Development of a statistical evaluation method for core hot spot temperature in sodium-cooled fast reactor under natural circulation conditions

Doda, Norihiro; Igawa, Kenichi*; Iwasaki, Takashi*; Murakami, Satoshi*; Tanaka, Masaaki

Nuclear Engineering and Design, 410, p.112377_1 - 112377_15, 2023/08

https://doi.org/10.1016/j.nucengdes.2023.112377

To enhance the safety of sodium-cooled fast reactors, the decay heat in the core must be removed by natural circulation even if the AC power supply to the forced circulation equipment is lost. Under natural circulation conditions, sodium flow is driven by buoyancy, and flow velocity and temperature distribution influence each other. Thus, it is difficult to evaluate the core hot spot temperature by deterministically considering the uncertainties affecting flow and heat. In this study, a statistical evaluation method is developed for the core hot spot temperature by using Monte Carlo sampling methods. The applicability of the core hotspot evaluation method was confirmed in three representative events during natural circulation decay heat removal operations in loop-type sodium-cooled fast reactors.

Development of 1D-CFD coupling method through benchmark analyses of SHRT tests in EBR-II

Yoshimura, Kazuo; Doda, Norihiro; Tanaka, Masaaki; Fujisaki, Tatsuya*; Murakami, Satoshi*; Vilim, R. B.*

Proceedings of 19th International Topical Meeting on Nuclear Reactor Thermal Hydraulics (NURETH-19) (Internet), 16 Pages, 2022/03

In Japan Atomic Energy Agency, the multilevel simulation system which enables consistent evaluation from the whole plant behavior to the local phenomena is being developed to optimize plant design and enhance the safety of sodium-cooled fast reactors. To validate the coupling method in the MLS system, the 1D-CFD coupling method using Super-COPD for 1D plant dynamics analysis and Fluent for multi-dimensional CFD analysis was applied to the analyses of loss of flow tests in EBR-II. It was confirmed that it could predict multi-dimensional thermal-hydraulic phenomena such as thermal stratification in the upper plenum, Z-shaped pipe, and cold pool, holding the whole plant behavior simultaneously. Moreover, the applicability of the 1D-CFD coupling method to the evaluation of the phenomena in natural circulation conditions was confirmed by comparing the results of the 1D-CFD couple analyses and the measured data.

Development of numerical estimation method using spatial connection methodology for thermal striping in upper plenum of reactor vessel of an advanced loop-type sodium-cooled fast reactor in Japan

Tanaka, Masaaki; Murakami, Satoshi*

Proceedings of 25th International Conference on Nuclear Engineering (ICONE-25) (CD-ROM), 10 Pages, 2017/07

Thermal striping on the core instrumentation plate (CIP) around the primary control rod (PCR) and backup control rod (BCR) channels and the radial blanket fuel assemblies (RBAs) may be caused. Since the interaction between neighbor areas exists in the UIS and the cold sodium flowing from the RBA is affected by the external flow around the UIS, a spatial connection method consisting of the numerical model for the whole upper plenum and the local target area has been developed. The numerical results were compared with the experimental results to confirm applicability of the method to the practical problem. And, sensitivity of mesh arrangement to the numerical results was discussed by using wide and narrow area models with two different spatial resolutions in each model. Through the examinations, appropriate local model for the spatial connection mothed could be proposed.

Decomposition studies of group 6 hexacarbonyl complexes, 1; Production and decomposition of Mo(CO) and W(CO)

Usoltsev, I.*; Eichler, R.*; Wang, Y.*; Even, J.*; Yakushev, A.*; Haba, Hiromitsu*; Asai, Masato; Brand, H.*; Di Nitto, A.*; Dllmann, Ch. E.*; et al.

Radiochimica Acta, 104(3), p.141 - 151, 2016/03

https://doi.org/10.1515/ract-2015-2445

Conditions of the production and decomposition of hexacarbonyl complexes of short-lived Mo and W isotopes were investigated to study thermal stability of the heaviest group 6 hexacarbonyl complex Sg(CO). A tubular flow reactor was tested to decompose the hexacarbonyl complexes and to extract the first bond dissociation energies. A silver was found to be the most appropriate reaction surface to study the decomposition of the group 6 hexacarbonyl. It was found that the surface temperature at which the decomposition occurred was correlated to the first bond dissociation energy of Mo(CO) and W(CO), indicating that the first bond dissociation energy of Sg(CO) could be determined with this technique.

Synthesis and detection of a Seaborgium carbonyl complex

Even, J.*; Yakushev, A.*; Dllmann, Ch. E.*; Haba, Hiromitsu*; Asai, Masato; Sato, Tetsuya; Brand, H.*; Di Nitto, A.*; Eichler, R.*; Fan, F. L.*; et al.

Science, 345(6203), p.1491 - 1493, 2014/09

https://doi.org/10.1126/science.1255720

A new superheavy element complex, a seaborgium carbonyl, has been successfully synthesized, and its adsorption property has been studied using a cryo-thermochromatography and -detection apparatus COMPACT. Nuclear reaction products of short-lived Sg preseparated with a gas-filled recoil ion separator GARIS at RIKEN were directly injected into a gas cell filled with He/CO mixture gas, and chemical reaction products of volatile carbonyl complexes were trasported to COMPACT. The Sg carbonyl complex detected with COMPACT was found to be very volatile with adsorption enthalpy of 50 kJ/mol, from which we have concluded that this complex should be a Sg hexacarbonyl Sg(CO). This is the first synthesis of organometallic compounds of transactinide elements for which only simple inorganic comounds have been synthesized so far.

Numerical simulations of thermal-mixing in T-junction piping system using large eddy simulation approach

Tanaka, Masaaki; Murakami, Satoshi*; Miyake, Yasuhiro*; Ohshima, Hiroyuki

Proceedings of ASME-JSME-KSME Joint Fluids Engineering Conference 2011 (AJK 2011-FED) (CD-ROM), 12 Pages, 2011/07

Authors have been developed a numerical simulation code MUGTHES by using the LES to investigate thermal striping phenomena in FBRs. In this paper, numerical simulations by the MUGTHES in T-junction piping system appear. The boundary conditions are chosen from an existing water experiment in JAEA. Numerical results are validated by comparisons with measured velocity and temperature profiles. Through the numerical simulations, generation mechanism of temperature fluctuation in thermal mixing process is revealed in the relation with the large-scale eddy motion.

Numerical investigation of thermal striping near core instruments plate around control rod channels in JSFR

Tanaka, Masaaki; Ohshima, Hiroyuki; Murakami, Satoshi*

Proceedings of 13th International Topical Meeting on Nuclear Reactor Thermal Hydraulics (NURETH-13) (CD-ROM), 12 Pages, 2009/09

This paper deals with numerical simulations focusing on several areas around typical CR channels in order to reveal thermal mixing phenomena and to confirm effect of mitigation measures to the thermal striping phenomena around the CR channel. By the numerical simulation, generation mechanism of influential temperature fluctuation on the CIP integrity is revealed and effect of mitigation measure based on the mixing mechanism is confirmed.

Study on Unsteady Heat Transfer with Fluid Temperature Fluctuation - Effect of the low-frequency fluid temperature fluctuation on the heat transfer characteristics -

Senda, Mamoru*; Inaoka, Kyoji*; Yoshimura, Shinya*; Muramatsu, Toshiharu; Murakami, Satoshi*; Tanaka, Masaaki

JNC TY9400 2005-003, 66 Pages, 2004/12

JNC-TY9400-2005-003.pdf:7.85MB

Heat transfer experiments have been carried out in order to clarify the effect of the low-frequency fluid temperature fluctuation on the unsteady heat transfer in a channel, which is related to the thermal striping phenomena. In this study, fluid temperature fluctuation was realized by the periodic large-scale shedding vortices in the channel with a rectangular cylinder, where the hot and cold water flows into the test section from the lower and upper parts of the contraction. The frequency of fluid temperature fluctuation was controlled by changing the width-to-height ratio of the cylinder. The unsteady heat transfer coefficient of the channel wall was measured by the thin-film heat flux sensor. The experiments were made for the Reynolds number of 9000 and the Strouhal numbers ranging from about 0.16 to about 0.2. It is found that the time averaged Nusselt numbers in the fluid temperature fluctuation field are almost equal to those of the constant fluid temperature regardless of the Strouhal number under the present experimental conditions.And numerical simulation was carried out for typical experiment condition. By the numerical simulation, dominant frequency of Nusselt number fluctuation and fluid temperature fluctuation showed good agreement between experiment and calculation.

Development of design window evaluation and display system (II); confermations of the basic performance of genetic algorism

Murakami, Satoshi*; Muramatsu, Toshiharu

JNC TN9400 2003-038, 59 Pages, 2003/05

JNC-TN9400-2003-038.pdf:2.28MB

A large-scale sodium-cooled fast breeder reactor in feasibility studies on commercialized fast reactors which has a tendency of cosideration of thorough simplified and compacted system is being investigated, however special attention should be paid to thermohydraulic designs for a gas entrainment behavior from free surfaces, a flow-induced vibration of in-vessel components, a thermal shock for various structures due to to high-speed coolant flows, nonsymmetrical coolant flows, etc. in the reactor vessel. As thus a lot of thermal-hydraulic issues relate to each other complicatedly on the reactor designs, multiple-criteria decision-making on the understanding of relationship among thermal-hydraulic issues is indispensable to design the reactor efficiently. Genetic Algorithm (GA),which is one of the methods, for multjple-criteria decision-making, was applied to the typical simPle objective optimization problems and then was confirmed its basic performance. From the Analyses, the following results have been obtained: (1)In the unimodal optimization problem, it was confirmed that GA is capable of sufficient searching ability. (2)It was confirmed that GA can be also applied to the discrete optimization problems. (3)In the case of applying GA to the combinational optimization problem, the searching efficiency is improved better by increasing the number of experiment times than the maximum of generation. (4)In the case of applying GA to the multimodal optimization problem, the searching ability is improved by using the two genetic operators (i.e., the mutation, and the elite strategy)at the same time.

Study on in-vessel thermohydraulics phenomena of sodium-cooled Fast reactors (II); Numerical investigations on proprieties of R/V upper plenum separation

; *; Yamaguchi, Akira

JNC TN9400 2001-129, 51 Pages, 2002/03

JNC-TN9400-2001-129.pdf:8.76MB

A large-scale sodium-cooled fast breeder reactor investigated in the feasibility studies on commercialized fasat reactors has a tendency of consideration of thorough simplified and compacted system designs to realize drastic economical improvements. Therefore, special attention should be paid to thermohydraulic designs for gas entrainment behavior from free surfaces, a flow-induced vibration of in-vessel components, thermal shock for various structures due to high-speed coolant flows, nonsymmetrical coolant flows, etc. in the reactor vessel. In-vessel thermohydraulic analyses were carried out using a multi-dimensional code AQUA to contribute to a planning of water scaled-model experiments for the separated upper plena of the reactor vessel. From the analysis, the following results were obtained. (1)It can be considered that there is little effect of volumetric flow rate between the upper plenum and the free surfase plenum on hydrodynamic characteristics in the whole upper plenum. Because the affected area is limited in the neighborhood of gaps of hot/cold leg pipes. (2)Change in flow velocity components is limited around the outer wall of hot leg pipes if the gap width of the dipped plate and penetrating components changes. From the above results, it was concluded that the assumption seems to be valid that the free surface plenum hydrodynamic characteristics is independent of the upper plenum flows. However it is necessary to consider jet effects due to the hot leg intake flows affecting vortex concentrations in the upper plenum.