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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] 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] 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] 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] Spin Density Matrix Elements (SDMEs) describing the angular distribution of exclusive ρ0 electroproduction and decay are determined in the HERMES experiment with 27.6 GeV beam energy and unpolarized hydrogen and deuterium targets. Eight (fifteen) SDMEs that are related (unrelated) to the longitudinal polarization of the beam are extracted in the kinematic region 1< Q2<7 GeV2, 3.0< W<6.3 GeV, and -t<0.4 GeV2. Within the given experimental uncertainties, a hierarchy of relative sizes of helicity amplitudes is observed. Kinematic dependences of all SDMEs on Q2 and t are presented, as well as the longitudinal-to-transverse ρ0 electroproduction cross-section ratio as a function of Q2. A small but statistically significant deviation from the hypothesis of s-channel helicity conservation is observed. An indication is seen of a contribution of unnatural-parity-exchange amplitudes; these amplitudes are naturally generated with a quark-exchange mechanism. (orig.)