The use of zirconium hydride blankets in a minor actinide thorium burner sodium-cooled reactor for void coefficient control with particular reference to UK's plutonium disposition problem

The use of zirconium hydride (Th–ZrH1.6) blankets in a thorium-fuelled sodium-cooled reactor for void reactivity control with particular reference to UK's plutonium disposition problem is proposed and considered. It is shown that, with the use of such blankets, a mild moderation effect is produced during voiding which compensates for the general hardening of the spectrum, enabling a net negative void coefficient at pin level to be attained without the need to rely on traditional neutron leakage enhancement techniques or neutron poisons, and with negligible impact on transmutation capabilities. One important difference in comparison with the traditional methods is that the void coefficient is obtained at the pin level, eliminating or mitigating substantially the spatial dependencies on the location of the void. Combining the use of such blankets with a suitable n-batch fuelling scheme yields a negative void reactivity coefficient throughout the life of fuel. Additional research and development are required to explore further this concept's potential.This is the author accepted manuscript. The final version is available from Elsevier via http://dx.doi.org/10.1016/j.pnucene.2015.03.01

An estimate of the order of magnitude of the explosion during a core meltdown-compaction accident for heavy liquid metal fast reactors: A disquieting result updating the Bethe - Tait model

Criticality and recriticality considerations in heavy liquid metal fast reactors (HLMFRs) after a hypothetical core meltdown accident are discussed. Although many aspects of system behaviour in such scenarios can be deduced directly from the classical theory of sodium-cooled fast reactors (SFRs), certain ideas that have been accepted as true for SFRs cannot be extrapolated to HLM- FRs without sufficiently careful thought. In this paper, we are concerned, as in SFRs, with fuel compaction, but with one important difference: there would be no boiling of the surrounding heavy liquid metal pool. Utilizing a Bethe-Tait model, it is shown that, due to the power attening effect of the heavy liquid metal, explosive excursions at least an order of magnitude higher than for SFRs in similar situations are conceivable.This is the accepted manuscript. The final version's available from Elsevier at http://www.sciencedirect.com/science/article/pii/S0149197014002947

On the Feasibility of Self-Sustainable Deuterium Production in Fusion Reactors Using an Ionization Chamber

In this technical note we examine a method for self-sustainable (in-situ) deuterium production in a fusion reactor, using a very different approach to those considered in previous studies. Here, instead of pursuing the production of deuterium via neutron capture (H + n ! D) inside and/or outside the fusion chamber, the deuterium is obtained by ionization induced by the neutronic flux in an ionization chamber and then electromagnetically separated. Using conservative modelling assumptions, an estimate of the amount of deuterium obtainable per day is made. The results show the feasibility of this approach, encouraging further research. Using the proposed method in combination with the use of lithium blankets for tritium breeding opens a new possibility for integral in-situ production of all the nuclear fuel required for fusion.This is the accepted manuscript. The final version is available from Springer at http://link.springer.com/article/10.1007%2Fs10894-015-9874-y

On the use of stimulated thermocapillary currents and virtual walls as computational tools for natural convection simulation in enclosed spaces

A new, alternative approach is proposed for natural convection simulation by means of stimulated thermocapillary currents created by virtual walls. In contrast to the well-known effective thermal conductivity model, in the proposed approach it is the mass motion due to the convective currents which is intended to be simulated and the heat flux is a consequence of such flows. As a result, no a priori knowledge of the Nusselt number is needed and thus the approach is more suitable for complex geometries. Utilizing a simplified physical model and the definition of hydraulic diameter, a generalized expression for enclosed geometries is derived which offers thermal engineers a powerful analysis tool that can use virtual walls with an associated fictitious Marangoni stress for pre-screening and estimation of Nusselt numbers.This is the accepted manuscript. The final version is available at http://www.sciencedirect.com/science/article/pii/S129007291500112X

Magnetic separation for a continuous solar-two-step thermochemical cycle for solar hydrogen/CO production using ferrites

A novel solar-two-step thermochemical concept for continuous production of H2 or CO from solar energy and H2O or CO2 using the redox pair MOFe2O3/MO as reactive particles is proposed and assessed. Here, an efficient continuous separation mechanism is devised by the use of an external magnetic field and the weak magnetization of MOFe2O3 at the working temperatures. The mechanism is suitable for systems of ferrites with a Curie temperature in the range 500–800 ∘C where water or CO2 decomposition occurs. One of the most promising candidates is the Fe3O4/FeO system. Pyromagnetic coefficients for Fe3O4 were obtained experimentally. A simple magnetic trap was employed and the separation ratios Fe3O4/FeO were obtained. The results are encouraging and motivate the development of full-scale solar reactor prototypes.This is the final published version of the article. It was originally published in the International Journal of Energy and Environmental Engineering (Arias FJ, Parks GT, International Journal of Energy and Environmental Engineering, 2015, doi:10.1007/s40095-015-0177-x). The final version is available at http://dx.doi.org/10.1007/s40095-015-0177-

Differential geometry tools for multidisciplinary design optimization, Part I: Theory

Analysis within the field of Multidisciplinary Design Optimization (MDO) generally falls under the headings of architecture proofs and sensitivity information manipulation. We propose a differential geometry (DG) framework for further analyzing MDO systems, and here, we outline the theory undergirding that framework: general DG, Riemannian geometry for use in MDO, and the translation of MDO into the language of DG. Calculating the necessary quantities requires only basic sensitivity information (typically from the state equations) and the use of the implicit function theorem. The presence of extra or non-differentiable constraints may limit the use of the framework, however. Ultimately, the language and concepts of DG give us new tools for understanding, evaluating, and developing MDO methods; in Part I, we discuss the use of these tools and in Part II, we provide a specific application.This research is supported by the Natural Sciences and Engineering Research Council of Canada (NSERC) and the Cambridge Commonwealth Trust and Cambridge Overseas Trust (CCT/COT).This is the author accepted manuscript. The final version is available from Springer via http://dx.doi.org/10.1007/s00158-014-1186-

Use of a fictitious Marangoni number for natural convection simulation

In this paper, a method based on the use of a fictitious Marangoni number is proposed for the simulation of natural thermocapillary convection as an alternative to the traditional effective diffusivity approach. The fundamental difference between these two methods is that the new method adopts convective mass flows in simulating natural convection. Heat transfer in the natural convection simulation is calculated through the mass transport. Therefore, empirical Nusselt numbers correlations required in the effective diffusivity method are eliminated. This represents a clear advantage in the context of design studies where flexibility in varying the geometry unconstrained by the availability of appropriate correlations is highly desirable. The new method is demonstrated using a simple geometrical model. An analytical expression of the fictitious Marangoni number associated with convection between vertical plates is derived and a computational fluid dynamics (CFD) simulation is performed to study the efficacy of the proposed method. The results show that the new method can approximate real natural convection quite accurately and can be used to simulate the convective flow in complex, obstructed or finned structures where the specific Nusselt correlation is not known.This is the author accepted manuscript. The final version is available from Elsevier via http://dx.doi.org/10.1016/j.ijheatmasstransfer.2015.04.08

Differential geometry tools for multidisciplinary design optimization, part II: application to QSD

Having previously developed a differential geometry framework for analyzing and conceptualizing Multidisciplinary Design Optimization (MDO) problems and methods, we now apply that framework to consider the Quasi-Separable Decomposition (QSD) architecture. Based on our theoretical investigations, we predict that QSD will fail to return feasible designs for MDO problems. In the same vein, we analyze the Individual Discipline Feasible (IDF) architecture, predict that IDF will converge to feasible designs, and propose a modified version of QSD which we believe will also output feasible design points. To test these predictions, we run all three architectures on a well-known analytical MDO problem. Our predictions regarding feasibility prove to be accurate: QSD does not return any feasible points, whereas all of the final design points from IDF and the modified QSD are feasible. Now that convergence to feasibility has been established, the next step is to investigate the optimization performance of various QSD modificationsThis research is supported by the Natural Sci- ences and Engineering Research Council of Canada (NSERC) and the Cambridge Commonwealth Trust and Cambridge Overseas Trust (CCT/COT).This is the author's accepted manuscript. The final version is available from Springer at http://link.springer.com/article/10.1007/s00158-014-1170-3

Pressurized water reactor in-core nuclear fuel management by tabu search

Optimization of the arrangement of fuel assemblies and burnable poisons when reloading pressurized water reactors has, in the past, been performed with many di erent algorithms in an attempt to make reactors more economic and fuel effi cient. The use of the tabu search algorithm in tackling reload core design problems is investigated further here after limited, but promising, previous investigations. The performance of the tabu search implementation developed was compared with established genetic algorithm and simulated annealing optimization routines. Tabu search outperformed these existing programs for a number of dffi erent objective functions on two di erent representative core geometries.This is the accepted manuscript. It is published by Elsevier here: http://www.sciencedirect.com/science/article/pii/S030645491400382X

The Spectral Shift Control Reactor as an option for much improved uranium utilisation in single-batch SMRs

The Spectral Shift Control Reactor (SSCR) uses a mix of D$_2$O and H$_2$O to moderate and cool the reactor. Initially, a high proportion of D$_2$O is used, such that the reactor is substantially under-moderated, with excess neutrons being primarily captured in $^{238}$U, breeding $^{239}$Pu. Towards the end of the cycle (EOC), the coolant is predominantly H$_2$O, thermalising the neutron spectrum and increasing reactivity. Recently, small modular reactors (SMRs) have gained significant interest as a means of providing a power source that requires little maintenance and refuelling. This motivates long cycles and reduced batch operation. For a single-batch reactor, there is typically a 33% penalty to uranium utilisation compared to a 3-batch reactor. Lattice calculations demonstrate the potential of the SSCR to greatly improve uranium utilisation in single-batch reactors over a range of enrichments. A relatively ‘wet’ lattice is employed which further improves uranium utilisation. Cases with 5% and 15% fissile loading are considered, for which it is respectively possible to achieve 47% and 39% increases in natural uranium utilisation using the SSCR relative to a ‘reference’ light water reactor. In the latter case, if 25% thorium is mixed into the fuel, the improvement in uranium utilisation increases to a total of 49%. Hence, in both cases, it is possible to in effect eliminate the penalty of using a single fuel batch. The ‘wet’ lattice introduces substantial thermal-hydraulic challenges due to the significantly higher fuel pin heat flux.Engineering and Physical Sciences Research CouncilThis is the final version of the article. It first appeared from Elsevier via https://doi.org/10.1016/j.nucengdes.2016.08.04