Tight Lattice Research Articles

Sustainable thorium nuclear fuel cycles: A comparison of intermediate and fast neutron spectrum systems

This paper presents analyses of possible reactor representations of a nuclear fuel cycle with continuous recycling of thorium and produced uranium (mostly U-233) with thorium-only feed. The analysis was performed in the context of a U.S. Department of Energy effort to develop a compendium of informative nuclear fuel cycle performance data. The objective of this paper is to determine whether intermediate spectrum systems, having a majority of fission events occurring with incident neutron energies between 1eV and 105eV, perform as well as fast spectrum systems in this fuel cycle. The intermediate spectrum options analyzed include tight lattice heavy or light water-cooled reactors, continuously refueled molten salt reactors, and a sodium-cooled reactor with hydride fuel. All options were modeled in reactor physics codes to calculate their lattice physics, spectrum characteristics, and fuel compositions over time. Based on these results, detailed metrics were calculated to compare the fuel cycle performance. These metrics include waste management and resource utilization, and are binned to accommodate uncertainties. The performance of the intermediate systems for this self-sustaining thorium fuel cycle was similar to a representative fast spectrum system. However, the number of fission neutrons emitted per neutron absorbed limits performance in intermediate spectrum systems.

Power Flattening on Design Study of Small Long-Life Boiling Water Reactor (BWR) with Tight Lattice Thorium Nitride Fuel

Preliminary study of thorium based fuel utilization with the addition of Pa-231 on tight lattice boiling water reactor (BWR) has been performed. In previous studies, the use of fuel composition Th-232 and U-233 as well as the use of protactinium as burnable poisons with hexagonal tight lattice fuel cell geometry has resulted the reactor life time of 30 years without refueling [1]. In this study, power flattening has been conducted on the reactor core by using radially heterogeneous fuel. Addition of the Pa-231 is expected to extend lifetime of the BWR core By optimizing the composition of the fuel elements (Th and Pa) at low moderation conditions (tight lattice) it can be obtained the reactor core which can be opeprated over 30 years without refueling or fuel shuffling. The Reactor core has a volume of 17,635.8 liter, power of 620 MWt, operating life of 30 and a maximum excess reactivity value of 0.384% dk/k, could be achieved by using a composition of U-233 enrichment of 8.1 to 11% and the addition of Pa-231 as much as 6.16 to 11.13% with a power density of 35.2 watts/cc.

Asymptotic Boundary Forms for Tight Gabor Frames and Lattice Localization Domains

We consider Gabor localization operators defined by two parameters, the generating function of a tight Gabor frame , indexed by a lattice , and a domain whose boundary consists of line segments connecting certain points of . We provide an explicit formula for the boundary form , the normalized limit of the projection functional , where are the eigenvalues of the localization operators applied to dilated domains , R is an integer and is the area of the fundamental domain. The boundary form expresses quantitatively the asymptotic interactions between the generating function and the oriented boundary from the point of view of the projection functional, which measures to what degree a given trace class operator fails to be an orthogonal projection. Keeping the area of the localization domain bounded above corresponds to controlling the relative dimensionality of the localization problem.

数値解析を用いた稠密バンドルの圧力損失予測に関する研究

数値解析を用いた稠密バンドルの圧力損失予測に関する研究

Computational fluid dynamics study on cross flow pressure drop for triangular array rod assemblies with wire

A numerical study on modeling of cross flow pressure drop coefficient for wire-wrapped triangular rod array has been performed. The objective is to clarify and also to extend the current modeling of cross flow pressure drop coefficient employed in subchannel analysis method. This study includes both pure laminar and fully turbulent flow conditions. Firstly, simulations employing pin pitch to diameter ratio (P/D) of 1.21 are carried out, and the results are compared with available experimental data in terms of wire correction parameter. The results for P/D=1.21 are in good agreement with experimental data. Calculations employing smaller values of P/D, representing tight lattice rod configuration, have also been carried out. Based on the numerical results, new correlations of cross flow pressure drop are proposed. The correlations can be used to evaluate cross flow pressure drop coefficient in subchannel analysis codes.

Collective mode evidence of high-spin bosonization in a trapped one-dimensional atomic Fermi gas with tunable spin

We calculate the frequency of collective modes of a one-dimensional repulsively interacting Fermi gas with high-spin symmetry confined in harmonic traps at zero temperature. This is a system realizable with fermionic alkaline-earth-metal atoms such as 173Yb, which displays an exact SU(κ) spin symmetry with κ⩾2 and behaves like a spinless interacting Bose gas in the limit of infinite spin components κ→∞, namely high-spin bosonization. We solve the homogeneous equation of state of the high-spin Fermi system by using Bethe ansatz technique and obtain the density distribution in harmonic traps based on local density approximation. The frequency of collective modes is calculated by exactly solving the zero-temperature hydrodynamic equation. In the limit of large number of spin-components, we show that the mode frequency of the system approaches that of a one-dimensional spinless interacting Bose gas, as a result of high-spin bosonization. Our prediction of collective modes is in excellent agreement with a very recent measurement for a Fermi gas of 173Yb atoms with tunable spin confined in a two-dimensional tight optical lattice.

Investigation on heat transfer non-uniformity in rod bundle

Previous CFD investigations show strong non-uniform circumferential distribution of the wall temperature, heat flux and heat transfer coefficient on the rod surface, especially in the tight lattice bundle. This phenomenon should be considered to evaluate the peak cladding temperature, which is one of the design criteria for some Generation IV reactors such as supercritical water-cooled reactor (SCWR) and liquid-metal fast reactor (LMFR). In this paper important dimensionless numbers which affect the non-uniformity of heat transfer are identified. CFD calculations are performed to study the local heat transfer behavior of different sub-channels and the effect of these dimensionless numbers. An empirical correlation describing the heat transfer non-uniformity is proposed based on CFD data.In addition, a three-dimensional fuel model with the proposed heat transfer correlation is developed and implemented into the sub-channel code COBRA-SC to calculate the distribution of local heat transfer coefficient and local cladding temperature in SCWR fuel assemblies.

A new lattice with enhanced heat transfer characteristics

A new lattice with non-uniform wall roughness and excellent heat transfer enhancement is introduced. The similar lattice with non-uniform wall thickness is also given in this paper. This kind of lattice could not only enhance the heat transfer and fluid mixing effectively but also avoid the disadvantages of tight lattice. The flow pulsation, vortex structure, flow and heat transfer in lattice were investigated with unsteady Reynolds Averaged Navier–Stokes simulation. The maximum heat transfer coefficient in the non-uniform wall roughness is about two times of that in traditional rod bundles. With the same power, the heat transfer could be increased by 40% compared to the traditional rod bundles in heat exchangers and nuclear systems.

Topological Fulde-Ferrell superfluid in spin-orbit-coupled atomic Fermi gases

We theoretically predict a new topological matter - topological inhomogeneous Fulde-Ferrell superfluid - in one-dimensional atomic Fermi gases with equal Rashba and Dresselhaus spin-orbit coupling near s-wave Feshbach resonances. The realization of such a spin-orbit coupled Fermi system has already been demonstrated recently by using a two-photon Raman process and the extra one-dimensional confinement is easy to achieve using a tight two-dimensional optical lattice. The topological Fulde-Ferrell superfluid phase is characterized by a nonzero center-of-mass momentum and a non-trivial Berry phase. By tuning the Rabi frequency and the detuning of Raman laser beams, we show that such an exotic topological phase occupies a significant part of parameter space and therefore it could be easily observed experimentally, by using, for example, momentum-resolved and spatially resolved radio-frequency spectroscopy.

Neutron imaging of annular flows in a tight lattice fuel bundle model

High conversion light water reactors (HCLWRs), featuring tight lattice fuel bundles, could fulfill the transition between present-day and future, fast reactor based technology allowing an improved fuel utilization. Nevertheless, the cooling of the tight lattice and the thermal-hydraulic feasibility should be thoroughly examined. We have studied annular flows and the influence of functional spacer on them in a tight lattice fuel bundle model using cold-neutron imaging, a non-intrusive technique. The investigation focused on adiabatic, air–water annular flows in a scaled-up model of four neighboring subchannels of a tight lattice fuel bundle model. Liquid film thickness distributions have been measured for different flow conditions with and without spacer to quantify the influence of the latter. The film thickness is determined with a minimal bias and a reasonable statistical uncertainty (7–10%) at a high spatial resolution (∼60μm). The entrained liquid hold-up fraction and the effect of the spacer on it is given as well.

LOCA analysis of reactor cores with tight lattice using the modified RELAP5 code

The previous paper analyzed the reflooding phase of reactor cores with tight lattice. Models calculating the wall to fluid heat transfer in the precursory cooling region and in the vicinity of the quench front were developed and validated in the previous paper (Wu et al., 2012). In this paper, these newly developed models were used to modify RELAP5/MOD3.2 in order to make the code be suitable for tight lattice. Besides, minor modifications to the wall friction model and bubbly-slug interfacial drag model were done. Then the newly developed code RELAP5/MOD3.2/TIGHT was used to analyze the LOCA transients of conceptually designed reactor cores with three types of tight lattice. The results showed that the peak cladding temperatures in the reflooding phase are much higher than that in the blow-down phase. Through comparison between the calculation results of LOCA transients of the three types of tight lattice, it was found that with smaller pitch to diameter ratio, the peak cladding temperature was much higher. LPIS injection flow rate should be increased in order to keep the rod cladding temperature be within the LOCA criteria. Steam generation will prevent the coolant from flowing downstream of the channel in reactor cores with a very small flow area. From the reactor safety aspect and the economic aspect, we do not recommend that reactor cores be designed with p/d ratio less than 1.10.

Abstract 1626: The impact on tumor-stromal interactions of loss of collagen XV from the basement membrane zone.

Abstract Most clinical therapeutics used to date depend on specific targeting of cellular components to treat cancers. However, the environment outside the tumor cell is also critical since it may provide new targets to treat malignant and resistant cancers, independent of the tumor. We aim to target the early stages of cancer, prior to metastasis by determining the role of a non-fibrillar collagen (Type XV) and its interactions with the tumor stroma and extracellular environment. Type XV collagen (COLXV) is found in basement membrane zones where it assumes a pretzel-like structure but unlike the majority of fibrillar collagens does not form tight lattice networks surrounding the cell. In aggressive cancers, including breast, pancreas, ovarian and melanomas, Loss of COLXV precedes basement membrane invasion and metastasis. Moreover, the loss of COLXV from the distal side of basement membrane zones and the resulting deficit in its interactions with other proteins may determine its specific function in tumor progression and eventual metastasis. In this context we have identified critical collagen-binding cell surface receptors on the tumor cell, which interact with COLXV and appear to mediate its functions. A number of these interacting proteins show altered signaling in cancer. We previously showed that over-expression of COLXV in cervical cancer cells alters the growth properties of these cells in vitro and that type XV collagen is a dose-dependent suppressor of tumorigenicity in vivo. We now show that over-expression of COLXV inhibits epithelial to mesenchymal transition (EMT) in vitro through interactions with cell surface receptors and has a dramatic effect on the associated signaling events and alterations on the tumor cell periphery. Alterations in the balance of downstream signaling events may be responsible for tumor progression after the loss of COLXV. We are now further investigating the mechanisms of tumor/stroma crosstalk that are impacted by COLXV and subsequently by its depletion. Citation Format: Anthony G. Clementz, Michael Mutolo, Ann Harris. The impact on tumor-stromal interactions of loss of collagen XV from the basement membrane zone. [abstract]. In: Proceedings of the 104th Annual Meeting of the American Association for Cancer Research; 2013 Apr 6-10; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2013;73(8 Suppl):Abstract nr 1626. doi:10.1158/1538-7445.AM2013-1626

Unsteady numerical simulations of single-phase turbulent mixing in tight lattice geometries

This paper focuses on the unsteady numerical simulations of the turbulent flow in tight lattice geometries with the explicit algebraic Reynolds stress model. The calculation results showed that the shape of the geometry, gap width and rod diameter as well as the Reynolds number were important parameters that would influence the characteristics of the flow (such as the dominant frequency and wavelength of the pulsation) and the turbulent mixing between the subchannels. And a modified correlation of turbulent mixing was proposed, which showed better agreement with the past experimental results compared to the other existing correlations, especially for the low Prandtl number fluids such as liquid sodium.

Studies on boiling water reactor design with reduced moderation and analysis of reactivity accidents using the code DYN3D-MG

Abstract The multi-group version of the DYN3D reactor dynamics code was used for calculations for a new concept of a boiling water reactor with tight lattice of fuel rods and reduced neutron moderation. For that purpose, a 5-group cross section library was prepared and connected to the DYN3D code. Comparison calculations with the steady-state finite-difference code ACADEM showed a very good agreement. The capability of the DYN3D multi-group code in modeling transients in boiling water reactors with tight fuel element lattices was demonstrated by the analysis of two reactivity accidents initiated by the ejection of one control rod and unauthorized withdrawal of a control rod bank from the reactor core. The corresponding analyses were performed for begin of cycle conditions, when the considered control rods are at their maximum insertion depth.

Reflooding characteristics investigation and predicted models improvement for the pressurized water reactor with the tight lattice core design

The advanced pressurized water reactor with a tight hexagonal lattice core design has its potential to improve uranium utilization. With a smaller pitch-to-diameter ratio (p/d) ranging from 1.05 to 1.20, a major problem of a tight lattice core is the emergency core cooling in a loss-of-coolant accident. The NEPTUN-LWHCR and FLORESTAN reflooding experiments preformed at PSI (Paul Scherrer Institute) and KfK (Kernforschungszentrum Karlsruhe) during the verification period 1985–1990 showed that a LWHCR (light water high conversion reactors) had higher peak cladding temperatures and smaller quench rates than that of a conventional LWR (Rouge and Dreier, 1992; Erbacher and Wiehr, 1988). Furthermore, the existing system codes like RELAP5, CATHARE, TRAC may not be able to simulate the reflooding phase of a LWHCR. In this paper, the characteristics of the reflooding phase of tight lattice cores have been investigated. Then improvements to heat transfer models of precursory cooling have been introduced into RELAP5/MOD3.2. In addition, a new model has been developed to predict the heat release in the vicinity of the quench front. These modifications are assessed using selected tests of NEPTUN-LWHCR and FLORESTAN experiments. Comparisons between the calculated results and measured data indicate that the modified code can predict the peak cladding temperatures and quench temperatures relatively well. While for droplet entrainment prediction, there is still large room for improvement. Further validation is needed for the models proposed in this paper especially for a tight lattice core with a p/d ratio less than 1.10, and more efforts are required to study the droplet distribution and droplet size downstream of the quench front for higher reflooding rate tests (larger than 4.5cm/s).

The optimum design of tight lattice reactor core with thin rod bundles

The fuel height, rod diameter, pitch, and the loading pattern are all important parameters in the reactor core design process. Based on the analysis of the core performance, optimization calculation is performed on the three objective functions of ABV-6M reactor, i.e., power density, coolant temperature difference between the inlet and outlet, and flow-induced vibration are proposed for optimization calculation. Then a multi-objective problem (MOP) model is applied and computed optimally by non-dominated sorting genetic algorithm (NSGA-II) with the aim of maximizing power density and temperature difference as well as minimizing the flow-induced vibration. The results of optimal designs called ‘Pareto-optimal solutions’ are a set of multiple optimum solutions, from which the final optimization can be chosen after sensitivity analysis is performed. On the basis of lattice parameters optimization, the radial one-dimensional fuel loading pattern was optimized for achieving the optimum fuel utilization. The typical optimum design considered to be safe in a verification check showed that tight lattice effectively improved the reactor performances and saved the fuel consumption.

Abstract 5174: Novel signaling interactions of type XV collagen: Implications for tumor suppression

Abstract Most clinical therapeutics used to date depend on specific targeting of cellular components to treat cancers. However, the environment outside the tumor cell is also critical since it may provide new targets to treat malignant and resistant cancers, independent of the tumor. We aim to advance the understanding of the early stages of cancer, prior to metastasis by determining the role of a non-fibrillar collagen (Type XV) and its interactions with the tumor stroma and extracellular environment. Type XV collagen (COLXV) is found in basement membrane zones where it assumes a pretzel-like structure but unlike the majority of fibrillar collagens does not form tight lattice networks surrounding the cell. Loss of COLXV during progression of aggressive cancers (including breast, pancreas, and ovarian carcinomas and melanomas) precedes basement membrane invasion and metastasis. Moreover, the loss of COLXV from the distal side of basement membrane zones and the resulting deficit in its interactions with other proteins may determine its specific function in tumor progression and eventual metastasis. In this context we have identified critical collagen-binding cell surface receptors on the tumor cell, which interact with COLXV and appear to mediate its functions. These receptors have also been reported to show altered signaling in cancer. We previously showed that over-expression of COLXV in cervical cancer cells alters the growth properties of these cells both in vitro and in vivo, and showed that type XV collagen is a dose-dependent suppressor of tumorigenicity in vivo. We now show that over-expression of COLXV inhibits epithelial to mesenchymal transition (EMT) in vitro and has a dramatic effect on the associated signaling events. We are now further investigating the mechanisms of tumor/stroma crosstalk that are impacted by COLXV and subsequently by its depletion. Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 103rd Annual Meeting of the American Association for Cancer Research; 2012 Mar 31-Apr 4; Chicago, IL. Philadelphia (PA): AACR; Cancer Res 2012;72(8 Suppl):Abstract nr 5174. doi:1538-7445.AM2012-5174

URANS simulation of the turbulent flow in tight lattice bundle

The flow structure in tight lattice is still of great interest to nuclear industry. An accurate prediction of flow parameter in subchannels of tight lattice is likable. Unsteady Reynolds averaged Navier Stokes (URANS) is a promising approach to achieve this goal. The implementation of URANS approach will be validated by comparing computational results with the experimental data of Krauss. In this paper, the turbulent flow with different Reynolds number (5000–215000) and different pitch-to-diameter(P/D) (1.005–1.2) are simulated with computational fluid dynamics (CFD) code CFX12. The effects of the Reynolds number and the bundle geometry (P/D) on wall shear stress, turbulent kinetic energy, turbulent mixing and large scale coherent structure in tight lattice are analyzed in details. It is hoped that the present work will contribute to the understanding of these important flow phenomena and facilitate the prediction and design of rod bundles.

CFD study of the single-phase turbulent mixing in tight lattice bundle geometry

CFD study of the single-phase turbulent mixing in tight lattice bundle geometry

Simulation of turbulent flow inside different subchannels in tight lattice bundle

In this paper, both steady and unsteady Reynolds Averaged Navier Stokes (RANS and URANS) methodology are applied to the prediction of turbulent flow inside different subchannels in tight lattice bundles. Two typical configurations of subchannels (i.e., wall subchannel and center subchannel) are chosen to be investigated. In this work the application of different turbulence models implemented in the commercial code CFX v12 is shown. The validity of the methodology is assessed by comparing computational results of axial velocity, wall shear stress and turbulent intensity distributions with the experimental data (Krauss, 1996; Krauss and Meyer, 1998). This study shows that RANS simulation with anisotropic turbulent model produces excellent agreement with experiment, whereas it failed to predict the flow behavior accurately in the case of tightly packed geometries ( P/ D < 1.1). On the other hand, the URANS simulation is in good agreement with the results in tightly packed geometries with flow oscillation in the gap region. The effects of the Reynolds number and the bundle geometry on the flow oscillation are investigated in details.