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[en] In 2018 the IPCC noted that nuclear power should be considered among the low-carbon generation technologies that could be used to limit carbon emissions, signaling a change in acceptance of this technology by the climate community. This was echoed when the Clean Energy Ministerial included nuclear energy as part of the ongoing energy future conversation (“NICE Initiative”) in 2018. Combined with the Sustainable Development Goals, global initiatives such as the Sustainable Energy for All partnership and the World Bank’s Energy Sector Management Assistance Program (ESMAP), there is a clear mandate to expand electricity access using clean technologies. Increasingly, nuclear power is being considered in this category. ESMAP’s Tiers of Electricity Supply set targets for household and community electrification. The top tier (Tier 5) threshold sets a minimum household provision of 8.2kWh daily use with availability of 23 hours per day. However, the lowest tier (Tier 1) of access is set at a minimum of 12Wh (which can power, for example, an LED light or phone charger) for 4 hours per day, of which only one of which is specific to after sunset hours. Much of this lower tier access could be provided by a variety of small-scale technology options, including rooftop solar panels. However, as the goal is to move towards reliable, productive, and community uses (the Technical Documentation includes targets for ancillary services such as streetlights) the Tier 5 access also includes grid connection and payment structures. As a result, the technology and management structures will need to evolve alongside technological investments. To facilitate this transition at the rapid pace of expanding access to all persons globally within a decade, innovative solutions are needed.
[en] Burning actinides in an inert matrix fuel to 750 MWd/kg IHM results in a significant reduction in transuranic isotopes. However, achieving this level of burnup in a standard light water reactor would require residence times that are twice that of uranium dioxide fuels. The reactivity of an inert matrix assembly at the end of life is less than 1/3 of its beginning of life reactivity leading to undesirable radial and axial power peaking in the reactor core. Here we show that axial grading of the inert matrix fuel rods can reduce peaking significantly. Monte Carlo simulations are used to model the assembly level power distributions in both ungraded and graded fuel rods. The results show that an axial grading of uranium dioxide and inert matrix fuels with erbium can reduces power peaking by more than 50% in the axial direction. The reduction in power peaking enables the core to operate at significantly higher power. (authors)
[en] Resilience against infrastructure failure is essential for ensuring the health and safety of communities during and following natural hazard situations. The Swiss Reinsurance Company Ltd (Swiss Re) estimated 2017 global infrastructure losses at 337 billion USD, with all but 7 billion resulting from natural hazards. These numbers are nearly double those from 2016 and have been increasing over the past two decades. The types of events that caused these losses have a particularly significant impact on critical infrastructure systems. Further, the US insurance industry estimates the annual loss from power outages caused by extreme events at $20-55 billion USD. These losses are expected to continue growing as climate change continues unless actions are taken to prevent them. Importantly, people and communities in developing and emerging economies are expected to be disproportionately affected. In the context of societal resilience, electricity supply is particularly important because many other critical infrastructure systems rely on it. Importantly, these include transportation (including evacuation and access operations), communication infrastructure, heating or cooling for residential and business structures, water services, supply chains for businesses and educational institutions as well as hospitals and other emergency services. For decision makers, specific information focused only on a single infrastructure asset is one part of a larger decision and planning framework that must include interdependencies with other systems.
[en] Traveling wave reactors are envisioned to run on depleted or natural uranium with no need for enrichment or reprocessing, and in a manner which requires little to no operator intervention. If feasible, this type of reactor has significant advantages over conventional nuclear power systems. However, a practical implementation of this concept is challenging as neutron irradiation levels many times greater than those in conventional reactors appear to be required for a fission wave to propagate. Radiation damage to the fuel and cladding materials presents a significant obstacle to a practical design. One possibility for reducing damage is to soften the neutron energy spectrum. Here we show that using a uranium oxide fuel form will allow a shift in the neutron spectrum that can result in at least a three fold decrease in dpa levels for fuel cladding and structural steels within the reactor compared with the dpa levels expected when using a uranium metal fuel. (authors)
[en] Conclusions: MMRs and SMRs are ideal in size to electrify many rural/under-electrified communities. Energy security - Reduced dependence on supply chains; Energy sustainability – Reduced GHG emissions; - Energy growth – provision of reliable, high-quantity electricity.
[en] The use of computation has become ubiquitous in science and engineering. As the complexity of computer codes has increased, so has the need for robust methods to minimize errors. Past work has show that the number of functional errors is related the number of commands that a code executes. Since the late 1960's, major participants in the field of computation have encouraged the development of best practices for programming to help reduce coder induced error, and this has lead to the emergence of 'software engineering' as a field of study. Best practices for coding and software production have now evolved and become common in the development of commercial software. These same techniques, however, are largely absent from the development of computational codes by research groups. Many of the best practice techniques from the professional software community would be easy for research groups in nuclear science and engineering to adopt. This paper outlines the history of software engineering, as well as issues in modern scientific computation, and recommends practices that should be adopted by individual scientific programmers and university research groups. (authors)
[en] Many groups have used neutron diffusion simulations to study fission wave phenomena in natural or depleted uranium. However, few studies of fission wave phenomena have been published that use Monte Carlo simulations to confirm the results of diffusion models for this type of system. In the present work we show the results of a criticality and burnup simulation of a traveling wave reactor using MCNPX 2.7.0. The characteristics of the fission wave in this simulation are compared with those from a simple one-dimensional, one-group neutron diffusion model. The diffusion simulations produce a wave speed of 5.9 cm/yr versus 5.3 cm/yr for the Monte Carlo simulations. The axial flux profile in the Monte Carlo simulation is similar in shape to the diffusion results, but with different peak values, and the two profiles have an R2 value of 0.93. The 238U, 239Np and 239Pu burnup profiles from the diffusion simulation show good agreement with the Monte Carlo simulations, R values of 0.98, 0.93 and 0.97 respectively are observed. (authors)
[en] In 2010, nuclear power accounted for 27% of electricity production in Japan. The March 2011 disaster at the Fukushima Daiichi power station resulted in the closure of all of Japan’s nuclear power plants and it remains an open question as to how many will reopen. Even before the loss of nuclear capacity, there were efforts in Japan to foster the use of renewable energy, including large scale solar power. Nuclear power plants in Japan provided more than just base-load by storing energy in large scale pumped hydroelectric storage systems, which was then released to provide some peaking capacity. If this storage were instead coupled to current generation rooftop solar systems in Tokyo, the combined system could help to meet peak requirements while at the same time providing ∼26.5% of the electricity Tokyo used to get from nuclear output, and do so 91% of the time. Data from a study of rooftop space and a 34 yr data set of average daily irradiance in the Tokyo metropolitan area were used. Using pumped hydroelectric storage with 5.6 times this rooftop area could completely provide for TEPCO’s nuclear capacity. (letter)
[en] Determining the time dependent concentration of isotopes in a nuclear reactor core is of fundamental importance to analysis of nuclear fuel cycles and the impact of spent fuels on long term storage facilities. We present a fast, conceptually simple tool for performing burnup calculations applicable to obtaining isotopic balances as a function of fuel burnup. The code (VBUDS: visualization, burnup, depletion and spectra) uses a two region, multigroup collision probability model to determine the energy dependent neutron flux and tracks the buildup and burnout of 24 actinides, as well as fission products. The model has been tested against benchmarked results for LWRs burning UOX and MOX, as well as MONTEBURNS simulations of zirconium oxide based IMF, all with strong fidelity. As an illustrative example, VBUDS burnup calculation results for an IMF fuel are presented in this paper. (authors)