Results 1 - 10 of 95
Results 1 - 10 of 95. Search took: 0.021 seconds
|Sort by: date | relevance|
[en] This work developed a new computational method for improving the ability to calculate the neutron flux in deep-penetration radiation shielding problems that contain areas with strong streaming. The “gold standard” method for radiation transport is Monte Carlo (MC) as it samples the physics exactly and requires few approximations. Historically, however, MC was not useful for shielding problems because of the computational challenge of following particles through dense shields. Instead, deterministic methods, which are superior in term of computational effort for these problems types but are not as accurate, were used. Hybrid methods, which use deterministic solutions to improve MC calculations through a process called variance reduction, can make it tractable from a computational time and resource use perspective to use MC for deep-penetration shielding. Perhaps the most widespread and accessible of these methods are the Consistent Adjoint Driven Importance Sampling (CADIS) and Forward-Weighted CADIS (FW-CADIS) methods. For problems containing strong anisotropies, such as power plants with pipes through walls, spent fuel cask arrays, active interrogation, and locations with small air gaps or plates embedded in water or concrete, hybrid methods are still insufficiently accurate. In this work, a new method for generating variance reduction parameters for strongly anisotropic, deep penetration radiation shielding studies was developed. This method generates an alternate form of the adjoint scalar flux quantity, ΦΩ, which is used by both CADIS and FW-CADIS to generate variance reduction parameters for local and global response functions, respectively. The new method, called CADIS-Ω, was implemented in the Denovo/ADVANTG software. Results indicate that the flux generated by CADIS-Ω incorporates localized angular anisotropies in the flux more effectively than standard methods. CADIS-Ω outperformed CADIS in several test problems. This initial work indicates that CADIS- may be highly useful for shielding problems with strong angular anisotropies. This is a benefit to the public by increasing accuracy for lower computational effort for many problems that have energy, security, and economic importance.
[en] Highlights : • Effect of fire protection systems on domino scenarios has been modelled using a Bayesian network technique. • Optimal allocation of fire protection systems has been performed by extending the Bayesian network to an influence diagram. • Optimal decisions obtained via application of maximized expected utility are in agreement with a graph theoretic approach's. - Abstract: The propagation of fire-induced domino effects in chemical plants largely depends on the primary fire scenario, on separation distances between the units, and on the presence of fire protection barriers. Passive and active safety barriers are widely employed to prevent or delay the initiation or propagation of domino effects. In the present study, a methodology has been developed based on Bayesian network to account for the impact of such safety barriers on the propagation of fire domino scenarios. The Bayesian network has been extended to a limited memory influence diagram in order to identify a cost-effective allocation of additional safety barriers to further mitigate the fire propagation. The application of the methodology has been demonstrated using a chemical tank farm. The results are in good agreement with the results of a graph theoretic approach developed in a previous study, proving the reliability of the developed methodology in cost-effective protection of process plants.
[en] Highlights: • A general, unified model of the hydroelectric generating system is established. • A novel expression of the unbalanced hydraulic force is proposed. • The interaction of these subsystems and oscillation modes are obtained. • This model is validated against the existing theory and operational data. - Abstract: Global hydropower growth continues to accelerate with 25% of total capacity installed in just the last 10 years. This accelerating expansion and the important storage facility hydropower means it is increasingly important to understand the reasons for operational failures. This is a challenge because the major reason for failures involves the complex interaction of hydraulic, mechanical and electric subsystems. Historically, reliability modelling has been split in two directions, focusing on different sub-systems, and has not yet been unified. Here these approaches are unified with a novel expression of unbalanced forces. This model with operational data are validated and the important modes of oscillation in the shaft are identified. Finally, the mechanism of the first-order oscillation mode exciting a second-order mode is presented. This integrated and accurate mathematical model is a major advance in the diagnosis and prediction of failures in hydropower operation.
[en] Highlights: • Propose real option model for evaluating underground gas storage investment. • Explore investment strategy of underground gas storage under multiple uncertainties. • Investigate effect of gas market reform on development of underground gas storage. • Seek tendency of optimal investment strategy through a sensitivity analysis. • The results show that implementing gas market reform is significant. - Abstract: Natural gas is expected to play a much more important role in China's energy supply, however, the lack of underground gas storage facilities becomes a serious barrier for its market penetration. Therefore, gas market reform is expected to be incentive for developing gas storage facilities. In the present study, a real option model was proposed to analyse the optimal investment strategy (investment timing and value) for underground gas storage facilities with/without the consideration of gas market reform. Uncertainties in gas market, government incentives and technological improvements were considered. The obtained results showed that it was not optimal for immediate investment in underground gas storage in China, and that to implement gas market reform would greatly contribute to gas storage construction. With the consideration of gas market reform, the investment of underground gas storage would be executed at 2026 with an investment value of 0.33 RMB/m3 if there were no government incentive, while to invest in 2030 would be the best decision without the consideration of gas market reform, and the investment value is only 0.05 RMB/m3. Through a sensitivity analysis, the effects of changes in parameters related to gas market, government incentives and technological improvements on the investment strategy were investigated. The conclusions can provide useful information for gas storage enterprise decision-makers on whether and when to invest underground gas storage facilities in China considering uncertainties.
[en] Introduction of the underground nuclear park (UNP) concept expanded the possible approaches to underground reactor siting. The number of reactors to be sited underground was increased from one to as many as 18, and the spent fuel storage facility and waste repository supporting those reactors was collocated underground along with the reactors in an open fuel-cycle configuration. The 2004 UNP concept included high temperature reactors and heat exchangers sited 200 meters deep in a thick, bedded-salt rock host rock. Multi-gigawatt levels of produced electricity were to be supplied to users by a high-capacity transmission system. Conceptual layout and preliminary excavation cost estimates were given for a hypothetical UNP with 18 reactors and their turbine/generators sited in an array of individual chambers at a depth of 100 to 300 meters in bedded salt. Collocation of waste management facilities underground with the reactors would reduce waste transportation cost, associated health and safety risks, and public concern. There are no spent fuels in common fusion power plants, compared to common fission power plants, since the gas fuels are mainly consumed in the fusion reaction of fusion power plants. However, it is necessary that the highly activated radio-wastes of surrounded components in the fusion reactors, including the fuel breeding structures, would be produced inevitably by the interaction of high-flux fast neutrons (especially, 2.5 and 14.1 MeV neutrons) produced in the fusion reactions. Based on the background information and review developed internationally for long-term investigation about the underground nuclear power plant siting, a new approach to construction and management of underground nuclear fusion power plants for future fusion power plants, such as K-DEMO, K-CFNS, K-PROTO Hybrid, K-PROTO FPP, K-FPP, etc. in Korea, is suggested and summarized in this presentation.
[en] EDF has initiated a programme to decommission its first generation nuclear power plants (Chooz A, Brennilis, Bugey-1, Saint-Laurent A1 and A2, Chinon A1, A2 and A3) and Creys-Malville plant. As part of the operations included in this programme, EDF will generate waste of which a small part (between 300 and 500 tons) consists of so-called 'long-lived intermediate level' waste (MAVL). The deep geological permanent disposal solution is currently being investigated for this type of waste, so EDF has opted to build a facility named ICEDA, to condition and store temporarily this type of waste, in the southern area of the Bugey site. ICEDA has the following 3 main functions: -) take delivery of the waste transport packaging (and send them back empty after inspection) and send waste packages to their respective outlets; -) condition the waste (after potential cutting) into cylindrical concrete packages of about 2 m3; and -) store these concrete packages in adapted halls until the waste outlets become available. ICEDA consists of 6 buildings spreading over 8,300 m2 and building it has required 35,000 m3 of concrete and 5,500 tons of steel frames. ICEDA will be operational in 2019.
[en] The characterization of historical and new waste at Cuban Central Storage facility was faced in cooperation between CIEMAT and CPHR under IAEA Regional project RLA/9/078. A set of definition and training activities at CIEMAT was carried out previous to the expert mission for setting up the system and calibration methods. A Self designed mechanical system and its electrical control was tested and refined according to the characterization needs, as well as the coupling with the low resolution gamma spectrometry system available. Experimental measurement and calibration methodologies were developed to characterized 220 liter drums containing homogeneous and heterogeneous matrices: contaminated soils, concrete and low density technological wastes. The methodology for activity estimation of relevant nuclides in the Managua Storage facility inventory and their distribution from the gamma spectra was also developed including the evaluation of the methodology proposed, the uncertainty estimation and the quality control/quality assurance of the characterization process.
[en] This publication covers the broad scope of requirements for fuel cycle facilities that, in light of the experience and present state of technology, must be satisfied to ensure safety for the lifetime of the facility. Topics of specific relevance include aspects of nuclear fuel generation, storage, reprocessing and disposal.
[en] Recently, the amount of waste generated from mid- and low-level radioactive waste and regulatory clearance wastes have been increasing in the process of maintenance due to aging of nuclear facilities. Therefore, it is necessary to establish a technology and system for efficient and safe processing of these. In addition, the disposal performance of regulatory clearance wastes in KAERI is lower than that of other nuclear-related organizations in Korea (such as Korea Hydro & Nuclear Power, KEPCO, Korea Atomic Energy Authority) in terms of frequency and quantity. In the future, the amount of radioactive wastes generated will continue to increase and the need for continuous control of the management system will increase. Through this project, the procedures of the regulatory clearance wastes management are established and the temporary facility has been acquisited for the storage of the regulatory clearance wastes. The status of the wastes managed by each facility is identified and the treatment priority order is set. In addition, by carrying out large-scale maintenance and repair of radioactive waste treatment facilities and storage facilities, the management safety and treatment efficiency of low- and intermediate-level radioactive waste was increased, and the preparation of 1000 drums was possible for disposal site transfer. The Belgoprocess radioactive waste disposal facility in Belgium was also visited to find ways to improve the management system and facilities of advanced facilities