. The differential equations describing FBG structures were solved and implemented in Matlab in order to simulate wavelength division multiplexing (WDM) of a distributed FBG sensing system. Distributed sensing with apodized FBGs written into the sapphire optical fibers is considered. Temperature measurement using wavelength division multiplexing of apodized FBGs written into silica optical fibers were also demonstrated in a test platform. The measured results corresponded with the theory. It was found that when there is a strong temperature gradient across the FBG, spectral widening of the reflection profile occurs. This fact should be taken into account when allocating bandwidth to a certain FBG and choosing a demodulation algorithm. Sapphire FBGs were also acquired and the optical properties investigated. Furthermore, high temperature stable FBGs written with femtosecond laser radiation in silica Sumitomo Z-Fiber have been evaluated and shown to be a good option for temperature measurement below 1000 °C. Finally, the implementation of FBGs in a high temperature nuclear reactor is discussed and recommendations are made for future work. © 2012 Elsevier Ltd. All rights reserved.


Grant
Agency: European Commission | Branch: FP7 | Program: CP | Phase: Fission-2007-6.0.01;Fission-2007-1.1-01 | Award Amount: 12.29M | Year: 2008

Gas-Cooled Reactors (GCR), RBMK and some Material Test Reactors (MTR) make use of graphite as moderator of the fuel, structures of the core and/or thermal columns. During operation, the graphite and other carbonaceous materials like carbon brick, pyrocarbon and silicon carbide coatings are contaminated by fission products and neutron activation. These irradiated carbonaceous wastes are problematic due to their content of long-lived radioisotopes (e.g. Carbon14, Chlorine 36) and due to their large volumes. About 250000 t of i-carbon are existing, worldwide. Acceptable solutions have not yet been established to handle this kind of waste. This fact also represents a significant drawback for the market introduction of graphite-moderated reactors like Very/High-Temperature Reactors (V/HTR) as a promising Generation IV system candidate. Graphite moderated reactors represent the very first generation of nuclear reactors and therefore need to be decommissioned ahead of other reactor types which evolved later. Presently, accelerated decommissioning of GCR and RBMK and subsequent disposal of i-graphite is the preferred option for not leaving this waste as a legacy for future generations. The CARBOWASTE project aims at an integrated waste management approach for this kind of radioactive wastes which are mainly characterized as Intermediate Level Waste (ILW), due to the varying content of long-lived radioisotopes. Methodologies and databases will be developed for assessing different technology options like direct disposal in adopted waste containers, treatment & purification before disposal or even recycling i-carbonaceous material for reuse in the nuclear field. The feasibility of the associated processes will be experimentally investigated to deliver data for modeling the microstructure and localization of contaminants. This is of high importance to better understand the origin of the contamination and the release mechanisms during treatment and/or disposal.


Gregory M.J.,Pebble Ltd | Gregory M.J.,University of British Columbia | Lang J.R.,Hunter Dickinson Inc | Gilbert S.,University of Tasmania | And 2 more authors.
Economic Geology | Year: 2013

The Pebble Cu-Au-Mo deposit in southwest Alaska is one of the world's largest porphyry deposits. The deposit contains over 80 billion pounds (Blbs) Cu, 107 million ounces (Moz) Au, and 5.6 Blbs Mo in all resource categories. Copper and gold grades vary across diverse hydrothermal alteration assemblages with higher grades associated with sericite- and pyrophyllite-rich assemblages in an advanced argillic alteration zone. Moderate grades are associated with the potassic and sodic-potassic alteration assemblages that dominate the deposit and low grades are found in quartz-illite-pyrite assemblages. These variations reflect fluctuations in both the temperature and composition of the magmatic-hydrothermal fluids in time and space. QEMSCAN scanning electron microscope-based mineral mapping and in situ laser ablation inductively coupled plasmamass spectrometry methods designed to document the spatial and temporal variations in metal deportment across alteration zones show that gold occurs as inclusions of electrum and high-fineness gold in chalcopyrite and pyrite and as free grains hosted by silicate minerals, with the proportion of each related to the principal host alteration assemblage. Gold associated with the earliest high temperature sodic-potassic and potassic assemblages occurs as electrum inclusions in chalcopyrite and to a lesser extent pyrite, and pyrite trace element signatures have high gold, silver, and copper concentrations (pyrite-1). During cooling of the hydrothermal system lower temperature illite and illite-kaolinite alteration overprinted the earlier assemblages with varying degrees of recrystallization and precipitation of more pyrite-rich assemblages with pyrite having a gold-poor trace element composition (pyrite-2). Gold released during recrystallization formed high-fineness gold inclusions in newly formed pyrite and narrow gold-rich pyrite rims (pyrite-3). A second magmatic-hydrothermal event resulted in a sericite- and pyrophyllite-rich advanced argillic overprint, which introduced more copper and gold to the system and recrystallized preexisting sulfides into both high and low sulfidation assemblages with high-fineness gold inclusions in pyrite and chalcopyrite and solid solution gold in bornite. A second generation of pyrite-1 with elevated palladium concentrations is associated with this hydrothermal fluid pulse and also possibly high arsenic pyrite (pyrite-4). Understanding the controls on gold deportment provides genetic constraints on ore deposit genesis. Alteration and sulfide assemblages and gold compositions provide information on the hydrothermal fluid compositions, pH, and temperature evolution of the magmatic-hydrothermal system. The presence of electrum inclusions in chalcopyrite and pyrite in potassic and sodic-potassic alteration is consistent with these zones forming from early high-temperature magmatic fluids because both gold and silver are transported together in such fluids. High-fineness gold inclusions in younger pyrite related to low-temperature clay alteration are evidence that the gold in early electrum was partially remobilized and reprecipitated. The low-temperature clay alteration most likely formed from a mixture of H2S-rich vapor with meteoric waters, conditions where gold is transported as a bisulfide complex and silver is not, resulting in the separation of the two metals. A second, structurally controlled pulse of magmatic fluids formed a well-mineralized advanced argillic alteration assemblage containing high-fineness gold inclusions in chalcopyrite and pyrite, the only part of the deposit where high-fineness gold is hosted by chalcopyrite. In the pyrophyllite stability field acidic fluid compositions transport gold and silver as different complexes and gold solubility is significantly lower than silver leading to the precipitation of highfineness gold inclusions. Palladium is transported by the same complex as gold under these conditions, consistent with the elevated palladium content of pyrite in the advanced argillic alteration assemblage. The temporal and spatial studies of variations in gold deportment across the Pebble deposit provide critical inputs to optimization of mineral processing design. The greatest influence on metallurgical gold recovery at Pebble is the proportion of gold that is hosted by pyrite. Pyrite-hosted gold may require different mineral processing methodologies compared with gold hosted by chalcopyrite. Therefore, defining domains of consistent hydrothermal alteration, and sulfide mineralogy and gold deportment is the key to the geometallurgical characterization of the deposit. © 2013 Society of Economic Geologists, Inc.


In the multi-pass fuel management scheme employed for the pebble bed modular reactor the fuel pebbles are re-circulated until they reach the target burn-up. The rate at which fresh fuel is loaded and burned fuel is discharged is a result of the core neutronics cycle analysis but in practice (on the plant) this has to be controlled and managed by the fuel handling and storage system and use of the burnup measurement system. The excess reactivity is the additional reactivity available in the core during operating conditions that is the result of loading a fuel mixture in the core that is more reactive (less burned) than what is required to keep the reactor critical at full power operational conditions. The excess reactivity is balanced by the insertion of the control rods to keep the reactor critical. The excess reactivity allows flexibility in operations, for example to overcome the xenon build up when power is decreased as part of load follow. In order to limit reactivity excursions and to ensure safe shutdown the excess reactivity and thus the insertion depth of the control rods at normal operating conditions has to be managed. One way to do this is by operational procedures. The reactivity effect of long-term operation with the control rods inserted deeper than the design point is investigated and a control rod insertion limit is proposed that will not limit normal operations. The effects of other phenomena that can increase the power defect, such as higher-than-expected fuel temperatures, are also introduced. All of these cases are then evaluated by ensuring cold shutdown is still achievable and where appropriate by reactivity insertion accident analysis. These aspects are investigated on the PBMR 400 MW design. © 2011 Elsevier B.V.


Grant
Agency: GTR | Branch: Innovate UK | Program: | Phase: Innovation Voucher | Award Amount: 5.00K | Year: 2016

PebblePad is an award-winning personal learning and assessment system, used in colleges, universities and professional bodies; by learners, teachers and assessors. We take pride in our customer focus and integrity commitments in the e-learning sector and therefore treat the privacy and integrity of the information stored in PebblePad as critical to our ongoing success. As such we would use the innovation voucher to enlist outside expertise in ensuring our security arrangements are appropriate to the threats faced by an online learning platform as the business operations expand.


Grant
Agency: GTR | Branch: Innovate UK | Program: | Phase: Innovation Voucher | Award Amount: 5.00K | Year: 2013

YouPower is an exciting new interactive energy generation and management system for hotels, events and meeting venues. This clean-tech system is a hybrid of solar and green energy gym technologies. The ‘clean energy’ that it generates will be used to power the electrical and presentation equipment used by delegates during their meetings. A dynamic management system will enable users to interact with equipment in exciting and educational way. It will also enable event managers to get crucial data on system performance.


Trademark
Pebble Ltd | Date: 2013-11-20

Chemicals for nuclear reactors, including uranium, uranium oxide, oxide, plutonium, plutonium oxide, strontium; nuclear fuel and processing materials for use as fuel in nuclear power reactors; additives, parts and components for the aforementioned.


Trademark
Pebble Ltd | Date: 2013-11-20

fuels, fossil, natural and synthetic fuels.


Trademark
Pebble Ltd | Date: 2013-11-20

Apparatus for heating, steam generating, drying, ventilating and water supply in Nuclear Power Plants.

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